Developmental changes in the expression of GABAA receptor subunits 1, 2, and 3 in the rat pre-Bötzinger complex

Liu, Qiuli, and Margaret T. T. Wong-Riley. Developmental changes in the expression of GABAA receptor subunits 1, 2, and 3 in the rat pre-Bötzinger complex. J Appl Physiol 96: 1825–1831, 2004. First published January 16, 2004; 10.1152/japplphysiol.01264.2003.—Previously, we reported that the pre-Bötzinger complex (PBC) exhibited a dramatic reduction in cytochrome oxidase activity at postnatal day (P) 12. This coincided in time with decreases in glutamate and NMDA receptor subunit 1 and increases in GABA, GABAB, glycine receptor, and glutamate receptor GluR2. To test our hypothesis that various -subunits of GABAA receptors also undergo changes in their expression during postnatal development, as they do in other brain regions, we undertook an in-depth immunohistochemical study of GABAA receptor subunits 1, 2, and 3 in the PBC of P0 to P21 rats. We found that 1) GABAA 3-subunit was expressed at relatively high levels at P0, which then declined with age; 2) GABAA 1-subunit was expressed at relatively low levels at P0 but increased with age; 3) the developmental trends of subunits 1 and 3 intersected at P12; and 4) GABAA 2-subunit expression was moderate to light at P0 and remained quite constant during development, being lowest at P21. These findings suggest that the apparent switch in relative expressions of subunits 3 and 1 during development and the intersection of slopes around P12 may be associated with possible changes in GABAA receptor subtypes that would mediate different functional properties of GABA transmission, such as primarily a less efficient inhibitory transmission before P12 and a more mature inhibitory effect at P12 and thereafter, as suggested by the kinetics of distinct postsynaptic potentials. This mechanism may contribute partially to the dramatic reduction in cytochrome oxidase activity within the PBC at P12, as shown previously.