Adrenocorticotropic hormone may be transported directly from the pituitary to the brain

The interaction of MC3R and MC4R with MRAP2, ACTH, α-MSH and AgRP in chickens

The interaction of melanocortin-4 (MC4R) and melanocortin-3 (MC3R) receptors with proopiomelanocortin (POMC)-derived peptides (e.g. α-MSH), agouti-related protein (AgRP) and melanocortin-2 receptor accessory protein 2 (MRAP2) is suggested to play critical roles in energy balance of vertebrates. However, evidence on their interaction in birds remains scarce. Our study aims to reveal their interaction in chickens and the results showed that (1) chicken (c-)MC3R and cMC4R expressed in Chinese hamster ovary (CHO) cells can be activated by α-MSH and ACTH_1-39 equipotently, monitored by a pGL3-CRE-luciferase reporter system; (2) cMC3R and cMC4R, when co-expressed with cMRAP2 (or cMRAP, a cMRAP2 homolog), show increased sensitivity to ACTH treatment and thus likely act as ACTH-preferring receptors, and the interaction between cMC3R/cMC4R and cMRAP2 was demonstrated by co-immunoprecipitation assay; (3) both cMC3R and cMC4R display constitutive activity when expressed in CHO cells, as monitored by dual-luciferase reporter assay, and cMRAP2 (and cMRAP) can modulate their constitutive activity; (4) AgRP inhibits the constitutive activity of cMC3R/cMC4R, and it also antagonizes ACTH/α-MSH action on cMC4R/cMC3R, indicating that AgRP functions as the inverse agonist and antagonist for both receptors. These findings, together with the co-expression of cMC4R, cMC3R, cMRAP2, cAgRP and cPOMC in chicken hypothalamus detected by quantitative real-time PCR, suggest that within the hypothalamus, α-MSH/ACTH, AgRP and MRAP2 may interact at the MC4R(/MC3R) interface to control energy balance. Furthermore, our data provide novel proof for the involvement of MRAP2 (and MRAP) in fine-tuning the constitutive activity and ligand sensitivity and selectivity of both MC3R and MC4R in vertebrates.

Addiction and the adrenal cortex

Substantial evidence shows that the hypophyseal–pituitary–adrenal (HPA) axis and corticosteroids are involved in the process of addiction to a variety of agents, and the adrenal cortex has a key role. In general, plasma concentrations of cortisol (or corticosterone in rats or mice) increase on drug withdrawal in a manner that suggests correlation with the behavioural and symptomatic sequelae both in man and in experimental animals. Corticosteroid levels fall back to normal values in resumption of drug intake. The possible interactions between brain corticotrophin releasing hormone (CRH) and proopiomelanocortin (POMC) products and the systemic HPA, and additionally with the local CRH–POMC system in the adrenal gland itself, are complex. Nevertheless, the evidence increasingly suggests that all may be interlinked and that CRH in the brain and brain POMC products interact with the blood-borne HPA directly or indirectly. Corticosteroids themselves are known to affect mood profoundly and may themselves be addictive. Additionally, there is a heightened susceptibility for addicted subjects to relapse in conditions that are associated with change in HPA activity, such as in stress, or at different times of the day. Recent studies give compelling evidence that a significant part of the array of addictive symptoms is directly attributable to the secretory activity of the adrenal cortex and the actions of corticosteroids. Additionally, sex differences in addiction may also be attributable to adrenocortical function: in humans, males may be protected through higher secretion of DHEA (and DHEAS), and in rats, females may be more susceptible because of higher corticosterone secretion.

Circadian alteration in neurobiology during 30 days of abstinence in heroin users

BACKGROUND

Previous studies have shown that individuals withdrawn from chronic opiate administration undergo substantial elevations of cortisol levels with blunted corticotropin (ACTH) rhythms and that these changes persist beyond the 7-10 days of acute withdrawal symptoms. However, there are no published studies of changes in expression of clock genes or of other neuropeptides related to circadian-rhythm regulation, which may influence relapse susceptibility.

