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This Article Full Text Full Text (PDF) All Versions of this Article: 294/1/R52    most recent 00635.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Saggu, S. Articles by Lundy, R. F. PubMed PubMed Citation Articles by Saggu, S. Articles by Lundy, R. F.

APPETITE, OBESITY, DIGESTION, AND METABOLISM

Forebrain neurons that project to the gustatory parabrachial nucleus in rat lack glutamic acid decarboxylase

Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine, Louisville, Kentucky

Submitted 4 September 2007 ; accepted in final form 1 November 2007

Evidence suggests that GABA might mediate the inhibitory influence of centrifugal inputs on taste-evoked responses in the parabrachial nucleus (PBN). Previous studies show that activation of the gustatory cortex (GC), bed nucleus of the stria terminalis (BNST), central nucleus of the amygdala (CeA), and lateral hypothalamus (LH) inhibits PBN taste responses, GABAergic neurons are present in these forebrain regions, and GABA reduces the input resistance of PBN neurons. The present study investigated the expression of glutamic acid decarboxylase immunoreactivity (GAD_67 ir) in GC, BNST, CeA, and LH neurons that project to the PBN in rats. After anesthesia (50 mg/kg ip Nembutal), injections of the retrograde tracer Fluorogold (FG) were made in the physiologically defined gustatory PBN. Brain tissue containing the above forebrain structures was processed and examined for FG and GAD_67 ir. Similar to previous studies, each forebrain site contained retrogradely labeled neurons. Our results suggest further that the major source of input to the PBN taste region is the CeA (608 total cells) followed by GC (257 cells), LH (106 cells), and BNST (92 cells). This suggests a differential contribution to centrifugal control of PBN taste processing. We further show that despite the presence of GAD_67 neurons in each forebrain area, colocalization was extremely rare, occurring only in 3 out of 1,063 FG-labeled cells. If we assume that the influence of centrifugal input is mediated by direct projections to the gustatory region of the PBN, then GABAergic forebrain neurons apparently are not part of this descending pathway.

amygdala; bed nucleus; hypothalamus; cortex; taste; GAD