Edward B. Pivorun

Differences in daily torpor patterns among three southeastern species ofPeromyscus

SummaryThree subspecies ofPeromyscus inhabiting the montane, foothill, and coastal plain regions of the Carolinas were trapped in midwinter and the occurrence of spontaneous and ration-induced daily torpor was monitored via biotelemetric determination of body temperature. All tests were undertaken with field-caught mice that were subjected to a minimum of laboratory acclimation (two days). The tendency to enter torpor in the presence of adequate food was highest inP. maniculatus nubiterrae, whose natural montane habitat presents it with the greatest seasonal stress in terms of ambient temperature and food availability. This species exhibited significantly (P<0.05) longer spontaneous torpor bouts than did the two lowland subspecies,P. gossypinus gossypinus andP. leucopus leucopus (Table 1). Restriction of food to one-half thead libitum level increased the frequency, duration, and depth (mean minimum body temperature) of torpor in all three species (Fig. 1).P. maniculatus, however, displayed significantly (P<0.001) longer episodes of torpor induced by rationing than did either of the other two subspecies. The ability to compensate for a reduction in energy intake by adjusting levels of energy utilization may profoundly affect survival during short-term environmental stress in any of these three species.

Seasonal Study of Daily Torpor in Southeastern Peromyscus maniculatus and Peromyscus leucopus from Mountains and Foothills

Over a 2½-yr period, the effects of season and food availability on daily torpor patterns were compared in wild-caught members of two southeastern species of Peromyscus with different elevational distributions. Animals were housed in large outdoor cages either in the mountains (P. maniculatus nubiterrae, n = 59) or in the foothills (P. leucopus leucopus, n = 52), and Tbs were continuously monitored biotelemetrically. All mice received food and water ad lib. for 2 wk, followed by a short period (4-6 days) of food restriction (75% of daily ration). The highest incidence of spontaneous torpor in each species occurred during winter and in the presence of lower Tas. No interspecific differences in the frequency, mean duration, and mean minimum Tb of spontaneous torpor bouts were found in any season. Food restriction increased the incidence of torpor in both species. However, the montane P. maniculatus were more likely to enter torpor in response to food restriction, and torpor episodes in this species were longer than those displayed by its lowland congener. These findings imply that mice living in the more stressful montane environment may be subjected to greater selection for the use of torpor as a survival mechanism to counter short-term starvation pressure.

Differential effect of food restriction on the induction of daily torpor in Peromyscus maniculatus and P. leucopus

Abstract 1. 1. T b in lab-born Peromyscus maniculatus and P. leucopus was monitored via surgically implanted transmitters during exposure to 10°C and 9L:15D. 2. 2. With food available ad lib , no significant interspecific differences in the incidence, frequency, and patterns of spontaneous daily torpor were found. 3. 3. Restriction of food to 75% daily ration increased the incidence of torpor in both species, and induced longer, deeper torpor bouts. 4. 4. A significantly greater proportion of P. maniculatus responded to rationing by becoming torpid. Furthermore, induced torpor boults in this species were more profound than those in P. leucopus . 5. 5. This differential response is consistent with differences in these species respective environments.

Pineal gland structure and respiration as affected by age and hypocaloric diet.

Abstract The effect of age and underfeeding on pineal gland structure and metabolism was determined in male rats. Both chronic and acute caloric restriction was imposed on selected groups of these animals to determine the process by which pineal cell number is altered. Oxygen consumption of single pineal glands was greatest in the tissues removed from neonatal animals and declined thereafter. Pineal respiration was enhanced in the chronically undefed animals when compared with similar tissue from their littermates, but was uneffected when food was withheld for a short period of time. Mitotic indices of pineal cells similarly decreased with age, but were not enhanced by either underfeeding schedule. Pineal cell number, which also decreased as time progressed, was significantly higher in chronically underfed rats than in controls. No such increase was evident in short term underfed animals. It is concluded that the enhanced metabolism of pineal glands from chronically underfed rats occurs due to the increased number of cells present. This increase results from a reduced loss of pineal cells rather than an enhanced production by stimulation of mitotic activity. Based upon the capacity of pineal compounds to alter neuroendocrine feedback sensitivities, life prolongation resulting from feed restriction may in part be due to the persistence of a juvenile type pineal gland in the chronically underfed rat.

The effects of photoperiod and different dosages of melatonin on metamorphic rate and weight gain in Xenopus laevis tadpoles.

This study examined the effects of photoperiod and three different dosages of melatonin on the rate of metamorphosis and weight gain in Xenopus laevis. Exposure of larvae to 23L:1D resulted in lower mean body weight and a retarded metamorphic rate in comparison to larvae exposed to 1L:23D. Larvae reared in either photoperiod and treated with exogenous melatonin demonstrated a dose-dependent suppression of weight attained, with short photoperiod larvae showing a more dramatic effect. Analysis of growth patterns indicate that photoperiod and exogenous melatonin have a greater effect on weights prior to Nieuwkoop and Faber stage 56 in the development of Xenopus. Larvae exposed to 1L:23D and exogenous melatonin metamorphosed at an accelerated rate when compared to larvae exposed to 23L:1D and the same dosages of melatonin. In both photoperiod regimens an exogenous melatonin concentration of 45 micrograms/100 ml resulted in an accelerated metamorphic rate, whereas 225 and 450 micrograms/100 ml retarded metamorphic rate of larvae in comparison to controls.

