Redistribution and increased specificity of GABA(B) receptors during development of the rostral nucleus of the solitary tract

Recent results show that there is an abundance of gamma -aminobutyric acid (GABA) before GABAergic synapses have formed in the gustatory zone of the n ucleus of the solitary tract. These results suggest that a non-synaptic, de velopmental function may exist for GABA prior to synaptogenesis. However, G ABA exerts its physiological effect via its receptors, the development of w hich is a largely unknown process. The developmental expression of one of t he GABA receptors in the young nucleus of the solitary tract is the focus o f this study. The development of GABA(B) receptors was investigated by ligh t and electron microscopy. The results suggest that before the development of GABAergic synapses, GABA(B) receptors are diffusely distributed. When GA BAergic synapses form, the receptors become clustered. Quantitative postemb edding immunohistochemical studies at the electron microscopic level show t hat extrasynaptic labeling for GABA(B) receptors decreases during developme nt, but synaptic labeling increases. Increased specificity of neurotransmit ter receptors at synapses has been shown in other systems during developmen t, including other central nervous system structures, but this may be the f irst demonstration of the phenomenon using quantitative electron microscopy . (C) 2001 ISDN. Published by Elsevier Science Ltd. All rights reserved.