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PubMed1982

Effects of posttrial vasopressin injections on appetitively motivated learning in rats.

Sixty male rats, maintained on 23-hr food deprivation were trained on two types of appetitive tasks: bar pressure responding under a CRF schedule, and under a differentially reinforced (light+, dark-) schedule. Performance of rats treated with lysing vasopressin, injected immediately after each training session, was compared to that of control animals injected with saline. In the CRF stage, treated animals reached learning criterion significantly later than did control rats, and made significantly fewer bar presses. During acquisition and extinction of a light-dark discrimination, learning and retention were not altered by vasopressin, though the number of bar presses was significantly decreased, and a differential effect was found according to previous CRF performance. The results are discussed considering the hypothesis of a facilitatory effect of vasopressin on memory processes.

Animals↗
PubMed1982

Body-weight regulatory mechanisms and food hoarding in hereditarily obese (fa/fa) and lean (Fa/Fa) Zucker rats.

Pre- and postprandial rectal temperatures and the defended level of body weight, as inferred from the critical body weight for the onset of hoarding behaviour, were compared in obese (fa/fa) and lean (Fa/Fa) Zucker rats. Body temperatures of the obese group were not significantly lower than those of the lean group, whether satiated or whether subjected to short- or long-term food deprivation. Defended body weights as inferred from the critical weights for hoarding, and the actual weights of the obese (fa/fa) rats were both abnormally high, nearly double those of their lean controls, but the percentage weight losses necessary to elicit hoarding activity were similar in the two groups. Thus the mechanism underlying the obesity of the Zucker rat appears to differ both from that of the hereditarily obese (ob/ob) mouse (which shows defective thermogenesis and is hypothermic) and from the obesity of rats with hypothalamic ventromedial lesions (in which the defended body weight is no higher than in intact controls). Unlike the ob/ob mouse and the ventromedial rat, the obese Zucker rat appears to regulate body weight in a normal way but at an abnormally high level.

Animals↗
PubMed1982

Effect of ovarian and exogenous hormones on defended body weight, actual body weight, and the paradoxical hoarding of food by female rats.

Normally cycling female rats maintained on a free diet and showing the usual female pattern of hoarding behaviour (greater than 5 pellets/day) underwent bilateral ovariectomy or sham surgery. Body weights after ovariectomy showed a rapid increase for four postoperative weeks, paralleled by a sharp increase in food hoarding. During the fifth and sixth weeks, when body weights had stabilised at a higher level, hoarding activity reverted to preoperative levels. Daily intramuscular administration of oestradiol benzoate (2.0 micrograms or 25 micrograms/day for five days) counteracted the increases in body weight and hoarding activity. Progesterone (0.5 mg/day) and testosterone (0.5 mg/day) were without significant effect. The increased hoarding activity after ovariectomy is an indication of a rise in the defended level of body weight, and supports earlier suggestions that oestrogen lowers the physiological setting about which body weight is regulated. Paradoxical findings that non-deprived intact females hoard more, not less, than males are considered in the light of nonregulatory constraints on body weight which would affect hoarding by shifting body weights above, or below regulated levels.

Animals↗
PubMed1982

Homeostatic competition in rats fed at varying distances from a thermoneutral refuge.

Rats were fed in an air temperature of -15 degrees C at distances of 1, 2, 4, 8 or 16 m from a thermoneutral refuge. As the distance between the feeder and thermoneutrality increased, the number of excursions to feed decreased from 37 +/- 5 to 7 +/- 1 during the 2-hour feeding sessions; concomitantly, the meal duration increased from 1.2 to 5.2 min. The rate of eating and total feeding time were the same at all distances. The mass of food ingested was also constant except for a slight decline at 16 m. Meal duration was strongly correlated (r = 0.9) with the time taken to reach the feeder at each distance while the estimated cost/benefit of feeding episodes increased with distance. Estimates of body temperature indicated that significant falls in skin temperature occur over even short distances, while over greater distances core temperature probably also decreases. In the range of distances studied, rats accorded their hunger drive a higher priority than thermal preference, and chose to feed while tolerating greater thermal disturbance.

Animals↗
PubMed1983

The role of adrenocorticotropin and norepinephrine in appetitive learning in the rat.

