Leighton J. Seal

The central melanocortin system affects the hypothalamo-pituitary thyroid axis and may mediate the effect of leptin.

Prolonged fasting is associated with a downregulation of the hypothalamo-pituitary thyroid (H-P-T) axis, which is reversed by administration of leptin. The hypothalamic melanocortin system regulates energy balance and mediates a number of central effects of leptin. In this study, we show that hypothalamic melanocortins can stimulate the thyroid axis and that their antagonist, agouti-related peptide (Agrp), can inhibit it. Intracerebroventricular (ICV) administration of Agrp (83-132) decreased plasma thyroid stimulating hormone (TSH) in fed male rats. Intraparaventricular nuclear administration of Agrp (83-132) produced a long-lasting suppression of plasma TSH, and plasma T4. ICV administration of a stable alpha-MSH analogue increased plasma TSH in 24-hour-fasted rats. In vitro, alpha-MSH increased thyrotropin releasing hormone (TRH) release from hypothalamic explants. Agrp (83-132) alone caused no change in TRH release but antagonized the effect of alpha-MSH on TRH release. Leptin increased TRH release from hypothalami harvested from 48-hour-fasted rats. Agrp (83-132) blocked this effect. These data suggest a role for the hypothalamic melanocortin system in the fasting-induced suppression of the H-P-T axis.

Actions of cocaine- and amphetamine-regulated transcript (CART) peptide on regulation of appetite and hypothalamo-pituitary axes in vitro and in vivo in male rats

Cocaine- and amphetamine-regulated transcript (CART) and CART peptide are abundant in hypothalamic nuclei controlling anterior pituitary function. Intracerebroventricular (ICV) injection of CART peptide results in neuronal activation in the paraventricular nucleus (PVN), rich in corticotrophin-releasing factor (CRH) and thyrotrophin-releasing factor (TRH) immunoreactive neurons. The aims of this study were three-fold. Firstly, to examine the effects of CART peptide on hypothalamic releasing factors in vitro, secondly, to examine the effect of ICV injection of CART peptide on plasma pituitary hormones and finally to examine the effect of PVN injection of CART peptide on food intake and circulating pituitary hormones. CART(55-102) (100 nM) peptide significantly stimulated the release of CRH, TRH and neuropeptide Y from hypothalamic explants but significantly reduced alpha melanocyte stimulating hormone release in vitro. Following ICV injection of 0.2 nmol CART(55-102), a dose which significantly reduces food intake, plasma prolactin (PRL), growth hormone (GH) and adrenocorticotrophin hormone (ACTH) and corticosterone increased significantly. Following PVN injection of CART(55-102), food intake was significantly reduced only at 0.2 and 0.6 nmol. However, PVN injection of 0.02 nmol CART(55-102) produced a significant increase in plasma ACTH. ICV injection of CART peptide significantly reduces food intake. Unlike many anorexigenic peptides, there is no increased sensitivity to PVN injection of CART(55-102). In contrast, both ICV and PVN injection of CART(55-102) significantly increased plasma ACTH and release of hypothalamic CRH is significantly increased by CART peptide in vitro. This suggests that CART peptide may play a role in the control of pituitary function and in particular the hypothalamo-pituitary adrenal axis.