METHODS

Blood samples were collected from 8 healthy control subjects and 16 heroin addicts during pharmacologically unassisted withdrawal on the 3rd, 10th, and 30th days of abstinence at 3-hour intervals for 24 hours. Outcome measures were the relative expression of clock gene mRNA (hperiod1, hperiod2, hclock) and the levels of serum cortisol, plasma ACTH, beta-endorphin (beta-EP), leptin, neuropeptide Y, interleukin-2 (IL-2), and tumor necrosis factor (TNF) in these subjects.

RESULTS

Compared with healthy volunteers, abstinent addicts showed disruptions in diurnal rhythms of hPER1 and hPER2 mRNA expression, along with disruptions in diurnal rhythms of cortisol, ACTH, beta-endorphin, leptin, and IL-2 release. Several of these disruptions (hPER1, hPER2, ACTH, beta-endorphin, and IL-2) persisted for the 30-day testing period, as did elevation of 24-hour levels of cortisol and decreases in 24-hour IL-2 and TNF levels.

CONCLUSIONS

These prolonged neurobiological changes may play a role in protracted opiate withdrawal symptoms and contribute to relapse vulnerability.

Involvement of central opioidergic and nonopioidergic neuroendocrine systems in the suppressive effect of acupuncture on delayed type hypersensitivity in mice

The effect of a single treatment of electroacupuncture (Acu) at early or late stages of the efferent phase on 2, 4, 6-trinitrochlorobenzene (TNCB)-induced delayed type hypersensitivity (DTH) was studied in intact and hypophysectomized (HPX) mice. Acu (2.5 Hz, 15 min) applied to the acu-point equivalent to GV4 at 0, 3, 18 or 21 h after TNCB challenge induced significant suppression (45-73%) of the maximal extent of ear swelling at 24 h after TNCB challenge. An immunosuppressive and antiinflammatory drug, prednisolone 10 mg/kg i.p., also suppressed the DTH to the same extent. Pretreatment with intracisternal injection of naloxone hydrochloride (2 micrograms) significantly blocked the Acu-evoked DTH suppression when Acu treatment was done at 0 or 3 h. On the contrary, naloxone did not block the effect of Acu treatment given at 21 h. In order to examine the potential involvement of the pituitary in the suppression of DTH by Acu, the DTH reaction was examined in HPX mice. Acu failed to produce suppressive response in the HPX mice unless given at 0 h. These findings indicate that Acu treatment at acu-point GV4 during the efferent phase of induced DTH can suppress the DTH through central opioidergic or nonopioidergic systems. The pituitary is apparently pivotal in this immunosuppression and it is suggested that the DTH suppression by Acu may be mediated via activation of the neuroendocrine system.

Analgesia produced by pituitary ACTH and dopaminergic transmission in the arcuate

Analgesia (NAA) caused by nonacupuncture point (abdominal muscle) stimulation after lesioning the analgesia inhibitory system (AIS) or treating the subject with proglumide was abolished by hypophysectomy or adrenalectomy. The final sector of the NAA afferent pathway from the nonacupuncture point to the pituitary gland and the initial sector of the descending pain inhibitory system were found in the anterior and posterior arcuate nucleus (A-HARN and P-HARN), respectively. Analgesia caused by ACTH microinjected into the P-HARN disappeared after denervation of the A-HARN, but that caused by dopamine did not. Firing rates of P-HARN neurons were increased by nonacupuncture point simulation (NAPS) after lesion of the AIS or treatment with proglumide. The NAPS responsive neurons also responded to ultramicroinjected dopamine, but not to ultramicroinjected ACTH. Both NAA and NAPS responsive neuron activity that were abolished by hypophysectomy were restored by concurrent application of NAPS and intraperitoneal ACTH. Reduction of sodium ions due to adrenalectomy was found to abolish NAA. It was concluded that NAA production involves dopaminergic transmission in the HARN and ACTH acting presynaptically on this transmission.

