Evidence For A GABAergic System In Rodent And Human Testis: Local GABA Production And GABA Receptors


Jan 6, 2015
Like dopamine and serotonin, gaba is not only active in the brain , it has peripheral functions too.

Evidence for a GABAergic system in rodent and human testis: local GABA production and GABA receptors. - PubMed - NCBI


The major neurotransmitter of the central nervous system, gamma-aminobutyric acid (GABA), exerts its actions through GABA(A), GABA(B) and GABA(C) receptors. GABA and GABA receptors are, however, also present in several non-neural tissues, including the endocrine organs pituitary, pancreas and testis. In the case of the rat testis, GABA appears to be linked to the regulation of steroid synthesis by Leydig cells via GABA(A) receptors, but neither testicular sources of GABA, nor the precise nature of testicular GABA receptors are fully known. We examined these points in rat, mouse, hamster and human testicular samples. RT-PCR followed by sequencing showed that the GABA-synthesizing enzymes glutamate decarboxylase (GAD) 65 and/or GAD67, as well as the vesicular GABA transporter vesicular inhibitory amino acid transporter (VIAAT/VGAT) are expressed. Testicular GAD in the rat was shown to be functionally active by using a GAD assay, and Western blot analysis confirmed the presence of GAD65 and GAD67. Interstitial cells, most of which are Leydig cells according to their location and morphological characteristics, showed positive immunoreaction for GAD and VIAAT/VGAT proteins. In addition, several GABA(A) receptor subunits (alpha1-3, beta1-3, gamma1-3), as well as GABA(B) receptor subunits R1 and R2, were detected by RT-PCR. Western blot analysis confirmed the results for GABA(A) receptor subunits beta2/3 in the rat, and immunohistochemistry identified interstitial Leydig cells to possess immunoreactive GABA(A) receptor subunits beta2/3 and alpha1. The presence of GABA(A) receptor subunit alpha1 mRNA in interstitial cells of the rat testis was further shown after laser microdissection followed by RT-PCR analysis. In summary, these results describe molecular details of the components of an intratesticular GABAergic system expressed in the endocrine compartment of rodent and human testes. While the physiological significance of this peripheral neuroendocrine system conserved throughout species remains to be elucidated, its mere presence in humans suggests the possibility that clinically used drugs might be able to interfere with testicular function.

Stimulation of TM3 Leydig cell proliferation via GABA A receptors: A new role for testicular GABA


The neurotransmitter gamma-aminobutyric acid (GABA) and subtypes of GABA receptors were recently identified in adult testes. Since adult Leydig cells possess both the GABA biosynthetic enzyme glutamate decarboxylase (GAD), as well as GABAA and GABAB receptors, it is possible that GABA may act as auto-/paracrine molecule to regulate Leydig cell function. The present study was aimed to examine effects of GABA, which may include trophic action. This assumption is based on reports pinpointing GABA as regulator of proliferation and differentiation of developing neurons via GABAA receptors. Assuming such a role for the developing testis, we studied whether GABA synthesis and GABA receptors are already present in the postnatal testis, where fetal Leydig cells and, to a much greater extend, cells of the adult Leydig cell lineage proliferate. Immunohistochemistry, RT-PCR, Western blotting and a radioactive enzymatic GAD assay evidenced that fetal Leydig cells of five-six days old rats possess active GAD protein, and that both fetal Leydig cells and cells of the adult Leydig cell lineage possess GABAA receptor subunits. TM3 cells, a proliferating mouse Leydig cell line, which we showed to possess GABAA receptor subunits by RT-PCR, served to study effects of GABA on proliferation. Using a colorimetric proliferation assay and Western Blotting for proliferating cell nuclear antigen (PCNA) we demonstrated that GABA or the GABAA agonist isoguvacine significantly increased TM3 cell number and PCNA content in TM3 cells. These effects were blocked by the GABAA antagonist bicuculline, implying a role for GABAA receptors. In conclusion, GABA increases proliferation of TM3 Leydig cells via GABAA receptor activation and proliferating Leydig cells in the postnatal rodent testis bear a GABAergic system. Thus testicular GABA may play an as yet unrecognized role in the development of Leydig cells during the differentiation of the testicular interstitial compartment.


Thread starter
Jan 6, 2015
Effect of GABA and benzodiazepines on testicular androgen production. - PubMed - NCBI

We have evaluated the effect of Ro5-4864, a selective probe to label peripheral type benzodiazepine receptor, on "in vitro" testicular androgen production. Decapsulated testes from adult rats showed a significant increase in the basal and hCG-stimulated testosterone secretion into the medium in response to 10(-5) M, 10(-6) M, and 10(-7) M Ro5-4864. In addition, we have studied the changes in testicular GABA content at three different ages and we found its highest concentration at 31 days of age. When we evaluated the effect of GABA on "in vitro" androgen production at different stages of gonadal maturation we observed that the highest concentration of GABA (10(-6) M) was able to modify the basal and hCG-stimulated androgen production from adult (60 days) and pubertal (45 days) testes. In addition, when prepubertal testes (31 days) were incubated under basal conditions, 10(-6) M GABA induced a significant increment of androstanediol production, while the stimulatory effect of hCG was reduced in the presence of the same GABA concentration. The present results suggest that GABA plays a physiological role in the regulation of rat testicular androgen production depending on the stage of sexual maturation.


May 17, 2018
The GABA activity of progesterone and other androgens came to mind, here's a quote from Haiduts post:

Just like allopregannolone (ALLO), androsterone is 5-AR derived neurosteroid, and just like allopreganolone, androsterone is a very potent GABA agonist (even more potent than progesterone).

Allopregnanolone has been in human clinical trials for everything from anxiety, to depression, to seizures, to schizophrenia, to autism, etc.
Anyways, the neurosteroid androsterone, which is a metabolite of DHT, has virtually the same benefits profile as ALLO... The studies below show its effects as a GABA agonist and in treatment of anxiety, seizures, and mental hyperactivity (sedating effect).
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