This study examines the involvement of ACTH/4-10 and norepinephrine during training and testing of a complex maze task. Hormones were administered post-trial to eliminate effects on processes other than learning and memory during training and testing sessions. ACTH/4-10, but not NE, facilitates acquisition of an appetitive maze task, but neither affect test performance. Facilitation of acquisition by ACTH/4-10 is discussed within two frameworks. ACTH/4-10 may enhance memory, presumably via a direct action on certain brain cells, resulting in stimulated protein synthesis and modified synaptic transmission. An interaction with serotonin synthesis and metabolism may be involved. Alternatively, during training and testing of a complex maze task, an ACTH-opiate receptor interaction may modify reinforcing properties, thus facilitating acquisition.

Adrenocorticotropic Hormone↗
PubMed1983

The effect of naloxone on feeding and spontaneous locomotion in the wolf.

The effect of naloxone on food intake and activity levels was studied in the wolf (Canis lupus). Naloxone decreased food intake at both the 1 mg/kg and 5 mg/kg dose. There was no quantitative difference in the magnitude of the decrease in food intake produced by naloxone in winter or summer. Wolves ate significantly greater amounts of deer meat than dog chow after naloxone when expressed on a mass basis but there was no difference when the amounts of food ingested were expressed in calories. This suggests a role for endogenous opiates in the regulation of energy intake. The putative satiety factor, cholecystokinin-octapeptide, had no effect on food intake in wolves. Naloxone decreased spontaneous locomotion and increased time spent resting in wolves. The effects of naloxone on activity were significantly more marked in winter compared to summer.

Animals↗
PubMed1983

Intravenous cholecystokinin octapeptide in pigs reduces operant responding for food, water, sucrose solution or radiant heat.

The effect of intravenous injections of 0 (Saline vehicle), 10, 20 or 40 units of CCK was studied in pigs performing operant responses for food, water, sucrose solution or radiant heat. In hungry pigs working for food, thirsty pigs responding for water, and non-deprived pigs working for sucrose, 20 and 40 units CCK produced significant dose-related decreases in response rates lasting for about 5 min. In pigs responding for 10 sec bursts of infra-red heat at an ambient temperature of 5 degrees C, 40 units CCK significantly reduced the response rate during the 5 min period following injection.

Animals↗
PubMed1983

Response to NaCl taste in mixture with sucrose by sodium deficient rats.

Sodium deficient, adrenalectomized rats and nondeficient control rats were offered, for 20 min, either a mixture of 0.15 M sodium chloride and 0.3 M sucrose, or a 0.3 M sucrose solution. The sodium deficient rats drank about 3 times more of the mixture than of the sucrose alone. Nondeficient control animals showed no differential preference for the mixture over the sucrose solution. Subsequent tests indicated that the amount of mixture ingested by the sodium deficient group was comparable to the intake of a much weaker (1/5 as strong) sodium chloride concentration given alone. These results are discussed in the context of taste component analysis of mixtures and suggest that the rodent taste system can specifically respond to sodium chloride in a sodium chloride-sucrose mixture.

Adrenal Glands↗
PubMed1984

Mouse-killing in Sprague-Dawley rats: effects of lighting conditions.

Sixteen male Sprague-Dawley rats were studied in artificial daylight and in red light for mouse-killing. Fifty percent of the rats killed mice. Killing varied, however, considerably: only seldom did it occur on consecutive days. More killing occurred during tests in red light than in artificial daylight. In red light, the mean latency between confrontation of the rat with the mouse and the killing was gradually shortened but not in daylight.

Animals↗
PubMed1985

Mouse killing, insect predation, and conspecific attack by rats with differing prior aggressive experience.

Mouse-killing, cockroach predation, and conspecific attack were examined in male Long-Evans rats with a history of intraspecific aggression (n = 20), defeat (n = 20), or no aggressive experience (n = 20). Roaches were more likely to be attacked during 30 min tests, and were attacked more rapidly than mice or rats regardless of previous social experience of subjects. Rats with aggressive experience attacked conspecifics more readily than subjects with defeat or no experience. There was no effect of prior experience on mouse-killing. These results indicate that mouse-killing does not correspond closely to either predation or intraspecific attack.

Aggression↗
PubMed1986

Sex differences in appetitive learning of mice.

