Water immersion, excessive grooming, and paper shredding in the rat

A critical role for the melanocortin 4 receptor in stress-induced relapse to nicotine seeking in rats

Tobacco addiction is characterized by a lack of control over smoking and relapse after periods of abstinence. Smoking cessation leads to a dysphoric state that contributes to relapse to smoking. After the acute withdrawal phase, exposure to stressors increases the risk for relapse. Blockade of melanocortin 4 (MC4 ) receptors has anxiolytic and antidepressant-like effects in animal models. The aim of these studies was to investigate the role of MC4 receptors in the dysphoria associated with nicotine withdrawal and stress-induced reinstatement of nicotine seeking. To study stress-induced reinstatement, rats self-administered nicotine for 16 days and then nicotine seeking was extinguished by substituting saline for nicotine. Nicotine seeking was reinstated by intermittent footshock stress. The intracranial self-stimulation (ICSS) procedure was used to assess the negative mood state associated with nicotine withdrawal. Elevations in the ICSS thresholds are indicative of a dysphoric state. The selective MC4 receptor antagonists HS014 and HS024 prevented stress-induced reinstatement of extinguished nicotine seeking. Drug doses that prevented stress-induced relapse did not affect responding for food pellets, which indicates that the drugs did not induce sedation or motor impairments. In the ICSS experiments, the nicotinic acetylcholine receptor antagonist mecamylamine elevated the ICSS thresholds of the nicotine-dependent rats. Pre-treatment with HS014 or HS024 did not prevent the elevations in ICSS thresholds. These studies indicate that MC4 receptors play a critical role in stress-induced reinstatement of nicotine seeking, but these receptors may not play a role in the dysphoria associated with acute nicotine withdrawal.

Effects of melanotan II, a melanocortin agonist, on grooming and exploration in rats after repeated restraint/immobilization

2mg/kg melanotan II (MTII, administered i.p.), a cyclic peptide analog of alpha-melanocyte stimulating hormone, at a single dose increased grooming in naive rats placed in an unfamiliar open-field device without changing locomotion or rearing. Male rats exposed to restraint/immobilization stress (IS) for 1h on three consecutive days displayed increased grooming after the second stressor exposure, compared to pre-stress levels. MTII, administered to the rats after IS, enhanced the grooming response compared both to the pre- and post-stress values. The increase was greatest after the first dose and declined over the following two applications. As to the locomotion of rats in the entire experimental space, IS reduced the distance moved only after the first two stressor exposures; MTII did not influence these alterations. Locomotion in the central part of arena was not reduced by the stressor or by MTII, on the contrary, there was an increase in both groups after the third intervention. The only observed change in rearing was an increase in the MTII group after the third restraint exposure. Thus, MTII selectively increased grooming without markedly affecting the spatio-temporal structure of locomotor behavior in the open-field. The decline of MTII enhanced grooming over the three test days may be interpreted in terms of adaptation to the stressor and of the developing tolerance to the peptide.

Corticotropin-releasing factor-1 receptors in the basolateral amygdala mediate stress-induced anorexia

Corticotropin-releasing factor (CRF) receptor activation within the basolateral amygdala (BLA) has been relatively unexplored compared with the central nucleus of the amygdala (CeA), despite the fact that CRF receptors are more densely distributed in BLA than in CeA. The authors show that infusion of CRF into BLA, but not CeA, decreases feeding and increases grooming. These effects are mediated by CRF-sub-1 receptors, because they are blocked by intra-BLA treatment with NBI27914 (NBI), a CRF-sub-1 antagonist, but not Astressin 2B, a CRF-sub-2 antagonist. Exposure to a stressor results in behaviors identical to those seen after intra-BLA CRF infusion. These stress-induced changes are prevented by pre-stress treatment with NBI but not Astressin 2B. These data demonstrate that stimulation of intra-BLA CRF-sub-1 receptors is both necessary and sufficient for eliciting stress-induced anorexia and grooming.

Altered grooming responses to stress in rats exposed prenatally to ethanol

The effects of prenatal alcohol exposure on grooming, locomotion, and rearing in response to stress were examined in adult rats whose mothers consumed a liquid diet containing 35% ethanol-derived calories (EDC). Offspring of both pair-fed 0% EDC mothers and ad libitum chow-fed mothers were included as controls. In Experiment 1, females groomed more than males following placement into a novel test chamber, but no differences due to prenatal treatment were observed. Ethanol-exposed animals groomed more than controls following the stress of a forced 1-min swim (Experiment 2), but when rats tested in Experiment 1 were observed again after forced swim stress (Experiment 3), no differences due to prenatal treatment or sex were observed. Experiment 4 examined the effects of pretreatment with 1 mg/kg naloxone on novelty-induced grooming and as in Experiment 1 prenatal treatment did not affect grooming responses. Females again groomed significantly more than males and naloxone reduced grooming equally for all groups. The results suggest that novelty-induced grooming is a sex-influenced behavior, with females grooming more than males, and that animals exposed prenatally to alcohol and tested as adults may have altered responses to certain stressors (i.e., forced swim) under specific conditions. The altered grooming response of alcohol-exposed rats to swim stress can be eliminated by preexposing them to novelty stress.

