Mature cells that are not capable of cell division.

Question that is being addressed here is: Compared to immature/developing neurons, does mature cells have a different machinery (or set of mechanisms) to synthesize RNA and different neurotransmittters?

A neurotransmitter that has reduced effects on the neurons.

Refers to a process during which a cell undergoes a shift in electric charge distribution. At rest, the membrane of a neuron has a potential of -60 to -70 millivolts (mV). This means the inside of the cell is negatively charged relative to the outside. Depolarization is when the potential becomes less negative than the resting potential.

The sodium influx caused by veratridine was cancelled out by tetrodotoxin exposure. Tetrodotoxin blocks the influx of sodium ions thereby stopping depolarization. Hence there is no increase in the activity of substance P in the presence of both drugs.

Dreyfus et al. used locus coeruleus, a region in the brain, to study neurotransmitter expression in brain. His group was able to show that the catecholamines can be expressed both in culture and in animals, making the locus coeruleus an excellent system to study the plasticity in brain.

Given that the plasticity occurs during development, the authors tested whether the plasticity can be observed in mature neurons as well. The authors performed these experiments in the ganglia of young and old rats and assessed the changes in the neurotransmitter, substance P.

Substance P had a significant increase in expression at young rats and at 6-month-old rats but not 2-year-old rats.

Jonakait et al. show that the loss of expression is not confined to the rat gut, but also observed in the cranial sensory and dorsal root ganglia of the embryonic rats. Here the authors have shown that the expression of catecholamine is lost for a certain time period during the development.

These studies suggest that, irrespective of embryonic origin, the loss in expression of neurotransmitters, catecholamine, and noradrenergic occur during development.

Jonakait et al. used the embryonic neural cells in the rat gut to understand the expression of noradrenergic cells.

It was shown that these neural cells exhibit several characteristics of noradrenergic cells at embryonic stages. The authors wanted to know if there were a change in expression levels of noradrenergic during the development. For a certain time period during the development, the expression of noradrenergic is lost; however, the uptake system of norepinephrine is present and functional.

In this review, Patterson discusses how we can manipulate the neurons’ decision to produce certain chemicals by altering the environmental factors. This manipulation can be performed during development by changing the fluid or culture conditions in which the neurons are growing.

This review by T. Hökfelt et al. discusses the identification of new neurotransmitters that are peptidergic in nature. Peptidergic refers to the neurons that release small peptides as their neurotransmitters.

The article provides a snapshot of peptidergic neurons identified in the nervous system, namely, the brain, spinal cord, and peripheral nervous system.

"Neo" meaning new, "synaptogenesis" referring to the formation of connections between neurons.

The tadpoles in these experiments tends to attach only to their kin.

However, there is neurotransmitter phenotype change from one to another. The researchers have found a mechanism that helps in regulation of this neurotransmitter phenotype change. The release of the neurotransmitter caused the tadpoles to bond to those who were not biologically related to them. The switching affected the social bond formation in tadpoles.

Read more at the Dana Foundation.

What could have been the cause of the increase in TH activity? The answers could be one of the two options: An increase in the number of TH-positive neurons in the sample or an increase in the amount of TH per neuron.

In other words, is it an individual neuron's effect or a collective effort of all neurons in the sample? To address this, the authors decided to measure the number of TH-positive cells in the control and veratridine-treated cultures.

The results show that the there is no difference in the number of neurons between both groups. Based on that, they concluded there is an increase in the amount of TH per neuron individually but not in the total number of TH-positive neurons.

Potassium (K+) is used as a depolarizing agent in this study. The depolarization using potassium is expected to behave similarly to the effects observed with veratridine as both the chemicals increase the influx of sodium channels.

The authors show that, in the presence of potassium, there is approximately a 35% increase in TH activity as compared to their controls.

Refers to the group of neurons present in the pons of the brain.

The pons is a brain region that links the medulla and the mid-brain. It serves as a message station between several areas of the brain.