Ultrastructural Characterization of Adrenocorticotrope Hormone (ACTH) Immunoreactive Fibres in the Mesencephalic Central Grey Substance of the Rat

The fine structural localization of fibres immunoreactive for the adrenocorticotrope hormone (ACTH) was studied in the mesencephalic central grey substance (MCG) of the male Wistar rat. Light microscopically, varicose ACTH-immunoreactive fibres were found throughout the MCG in a dorsal, lateral and ventral, periventricular position. Electron microscopically, the immunoreactivity was most prominent in the direct vicinity of electron-dense secretory granules in axonal varicosities, and, although to a lower degree, around other cytoplasmic organelles such as electron-lucent synaptic vesicles, mitochondria and microtubules. With serial section analysis two types of ACTH-immunoreactive varicosity were discerned. The first type is large, contains many, small electron-lucent synaptic vesicles, that are located in the vicinity of a morphologically well-defined synaptic contact. In this type of varicosity, large dense-core secretory granules are scarce. Immunoreactivity is low or absent, particularly near the active zone. The second type is strongly immunoreactive. It always contains many large, dense-core secretory granules; electron-lucent vesicles are rare. The smaller varicosities of this type never make synaptic contacts, but a few of the larger varicosities have synaptic contacts with dendrites of MCG cells.

Hypophysectomy prevents ACTH-induced yawning and penile erection in rats

The intracerebroventricular administration of ACTH1-24 (3-5 micrograms/rat) produced a behavioural syndrome characterized by recurrent episodes of penile erection and yawning in rats. Hypophysectomy prevented ACTH1-24-induced yawning and penile erection. These results suggest that pituitary has a "trophic" action not only on peripheral target organs but also on structures in brain controlling specific behavioural responses.

The effects of the systemic administration of N-methylmorphine chloride, a quaternary analogue of morphine that does not cross the blood-brain barrier, on the release of anterior pituitary hormones in the rat

The acute administration of morphine elicits changes in the release of anterior pituitary hormones. The locus of this action is thought to be in the central nervous system, specifically the hypothalamus. There are some data suggesting that systemically administered opiates and opioid peptides can act outside of the blood-brain barrier to influence anterior pituitary hormone release. To test this hypothesis we examined the effects of the systemic administration of N-methylmorphine chloride, a quaternary analogue of morphine that does not cross the blood-brain barrier, on the release of corticosterone, growth hormone, prolactin, luteinizing hormone, and thyroid stimulating hormone in the rat. N-methylmorphine caused increases in the release of growth hormone and prolactin, but serum levels of corticosterone, luteinizing hormone and thyroid stimulating hormone were unaffected. These results indicate that the opiate-induced release of growth hormone and prolactin may be mediated in part by sites outside of the blood-brain barrier.

Anatomical evidence for interactions between catecholamine- and adrenocorticotropin-containing neurons

Recent studies suggest that neurons containing adrenocorticotropin and catecholamines are localized to similar areas of the brain. In this immunocytochemical study, the distributions of neurons and terminals containing adrenocorticotropin and tyrosine hydroxylase, the first enzyme in the catecholamine biosynthetic pathway, were compared using the peroxidase-antiperoxidase technique. Neurons containing adrenocorticotropin and tyrosine hydroxylase formed overlapping hyperbolic lamina in the mediobasal hypothalamus. Although adrenocorticotropin and tyrosine hydroxylase containing neurons often formed small clusters, no double labeled cells were observed. Overlap also occurred between adrenocorticotropin and tyrosine hydroxylase terminal fields in several diencephalic nuclei including the periventricular hypothalamic gray and paraventricular thalamus. In contrast, other regions displayed striking compartmentalization of terminal fields; for example, in both the paraventricular hypothalamus and central nucleus of the amygdala, adrenocorticotropin was located in ventral and tyrosine hydroxylase in more dorsal aspects of the nuclei. Adjacent sections also showed a close correspondence between adrenocorticotropin terminals and tyrosine hydroxylase cell bodies in paraventricular, periventricular, dorsomedial and ventral hypothalamic nuclei. These data provide anatomical substrates for potential functional interactions between catecholamine and adrenocorticotropin systems in forebrain.

