The role of central melanocortin receptors in the activation of the hypothalamus-pituitary-adrenal-axis and the induction of excessive grooming

1. In accord with previous studies intracerebroventricular (i.c.v.) injections of ACTH1-24 (1 microg) induced a display of excessive grooming, and increased the plasma concentrations of ACTH and corticosterone. Pituitary-adrenal activation was blocked by pretreatment with dexamethasone, indicating that the effect of the (i.c.v.) injected peptide was not caused by a peripheral effect on the adrenal cortex. 2. Doses of 1 and 3 microg of a non-selective melanocortin-3/4-receptor antagonist (SHU 9119), or of 5 and 10 microg of a selective melanocortin-4-receptor antagonist ([D-Arg8]ACTH4-10), coadministered (i.c.v.) with 1 microg ACTH1-24, inhibited the ACTH1-24-induced activation of the hypothalamus-pituitary-adrenal-axis and excessive grooming. 3. In addition, several doses of the selective melanocortin-3-receptor agonist Lys-gamma2-MSH were centrally administered, but neither neuroendocrine, nor excessive grooming responses were observed. 4. These results imply that the melanocortin-4-receptor, and not the melanocortin-3-receptor, is involved in the ACTH1-24-induced rise in plasma levels of ACTH and corticosterone, and excessive grooming.

Inhibition of stress-induced neuroendocrine and behavioral responses in the rat by prepro-thyrotropin-releasing hormone 178-199

A corticotropin release-inhibiting factor (CRIF) in brain has been postulated for several decades, based on increased plasma levels of ACTH and corticosterone after hypothalamic-pituitary disconnection. Recent in vitro studies indicate that prepro-TRH178-199 may function as an endogenous CRIF, prompting us to examine stress-related neuroendocrine and behavioral responses after in vivo administration to the adult male rat. Animals that were administered prepro-TRH178-199 intravenously 5 min before restraint stress exhibited a significant attenuation of stress-induced elevations of ACTH, corticosterone, and prolactin, as compared with controls infused with vehicle, whereas thyroid-stimulating hormone (TSH) secretion was not changed. In behavioral studies of stress responsiveness, either the vehicle or prepro-TRH178-199 was administered intracerebroventricularly (ICV) 5 min before testing. In the open field, prepro-TRH178-199 significantly increased grooming, locomotor activity, rearing, and sniffing behaviors. In the light/dark box, it significantly increased the time animals spent in the light compartment and increased the number of crossings between the light/dark compartments. In the plus maze, the peptide significantly increased the amount of time animals spent in the open arms. The same dose of peptide, administered ICV, had no effect on peripheral hormone release in response to restraint stress. Overall, these results support a role for prepro-TRH178-199 in the inhibition of the neuroendocrine responses to stress at the level of the pituitary and indicate that it has central modulatory influences over stress-related behaviors.

Conserved and sexually dimorphic behavioral responses to biogenic amines in decapitated Drosophila

A preparation of decapitated Drosophila melanogaster has been used for direct application of drugs to the nerve cord. Serotonin, dopamine, and octopamine stimulate locomotion and grooming, showing distinguishable effects that often are potentiated by addition of the vertebrate monoamine oxidase-inhibitor hydrazaline. Many of the hydrazaline-induced effects are sexually dimorphic, with males showing greater responses than females. Behaviors similar to those induced by dopamine can be induced by application of the vertebrate dopamine D2-like receptor agonist quinpirole, whose effects are also sexually dimorphic. In contrast, vertebrate D2-like and D1-like dopamine antagonists result in akinesic states, and D1-like agonists selectively stimulate grooming. These data indicate that Drosophila nerve cord amine receptors are coupled to reflexive behaviors similar to those stimulated by brain dopamine receptors in vertebrates.

Implementation of action sequences by a neostriatal site: a lesion mapping study of grooming syntax

The neostriatum and its connections control the sequential organization of action ("action syntax") as well as simpler aspects of movement. This study focused on sequential organization of rodent grooming. Grooming syntax provides an opportunity to study how neural systems coordinate natural patterns of serial order. The most stereotyped of these grooming patterns, a "syntactic chain," has a particularly stereotyped order that recurs thousands of times more often than could occur by chance. The purpose of the present study was to identify the crucial site within the striatopallidal system where lesions disrupt the syntax or serial order of syntactic grooming chains without disrupting constituent movements. Small excitotoxin lesions were made using quinolinic acid at bilateral sites within the dorsolateral, dorsomedial, ventrolateral, or ventromedial neostriatum, or in the ventral pallidum or globus pallidus of rats. An objective technique for mapping functional lesions was used to quantify cell death and to map precisely those lesions that disrupted grooming syntax. Our results identified a single site within the anterior dorsolateral neostriatum, slightly more than a cubic millimeter in size (1.3 x 1.0 x 1.0 mm), as crucial to grooming syntax. Damage to this site did not disrupt the ability to emit grooming actions. By contrast, damage to sites in the ventral pallidum and globus pallidus impaired grooming actions but left the sequential organization of grooming syntax intact. Neural circuits within this crucial "action syntax site" seem to implement sequential patterns of behavior as a specific function.