The Hypothalamic Mechanisms of the Hypophysiotropic Action of Ghrelin

Ghrelin is an endogenous ligand for the growth hormone secretagogue (GHS) receptor, expressed in the hypothalamus and pituitary. Ghrelin, like synthetic GHSs, stimulates food intake and growth hormone (GH) release following systemic or intracerebroventricular administration. In addition to GH stimulation, ghrelin and synthetic GHSs are reported to stimulate the hypothalamo-pituitary-adrenal (HPA) axis in vivo. The aims of this study were to elucidate the hypothalamic mechanisms of the hypophysiotropic actions of ghrelin in vitro and to assess the relative contribution of hypothalamic and systemic actions of ghrelin on the HPA axis in vivo. Ghrelin (100 and 1,000 nM) stimulated significant release of GH-releasing hormone (GHRH) from hypothalamic explants (100 nM: 39.4 ± 8.3 vs. basal 18.3 ± 3.5 fmol/explant, n = 49, p < 0.05) but did not affect either basal or 28 mM KCl-stimulated somatostatin release. Ghrelin (10, 100 and 1,000 nM) stimulated the release of both corticotropin-releasing hormone (CRH) (100 nM: 6.0 ± 0.8 vs. basal 4.2 ± 0.5 pmol/explant, n = 49, p < 0.05) and arginine vasopressin (AVP) (100 nM: 49.2 ± 5.9 vs. basal 35.0 ± 3.3 fmol/explant, n = 48, p < 0.05), whilst ghrelin (100 and 1,000 nM) also stimulated the release of neuropeptide Y (NPY) (100 nM: 111.4 ± 25.0 vs. basal 54.4 ± 9.0 fmol/explant, n = 26, p < 0.05) from hypothalamic explants in vitro. The HPA axis was stimulated in vivo following acute intracerebroventricular administration of ghrelin 2 nmol [adrenocorticotropic hormone (ACTH) 38.2 ± 3.9 vs. saline 18.2 ± 2.0 pg/ml, p < 0.01; corticosterone 310.1 ± 32.8 ng/ml vs. saline 167.4 ± 40.7 ng/ml, p < 0.05], but not following intraperitoneal administration of ghrelin 30 nmol, suggesting a hypothalamic site of action. These data suggest that the mechanisms of GH and ACTH regulation by ghrelin may include hypothalamic release of GHRH, CRH, AVP and NPY.

Diurnal variation in orexin A immunoreactivity and prepro-orexin mRNA in the rat central nervous system

Orexins are a family of neuropeptides originally believed to be important mediators of food intake. The wide distribution of orexins and their receptors, however, has suggested other regulatory functions for these peptides including involvement in sleep and arousal mechanisms. In this study, we have demonstrated diurnal variation in orexin A immunoreactivity in the pons, from where locus coeruleus noradrenergic neurones innervate other brain areas to stimulate arousal, and in the preoptic/anterior hypothalamic region, an area implicated in the regulation of sleep and circadian rhythms. Orexin A immunoreactivity decreased by 50% in the preoptic/anterior hypothalamus from 09:00 to 21:00 h (P < 0.0001), whilst in the pons, it increased by over 30% from 09:00 to 01:00 h (P = 0.02). Prepro-orexin mRNA also displayed diurnal variation. This further suggests that orexins are involved in the regulation of the sleep/wake cycle.

Non-binary or genderqueer genders

Abstract Some people have a gender which is neither male nor female and may identify as both male and female at one time, as different genders at different times, as no gender at all, or dispute the very idea of only two genders. The umbrella terms for such genders are ‘genderqueer’ or ‘non-binary’ genders. Such gender identities outside of the binary of female and male are increasingly being recognized in legal, medical and psychological systems and diagnostic classifications in line with the emerging presence and advocacy of these groups of people. Population-based studies show a small percentage – but a sizable proportion in terms of raw numbers – of people who identify as non-binary. While such genders have been extant historically and globally, they remain marginalized, and as such – while not being disorders or pathological in themselves – people with such genders remain at risk of victimization and of minority or marginalization stress as a result of discrimination. This paper therefore reviews the limited literature on this field and considers ways in which (mental) health professionals may assist the people with genderqueer and non-binary gender identities and/or expressions they may see in their practice. Treatment options and associated risks are discussed.

Effect of direct injection of melanin-concentrating hormone into the paraventricular nucleus: Further evidence for a stimulatory role in the adrenal axis via SLC-1

Melanin‐concentrating hormone (MCH) is implicated in the control of a number of hormonal axes including the hypothalamic‐pituitary adrenal (HPA) axis. Previous studies have shown that there is evidence for both a stimulatory and an inhibitory action on the HPA axis; therefore, we attempted to further characterize the effects of MCH on this axis. Intracerebroventricular injection of MCH increased circulating adrenocorticotropic hormone (ACTH) at 10 min post injection. Injection of MCH directly into the paraventricular nucleus (PVN) was found to increase both circulating ACTH and corticosterone 10 min after injection. Additionally, MCH was found to increase corticotropin‐releasing factor (CRF) release from hypothalamic explants, and this effect was abolished by the specific SLC‐1 antagonist SB‐568849. Neuropeptide EI, a peptide from the same precursor as MCH was also found to increase CRF release from explants. These results suggest that MCH has a stimulatory role in the HPA axis via SLC‐1, and that MCH exerts its effects predominantly through the PVN CRF neuronal populations

The hypothalamic melanocortin system stimulates the hypothalamo-pituitary-adrenal axis in vitro and in vivo in male rats.

