Harry J. Carlisle

Intragastric drinking in the rat: evidence for a role of oropharyngeal stimulation.

Abstract Two experiments analyzed the contribution of oropharyngeal stimulation to the acquisition and maintenance of intragastric self-injection of water in the rat. Animals were trained to press a lever for delivery of intragastric water routed to the stomach by either a subcutaneous gastric cannula or a nasopharyngeal catheter. Animals readily acquired the response via the nasal catheter but not via the gastric cannula. When switched from intragastric drinking via the nasal catheter to the gastric cannula, three of four animals showed extinction. Acquisition of self-injection behavior was precluded in nasal catheter animals if the water was warmed to 36.5°C, but when switched from 22°C to 36.5°C water, only one of five animals reached extinction. The one rat self-injecting by gastric fistula and all nasal catheter animals invariably licked and chewed metal objects during self-injections and thereby appeared to mediate the reinforcing properties of intragastric water with self-produced oral stimulation. Oropharyngeal stimulation, either experimenter-controlled or self-produced during metal licking, is important for reinforcing operant behavior with intragastric delivery of water in the rat.

Diurnal cycle of core temperature in huddling, week-old rat pups ☆

Lean Zucker rat pups were reared at 25 degrees C on four staggered 12:12 light:dark cycles with lights on at 0100, 0700, 1300 or 1900 hr. Core temperature (Tc) of 5- to 8-day-old pups was measured repeatedly at the rearing temperature of 25 degrees C between 0700 and 1900 hr using a procedure that minimally interfered with spontaneous nursing cycles and huddling of the pups. Tc of litters measured 30 to 60 min after the mother spontaneously left the nest was low and variable (32.2-35.4 degrees C) during the first few hours after lights-on, but was uniformly high and much less variable (35.5-36.5 degrees C) around the time of lights-off. Pup Tc was phase-advanced to the nocturnal elevation of maternal Tc, and lagged several hours behind the diurnal elevation of nursing activity. Cyclic variations in Tc of pups huddling in the nest thus reflect a diurnal rhythm in the ability and/or drive for body temperature defense that is independent of heat derived from the mother during nursing.

Effect of fixed-ratio thermal reinforcement on thermoregulatory behavior

Abstract Rats and squirrel monkeys were tested on fixed-ratio schedules for radiant heat reinforcement in a cold environment. Monkeys worked at a rate determined by the schedule as well as the parameters of thermal reinforcement. Rats failed to demonstrate a behavioral regulation of body temperature on ratio schedules by failing to maintain a rate of work great enough to insure a constant rate of reinforcement per unit time. Body temperature was maintained when continuous reinforcement was available, but decreased on ratios. A low ambient temperature or low body temperature facilitated rate of responding by the rat. Repeated daily tests produced a form of cold acclimatization in rats; behavioral response rate decreased, while the usual decrease in body temperature was attenuated as daily testing progressed.

Observations on the thermoregulatory effects of preoptic warming in rats

Abstract Experimental warming of the preoptic-anterior hypothalamic area was used to evaluate behavioral and autonomic thermoregulatory heat-loss responses. Hypothalamic warming was associated with reduced behavioral heat intake and decreased core and peripheral temperatures in rats working for radiant heat reward in a cold environment. Baseline rates of responding for external heat were determined by ambient temperature, but the magnitude of changes in core or peripheral temperatures during preoptic warming were not. Behavioral responses compensated for variations in ambient temperature so that the threshold hypothalamic temperature above which heat loss was activated by preoptic warming was not altered by changing ambient temperatures. Heat loss during hypothalamic warming was a function of both autonomic and behavioral thermoregulatory responses because the decrease in body heat content during preoptic warming could not be accounted for by the decreased behavioral heat intake alone. The threshold hypothalamic temperature for elicitation of tail vasodilation decreased systematically as ambient temperature increased when no behavioral option was available. In the rat, both behavioral and autonomic thermoregulatory responses cooperate to determine the magnitude of heat loss which is proportional to the magnitude of preoptic warming.

Estrogenic effects on behavioral thermoregulation and body temperature of rats

Abstract Estradiol benzoate increases responding for heat reinforcement of ovariectomized female and intact and castrate male rats placed in the cold. In females, both pre- and postsession rectal temperatures are depressed by the steroid. The maintenance of low temperatures despite increased heat intake suggests that body temperature is regulated at a lower level as a result of estradiol-induced increases in heat loss or decreases in heat production.

Initiation of Behavioral Responding for Heat in a Cold Environment

Abstract Clipped and unclipped rats were exposed to a cold (0°C) environment, and given the opportunity to learn a lever-pressing response to obtain radiant heat. Unclipped rats failed to learn the response, while clipped rats learned after several hours of exposure. Hypothalamic temperature rose initially in both the clipped and unclipped animals in response to a decreasing ambient temperature, while subcutaneous temperature fell. Hypothalamic temperature was maintained for many hours in unclipped rats, but began to fall rapidly after approximately 30 minutes of cold exposure in clipped subjects. Hypothalamic temperature typically fell below 37°C prior to initiation of responding, but this result was not invariant. A decrease in peripheral temperature is considered a sufficient condition for learning in this situation.

Effects of lateral hypothalamic lesions on thermoregulation in the rat

The effects of bilateral lesions in the lateral hypothalamus (LH) of the rat on several thermoregulatory and non-thermoregulatory variables were studied. In agreement with the literature, a reduction in food and water intake and in body mass were observed in the experimental animals but not in the operated controls. Rectal temperature and metabolism increased for a few hours after the lesion, decreased below pre-lesion level for a day or two, and finally returned to baseline level. The increase in rectal temperature during a 1-hr exposure to 5 degrees C was accentuated in the control but not in the experimental subjects. An improvement in operant thermoregulatory behavior, measured by nose-poke and lever-press responses, was observed in most LH-lesioned animals. Thermal preference in a gradient, two measures of general activity, and light avoidance were not affected by the lesions. The post-lesion improvement in operant thermoregulatory behavior does not support the view of the LH as a necessary locus for the integration of behavioral thermoregulatory responses.

Body temperature of huddling newborn Zucker rats

SummaryDaily mean core temperature (

Effect of conventional (mixed β1/β2) and novel (β3) adrenergic agonists on thermoregulatory behavior

\bar T_c