1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

233 Symposium Changing the Development of Tasteand OlfactionEARLY ENVIRONMENTAL EVENTS SHAPE THENEUROBIOLOGICAL DEVELOPMENT OF THE GUSTATORYSYSTEMHill D.L. 1 , Mangold J. 1 1 Psychology, University of Virginia,Charlottesville, VAImpressive morphological, physiological, and behavioral changescharacterize the postnatal development of the rat gustatory system.While much has been learned by studying developmental processes incontrol rats, complementary experiments using early dietary sodiumrestriction have been of great value in learning how the taste system isorganized. For example, recent findings from our laboratorydemonstrate that the dramatic diet-related differences in theorganization and size of gustatory afferent terminal fields in the ratbrainstem are due to a reorganization of terminal fields with age incontrol rats and a lack of an age-related reorganization in experimentalrats. Due to large differences in primary afferent taste responsesbetween groups, this finding suggests that activity-dependent “pruning”of axonal arbors may occur in controls but not in early sodiumrestrictedrats. This symposium presentation will provide a summary ofearly developmental diet-related changes in peripheral taste functionand changes in central structure and function. An emphasis will beplaced on more recent experiments in which we have examined theinterrelationships among the terminal fields of three gustatory nerves inthe rat NTS during normal development and how various dietarymanipulations instituted during embryonic development differentiallyalters this development. Supported by NIH grant R01 DC00407.235 Symposium Changing the Development of Tasteand OlfactionNEURAL NETWORKS INVOLVED IN OLFACTORY FEARCONDITIONING IN RATS FROM INFANCY TO ADULTHOODMouly A. 1 1 Institut des Sciences Cognitives, CNRS-Université Lyon1,Bron, Rhone, FranceIn a recent study, we investigated whether synaptic changes could bedetected at different levels of the olfactory pathways following an odorfear conditioning learning. For this, evoked potentials induced in fourrecording sites (anterior piriform cortex, posterior piriform cortex,cortical and basolateral nuclei of the amygdala) in response to electricalstimulation of the olfactory bulb were collected before odor-shocktraining (baseline) and during the retention test. The data showed thatlearning was accompanied by a lasting increase in signal amplitude incortical amygdala, and a transient increase in posterior piriform cortexand basolateral amygdala, suggesting a differential involvement of thesestructures in recognition of the learned odor. Paradoxically earlyolfactory fear conditioning causes odor preferences in rat pups during atemporally defined sensitive period. We assessed the effects of thisearly experience on adult olfactory fear conditioning. Specifically,infant rats were trained daily from 8-12-days old in an odor fearconditioning paradigm. In adulthood, these animals were trained againin the same paradigm and tested for freezing to the presentation of odoralone. In parallel, amygdala activation following acquisition wasassessed using 2-DG mapping.The data showed that, compared tocontrol animals, early trained animals presented lower levels of freezingand no detectable amygdala participation in the adult fear conditioningparadigm. This suggests that early neonatal experience has lastingconsequences on both the behavior and the neural network observed inadulthood in odor fear learning.234 Symposium Changing the Development of Tasteand OlfactionONTOGENETIC EMERGENCE OF LEARNED/NATURALFEAR AND DEVELOPMENT OF THE ODOR PATHWAY TOTHE AMYGDALASullivan R.M. 1 1 Department of Zoology, University of Oklahoma,Norman, OKInfant rats do not express fear to natural predator odors, nor do theylearn to avoid odors from olfactory fear conditioning until postnatal day10. This is coincident with the emergence of walking suggesting fearemerges when the risk of predation increases. The ability to express fearappears to be due to the functional emergence of the amygdala at PN10in both natural fear and conditioned fear. Fear to predator odor andlearned fear can be either retarded or advanced by manipulatingcorticosteroid (CORT) levels. Moreover, CORT is capable of changingthe neural pathway of the odor and presumably underlies the behavioralchange. Specifically, before the emergence of fearful behaviors (learned& unlearned), odor are relayed from the bulb to the anterior piriformcortex. For the expression of fear, either in older pups or younger pupsgiven CORT, the olfactory circuit is bulb, posterior piriform andamygdala, although a direct bulb-amygdala pathway also exists. Wewill present data suggesting odor-shock fear conditioning in 14-day-oldpups produces an odor aversion with amygdala participation when themother is absent but an odor preference with amygdala nonparticipationwhen the mother is present. The ability of maternal presence to alterolfactory fear learning appears due to the mother´s regulation of pups´CORT with maternal odor and tactile stimulation maintaining pups lowCORT levels, even during stressful presentations of 0.5-mA shock.This work is supported by NIH-NICHD, NSF-IBN and OCAST.236 Symposium Changing the Development of Tasteand OlfactionNEURAL ANALYSIS OF PREDATOR ODOR-INDUCED FEARAND EMOTIONAL MEMORYTakahashi L.K. 1 1 Psychology, University of Hawaii, Honolulu, HIInfant and adult rodents exposed to predator odor exhibit diversefear-related responses including freezing, avoidance, and stresshormone secretion. Brain structures, with prominent binding of stresshormones, such as the hippocampus and the amygdala likely play keyroles in the development and modulation of fear behavior. However,very little information is known on the neural basis of emotionallearning and memory associated with predator odor. We are especiallyinterested in the amygdala, a brain region implicated in fearconditioning using aversive electric shock, in mediating predator odorinducedemotional behavior. Our predator odor studies in adult ratshave shown that basolateral amygdalar (BLA) lesions impair theelicitation of cat odor-induced unconditioned and conditioned fearresponses. In addition, the medial amygdala (MeA), which is associatedwith aggressive and sexual behavior, plays an important role inmodulating cat odor-induced fear. MeA lesions were as effective asBLA lesions in attenuating predator odor-induced unconditioned andconditioned behavior. The specific roles of the BLA and MeA inpredator odor fear consolidation and memory retrieval were furtherevaluated using temporary brain inactivation methods. Muscimolinjections made immediately after exposure to cat odor produced asubsequent impairment in conditioned fear behavior but only wheninjected in the BLA. In contrast, the retrieval of conditioned fearbehavior was attenuated but only when lidocaine was injected into theMeA just prior to the conditioned fear test. Our novel resultsunderscore the unique participation of the BLA and MeA inconsolidation and retrieval processes underlying predator odoremotional memory. Supported by NS39406.59