The level and distribution of the GABABR1 and GABABR2 receptor subunits in the rat's inferior colliculus

Abstract

The type B γ-aminobutyric acid receptor (GABAB receptor) is an important neurotransmitter receptor in the midbrain auditory structure, the inferior colliculus (IC). A functional GABAB receptor is a heterodimer consisting of two subunits, GABABR1 and GABABR2. Western blotting and immunohistochemical experiments were conducted to examine the expression of the two subunits over the IC including its central nucleus, dorsal cortex, and external cortex (ICc, ICd, and ICx). Results revealed that the two subunits existed in both cell bodies and the neuropil throughout the IC. The two subunits had similar regional distributions over the IC. The combined level of cell body and neuropil labeling was higher in the ICd than the other two subdivisions. Labeling in the ICc and ICx was stronger in the dorsal than the ventral regions. In spite of regional differences, no defined boundaries were formed between different areas. For both subunits, the regional distribution of immunoreactivity in the neuropil was parallel to that of combined immunoreactivity in the neuropil and cell bodies. The density of labeled cell bodies tended to be higher but sizes of cell bodies tended to be smaller in the ICd than in the other subdivisions. No systematic regional changes were found in the level of cell body immunoreactivity, except that GABABR2-immunoreactive cell bodies in the ICd had slightly higher optic density (OD) than in other regions. Elongated cell bodies existed throughout the IC. Many labeled cell bodies along the outline of the IC were oriented in parallel to the outline. No strong tendency of orientation was found in labeled cell bodies in ICc. Regional distributions of the subunits in ICc correlated well with inputs to this subdivision. Our finding regarding the contrast in the level of neuropil immunoreactivity among different subdivisions is consistent with the fact that the GABAB receptor has different pre- and postsynaptic functions in different IC regions.

Differential distribution of GABA and glycine terminals in the inferior colliculus of rat and mouse

“…The GABA‐A receptor binding was significantly higher in the dorsal cortex than in the ICC and LC (Milbrandt et al, ). A similar pattern was seen for GABA‐BR1 and GABA‐BR2 receptors with immunohistochemical methods (Jamal et al, ). In a similar study of GLY receptors in the IC of the gerbil (Sanes et al, ), their distribution was described as being at the highest concentrations in the ventral, high‐frequency region of the IC.…”

GABAA and GABAB receptor subunit localization on neurochemically identified neurons of the human subthalamic nucleus

“…Detection of the GABA B receptor subunits was conducted using two polyclonal antibodies, GABA B R1 and GABA B R2 (Merck Millipore, Billerica, MA, cat# AB1531, AB5394, RRID:AB_2314472, RRID:AB_91623), raised in guinea pigs immunized with synthetic peptides. Both antibodies have been extensively characterized by immunohistochemistry and western blotting in rat (Díaz, Bravo, Rojas, & Concha, ; Jamal, Khan, Butt, Patel, & Zhang, ; Rekik, Daguin‐Nerrière, Petit, & Brachet, ; Yung, Ng, & Wong, ) and human tissue (Allen et al, ; Waldvogel et al, ). Western blotting of both antibodies in human brain homogenates from multiple regions showed detection of protein bands at approximately 100 kDa (corresponding to GABA B R1a), 130 kDa (corresponding to GABA B R1b), and a band of approximately 120 kDa (corresponding to GABA B R2) (Waldvogel et al, ).…”

Auditory System

“…The rat IC neurons possess GABA A , GABA B and glycine receptors (Bowery et al, 1987;Edgar and Schwartz, 1990;Vaughn et al, 1996;Campos et al, 2001). The GABA B receptors seem to be more abundant in the DCIC, RCIC and LCIC than in the CIC (Jamal et al, 2011(Jamal et al, , 2012. Ma et al (2002) have shown a role for presynaptic GABA B receptors.…”