α-Melanocyte-stimulating hormone (α-MSH) is an agonist, and agouti-related protein (Agrp) an endogenous antagonist at the melanocortin 3 and 4 receptors which are found in the central nervous system (CNS). We have examined the effect of α-MSH and Agrp on the hypothalamo-pituitary-adrenal (HPA) axis in vitro and in vivo in male rats. Intraparaventricular nuclear (iPVN) injection of [Nle4,D-Phe7]-α-MSH (NDP-MSH) (a long-acting α-MSH analogue) increased plasma adrenocorticotropic hormone (ACTH) (10 min post-injection: 25.0 ± 3.9 vs. saline 10.9 ± 2.0, p < 0.05) and plasma corticosterone (10 min post-injection: 174.1 ± 14.2 vs. saline 124.7 ± 16.3 ng/ml, p < 0.05). iPVN injection of Agrp(83–132) increased plasma ACTH (24.2 ± 4.0 vs. saline 10.1 ± 1.0 pg/ml, p < 0.01). The combination of NDP-MSH and Agrp(83–132) administered iPVN significantly increased plasma ACTH (10 min post-injection: 21.3 ± 3.8 vs. 10.9 ± 2.0, p < 0.05) and plasma corticosterone (10 min post-injection: 169.0 ± 15.1 vs. saline 124.7 ± 16.3 ng/ml, p < 0.05), but there was no additive effect. Hypothalamic explants treated with α-MSH (100 nM) resulted in a 159 ± 23% increase in corticotropin-releasing hormone (CRH) release (p < 0.01) and 175 ± 12% increase in arginine vasopressin (AVP) release (p < 0.001) compared to basal. Agrp(83–132) (100 nM) administered to hypothalamic explants resulted in a 161 ± 20% increase in CRH (p < 0.01) and 174 ± 13% increase in AVP release (p < 0.001) compared to basal. Hypothalamic explants treated with the combination of α-MSH and Agrp(83–132) (100 nM) resulted in a 179 ± 31% increase in CRH release (p < 0.01) and 130 ± 9% increase in AVP release (p < 0.01) compared to basal, but there was no additive effect. This is the first report that both α-MSH and Agrp(83–132) stimulate the HPA axis. The combination of α-MSH and Agrp(83–132) has no additive effect in vitro and in vivo in male rats. These results suggest that there may be another receptor independent of the known melanocortin receptors at which Agrp is acting.

Hypothalamic Interactions Between Neuropeptide Y, Agouti‐Related Protein, Cocaine‐ and Amphetamine‐Regulated Transcript and Alpha‐Melanocyte‐Stimulating Hormone In Vitro in Male Rats

A number of neuropeptides implicated in the hypothalamic regulation of appetite are synthesized in the arcuate nucleus (Arc). Neuropeptide Y (NPY) and agouti‐related protein (Agrp) are orexigenic. The pro‐opiomelanocortin (POMC) product alpha‐melanocyte‐stimulating hormone (α‐MSH) is anorectic. Intracerebroventricular administration of cocaine‐ and amphetamine‐regulated transcript (CART) decreases food intake. However, recent results show that CART is orexigenic when injected into discrete hypothalamic nuclei. There is almost complete coexpression of NPY and Agrp mRNA in Arc neurones, and the majority of CART‐containing neurones in the Arc also contain POMC mRNA. We investigated possible interactions between these neuropeptides in vitro using a rat hypothalamic explant system. Administration of 1, 10 and 100 nm of NPY to hypothalamic explants significantly increased release of Agrp(83‐132)‐immunoreactivity (IR). NPY (10 and 100 nm) significantly increased the release of CART(55‐102)‐IR and α‐MSH‐IR from hypothalamic explants. Agrp(83‐132) (10 nm) administered to hypothalamic explants significantly increased the release of NPY‐IR. Agrp(83‐132) (10 and 100 nm) significantly decreased the release of CART(55‐102)‐IR from hypothalamic explants. Administration of 1, 10 and 100 nm CART(55‐102) to hypothalamic explants resulted in a significant increase in NPY‐IR release. Administration of 10 nm CART(55‐102) to hypothalamic explants significantly increased the release of Agrp(83‐132)‐IR. NDP‐MSH (10 nm) administered to hypothalamic explants significantly increased the release of NPY‐IR. NDP‐MSH (10 and 100 nm) significantly increased the release of Agrp(83‐132)‐IR from hypothalamic explants. These data suggest that orexigenic neuropeptides in the arcuate nucleus stimulate the release of each other, perhaps reinforcing orexigenic behaviour via a positive‐feedback loop. Our results are also in keeping with the possibility that the melanocortin‐3 receptor in the arcuate nucleus may influence the release of arcuate neuropeptides.

