Activation of A‐Type γ‐Amino Butyric Acid Receptors Excites Gonadotrophin‐Releasing Hormone Neurones Isolated from Adult Rats

Abstract

Gonadotrophin-releasing hormone (GnRH) neurones represent the final output neurones in the neuroendocrine control of reproduction, and gamma-amino butyric acid (GABA) is one of the major players in the regulation of GnRH neurones. GABA inhibits a large proportion of brain neurones in adult animals by acting on A-type GABA receptors (GABA(A)Rs). Two contradictory reports on the action of GABA in the GnRH neurones of adult mice have been published. DeFazio et al. (Mol Endocrinol 2002; 16: 2872) demonstrated that activation of GABA(A)Rs excites the GnRH neurones of adult mice, whereas Han et al. (Endocrinology 2002; 143: 1459) showed that the response to GABA on GnRH neurones switches from depolarisation to hyperpolarisation around puberty in female mice. Therefore, we examined the reversal potential of GABA(A)R currents by means of perforated patch-clamp recording with gramicidin in overnight-cultured GnRH neurones isolated from adult GnRH-enhanced green fluorescent protein transgenic rats. The reversal potential was -26 +/- 1.4 mV (mean +/- SEM, n = 42) in GnRH neurones, whereas it was -57 +/- 2.7 mV (n = 34) in unidentified neurones, and GABA depolarised the GnRH neurones in current-clamp condition. The GABA(A)R currents in rat GnRH neurones were augmented by neurosteroids, allopregnanolone and 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one, at submicromolar concentrations. In addition, the expression patterns of GABA(A)R subunit mRNAs were determined by multi-cell reverse transcription-polymerase chain reaction, which revealed that the alpha2, beta 3, gamma 1 and gamma 2 subunits were dominant and the alpha 6 and gamma 3 subunits were negative in rat GnRH neurones. These results indicate that GABA(A)Rs in the soma of rat GnRH neurones are comprised mainly of alpha2, beta 3 and gamma 1 or gamma 2 subunits and that they are sensitive to neurosteroids; moreover, they suggest that activation of these receptors depolarises GnRH neurones. Thus, GABA and neurosteroids influence the electrical activity of GnRH neurones.

Gene structures, biochemical characterization and distribution of rat melatonin receptors

“…To avoid amplifying any contaminating genomic DNA, the primer pairs were designed from different exons. Multi-cell RT-PCR Slice preparation and cell harvest are described in detail elsewhere [15,16]. In brief, coronal slices (200 lm thick) containing medial septum, diagonal band of Broca, organum vasculosum of the lamina terminalis and medial preoptic area were prepared from adult male and female transgenic rats.…”

Excitatory Action of GABA in the Terminal Nerve Gonadotropin-Releasing Hormone Neurons

“…This depolarizing GABA A response is suggested to mediate various physiological signals in the hypothalamic GnRH neurons. For example, Christian and Moenter (2007) demonstrated that the rate of GABAergic transmission changes in a diurnal manner but also that the response to GABA does not change in a diurnal manner; i.e., the ability to induce action potentials is not altered (Christian and Moenter 2008); this was also shown in the rat (Yin et al 2008). Thus considering the results of the present study, it is tempting to hypothesize that depolarizing GABA A response is a common property shared by GnRH neurons in general, although the anatomy and function are clearly different between TN-GnRH neurons and hypothalamic GnRH neurons, and GABA A response of the third GnRH system in the tegmentum (midbrain GnRH neurons) remains to be investigated.…”

“…Although the response to GABA A receptor activation is predominantly hyperpolarizing in mature neurons, depolarizing GABA A response has been reported in some neurons of adult animals such as the dorsal root ganglion cells (Sung et al 2000) and fast-spiking interneurons of the cortex and amygdala (Martina et al 2001). The hypothalamic GnRH neurons also show depolarization in response to GABA A receptor activation in the mouse (Constantin et al 2009;DeFazio et al 2002) and rat (Yin et al 2008). This depolarizing GABA A response is suggested to mediate various physiological signals in the hypothalamic GnRH neurons.…”

A simple integrative electrophysiological model of bursting GnRH neurons

“…As it is described in , the postsynaptic currents measured in this configuration correspond to GABAa receptor activation, which, although there are some controversial results (Han et al, 2002(Han et al, , 2004, is assumed to affect adult GnRH neurons in an excitatory way Moenter & DeFazio, 2005;Watanabe et al, 2009;Yin et al, 2008). Although there are other types of (mainly glutamate mediated) synaptic inputs to GnRH neurons (Suter, 2004;Kuehl-Kovarik et al, 2002), measurements of postsynaptic currents in this configuration usually fail to detect these glutamatergic excitatory currents.…”