The postnatal development of GABA receptors in the rostral nucleus of the solitary tract

The rostral nucleus of the solitary tract (rNST) is the first relay nucleus involved in the processing of taste information. Although synaptic circuitry responsible for gustatory processing in the rNST is not well understood, the inhibitory neurotransmitter γ-aminobutyric acid (GABA) is thought to play an important role. The rNST undergoes dramatic changes in structure and function during postnatal development. In particular, recent work has focused on the how the expression and function of GABA changes during postnatal development of this gustatory nucleus. In order to fully understand the effects of GABA, one must look to the expression and function of its receptors. Therefore, the goal of this research was to characterize the expression and function of GABA_A receptors and GABA_B receptors in the adult and developing rNST. The methods employed include immunohistochemistry for light microscopy, post-embedding immunohistochemistry for electron microscopy, and whole cell patch clamp recordings.; In the adult rNST, GABA_A receptor labeling is seen in neuropil, cell somata, and processes. GABA_B receptor labeling is seen in cell somata and processes. There is an interesting appearance of clusters of label in many cell somata and processes. At the ultrastructural level, these clusters appear to be related to synapses. GABA_B receptors can be localized to the presynaptic terminal, postsynaptic target, and/or synaptic cleft. GABA_B receptors can also be seen in extrasynaptic profiles.; During postnatal development of the rNST, GABA_A receptors and GABA_B receptors are present and functional. Three phases of change occur during development that may reflect the changing role of GABA. First, there is a general increase in GABA receptor immunoreactivity from PND1 to PND10 that correlates when GABA is plentiful but GABAergic synapses are rare. This may reflect a neuromodulatory or neurotrophic role of GABA. Next, there is a general decrease in GABA receptor immunoreactivity from PND11 to PND20 at a time when GABAergic synapses are abundant and this may correlate to increased specificity of receptor placement reflecting the emerging neurotransmitter role of GABA. Finally, there is a late postnatal rise in GABA receptor immunoreactivity that correlates to the late maturation of rNST neuronal. response properties to GABA.