Prolactin-Releasing Peptide Releases Corticotropin-Releasing Hormone and Increases Plasma Adrenocorticotropin via the Paraventricular Nucleus of the Hypothalamus

Intracerebroventricular (ICV) injection of prolactin-releasing peptide (PrRP) is known to increase plasma adrenocorticotropin (ACTH) and cause c-fos expression in the hypothalamic paraventricular nucleus (PVN). We hypothesize that this is the site at which PrRP acts to increase plasma ACTH. We have used ICV injection and direct intranuclear injection of PrRP into the PVN to investigate the sites important in the stimulation of ACTH release in vivo. To investigate the mechanism of action by which PrRP increases ACTH, we have used primary culture of pituitary cells and measured neuropeptide release from in vitro hypothalamic incubations. ICV administration of PrRP increased plasma ACTH 10 min post-injection (PrRP 5 nmol 81.0 ± 23.5 pg/ml vs. saline 16.8 ± 14.1 pg/ml, p < 0.05). Intra-PVN injection of PrRP increased ACTH 5 min post-injection (PrRP 1 nmol 22.9 ± 5.0 pg/ml vs. saline 10.3 ± 1.4 pg/ml, p < 0.05). This effect continued until 40 min post-injection (PrRP 1 nmol 9.9 ± 1.5 pg/ml vs. saline 6.2 ± 0.5 pg/ml, p < 0.05). In vitro PrRP (1–100 nmol/l) did not effect basal or corticotropin-releasing hormone (CRH)-stimulated ACTH release from dispersed anterior pituitary cells. PrRP increased hypothalamic release of CRH (PrRP 100 nmol/l 1.4 ± 0.2 nmol/explant vs. the basal 1.1 ± 0.2 nmol/explant, p < 0.05) but not arginine vasopressin. PrRP also stimulated neuropeptide Y release (PrRP 100 nmol/l 56.5 ± 11.8 pmol/explant vs. basal 24.0 ± 1.9 pmol/explant, p < 0.01), a neuropeptide known to stimulate the hypothalamo-pituitary-adrenal axis. Our data suggest that in vitro PrRP does not have a direct action on the corticotrope but increases plasma ACTH via the PVN and this effect involves the release of hypothalamic neuropeptides including CRH and neuropeptide Y.

Orexin A immunoreactivity and prepro-orexin mRNA in the brain of Zucker and WKY rats

The primary role of the orexins was originally believed to be appetite regulation, but is now believed to be the regulation of sleep, arousal and locomotor activity. Orexin A immunoreactivity (orexin A-IR) and prepro-orexin mRNA were measured in the CNS of obese and lean Zucker rats. There were no differences in orexin A-IR or prepro-orexin mRNA levels between obese and lean Zucker rats. The orexins are therefore unlikely to be important in this model of obesity. Levels of orexin A-IR and prepro-orexin mRNA were measured in the CNS of Wistar-Kyoto (WKY) rats, which are hypoactive and have abnormal sleep architecture. Compared to Wistar rats, WKY rats had significantly lower orexin A-IR (with differences of up to 100% in some brain regions) and prepro-orexin mRNA levels. These observations suggest that the sleep and activity phenotype of the WKY strain may be related to orexin deficiency and that this strain may be a useful model of partial orexin deficiency.