The inferior colliculus of the rat: Quantitative immunocytochemical study of GABA and glycine
Section snippets
Immunocytochemistry for GABA and Gly
Six adult Wistar rats of either sex (B.W., 250–300g) were anesthetized with sodium pentobarbital (60mg/kg, i.p.) and perfused transcardially with a cold (6°C) wash solution (40ml) composed of 2% dextran (MW 70,000) in 0.1M sodium phosphate buffer, pH 7.4 (PB), followed by 750ml of a fixative containing 1% paraformaldehyde and 2.5% glutaraldehyde in the same buffer at room temperature. The specimens were kept at 4°C overnight, and the next day the brains were removed. The brainstems were cut
Standard microscopic analysis of GABA and Gly immunoreactivity in the IC
Visual inspection of the immunostained tissue under the light microscope revealed that all parts of the IC show (1) dense punctate immunostaining of the neuropil to both GABA (Fig. 1, Fig. 2) and Gly (Fig. 2), (2) some IC neurons are GABA-IR, and (3) no IC neurons are Gly-IR.
GABA-IR neurons show a variable degree of immunostaining regardless of their topographical location. They are found in all subdivisions of the IC in slightly different proportions, and have cell bodies of variable sizes and
Discussion
The present account demonstrates that all neurons in the IC are under the influence of GABAergic and/or glycinergic inhibitory input. Furthermore, a quarter of the IC neurons in the rat are GABAergic and, in contrast to lower auditory centers, the IC lacks glycinergic cells.
Fig. 11 illustrates our main findings in schematic representations of the IC subdivisions (A) and of the CNIC lamina seen en face (B). The results may be summarized as follows: 1) GABAergic neurons are larger than
Acknowledgments
Dr. Ole P. Ottersen kindly provided GABA and glycine antibodies. We thank Ignacio Plaza for his excellent technical assistance, and Jack Kelly, Douglas Oliver, Kirsten Osen and Bruce Warr for their critical reading and comments on a previous version of the manuscript. This study was supported by the Spanish DGES; grant number: BFI-2000-1396, Spanish DGES; grant number BFI-2003-09147-02-01 to M.A.M. and M.S.M.; the Spanish JCYL-UE grant number: SA040/04 to M.S.M. and M.A.M.), and the Spanish
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Present address: University Cayetano Heredia, Division of Neuroscience and Behavior, Lima, Peru.