Tetrodotoxin is a sodium channel blocker while veratridine does the opposite, it activates these channels causing an influx of sodium. Since these two drugs act in opposition to each other, we expect them to have no net effect in the cultures. And that’s what was observed in the cultures exposed to veratridine in the presence of tetrodotoxin (see TTX+Ver in Figure 4). There is no further effect in the TH activity as compared to their controls.

Veratridine binds to the sodium channel binding site thereby increasing the flow of sodium ions into the cell. The authors have shown that, when the cultures are exposed to veratridine, there is approximately a 40% increase in the activity of tyrosine hydrolase (TH) compared to their controls. Controls are cultures that are not exposed to any drugs.

Used to compare average means of two or more samples.

Here, the authors used this test to measure the activity of substance P across the following groups: (1) control, (2) in the presence of tetrodotoxin, (3) in the presence of veratridine, and (4) in the presence of tetrodotoxin and veratridine.

Read more at Khan Academy.

Stands for standard error, a measure to test how far the mean of the sample is from the estimated mean of the population.

These are explants obtained from nucleus locus ceruleus. These explants are placed in a nutrient medium and no drugs are provided to this group. This group serve as a comparison group to the groups treated with the drugs.

The last step in the dot blot to detect the materials of interest using a radioactive probe. Here, the radioactive probes tagged to proenkephalin were observed for three time points: 0 days, 1 day, and 3 days.

Medullary explants were obtained from adult rats to understand the mechanism behind the different transmitter expression. 

The tyrosine hydroxylase (TH) activity stayed consistent throughout the seven-day period. TH enzyme is responsible for the synthesis of catecholamines. The consistent TH activity indicates that there is no change related to the expression of catecholamines in this experiment. 

Next, the PNMT enzyme is responsible for adrenergic expression. PMNT exhibited a 60% decrease in four hours and was maintained at that level for the remainder time period. 

The [leu]enkephalin (opiate expression) showed a 50-fold increase in four days and continued to increase until seven days. There is a continuous increase in the expression of opiates as opposed to catecholamines.

A structure that gives rise to the peripheral nervous system and non-neuronal cells.

These bodies, consisting of receptors and cells, are located near the carotid arteries. There are two carotid arteries that run on either side of the neck, carrying blood to the neck, face, and brain.

A structure that gives rise to neurons and other structures in the nervous system.

Learn more about placodes with another annotated paper: https://www.scienceintheclassroom.org/research-papers/hair-feathers-and-scales-evolutionary-tale

Technique used to mark the target of interest using an antibody-based test. In this study, tyrosine hydroxylase and dopamine β-hydroxylase are the target molecules of interest. The antibodies against tyrosine hydroxylase—namely dopamine β-hydroxylase—are used to detect the molecule of interest.

Explants were depolarized with veratridine, leading to a decrease in the levels of substance P.

Explants from the superior cervical ganglia were obtained to address the question: Is there transmitter plasticity in mature neurons?

Explants were obtained from rats of age six months and one year. A ten-fold increase was observed in the activity of substance P.

The ganglia was removed from the animal and transferred to a nutrient medium. These explants were maintained in the medium for six months to one year. At several time points, the explants were taken and observed for the activity of substance P.

The neurons are dissected from the animal and grown in a dish. The dish contains supplemental factors and a medium that mimics the composition of the fluid inside the animal.

The conversion of norepinephrine to epinephrine is dependent on the mRNA synthesis and hormones released by the pituitary-adrenal axis.

A regulation that controls the conversion of DNA to RNA in organisms. Learn more with this HHMI BioInteractive video.

A set of codes that helps the organism adapt and maintain life.

In this instance, regulation occurs at the gene level to adapt to environmental conditions.

A gland situated above the kidneys. Adrenal glands produce a variety of hormones.

