Effects of intraventricular infusions of ACTH1-24 and ACTH4-10 on LH release, ovulation and behavior in the rabbit

Diabetic rats are unresponsive to the penile erection-inducing effect of intracerebroventriculary injected adrenocorticotropin

The penile erection-inducing effect of intracerebroventricularly (i.c.v.) injected adrenocorticotropin-(1-24) [ACTH-(1-24)] (4 or 10 microg/animal) was almost completely absent in diabetic rats, either 8 days or 2 months after streptozotocin administration. The other behavioral symptoms (stretching, yawning, excessive grooming) were unevenly affected: stretching was significantly reduced either in early or in long-standing diabetes; yawning was practically absent in early diabetes and significantly reduced at the highest dose of ACTH-(1-24) in long-standing diabetes; grooming was reduced only at the highest dose of ACTH-(1-24), both in early and in long-standing diabetes. The fact that ACTH-induced penile erections (a centrally mediated effect) are practically absent even a few days after streptozotocin injection suggests that diabetes mellitus-induced penile dysfunction occurs, at least in part, through central mechanisms, and is not solely the consequence of peripheral nerve and vascular lesions.

State-dependent cellular activity patterns of the cat paraventricular hypothalamus measured by reflectance imaging

Activity within the cat paraventricular hypothalamus (PVH) during sleep and waking states was measured by quantifying intrinsic tissue reflectivity. A fiber optic probe consisting of a 1.0 mm coherent image conduit, surrounded by plastic fibers which conducted 660 nm source light, was attached to a charge-coupled device camera, and positioned over the PVH in five cats. Electrodes for assessing state variables, including electroencephalographic activity, eye movement, and somatic muscle tone were also placed. After surgical recovery, reflected light intensity was measured continuously at 2.5 Hz during spontaneously varying sleep/waking states. Sequential state transitions from active waking to quiet waking, quiet sleep and active sleep were accompanied by progressively increased levels of PVH activity. Overall activity was highest during active sleep, and decreased markedly upon awakening. Moment-to-moment activity oscillated in the 0-0.1 Hz range, especially during active sleep and active waking; this oscillation diminished during quiet sleep. Distinct sub-regions of enhanced or diminished activity emerged within the imaged area in a state-dependent manner. We conclude that PVH activity changes with behavioral state in a regionally specific manner, and that overall activity increases during quiet sleep, and is even more enhanced in active sleep. PVH activation could be expected to stimulate pituitary release of adrenocorticotropic hormone (ACTH) and affect input to autonomic regulatory sites. Since ACTH and corticotropin releasing factor elicit arousal, and since the PVH projects to other brain areas which modulate state, we speculate that the PVH plays a role in shaping characteristics of sleep/waking states.

The opioid/anti-opioid balance in shock: a new target for therapy in resuscitation

Teleologically, pain is of paramount importance for survival and induces the organism to cope in an active way with aggressions from a basically hostile environment. While the activation of endogenous analgesic (opioid) systems typically occurs in conditions of surrender (pre-terminal conditions, sustained tortures, etc.), the activation of endogenous anti-analgesic systems triggers mechanisms of active or passive defence (such as camouflage) aimed at survival. The distinctive features of the main anti-analgesic systems (melanocortinergic, cholecystokininergic, thyroliberinergic) and the dramatic results obtained in experimental pre-terminal conditions (hemorrhagic shock, prolonged respiratory arrest) with the administration of their neuropeptide transmitters (ACTH and several ACTH-fragments, including alpha-MSH, CCK peptides and thyrotropin-releasing hormone) are here reviewed. The study of the mechanisms underlying the resuscitating effects of these neuropeptides has led to the discovery of the (often extremely potent) resuscitating effect of other drugs (protoveratrines, nicotine, centrally-acting cholinergic agents, ganglion-stimulating drugs). It is particularly remarkable that in pre-terminal conditions these neuropeptides and drugs have highly impressive effects on cardiocirculatory parameters at doses that are almost or actually inactive under normal conditions, and that their resuscitating effect is obtained without the need for any other supportive treatment and at dose-levels well below toxic ranges. Finally, in hemorrhage-shocked animals, the treatment with anti-analgesic neuropeptides shortly after bleeding considerably extends the time-limit for an effective and definitively curing blood reinfusion. This would be of self-evident importance in clinical practice, because an extremely simple, non-toxic first-aid treatment in the field, shortly after a massive hemorrhage, could resuscitate the patient for a period sufficient to effectively set up the most appropriate in-hospital treatment.

Corticotropin inhibits food intake in rats

The synthetic corticotropin ACTH (1-24) (tetracosactide), injected into a brain lateral ventricle after a 24h starvation period or into the ventromedial hypothalamus during the nocturnal feeding phase, markedly inhibited food intake, in rats. In starved rats, the dose of 4 micrograms/rat was maximally effective and reduced food intake by 76.6% during the first hour after treatment. The same dose, injected into the ventromedial hypothalamus, significantly inhibited food intake also in normally fed rats during the nocturnal phase (58.6% reduction during the 90 minutes of observation). These findings suggest that corticotropin may play a role in the central control of appetite.