Learning abilities of male and female ddY mice were compared in two appetitive tasks (a lever-press task and an 8-arm radial maze task), and two avoidance tasks (a shuttle box task and a light-dark discrimination T-maze task). In the two types of appetitive learning, male mice were significantly superior to female mice. Sex differences were particularly apparent in the acquisition process. In contrast, there was no significant sex difference in learning of the two avoidance tasks. A sex difference in appetitive learning was not found in juvenile mice prior to sexual maturation, and the mice which had established a lever-press response as juveniles did not show any significant difference in the performance level when tested as adults. Thus, a sex difference appeared only in the acquisition stage of adult mice. These results suggest that there exists a sex difference in motivation level for hunting food but not for feeding, and that it causes a sex difference in appetitive learning.

Aging↗
PubMed1986

Aversive-CS-specific alterations of evoked potentials in limbic and related areas of rats.

Averaged evoked potentials (EP) to a CS (flash) were recorded sequentially in classical appetitive conditioning, satiated state after appetitive conditioning, highly alert state by noncontingent shocks, and classical aversive conditioning from a rat. The EPs were obtained from the central gray matter, superior colliculus, perifornical hypothalamic area, dorsal frontal cortex, and occipital cortex. Alterations unique to aversive conditioning were found in the dorsal frontal cortex (40-60 msec in latency) and in the perifornical hypothalamus (80-120 msec) but not in the central gray or occipital cortex. The frontal cortex might start processing information related to aversive or defensive emotion before the perifornical hypothalamic area might do it.

Animals↗
PubMed1988

Defensive aggression and testosterone-dependent intermale social aggression are each elicited by food competition.

Castrated rats with medial hypothalamic lesions or sham lesions and castrated rats with testosterone implants or sham implants were placed on a 23-hr food deprivation schedule, adapted to a highly palatable liquid food, and then housed in pairs. The pairs were observed in competition for the highly palatable food over a 4-min period on each of six days. On the first three days, the food was dispensed in a way that allowed only one animal at a time to drink while during the second three days both animals could drink simultaneously. The pairs of animals were then separated, individually adapted to a bland liquid food, and paired with a different animal for a second series of competition tests. With highly palatable food as the incentive, rats made hyperdefensive by medical hypothalamic lesions were more successful at maintaining access to the food and more aggressive than their sham-lesioned competitors on tests when food access was restricted to a single animal but not on tests when both animals could drink simultaneously. With bland food as the incentive, lesioned animals were not consistently more successful in maintaining access to the food but were significantly more aggressive than their cagemates. With the highly palatable food, castrated males with testosterone implants were neither more successful in maintaining access to the food nor more aggressive than their cagemates with sham implants. However, when paired with an unfamiliar cagemate in preparation for competition tests with the bland food, most rats with testosterone implants attacked the new cagemate using a lateral attack and displaying piloerection.(ABSTRACT TRUNCATED AT 250 WORDS)

Aggression↗
PubMed1988

Brief exposure to a natural predator, the short-tailed weasel, induces benzodiazepine-sensitive analgesia in white-footed mice.

Exposure to a natural predator, the short-tailed weasel, Mustela erminea, elicited significant increases in the nociceptive responses of wild male white-footed mice, Peromyscus leucopus. A short (30 sec), ecologically relevant, nonvisual exposure to a weasel elicited a relatively brief (15 min) analgesia that was insensitive to the opiate antagonist, naloxone (1.0 mg/kg), and was blocked by either pre- or post-exposure injections of the benzodiazepine antagonist, Ro15-1788 (10 mg/kg), or agonist, diazepam (4.0 mg/kg). A 5 min exposure to the weasel elicited an analgesic response of longer duration (15-30 min) that was sensitive to both naloxone and the benzodiazepine agonist and antagonist. A 15 min exposure to the weasel induced a higher amplitude analgesia that was of relatively long duration (45 min), blocked by naloxone, and insensitive to the benzodiazepine manipulations. Exposures of 5 and 15 min to a nonpredator, the European rabbit, Oryctolagus cuniculus, elicited low amplitude, naloxone-reversible analgesic responses that were unaffected by the benzodiazepine manipulations. Thirty-sec exposures to the rabbit had no significant effects on the nociceptive response of the rabbit. These results indicate that a brief, ecologically appropriate, exposure to a predator elicits a benzodiazepine-mediated analgesia while a more prolonged exposure to a predator induces opioid-mediated analgesia. These results show that the opioid and nonopioid distinction between the effects of long- and short-term laboratory stresses is also evident with a natural, ecologically relevant, stressor.

Analgesia↗