Morphological evidence for direct interaction between glycine transporter immunoreactive cells and GnRH neurons in the mouse brain

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 134-163-GnRH & Gonadotroph Biology & Signaling
Bench to Bedside
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-142
Zsuzsa Bardóczi1, Barbara Vida1, Masahiko Watanabe2 and Imre Kalló*1
1Institute of Experimental Medicine, HAS, Budapest, Hungary, 2Hokkaido University School of Medicine, Abiko-Shi, Japan
The amino acid neurotransmitter glycine has been implicated in pubertal development and estrogen’s positive feedback action on luteinizing hormone secretion. Glycine is synthesized and secreted by neurons, which are mainly located in the caudal parts of the CNS and use the type 2 glycine transporters (GLYT2) to replenish their synaptic vesicles. At certain conditions glycine is also released from astrocytes and neurons via the type 1 glycine transporter (GLYT1) and has been suggested to influence neuronal functions via receptors located in non-synaptic membranes.

The current study used immunohistochemical double labeling of mouse forebrain sections to reveal, whether gonadotropin releasing hormone (GnRH) neurons, which control both sexual maturation and adult reproductive function, are at their preoptic/hypothalamic location, in morphological relationship with GLYT1- or GLYT2-immunoreactive (IR) cells. In addition, it was also tested, whether GnRH neurons are immunoreactive for glycine receptors.

Strong, patched GLYT1-immunoreactivity was found in the medial septum, the medial preoptic area and anterior hypothalamus, where the immunoreactive loci, resembling the shape of astrocytes, surrounded each subpopulation of GnRH-IR neurons. In accordance with previous studies, abundant GLYT2-IR projections showing axonal varicosities were also present at these sites. Analysis at light- and confocal microscopic levels identified GLYT2-IR boutons in apposition to GnRH-IR perikarya and dendrites. At the ultrastructural level synaptic contacts between GLYT2-IR axon terminals and GnRH-IR neurons showing asymmetric characteristics were found, suggesting a direct neuronal release of glycine into the synaptic cleft. The presence of glycine receptors in preoptic neurons was investigated at confocal microscopic level by using a pan-GlyRα antibody recognising all α1-4 subunits. Although many neurons in the septal-preoptic area were immunopositive for these subunits, double-labeling failed to reveal receptor immunoreactivity in GnRH neurons.

These data provide the first morphological evidence that glycinergic cells have the capacity to directly influence GnRH neurons in the mouse basal forebrain, but leaves the question open, whether the effect is mediated by glycine receptors assembled from GlyRβ subunit and polypeptides other than GlyRα subunits, and/or via the glycineB binding site of NMDA receptors present in the GnRH neurons and/or their afferents.

Nothing to Disclose: ZB, BV, MW, IK

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: Support contributed by: grants from the National Science Foundation of Hungary(OTKA K101326; OTKA K83710; OTKA 100722).  The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under GrantAgreement 245009.