Association of spontaneous and dopaminergic-induced yawning and penile erections in the rat

In a Sprague-Dawley-derived line of rats, selectively bred to establish a high incidence of spontaneous yawning behavior, the simultaneous and systematic monitoring of yawning and penile erections, during observation periods of one hour, demonstrates a linear correlation between these two behavioral patterns. Dose-effect curves of yawning and penile erections elicited by apomorphine and bromocriptine, and their inhibition by metoclopramide are quite similar. These results strongly suggest that yawning and penile erection are subject to some common regulating and modulating mechanisms, one of which seems to involve dopaminergic pathways.

Intracranial administration of corticotropin-like peptides increases incidence of amphibian reproductive behavior

Male rough-skinned newts (Taricha granulosa) exhibit an increase in sexual behavior (amplectic clasping) following intracerebroventricular (ICV) injection of adrenocorticotropin (ACTH 1-39), ACTH 4-10, or melanocyte-stimulating hormone (alpha MSH). In contrast, intraperitoneal (IP) administration of ACTH 1-39 or corticosterone significantly decreases the incidence of sexual behavior in male newts. These results suggest that a corticotropin-like peptide acts centrally to enhance sexual behavior and that systemic ACTH acts on the interrenal tissue to inhibit sexual behavior by stimulating the release of corticosterone.

Effects of dexamethasone, corticosterone, and ACTH on lordosis in ovariectomized and adrenalectomized-ovariectomized rats

The involvement of the pituitary-adrenocortical axis in the control of the lordosis reflex was investigated; In Experiment 1, estrogen-primed ovariectomized (ovx) and adrenalectomized-ovariectomized (adx-ovx) females were treated chronically with dexamethasone, a compound blocking ACTH release from the pituitary. Dexamethasone inhibited lordosis, effectively blocking an adrenalectomy-induced facilitation of the reflex. In Experiment 2, corticosterone was similarly administered chronically; this compound also inhibited lordosis in adx-ovx females. In Experiment 3, acute peripheral administration of synthetic ACTH caused a marked increase in lordosis in ovx females. The results suggest that in the adrenally intact animal, ACTH may exert its effect through adrenal steroids. An acute elevation of adrenal steroids may increase lordosis, whereas a chronic elevation may decrease it.

Direct evidence for involvement of dopaminergic inhibition and cholinergic activation in yawning

A behavioral study was performed in an attempt to understand the neurological mechanism involved in yawning in rats. Intraperitoneal injections of low doses (0.25 mg/kg) of apomorphine, which preferentially activate presynaptic dopamine autoreceptors, elicited yawning. Whereas apomorphine, at a high dose of 2 mg/kg, produces stereotypy which has been thought to be mediated by stimulation of postsynaptic dopamine receptors. The yawning and stereotypy did not occur simultaneously in the rat. The apomorphine-induced yawning was completely inhibited by pretreatment with fluphenazine (9 mg/kg, IM) or scopolamine (0.5 mg/kg IP), but markedly increased by reserpine (5 mg/kg, SC), however it was not affected by methylscopolamine (0.5 mg/kg, IP). Both physostigmine (0.2 mg/kg, IP), an indirect acetylcholine agonist, and pilocarpine (4 mg/kg, IP), a direct acetylcholine agonist, also induced yawning. This was abolished by scopolamine (0.5 mg/kg, IP) and increased by reserpine (5 mg/kg, SC). Fluphenazine (9 mg/kg, IP) did not affect the pilocarpine-induced yawning but increased the physostigmine-induced yawning. The results indicate that apomorphine elicits yawning by stimulating presynaptic dopamine receptors, and that dopaminergic inhibition and cholinergic activation are concomitantly involved in the yawning.

The neurohypophyseal capillary bed. II. Specializations within median eminence

Vascular casts of the pituitary gland, median eminence and hypothalamus from several mammalian species were examined by scanning electron microscopy. These observations were correlated with light microscopic studies of injected, cleared median eminence-pituitary specimens and with light microscopic examination of serial sections of injected hypothalamic, median eminence, and pituitary specimens employing reflected lighting or epi-illumination. Transmission electron microscopy was employed to study long portal vessels on the ventral surface of the rat median eminence. In each of the species examined, the median eminence (infundibular) capillary bed is subdivided into an external and an internal plexus. The external plexus (the neurohemal contact zone) receives an arterial supply from the superior hypophyseal arteries and is continuous with the capillary bed of the infundibular stem and process. Egress from the external plexus is possible via three vascular routes: (a) by fenestrated portal vessels and capillaries to the adenohypophysis, (b) by capillary connections to the medial basilar hypothalamus and, (c) by internal plexus capillaries to the ependyma of the median eminence. Median eminence vasculature is structurally organized to deliver (1) hypothalamic and neurohypophyseal peptides to the glandular pituitary via portal vessels, (2) hypothalamic and pituitary secretions to the medial basilar hypothalamus via capillaries, and (3) hypothalamic and pituitary secretions to distant brain sites through cerebrospinal fluid via ventricular and subarachnoid routes.

The behavioural actions of the hypothalamic peptides: a review

Recent work has shown that the hypothalamic peptides commonly associated with the control of pituitary function have important behavioural actions of possible psychiatric significance. Thus, vasopressin, ACTH and like peptides may influence memory processes, and ACTH and MSH given intracranially induce a peculiar stretching and yawning syndrome accompanied by penile erection and ejaculation. Thyrotrophic hormone-releasing factor potentiates behavioural excitation, somatostatin is depressive, while luteinizing hormone-releasing hormone facilitates sexual behaviour and the newly identified endorphins are markedly opioid in character. These and other activities of the hypothalamic peptides are reviewed and assessed alongside the clinical information available.