Effect of the chronic ingestion of chlorimipramine and desipramine on the hole board response to acute stresses in male rats

The effect of the chronic ingestion of chlorimipramine (CI) or desipramine (DS) on the alterations of hole board behavior caused by a model stress (2 IP injections of physiological saline) and by a short restraint stress (5 min) is analyzed in this study. The experimental groups ingested about 3 mg/kg/24 hr CI or DS for 15 days. Then some experimental and control rats were assigned to control of drug effects on baseline activity. The remaining rats were submitted to saline stress (Experiment I) or restraint stress (Experiment II). The baseline scores of hole board locomotion, head dipping, grooming and defecation were not affected by DS treatment but locomotion slightly increased in the CI treated group. Saline stress impaired significantly head dipping and caused excessive grooming in control rats. The CI treatment induced almost full protection against these behavioral effects of saline stress but DS treatment was ineffective. Restraint stress was found to cause a pronounced inhibition of head dipping as well as a great increase of the scores of grooming in the control group. The CI treatment clearly attenuated these effects of restraint but DS treatment was not effective. The results suggest that male rats treated chronically with CI tolerated both acute stresses better than untreated rats, and that a similar treatment with DS did not provide protection against the effect of such stresses on hole board responding. Inasmuch as CI and DS have different relative potency at noradrenergic and serotonergic systems, it is speculated that this might be in part responsible for their differences as stress protectors.

The influence of neurotensin, naloxone, and haloperidol on elements of excessive grooming behavior induced by ACTH

Naloxone, haloperidol, and neurotensin suppress ACTH-induced grooming. The suppressive effects of naloxone and of haloperidol on ACTH-induced grooming are observed following subcutaneous as well as intracerebroventricular administration. The suppression of ACTH-induced grooming by these drugs is not accompanied by a change in the relative distribution of grooming elements. From previous data and from the results of the present study it is suggested that the underlying substrate involved in ACTH-induced excessive grooming may differ from that of bombesin-induced grooming.

Ethanol-induced grooming in mice selectively bred for differential sensitivity to ethanol

In rats, excessive grooming follows the application of several forms of stress. The injection of alcohol may be considered as a stressor, since it increases plasma corticosterone levels. The present study examines the effects of ethanol injections on grooming in two lines of mice selected for differences in their hypnotic response to ethanol, i.e., the long sleep (LS) and short sleep (SS) lines developed at the Institute for Behavior Genetics at the University of Colorado at Boulder. Various subhypnotic doses of ethanol produced excessive grooming in the SS line, but this did not occur in the LS line. The SS mice also displayed more "novelty-induced" grooming compared to the LS mice after repeated exposure to the testing situation. The increase in excessive grooming in both the ethanol-induced and the novelty-induced excessive grooming situations was most apparent in the second half of the observation period.

Serotonin and antidepressant drugs antagonize melatonin-induced behavioural changes after injection into the nucleus accumbens of rats

Small doses of melatonin (0.1-100 ng), injected into the nucleus accumbens of rats, decreased locomotor activity and rearing, and increased grooming and sniffing behaviour when the animals were tested in small test-cages. Larger doses of melatonin appeared to be less effective. The action of melatonin is apparently not mediated by dopaminergic systems, because the behavioural changes were not antagonized by local pretreatment with haloperidol or sulpiride. Injection of serotonin antagonists (methysergide and cyproheptadine) into the nucleus accumbens resulted in similar behavioural changes as was found after treatment with melatonin. Treatment with serotonin and various antidepressant drugs (zimelidine, mianserin, nortriptyline, clomipramine, desipramine) injected into the nucleus accumbens, completely inhibited the melatonin-induced behavioural responses. The antidepressants did not significantly interfere with the decrease of locomotor activity and rearing induced by injection of small doses of the dopamine agonist, apomorphine, into the nucleus accumbens. These results suggest that there is an interrelationship between melatonin and serotonin systems in the nucleus accumbens and showed that various antidepressant drugs, similar to serotonin, antagonized the behavioural effects of melatonin after injection into the nucleus accumbens.

Neurotensin diminishes grooming and stimulates paper shredding behavior induced by water immersion of rats

Intracerebroventricular (i.c.v.) administration of 2 micrograms neurotensin, a brain and gastro-intestinal peptide which elicits various behavioral responses, diminishes grooming but stimulates paper shredding behavior of rats evoked by water immersion. Neither naloxone (2 micrograms i.c.v.) nor haloperidol (2 micrograms i.c.v.) affect grooming and paper shredding behavior as observed following water immersion of rats.