GABA(A) RECEPTOR-LIKE IMMUNOREACTIVITY IN THE GOLDFISH BRAIN-STEM WITH EMPHASIS ON THE MAUTHNER CELL

The distribution of the GABA(A) receptor in the goldfish brainstem and on the Mauthner cell membrane was investigated with both optical and electron microscopy using a polyclonal antibody raised against the int racellular loop of the rat gamma 2 subunit. At the optical level, immu nofluorescent dots were detected on small and large neurons belonging to vestibular and reticular nuclei. On the Mauthner cell plasmalemma, a gamma 2-like immunoreactivity was observed predominantly on the tip of the lateral dendrite. Fluorescent parches were intermingled with a more diffuse staining. Immunoreactive spots of weaker intensity were a lso present on the soma and some were also observed inside and within the periphery of the axon-cap as well. Observations at the electron mi croscopic level revealed that the peroxidase end-product predominates postsynaptically in front of release sites in the studied nuclei and o n the Mauthner cell. On the lateral dendrite of the neuron, numerous i mmunopositive postsynaptic differentiations were encountered on spines . Stained glial elements were encountered in the different areas studi ed. These results demonstrate that the GABA(A) receptor gamma 2 subuni t has a precise distribution on neuronal membranes and suggest that it could be involved in the remote dendritic inhibition of the Mauthner cell and in the control of input-output properties of both vestibular and reticular nuclei.