Neuroendocrine cells are the cells that receive input from neurons and release a hormone into blood for output. Any hormone produced and released by neuroendocrine cells are referred to as neurohumoral products.

Connections between the sympathetic nervous system and adrenal system.

Neurons in rat sweat glands can convert from catecholaminergic to cholinergic groups during development. This is evident from the lack of enzymes that are responsible for catecholamine synthesis.

A neurotransmitter that can be released from exocrine glands; for instance, sweat glands.

Functions include relaxation of smooth muscles in the stomach and gall bladder, and contraction of heart muscles.

It has been shown that in sweat glands, both VIP and acetylcholine (or cholinergic) are released from the same population of neurons.

An enzyme that converts dihydroxyphenylalanine (DOPA) to dopamine.

Since this paper was published in 1984, the field of synaptic plasticity has progressed. This NeuWire article is an example to show that, in response to environmental conditions (such as changes in day length), the brain can switch the neurotransmitters they produce and release. These neurotransmitter switches also have an impact on behavior in these animals.

See the original research in Science in the "Related Content" tab and here.

When this paper was published, it was assumed that each neuron produces only one transmitter. However, more recent research has challenged this assertion. Contrary to traditional teaching, this article summarizes the new findings in the field of neurotransmitter plasticity, some of which include mechanisms of neurotransmitter plasticity, mechanisms of neurotransmitter switching, and their impact in neurological disorders.

Read more here.

Plasticity can be defined as the ability of the brain to mold and shape in response to experience. The change can be due to change in the receptors present in the brain, the chemicals itself, or the mechanism by which receptors respond to chemicals. 

Neurotransmitter plasticity refers to changes in neurotransmitters in response to plasticity.

Experiments that are performed on animals or humans.

Functions of the body that are essential for life; e.g., sleeping, eating, breathing, bladder activity.

The sympathetic nervous system is a part of the nervous system that controls the essential functions of life; for example, blood pressure and heart rate. The neurons present in this system are called sympathetic neurons.

You can think of the nervous system as electrical wiring, transmitting signals to and from different parts of the body. The system is made up of the brain, spinal cord, and nerves. Neurons are cells found in the brain.

The human nervous system is made up of two components, the central nervous system (CNS) and the peripheral nervous system (PNS). The PNS consists of nerves and fibers outside of the brain and spinal cord (which make up the CNS).

These are a class of neurotransmitters. Peptides are made of amino acids or a chain of amino acids.

Read more about the different neurotransmitters here.

Refers to the cells that release neurotransmitter acetylcholine.

Learn more in this video about neurotransmitter release: https://www.khanacademy.org/science/health-and-medicine/nervous-system-and-sensory-infor/neural-cells-and-neurotransmitters/v/neurotransmitter-release

Refers to cells that release the neurotransmitter, norepinephrine. An alternative name for norepinephrine is noradrenalin.

In these studies, the authors examined the role of the neurotransmitter substance P in nerve ganglia. The authors confirmed that the activity of substance P is dependent on sodium currents, changes within the cell, and impulsive activity.

Cutting down the axons in the petrosal neurons causes a decrease in TH activity and immunoreactivity. However, there is a certain level of TH recovery after four weeks, which could be due to the regeneration or recovery of the severed axon.

With nicotinic receptor stimulation, the depolarization or the influx of sodium ions across the membrane causes a decrease in substance P in both mature and developing neurons.

A drug that blocks the binding of acetylcholine to its nicotinic receptors.

Formation of new neurons.

Referring to a case where the neurotransmitter and the receptors are present on the same cell. The released neurotransmitter binds to the receptor on the same cell.

A quantitative measurement of a neuron size, shape, or density.

Veratridine is a drug that causes an increase in the sodium influx. The authors used the drug to cause depolarization.

Decrease in [leu]enkephalin in adrenal medulla is dependent on two related factors: Membrane depolarization and the sodium influx through the membranes.

At four days, mRNA of proenkephalin showed a greater increase similar to the increase observed in [leu]enkephalin in medullary explants.