Effect of naltrexone on food intake and hoarding in white-footed mice (Peromyscus)

Increases in food consumption and hoarding in mammals have been shown to be immediate and preparative adjustments to the energetic stresses of temperate winters. The sensitivity of these behaviors to the opiate antagonist naltrexone was tested in non-deprived white-footed mice (Peromyscus leucopus). Mice received naltrexone hydrochloride intraperitoneally (10 mg/kg in saline vehicle) once daily for four consecutive days subsequent to an equivalent period of injection with saline as control. Daily food intake was significantly (p less than 0.05) lower after naltrexone treatment. Hoarding, as assessed by logarithmic hoarding scores and the weight of cached food, was not affected by administration of this drug at this dosage. These results suggest that hoarding, a complex behavioral pattern that does not immediately affect internal energy stores, may not fall within the opiate regulatory scheme.

Effects of intrahypothalamically administered norepinephrine, serotonin and bombesin on thermoregulation in the deermouse (Peromyscus maniculatus)

Norepinephrine, serotonin, and bombesin administered intrahypothalamically affected thermoregulation in the deermouse, Peromyscus maniculatus. At a Ta of 22 degrees C, doses of 3 micrograms and 6 micrograms of NE resulted in transient hypothermia (maximum drop of 1.6 +/- 1.0 degrees C and 4.3 +/- 2.3 degrees C, respectively). A 1.5 microgram dose of 5-HT induced a persistent hyperthermia (maximum increase of 1.8 +/- 0.8 degrees C) which persisted for more than 2 h. A 6 microgram dose of 5-HT did not produce any significant effects. At a Ta of 22 degrees C, doses of 1 ng and 10 ng of bombesin produced a transient hyperthermia (maximum increase of 1.8 +/- 0.3 degree C and 2.1 +/- 1.2 degrees C, respectively) immediately postinjection. At a Ta of 5 degrees C, a 1 ng dose of bombesin resulted in a prolonged hypothermia (maximum decrease of 2.0 +/- 0.4 degrees C), while a 10 ng dose of bombesin produced a hyperthermic response (maximum increase of 1.3 +/- 0.8 degree C) at 2 h postinjection.

Analysis of serotonin, dopamine and their metabolites in the caudate putamen, the suprachiasmatic nucleus and the median raphe nucleus of euthermic and torpid deermice, Peromyscus maniculatus

Deermice, subjected to food rationing and low ambient temperature, were sacrificed in normothermia or during daily torpor. Levels of monoamines and their metabolites in the caudate putamen (CPN), the suprachiasmatic nuclear area (SCN), and the median raphe nucleus (MRN) were quantified through the use of HPLC with electrochemical detection. Significant elevations in levels (pg/mg protein) of the serotonin (5-HT) metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were noted in torpid individuals in all nuclei examined. The dopamine (DA) metabolite, homovanillic acid (HVA) was significantly elevated in the CPN and MRN of torpid individuals. Moreover, a significant increase in the HVA to DA ratio was also noted in the CPN and the MRN. In the SCN, the concentrations of 5-hydroxytryptophan (5-HTP), 5-HT, DA and 3,4-dihydroxyphenylacetic acid (DOPAC) were also increased significantly during torpor. These significant elevations suggest that an increase in the activity of the serotonergic and dopaminergic systems occurs in these nuclei during daily torpor in the deermouse.

Naloxone inhibition of stress-induced daily torpor.

Peromyscus maniculatus, deermice , were induced into daily torpor by restricting food to one-half daily ration. Intraperitoneal injection of naloxone (20 mg/kg) into mice habituated to daily IP injections of saline inhibited or modified the expression of daily torpor. In those individuals demonstrating long duration/deep bouts (greater than 300 min/body temperature 20 degrees C or below) naloxone administration resulted in 1) a significant decrease in the duration of torpor, 2) a significant elevation in minimum body temperatures attained during torpor and 3) a significant delay in the initiation time of torpor. In those individuals demonstrating short duration/shallow bouts (less than 300 min/body temperatures above 20 degrees C), naloxone administration resulted only in a significant delay of initiation time. Upon subsequent return to saline administration, however, these mice displayed a significant increase in the duration and depth of torpor. The results suggest that the endogenous opiates modulate the state of daily torpor.

Influence of Temperature on the Water Balance of Three Parapatric Species of Peromyscus

The water balance responses of Peromyscus maniculatus, P. leucopus , and P. polionotus were investigated to assess the significance of physiological adaptations in delimiting distributions. Daily ad libitum water consumption, urine volume, evaporative water loss, fecal water content, total urine osmolality, and urinary urea concentrations were measured for each species after acclimation at 5°, 15°, and 27°C. Evidence is not sufficient to conclude that one species may be physiologically excluded from the habitat of another; however, the data strongly indicate that P. polionotus is better adapted for a more xeric environment because of its smaller body size, low levels of water intake, reduced urine volume, and greater renal concentrating abilities. The greater urine volume and extremely low urinary urea concentrations observed for P. maniculatus nubiterrae at 5°C suggest that it may have adapted to the lower ambient temperatures of its montane habitat by developing the capacity to mobilize lipid reserves to a greater degree than the other two species. All three species displayed similar evaporative water losses at 27°C. Although P. polionotus occupies a mildly xeric habitat, this species apparantly lacks the ability to reduce evaporative losses significantly below those exhibited by P. maniculatus or P. leucopus , species occupying montane and piedmont habitats.