Endocannabinoid Signaling at Hypothalamic Steroidogenic Factor-1/Proopiomelanocortin Synapses Is Sex- and Diet-Sensitive

Abstract

We tested the hypotheses that steroidogenic factor (SF)-1 neurons in the hypothalamic ventromedial nucleus (VMN) provide sexually disparate, endocannabinoid (EC)- and diet-sensitive glutamatergic input onto proopiomelanocortin (POMC) neurons. Electrophysiological recordings were performed in hypothalamic slices from intact and castrated guinea pigs, along with in vitro optogenetic experiments in intact male as well as cycling and ovariectomized female NR5A1-Cre mice. In slices from castrated male and female guinea pigs, depolarized-induced suppression of excitation (DSE) time-dependently reduced the amplitude of evoked excitatory postsynaptic currents (eEPSCs) in POMC neurons generated by electrically stimulating the dorsomedial VMN. Androgen stimulation rapidly enhanced this DSE, which was also found in insulin-resistant, high-fat diet (HFD)-fed males. By contrast, retrograde signaling at VMN/ARC POMC synapses was markedly attenuated in periovulatory females. HFD potentiated central cannabinoid-induced hyperphagia in both males and females, but exerted differential influences on cannabinoid-induced increases in energy expenditure. In NR5A1-Cre mice, the reduction in light-evoked EPSC amplitude caused by postsynaptic depolarization in cycling females was modest in comparison to that seen in intact males. Estradiol attenuated the DSE in light-evoked EPSC amplitude in slices from ovariectomized females. Moreover, the retrograde inhibition of transmission was further accentuated in HFD-fed males. Chemogenetic activation of SF-1 neurons suppressed appetite and increased energy expenditure in males, effects which were attenuated by HFD. Conversely, energy expenditure was increased in estradiol- but not vehicle-treated ovariectomized females. Together with our previous studies indicating that DSE in POMC neurons is EC-mediated, these findings indicate that VMN SF-1/ARC POMC synapses represent a sexually differentiated, EC- and diet-sensitive anorexigenic component within the hypothalamic energy balance circuitry.

Nociceptin/orphanin FQ modulates energy homeostasis through inhibition of neurotransmission at VMN SF-1/ARC POMC synapses in a sex- and diet-dependent manner

“…We have shown previously that long-term exposure to HFD leads to a potentiation of the CB1 receptor-mediated inhibition of glutamatergic transmission at VMN SF-1/ARC POMC synapses in male but not female mice [21]. We then wanted to see if long-term exposure to HFD could also potentiate the NOP receptor-mediated reduction in glutamatergic input at these synapses.…”

“…For the optogenetic studies described in experiments 1–3 that were designed primarily to test the hypothesis that N/OFQ decreases glutamate release at VMN SF-1/ARC POMC synapses in a sex- and diet-dependent manner, recordings were performed in slices from NR5A1-Cre mice that were injected with a ChR2-containing viral vector into the VMN 2–3 weeks prior to experimentation. Once glutamatergic SF-1-expressing fibers (visualized with YFP) impinging on ARC neurons were encountered, functional synaptic connectivity was ascertained by applying a photo-stimulus (25–100-ms pulses delivered every 2 s) from a light-emitting diode (LED) blue light source (470 nm) controlled by a variable 2A driver (ThorLabs, Newton, NJ, USA) that directly delivered the light path through the Olympus 40X water-immersion lens to generate a fast excitatory postsynaptic current (EPSC) as described previously [21]. We then determined whether the neuron under consideration was a likely POMC neuron by prescreening for intrinsic membrane currents like the A-type K + current and the hyperpolarization-activated mixed cation current [37, 39, 40] via the current-voltage (I/V) relationships generated as described in the next paragraph.…”

“…Bath application of N/OFQ has also been shown to decrease glutamatergic excitatory postsynaptic currents (EPSCs) in rat lateral amygdala, as well as the ARC [16, 17], indicating that N/OFQ acts presynaptically to reduce the amount of glutamate that is released onto its postsynaptic target. Anorexigenic ARC proopiomelanocortin (POMC) neurons have also been shown to be activated from presynaptic glutamatergic inputs emanating from the steroidogenic factor (SF)-1 neurons in the hypothalamic ventromedial nucleus (VMN) [18–21], which have been shown to synapse directly onto POMC neurons [22]. It has also been shown that chemogenetic stimulation of SF-1 neurons causes a decrease in food intake as well as an increase in energy expenditure and that optogenetic stimulation evokes a robust light-induced EPSC in POMC neurons [21].…”

“…Anorexigenic ARC proopiomelanocortin (POMC) neurons have also been shown to be activated from presynaptic glutamatergic inputs emanating from the steroidogenic factor (SF)-1 neurons in the hypothalamic ventromedial nucleus (VMN) [18–21], which have been shown to synapse directly onto POMC neurons [22]. It has also been shown that chemogenetic stimulation of SF-1 neurons causes a decrease in food intake as well as an increase in energy expenditure and that optogenetic stimulation evokes a robust light-induced EPSC in POMC neurons [21]. It has also been known that a lesioning of the VMN causes rampant hyperphagia and obesity [23, 24].…”

Signaling through non-membrane nuclear phosphoinositide binding proteins in human health and disease

“…Well-executed tissue-specific knockout studies have shown that SF-1 VMH neurons control insulin-mediated protection from diet-induced leptin resistance, weight gain, adiposity, and impaired glucose tolerance (133)(134)(135)(136); and SF-1 neurons are well-known to be critical in mediating diet-induced obesity (72). Tissue-specific knockout studies of SF-1 in the VMH have demonstrated SF-1 as an anorexigenic factor regulated by nutritional status (137), and have shown that SF-1 is required for the development of the complete functional hypothalamic-pituitarygonadal axis, as well as the hypothalamic-pituitary-adrenal axis (64,134,138). These studies are very important clinically because nuclear receptors like SF-1 are some of the Fig.…”