Fluorescent markers are used to label catecholamine in the neurons and visualized using a fluorescent microscopy.

No change; unaltered.

These are receptors that respond to the neurotransmitter, acetylcholine.

Using a blocking agent for nicotinic receptors, the binding of acetylcholine was blocked in the ganglia. This manipulation is similar to denervation technique and hence, the authors observed an increase in the activity of substance P.

Refers to the connections and interactions between the pituitary gland and adrenal glands. 

Precursors.

Sodium channel blocker. It blocks the influx of sodium into the cell.

Act of flowing in.

Example: An influx of tourists was observed over the holidays.

Refers to the cell group that releases one of the neurotransmitters, dopamine or norepinephrine.

An enzyme responsible for the conversion of tyrosine (an amino acid) to dopamine, a neurotransmitter.

The uptake of norepinephrine in these neurons remain unaffected. The neurons are capable of producing noradrenaline.

Noradrenergic neurons produce norepinephrine, the neurotransmitter expressed in rat sweat glands during postnatal stages of development. For a short period of time in development, the neurons lose the noradrenergic expression, but pick up the expression of acetylcholine.

Refers to the measurement of quantities, a countable amount of something. For example: A baby weighs 7 pounds and 4 ounces.

Refers to the measurement of qualities, a describable trait of something. For example: The girl has brown eyes.

Here, referring to the physical characteristics of the neurons.

Widely accepted class of neurotransmitters.

Read more about the different neurotransmitters here.

A chemical that is released by brain cells called neurons. These chemicals aid in communication or passing messages between neurons.

Drug that increases the influx of sodium into the cell.

The ability to change.

For example, think of a caterpillar, which has the ability to change to butterfly.

Maintaining the body’s temperature within the normal limits.

Normal or minimum level.

Research that can be useful to prevent or treat disease

Relating to the growth of the individual.

Following.

The response prompted by cocaine.

Response prompted by nicotine.

Prone to; susceptible.

Treatment received prior to something in advance

Evaluate; measure.

Given.

Pushed; urged; required.

Reduced.

A technique used to measure the movement or locomotor activity of the animal assessed in the open field box. It is thought that with repeated administration of the drug, the animals can show an increase in locomotor activity, which is a sign of sensitization.

Photobeams are placed on the walls of the box to record the movements of the animal. The mice can explore and get used to the test area of the open field.

The animal is tracked for the distance covered in centimeters using an automated video system. The experiment is repeated on day 1 and on each day following the injection of cocaine (on days 8, 9, 10, 11). The total distance covered by the animal is recorded for each day.

Watch the technique here at: https://www.jove.com/video/53107/assessment-cocaine-induced-behavioral-sensitization-conditioned-place

A three-chamber apparatus is constructed with access to two chambers for the animal for this experiment. There are 3 phases to this experiment: pre-conditioning, conditioning, and testing.

Pre-conditioning: Animal can freely move on any side of the chamber. For each animal, the first preference of the chamber is noted. This was done on days 7 and 8 of the experimental protocol.

Conditioning: Train the animals to saline on its preferred chamber and to cocaine on the least preferred side. This was done on days 9, 10, and 11 of the experimental protocol.

Testing: On day 12 of the experiment, the animals are allowed to have access to both sides of the chamber for 30 minutes. The time spent in the preferred chamber and the less preferred chamber is recorded.

View the video to learn more about the conditioned place preference protocol. The protocol is describing how to measure craving in animals using morphine as the drug of preference. https://www.jove.com/video/58384/a-conditioned-place-preference-protocol-for-measuring-incubation

Outcome

Strengthening of synapses between neurons

Slice electrophysiology is a technique that is widely used to study synaptic plasticity. Brain slices containing the nucleus accumbens region was obtained from the mice.

