Frequency-Dependent Recruitment of Fast Amino Acid and Slow Neuropeptide Neurotransmitter Release Controls Gonadotropin-Releasing Hormone Neuron Excitability

Abstract

The anteroventral periventricular nucleus (AVPV) is thought to play a key role in regulating the excitability of gonadotropin-releasing hormone (GnRH) neurons that control fertility. Using an angled, parahorizontal brain slice preparation we have undertaken a series of electrophysiological experiments to examine how the AVPV controls GnRH neurons in adult male and female mice. More than half (59%) of GnRH neurons located in the rostral preoptic area were found to receive monosynaptic inputs from the AVPV in a sex-dependent manner. AVPV stimulation frequencies Ͻ1 Hz generated short-latency action potentials in GnRH neurons with GABA and glutamate mediating Ͼ90% of the evoked fast synaptic currents. The AVPV GABA input was dominant and found to excite or inhibit GnRH neurons in a cell-dependent manner. Increasing the AVPV stimulation frequency to 5-10 Hz resulted in the appearance of additional poststimulus inhibitory as well as delayed excitatory responses in GnRH neurons that were independent of ionotropic amino acid receptors. The inhibition observed immediately following the end of the stimulation period was mediated partly by GABA B receptors, while the delayed activation was mediated by the neuropeptide kisspeptin. The latter response was essentially absent in Gpr54 knock-out mice and abolished by a Gpr54 antagonist. Together, these studies show that AVPV neurons provide direct amino acid and neuropeptidergic inputs to GnRH neurons. Low-frequency activation generates predominant GABA/glutamate release with higher frequency activation recruiting release of kisspeptin. This frequency-dependent release of amino acid and neuropeptide neurotransmitters greatly expands the range of AVPV control of GnRH neuron excitability.

Expression of ESR1 in Glutamatergic and GABAergic Neurons Is Essential for Normal Puberty Onset, Estrogen Feedback, and Fertility in Female Mice

“…Studies over the last decade have focused intensely, if not exclusively, upon the roles of ESR1-expressing kisspeptin neurons in these feedback loops. Whereas a strong case can been made for ESR1-expressing kisspeptin neurons located in the rostral periventricular area of the third ventricle (RP3V) to be involved in the positive feedback mechanism Ohkura et al, 2009;Smith, 2013), the roles of ESR1-positive kisspeptin neurons in the arcuate nucleus (ARN) remain unclear (de Croft et al, 2012;Dubois et al, 2015).…”

“…VGLUT2 is the glutamate transporter used by all glutamatergic neurons in the hypothalamus, thalamus, midbrain, and hindbrain (Takamori, 2006), whereas all GABAergic neurons express VGAT (Wojcik et al, 2006). Both the Vgat-ires-Cre and Vglut2-ires-Cre knock-in mouse lines have been fully characterized and shown to express Cre selectively in GABAergic and glutamatergic neurons, respectively (Vong et al, 2011). To fluorescently label GABAergic and glutamatergic neurons, the different Cre driver lines were crossed with the Ai9 Cre-dependent tdTomato reporter (Madisen et al, 2010).…”

“…Both the Vgat-ires-Cre and Vglut2-ires-Cre knock-in mouse lines have been fully characterized and shown to express Cre selectively in GABAergic and glutamatergic neurons, respectively (Vong et al, 2011). To fluorescently label GABAergic and glutamatergic neurons, the different Cre driver lines were crossed with the Ai9 Cre-dependent tdTomato reporter (Madisen et al, 2010). To delete ESR1 from all GABA or VGLUT2 neurons, the different Cre driver lines were crossed with Esr1 lox/lox mice (Wintermantel et al, 2006).…”

Current and future applications of GnRH, kisspeptin and neurokinin B analogues

“…Remarkably, the suppression of testosterone was apparently faster and more pronounced, and reproductive organ weights more reduced than after administration of the GnRH analogue, Leuprolide. This result is unexpected as kisspeptin stimulation of LH in humans and a number of animal studies is much less than that of GnRH and kisspeptin antagonists, and only partially suppresses LH, suggesting that there is an element of GnRH secretion which is kisspeptin independent 110,114 .…”

Staggered multi-site low-frequency electrostimulation effectively induces locomotor patterns in the isolated rat spinal cord

“…Such a system is reminiscent of the relay neurons in the sacrococcygeal spinal cord that were previously suggested to drive lumbar rhythms. 10 On the other hand, previous studies have shown that stimulation frequency might sculpt circuit synapses through different plasticity mechanisms: modifying either the amount 16 or type 17 of released neurotransmitters, reversing the balance between excitation and inhibition, 18 or limiting negative-feedback pre-synaptic processes. 19 In addition, circuit architecture can be flexibly reconfigured by distinct stimulation frequencies.…”