GABA‐like immunoreactivity in the tuberomammillary nucleus: An electron microscopic study in the rat

Abstract

The organization of GABAergic elements in the histaminergic tuberomammillary nucleus has been examined by using antibodies against γ‐aminobutyric acid (GABA) and light and electron microscopy. Most neuronal perikarya of the ventral subgroup of the tuberomammillary nucleus were GABA immunoreactive (GABA‐i). The morphology of the GABA‐i perikarya was similar to the morphology of histaminergic perikarya described by Hayashi et al. ('84: J. Comp. Neurol. 229:233–241) and Wouterlood et al. ('86: J. Comp. Neurol. 252:227–243). The GABA‐i perikarya were contacted by relatively few terminals. The mean bouton covering ratio of GABA‐i perikarya was 6.1%, whereas the mean bouton covering ratio for GABA‐i dendrites in the tuberomammillary nucleus was 31%. Some of the presynaptic terminals were GABA‐i. In addition, GABA‐i perikarya and dendrites formed close contacts that never presented synaptic specializations. These results suggest that neurons of the histaminergic tuberomammillary nucleus contain the neurotransmitter GABA. Furthermore, GABA may act as a modulator of cellular processes within the tuberomammillary nucleus.