For this technique, stimulating and recording electrodes are needed. Recording electrodes measure the electrical activity of the neurons in the area. Stimulating electrodes are used to stimulate a dendrite (s) in the brain region that can elicit a response which can be recorded via the recording electrode. The stimulus is given at a rate of 1 per minute.

The stimulating electrode was placed in the nucleus accumbens, and the recording electrode was placed near to the stimulating electrodes.

The amplitude or the size of the response can be calculated from each stimulus. Baseline values were obtained. After that, an LTP stimulus was given, and the post-LTP data was collected. The data were normalized to baseline values.

Watch the video here on LTP is done in hippocampus, a brain region involved in memory: https://www.jove.com/video/2330/preparation-acute-hippocampal-slices-from-rats-transgenic-mice-for

The neurons are activated by a high frequency of 100Hz. The protocol used here: 4 trains of 100 Hz tetanus 3 mins apart and are represented below:

Chromatin immunoprecipitation technique is used to measure FosB expression.

Briefly, the brain tissue was fixed with formaldehyde to crosslink the DNA binding proteins. The DNA was sheared into small fragments, some of which contains the DNA binding proteins. Using specific antibodies (H4, H3), the DNA binding protein complex was isolated. The proteins are digested, and the DNA is released. The specific DNA sequences of interest were amplified to see if they precipitated with the antibody.

Watch the video here: https://www.jove.com/science-education/5551/chromatin-immunoprecipitation

mRNA was isolated from the brain tissue using the Trizol reagent. RNA was later reverse transcribed to cDNA or complementary DNA using primers of interest. The fold difference of mRNA over control values is calculated and compared across the groups.

Check the video here on the technique: https://www.youtube.com/watch?v=0MJIbrS4fbQ

Protein was extracted from the tissue. Proteins are separated based on molecular weights in a SDS-Page gel. The gel was transferred to nitrocellulose membrane.

The antibodies to H3 and H4 were applied to the membrane to detect the bands of interest.

Watch the technique here: https://www.jove.com/science-education/5065/the-western-blot

The drug was administered directly to the nucleus accumbens of the mice.

In order to do so, the coordinates of the nucleus accumbens are obtained from the mouse brain atlas. The mouse is placed in a stereotaxic chamber, and the cannula was inserted into the brain to inject the drug every day for 7 days. The cannula was guided to be inserted into the brain using the coordinates

The nuclear fractions are obtained from the mice using a nuclear extraction kit. HDAC activity was measured using the kit.

before birth; during pregnancy

mimicked; acted similarly

only for a short time

normal

help; make the process easy

modified

signaling pathways that help in gene regulation

adding phosphate residues

happening at the same time

not enough acetylation

removal of acetyl groups

increase or excessive acetylation

DNA sequences that define where the transcription should start in a gene

restrain

prompt or trigger

drugs that cause an increased behavioral or motor response

widely used

a model designed to perform behavioral experiments

Process by which acetyl groups are added to preferred residues in a protein.

For instance, acetyl groups are added to lysine residues in a protein structure

components of chromatin that helps in gene regulation

DNA + histone

it is one of the transcription factors that help in gene expression

the process by which a copy of genetic information is made from DNA to RNA

A synapse is a space between the neurons that allows passage of electric or chemical signals between the neurons.

Anything that occurs between synapses is referred to as synaptic

the ability of the neurons (brain cells) to change and learn new things by changing their synaptic strength

Medium sized neurons that have dendritic branches

slowing down, hold back, restrain, negatively affecting a response

neurons that contain inhibitory neurotransmitter, GABA

Part of the frontal cortex in the brain. Its function includes planning, organization, and decision making

A brain region present in the temporal lobe. It is almond In shape. It plays an important role in emotions.

Eg. When we see a lion, we immediately run due to fear. The fear response is due to the amygdala.

