we monitored thestrength of LOT and ASSN inputs onto the same pyramidal cells7554 • J. Neurosci., July 11, 2007 • 27(28):7553–7558 Poo and Isaacson • A Critical Period for Plasticity in Olfactory Cortex

In olfactory cortex, however, pyramidal cells receive direct sensory input fromthe olfactory bulb, and it is unclear whether the development of olfactory sensory circuits is governed by a critical period. Here, we showthat NMDA receptor-dependent long-term potentiation and dendritic spine maturation occur only during a brief postnatal time windowat sensory synapses of olfactory cortex pyramidal cells. In contrast, associational synapses onto the same cells retain the capacity forplasticity into adulthood.

References

Together, the physiological and anatomical features of devel-oping LOT synapses provide strong support for the notion thatthere is a critical period for the modification of olfactory input tothe cortex.

Thus, although thedevelopmental time courses over which LTP at LOT inputs de-clines and spine density matures do not overlap completely, thesimilarities in their time courses suggest the possibility of a com-mon underlying mechanism.

Our results using intracellular recording and pairing of stim-ulation with depolarization indicate that strong NMDAR-dependent LTP of LOT synapses occurs during a brief postnatalperiod, after which there is a decrease in the ability of LOT syn-apses to undergo potentiation with our pairing protocol.

it has been sug-gested that activity-dependent plasticity of ASSN inputs couldenhance the salience of odor-evoked responses in pyramidal cellsand contribute to olfactory learning in adults

In this study, we examined NMDAR-dependent plasticity and thestructural maturation of sensory synapses in primary olfactorycortex.

A consistent decrease in theamount of LTP expressed at LOT synapseswas observed at later developmental timepoints. By the fourth postnatal week, LOTsynapses failed to express any long-termplasticity

In contrast to neonatal rats, we found that plasticity of sensorysynapses was markedly reduced in animals that were slightlyolder (P15–P19).

This pairing-induced LTP dem-onstrates that synapse specific plasticity at sensory LOT synapsesdoes not require widespread activation of fibers through tetanicstimulation.

We used whole-cell recording to study LOT-evoked EPSCs re-corded from layer II pyramidal cells in rat anterior piriform cor-tex slices (Franks and Isaacson, 2005)

Previous reports of activity-dependent plasticity at sensory syn-apses in olfactory cortex monitored the effect of theta-burst ortetanic stimulation on LOT-evoked extracellular fEPSPs

we examine whether a critical period for synapticplasticity and structural development may occur in olfactory cor-tex.

Together, these results suggest a developmentalcritical period for the plasticity of olfactory sensory inputs inpiriform cortex.

postnatal day 5 (P5) to P35 Sprague Dawley rats

It may be that thisearly maturation of sensory dendritic regions in piriform cortexis associated with olfaction being completely functional in ro-dents at birth

early development are associated withmaturation of cortical circuits

Structural changes of neuronal mor-phology are correlated with critical peri-ods for plasticity (Hensch, 2004), and in-creases in dendritic spine density duringearly development are associated withmaturation of cortical circuits

hus, although there is astrong correlation between age and LTP atLOT synapses, there is no significant cor-relation at ASSN synapses

tal life and found a significant decrease inthe amount of LTP expressed at sensorysynapses by the second postnatal week

Together, these results show that synapse-specific, NMDAR-dependent LTP can be triggered at olfactorysensory inputs of newborn rats.

These findings imply that in addition tobeing both functional and necessary at birth, central olfactorycircuits could display enhanced plasticity during the early post-natal stage.

Newborn animals (including humans) use olfactory informa-tion to form strong maternal attachments, and this “imprinting”to maternal odors is crucial for survival in many species