Summary: Expression of GABAB Receptors in Magnocellular Neurosecretory
Cells of Male, Virgin Female and Lactating Rats
D. S. Richards,* R. M. Villalba,* F. J. Alvarez* and J. E. Stern
*Department of Physiology and Anatomy, Wright State University, Dayton, OH, USA.
Department of Psychiatry, University of Cincinnati, Cincinnati, OH, USA.
Key words: GABA, synaptic, supraoptic, paraventricular, hypothalamus.
GABA is one of the key neurotransmitters that regulate the firing activity of neurones in the supraoptic
(SON) and paraventricular (PVN) nuclei. In the present study, we used immunohistochemical techniques to
study the distribution and subcellular localisation of metabotropic GABAB receptors in magnocellular
neurones in the SON and PVN. Robust GABAB receptor immunoreactivity (GABABR; both subunit 1 and
subunit 2 of the heterodimer), was observed in the SON and PVN. At the light microcope level, GABABR
immonoreactivity displayed a clustered pattern localised both intracytoplasmically and at the plasma
membrane. Densitometry analysis indicated that GABABR immunoreactivity was significantly more intense
in vasopressin cells than in oxytocin cells, both in male, virgin female and lactating rats, and was denser in
males than in virgin females. Light and electron microscope studies indicated that cytoplasmic GABABR was
localised in various organelles, including the Golgi, early endosomes and lysosomes, suggesting the cycling
of the receptor within the endocytic and trafficking pathways. Some smaller clusters at the level of the cell
plasma membrane were apposed to glutamic acid decarboxylase 67 immunoreactive boutons, and
appeared to be colocalised with gephyrin, a constituent protein of the postsynaptic density at inhibitory