A brain region in the midbrain. Serves as a center for the origin of dopaminergic neurons

neurons that can modulate (or alter or modify) the neurotransmitter, glutamate. Glutamate is an excitatory neurotransmitter

neurons that contain neurotransmitter, dopamine. Dopamine plays a vital role in the reward pathway

to combine the similarities together

bringing together two different concepts that share similarities

recognition of one’s work or effort

contains the brain region, nucleus accumbens

A brain region in the forebrain. It has two parts: core and shell

causing someone to become dependent

Recreational drug. Referred as coke.

primary chemical present in tobacco

dependency, craving

modify

increased

preferred choice of one place over another

trained or habituated

Repeated administration of a stimulus can cause a response to the stimulus.

Eg. If you give your cat piping hot milk the first day, the cat may not drink it as it will burn its mouth. However, if you continue to give your cat hot milk for several days in a row, the cat will eventually start drinking the milk as it is habituated to the new stimulus (hot milk) and will not complain

the movement of a living being from one place to another

one by one; logical order

a key factor

not important

study of the structure and function of genes involved in the behavior

observing the electrical properties of neurons in the mouse brain

observing the behavior of the mouse

influence

the substances are mild and not addictive on consumption. However, the continuous consumption of these mild substances can lead to the use of other addictive drugs. They are also known as ‘habit-forming drug.’

Eg. Alcohol, Cigarettes.

Deals with incidence and distribution of diseases and societal issues

Substances that are addictive to the central nervous system.

These substances are illegal to be possessed, have no documented therapeutic effect, and are referred to as drugs of abuse.

Eg. Cocaine, Heroin

‘weed’ or ‘pot.’

Read more about marijuana here: https://www.drugabuse.gov/publications/research-reports/marijuana/what-marijuana

In contrast to the results we obtained with 7 days of nicotine treatment paired with cocaine, these animals did not show any change in the magnitude of LTP, no increase in locomotor activity of in FosB gene expression.

This indicates that the priming effect of nicotine can occur only when the drugs are given in a close window and not otherwise.

The mice receive 7 days of nicotine or water, and then the animals are weaned off the drug for 14 days. Cocaine was administered to animals after day 14 of treatment.

What is the duration of nicotine exposure that is needed to obtain the priming response we see in these animals?

Does nicotine need to be given closer to another drug or separated a few days apart?

A reduction in acetylated levels of histone H4 was observed

Figures 5 and 6 suggest that the nicotine inhibits HDAC activity, thereby causing global acetylation in the striatum and affecting gene expression.

In response to cocaine, this acetylation is further enhanced, thus allowing a more significant response in gene expression.

FosB gene expression is also reduced in mice treated with theophylline and cocaine compared to theophylline alone.

As expected, in LTP experiments, the mice treated with theophylline and cocaine injections showed a decrease in the magnitude of LTP compared to mice treated with theophylline alone.

Next, the authors tested the idea of histone acetylation by using a low dosage of theophylline, an HDAC stimulator. In contrast to SAHA, the theophylline should decrease the response to cocaine.

SAHA alone did not impair LTP just like nicotine did not impair LTP.

Pretreatment with SAHA followed by cocaine caused a dramatic decrease in the magnitude of LTP response at 180 mins. These results suggest that nicotine does inhibit HDAC activity.

Further, when SAHA was infused into nuclear accumbens for 7 days followed by cocaine injection, the FosB expression levels and acetylation of histone residues in striatum increased than the pretreatment with SAHA.

Similar to nicotine, SAHA increased the FosB expression levels by 71% and caused acetylation of histone residues in the striatum.

If nicotine is inhibiting HDAC activity, then by using an HDAC inhibitor, we should be able to mimic the effects of nicotine on LTP and FosB expression. This hypothesis was tested by using SAHA, an HDAC inhibitor.

28% reduction in HDAC activity was measured in animals treated with nicotine, suggesting that the nicotine inhibits the HDAC activity, thereby decreasing deacetylase activity.

To confirm that, histone deacetylase activity (HDAC) was measured in the striatum.