NH2-terminal specificity and axonal localization of adrenocorticotropin binding sites in rat median eminence

Adrenocorticotropin binding sites in the rat median eminence have been localized in vivo. These binding sites occur in the basalar zone, which is rich in axonal endings. Using competitive binding and quantitative light-microscope radioautography, we found that the median-eminence binding site, in contradistinction to the adrenal receptor, binds specifically the residue 4-10 region of the adrenocorticotropin molecule. Using quantitative electron-microscope radioautography and median-eminence deafferentation, we localized the binding sites to axon terminals in this region. In time-delayed uptake studies using light-microscope radioautography, we failed to observe concentration of radiolabel in neurons of the medial basal hypothalamus after the direct injection of radioiodinated adrenocorticotropin(1-24) into the median eminence.

Causal links between plasma and CSF endorphin levels in stress: vector-ARMA analysis

To explore causal links between vital sign responses and immunoreactive beta-endorphin ("i-BE") rises in blood and CSF during ovine endotoxin stress, we analyzed concurrent i-BE levels in these two compartments by a "vector-ARMA" (= autoregressive moving average) method. This technique--widely used for modeling in other applications--has not to our knowledge been employed to study dynamic relationships of neuropeptides. Log-transformed i-BE levels were first "filtered" by repeated observations ANOVA to confirm significance of rises in both compartments. Next, vector-ARMA methodology was applied to derive an optimal causal model of vital sign changes and i-BE entry into plasma vs. CSF pools. The model indicated that reflux of i-BE from blood into CSF contributed to increases in CSF levels of this hormone. This novel application to neuroendocrinology of this approach illustrates its utility in evaluating changes in one or more neuropeptide levels in multiple compartments to indicate potentially causal relationships.

Hypophysectomy prevents yawning and penile erection but not hypomotility induced by apomorphine

A small dose of apomorphine (25 or 50 micrograms/kg, SC) induced repeated episodes of yawning, penile erection, genital grooming and a decrease in locomotor activity in rats. Hypophysectomy almost completely abolished yawning, penile erection and genital abolished yawning, penile erection and genital grooming but failed to modify the hypomotility induced by apomorphine. These results suggest that pituitary hormones are directly or indirectly involved in the apomorphine-induced yawning, penile erection and genital grooming but not in the sedative response to this drug.

Plasma cortisol and beta-endorphin in horses subjected to electro-acupuncture for cutaneous analgesia

Electro-acupuncture (EA) treatment of horses to induce cutaneous analgesia also increased plasma concentrations of beta-endorphin (beta-EP) and cortisol. The magnitude of these increases did not relate consistently to the degree of EA-induced analgesia. Respiration and heart rates were also markedly increased during EA treatment. Intact female horses had higher packed cell volume and plasma beta-EP as well as lower plasma total protein than castrated male horses. Plasma cortisol, heart rate, and respiration rate did not differ significantly between sexes. None of the parameters measured before or during EA treatment provided an explanation for the differential cutaneous analgesia which depended on sex of subject and locus of stimulation as reported elsewhere.

Endotoxin-stimulated opioid peptide secretion: two secretory pools and feedback control in vivo

Small doses of endotoxin evoked a dramatic biphasic response of opioid peptide secretion into blood in sheep. The first phase began within minutes and coincided with a brief hypertensive response to endotoxin well before the appearance of fever or hypotension. The ratio of beta-endorphin to beta-lipotropin fell abruptly at the onset of the second phase of release, suggesting early depletion of a pool rich in beta-endorphin and subsequent emergence of a pool rich in unprocessed precursor. The concentration of cerebrospinal fluid opioids increased tenfold during the second phase. Naloxone administration augmented endotoxin-induced opioid secretion in both early and late phases, suggesting a short-loop feedback regulation of stress-induced endorphin secretion.

