Systematic presence of GABA-immunoreactivity in the tubero-infundibular and tubero-hypophyseal dopaminergic axonal systems: an ultrastructural immunogold study on several mammals

Abstract

Immunoreactivities for tyrosine hydroxylase (TH), gamma-aminobutyric acid (GABA) and, in some cases, glutamic acid decarboxylase (GAD) were detected by light and electron microscopy in axons projecting into the median eminence and pituitary gland of various mammals (rats, mice, guinea pigs, cats, rabbits and hares). Light microscope immunoperoxidase reactions were performed on adjacent semithin sections of plastic-embedded samples. In the median eminence external zone, the distributions of the TH- and GAD- or GABA-immunoreactive endings were very similar in the anterior and lateral areas, while medially the GABA-labelled endings predominated. Comparable distribution patterns were found in the various species examined. In the pituitary gland, the distributions of GABA- and TH-immunoreactivities were superimposable in the intermediate lobes of all species examined, except in the rabbit and hare in which both types of innervation were lacking. For electron microscopy, the immunogold procedure was applied to sections of lowicryl-embedded samples; simultaneous detection of GABA- and TH-immunoreactivities was enabled by recto-verso double labelling with gold particles of distinct diameters. In the median eminence, GABA-immunoreactivity occurred systematically in the TH-positive endings, while distinct GABA-positive/TH-negative axons were also detected. In the intermediate lobe, the colocalization of TH- and GABA-immunoreactivities was a constant feature of the axons innervating the melanotrophic cells in all the species examined, except in the Leporidae. The functional significance of this colocalization remains to be determined.

Computational models of reinforcement learning: the role of dopamine as a reward signal

“…In the NAc, DA modulates glutamate co-transmission in a frequency-dependent manner, whereby only highfrequency stimulation of VTA neurons leads to DA facilitation of glutamate transmission (Chuhma et al 2009). DA cells of the VTA are also known to co-release GABA (Gall et al 1987;Maher and Westbrook 2008;Schimchowitsch et al 1991). The network activity in the target brain areas also plays an important role in controlling local activity, and therefore in controlling the influence of DA on its postsynaptic cells.…”

Effectiveness of GABAB antagonists in inhibiting baclofen‐induced reductions in cytosolic free Ca concentration in isolated melanotrophs of rat

“…The nerves, which course from the hypothalamus through the infundibular stalk to form synaptic-like contacts with the melanotrophs, exert a tonic inhibitory influence on melanotroph secretion which otherwise occurs at a high spontaneous rate. The classic inhibitory transmitter is dopamine (see Holzbauer & Racke, 1985), but y-aminobutyric acid (GABA) has also been detected in the nerves by immunohistochemical methods (Oertel et al, 1982;Vincent et al, 1982;Sakaue et al, 1988), seemingly as a co-stored transmitter (Stoeckel et al, 1985;Vuillez et al, 1987;Schimchowitsch et al, 1991).…”

Molecular and Physiological Evidence for Functional γ-Aminobutyric Acid (GABA)-C Receptors in Growth Hormone-secreting Cells

“…The opening of GABA-C channels may induce a membrane depolarization as suggested by an increase in Ca 2ϩ i levels measured by fluorometry on GH3 cells. In the pituitary gland, all types of GABA receptors are expressed (7,8,17), and GABA, produced either by the hypothalamus or by the pituitary itself (7,18,19), is known to be involved in the regulation of hormone levels (8,20,21). Interestingly GABA-C receptors were demonstrated previously in pituitary TSH cells (6).…”