The authors next addressed whether the acetylation of residues is due to an increase in activation of acetylases or due to inhibition of deacetylase.

Again, there was an increase in acetylation levels of H3 and H4 in the striatum.

These results suggest that the nicotine increases the effect of cocaine on FosB expression by increasing the acetylated residues in FosB, thereby enhancing chromatin reorganization.

The authors observed the acetylation levels of H3 and H4 after 7 days of nicotine treatment in striatum tissue using chromatin immunoprecipitation and immunoblotting.

Authors observed the acetylation of histone H3 and H4. It is shown that both H3 and H4 got acetylated after a single dose of cocaine injection and after nicotine pretreatment.

The authors asked the question: does nicotine increase FosB expression by altering the chromatin structure at FosB promoter?

This suggests that the nicotine precedes cocaine and not in the reverse order.

On the contrary, the increase in FosB expression we observed in nicotine pretreatment is entirely absent with the cocaine pretreated animals.

The animals were given cocaine in drinking water for 7 days. Later, the mice were administered nicotine for 4 days. FosB mRNA levels were measured.

These experiments were performed to determine if the nicotine pretreatment combined with cocaine injection produces similar results to cocaine pretreatment combined with nicotine injection.

It could be that the nicotine causes a gene expression in animals. This primed response serves as a precursor for the brain to respond differently to cocaine to produce long term plasticity changes.

On the contrary, FosB expression was increased only in animals that received a cocaine injection after 7 days of nicotine treatment and not in 24 hours of treatment.

This suggests that the long term nicotine effect is responsible for the changes in gene expression.

Both 24 hours and 7 days of nicotine administration caused an increase in FosB expression by 50% and 61%.

However, mice treated with cocaine show a 17% decrease in the observed LTP.

In this experiment, the authors wanted to determine if the sequential drug use of cocaine can alter the cocaine-induced synaptic plasticity.

After high-frequency stimulation (HFS), mice treated with nicotine alone or water exhibit LTP that lasts for 180 mins. Mice pretreated with nicotine combined with cocaine injection show a dramatic reduction (~40%) in the observed LTP.

This suggests that the changes in LTP in nucleus accumbens is caused by pre-exposure of nicotine to the mouse.

Cocaine is capable of producing LTP in several brain regions.

Similar to the results obtained from animals, the individuals who started using cocaine were also active smokers, i.e., they initiated cocaine after smoking.

Mice pretreated with nicotine coupled with cocaine injections showed a further 78% increase in preference to cocaine-coupled chamber than cocaine-treated animals.

This suggests that persistent treatment of nicotine for 7 days increases the locomotor activity and behavioral responses of the animals

The experiment was performed to determine the behavioral response in the 4 groups of animals.

Do these animals have a conditioned place preference or aversion to cocaine? If the place preference to cocaine exists, which group out of 4 show the most sensitization to the CPP?

In the conditioned place preference test, mice pretreated with cocaine alone showed preference to the cocaine-coupled chamber by 223%.

Mice treated with nicotine for 7 days, followed by cocaine for 4 days show a 98% increase in locomotor activity than the control mice

Mice treated with an injection of cocaine for 4 days show a 58% increase in locomotor activity than the control mice

There is no difference in the distance traveled by the animals that were treated with nicotine in drinking water versus drinking water. (yellow vs. black bars, fig 1A).

Nicotine was added to the drinking water for the mice.

7 days treatment: The mice were fed with the nicotine-containing water for 7 days. For the next 4 days, mice received a cocaine injection intraperitoneally (injection into a body cavity) with continuous exposure to nicotine-containing water. The injections were given once per day.

24 hours of treatment. The mice were exposed to the nicotine-containing water for 24 hours, and the next 4 days; the mice received a cocaine injection (once per day) intraperitoneally with continuous exposure to nicotine-containing water.

Similar to nicotine, SAHA also causes an increase in the expression levels of FosB