The influence of selective adeno- and neurointermedio-hypophysectomy upon plasma and brain levels of beta-endorphin and their response to stress in rats

Selective ablation of the anterior lobe (AL) of the pituitary led to a fall in basal plasma levels of beta-endorphin immunoreactivity (beta-EI) at 3 and 20 weeks post-surgery (p.s.). Further, the stress-evoked rise in circulating levels of beta-EI was abolished. This operation did, however, severely deplete the beta-EI content of the neurointermediate lobe (NIL). Removal of the NIL did not, in contrast, decrease the beta-EI content of the AL but depressed basal plasma levels of beta-EI at 3 weeks p.s. and attenuated, but did not abolish, the increase in these elicited by stress at both 3 and 20 weeks p.s. In rats not possessing a NIL, a secretion of beta-EI into plasma can thus occur. The possibility that NIL pools of beta-EI contribute to circulating levels of beta-EI is discussed. Removal of the AL depressed the beta-EI content of the hypothalamus and periventricular tissue at 3 and 20 weeks p.s. The Met-enkephalin-immunoreactivity (ME-I) content of the hypothalamus was, in contrast, unaffected. These animals still responded to stress at 20 weeks p.s. with a significant fall in hypothalamic levels of beta-EI. Extirpation of the NIL did not, in contrast, change brain levels of either beta-EI or ME-I. The presence of the AL, but not the NIL, is thus essential for the maintenance of usual levels of beta-EI and ME-I in the brain.

The distribution and cells of origin of ACTH(1-39)-stained varicosities in the paraventricular and supraoptic nuclei

ACTH(1-39)-immunoreactive fibers and varicosities were localized using indirect immunofluorescence histochemistry in normal rats, and were found to be distributed in specific parts of the parvocellular division of the paraventricular nucleus, and in regions of the magnocellular division of the paraventricular and supraoptic nuclei in which oxytocinergic cells predominate. A combined retrograde transport-immunohistochemical method was used to confirm that these projections arise from a group of ACTH(1-39)-stained cells in the arcuate nucleus (and in adjacent regions along the base of the hypothalamus), and to describe their distribution within this region.

Calcitonin: regional distribution of the hormone and its binding sites in the human brain and pituitary

Immunoreactive calcitonin (CT), indistinguishable from human CT-(1-32) and its sulfoxide, has been identified in extracts of the hypothalamus, the pituitary, and the thyroid obtained from human subjects at autopsy. DCT concentrations were highest in a region encompassing the posterior hypothalamus, the median eminence, and the pituitary; intermediate in the substantia nigra, the anterior hypothalamus, the globus pallidus, and the inferior colliculus; and low in the caudate nucleus, the hippocampus, the amygdala, and the cerebral and cerebellar cortices. Specific CT binding measured with 125I-labeled salmon CT was highest in homogenates of the posterior hypothalamus and the median eminence, shown to contain the highest concentrations of endogenous CT in the brain; CT binding was less than 12% of hypothalamic binding in all of the other regions of the brain examined and was negligible in the pituitary. Half-maximal binding was achieved with 0.1 nM nonradioactive salmon CT-(1-32), and the binding was directed to structural or conformational sites, or both, in the COOH-terminal half of salmon CT. The rank order of the inhibition of the binding by CT from different species and analogues of the human hormone was the same as in receptors on a human lymphoid cell line (Moran, J., Hunziker, W. & Fischer, J. A. (1978) Proc. Natl. Acad. Sci. USA 75, 3984-3988). The functional role of CT and of its binding sites in the brain remains to be elucidated.

Clonidine releases immunoreactive beta-endorphin from rat para distalis

Clonidine (10(-6), 10(-7) M) evokes the release of beta endorphin-like immunoreactivity (beta-END-LI) from cell cultures of anterior (pars distalis) but not neurointermediate (pars nervosa plus pars intermedia) lobe of the rat pituitary. This drug-induced secretion is blocked by alpha-adrenergic (phenoxybenzamine, yohimbine; 10(-5) M) but not beta-adrenergic (propranolol, 10(-5) M) antagonism. Gel filtration (Sephadex G-50) reveals that beta-END-LI released from anterior lobe cells consists of 2 major forms of immunoreactivity which coelute with beta-lipotropin or beta-endorphin standards. Conversely, beta-END-LI released spontaneously from neurointermediate lobe cells almost entirely corresponds to beta-endorphin. The data show that alpha-adrenergic stimulation by clonidine releases beta-END-LI selectively from cells of anterior but not neurointermediate lobe in vitro and suggests that the clonidine-induced release of pituitary beta-END-LI we have observed in vivo occurs in part by direct action on the corticotrophs of the pars distalis.