Avian pancreatic polypeptide-like immunoreactivity in ground squirrel hypothalamus.

The distribution of avian pancreatic polypeptide-like immunoreactivity (APP-LI) within the hypothalamus of the golden-mantled ground squirrel (Spermophilus lateralis) was analyzed using the indirect peroxidase-antiperoxidase immunocytochemical technique. Avian pancreatic polypeptide-LI is widely distributed within the hypothalamus of the golden-mantled ground squirrel and in general, the distribution of APP-LI containing neuronal fibers in this species is qualitatively similar to the distribution found in the laboratory rat. This similarity in APP-LI distribution in two rodents from different taxonomic Families suggests that the distribution of APP-LI containing neurons is probably very conservative within the Order Rodentia.

Electron microscope study of the association between hypothalamic blood vessels and oxytocin-like immunoreactive neurons.

An association between oxytocin-like immunoreactive neurons and hypothalamic blood vessels has been observed with the light microscope. Recently, it has been demonstrated that oxytocin stimulates vascular smooth muscle contraction in vitro. A hypothesis has thus been proposed that oxytocin may play a role in modulating blood flow in certain brain regions. In a study on the golden-mantled ground squirrel (Spermophilus lateralis) we noted the association at the light microscope level between oxytocin-like immunoreactive neurons and blood vessels in preoptic and paraventricular nuclei of the hypothalamus. To determine if these neurons were associated with hypothalamic capillaries, transverse 30 micron immunostained hypothalamic sections were prepared for thin sectioning and observation by transmission electron microscopy. Oxytocin-like immunoreactive neurons were observed to lie within 77 nm of the edge of the lumen of capillary blood vessels. One neuronal cell body was observed approximately 380 nm from the edge of a capillary lumen and what appears to be an output region of a neuron was observed to terminate on the basement membrane of a capillary blood vessel.

The energetic cost of the fever response in three species of ectothermic vertebrates.

Three species of ectothermic vertebrates: goldfish (Carassius auratus), green tree frogs (Hyla cinerea), and desert iguanas (Dipsosaurus dorsalis) were used in this study. Metabolic rates for each species were determined at the normal afebrile preferred body temperature and at the febrile preferred body temperature or other higher body temperatures. The febrile metabolic rate (or higher rate) was significantly greater than the afebrile metabolic rate (or lower rate) in each species. The average increase in energetic cost for goldfish and desert iguana was 64.5% while the increase for the green tree frog was between 24 and 70%.

Body temperature regulation in a desert lizard, Sauromalus obesus, under undisturbed field conditions.

1. Mean selected body temperatures (MSBTs), measured by radiotelemetry, are presented for 15 chuckwallas on 26 animal days. 2. MSBT, during the period of activity, ranged from 37.3 to 39.8 degrees C (means = 38.8 +/- 0.2 SE degrees C) while MSBTs, from the time lizards attained their first high set point to the time that solar radiation ceased, ranged from 36.1 to 39.6 degrees C (means = 38.3 +/- 0.2 SE degrees C). 3. On cloudy, cool days, animals could not maintain high Tbs because of the absence of solar radiation. 4. On sunny March and April days, animals were active for 5-6 hr but Tb then fell rapidly to low levels. 5. From late April to mid May, animals were active for 7-8 hr and Tbs did not fall as drastically because of higher Tas after sunset. 6. August was the time of year (for this study) when chuckwallas had the highest effective 24 hr Tb but it was also the time when they had the shortest activity interval.

Stress fever magnitude in laboratory-maintained California ground squirrels varies with season.

A previous study demonstrated that California ground squirrels (Spermophilus beecheyi) living in the natural environment had, independent of season, a significantly higher mean diurnal body temperature (T(b)) (39.6 degrees C) than either summer (37.5 degrees C) or winter (36.5 degrees C) laboratory maintained animals. Based upon the previous study it has been suggested that California ground squirrels living in the natural environment may have an elevated set-point for body temperature in a manner analogous to a stress fever response. The present study was conducted to determine if season and/or duration of laboratory open-field exposure influenced the magnitude of laboratory open-field stress fever. If stress fever was involved to some extent in the higher body temperature observed in animals from the natural environment, laboratory maintained animals should exhibit a lower magnitude stress fever during the summer months and a higher magnitude stress fever during the winter months. It was hypothesized that laboratory maintained animals would exhibit the same set-point for stress fever T(b) independent of season, and that the duration of open-field exposure would not influence the magnitude of stress fever. Adult California ground squirrels were acclimated to an ambient temperature of 20+/-1.0 degrees C under either LD 14:10 (summer) or LD 10:14 (winter) photoperiod conditions and individuals from both photoperiod conditions were exposed for periods of 2, 4, and 6 h to an open-field arena. An analysis of the data with a two-factor ANOVA demonstrated that season (photoperiod) significantly influenced the magnitude of the stress fever response (1.1+/-0.1 degrees C for summer animals; 2.1+/-0.2 degrees C for winter animals) while there was no significant influence of open-field exposure duration on stress fever magnitude. These results demonstrate that although the set-point for body temperature in unstressed laboratory maintained California ground squirrels varies with season, the set-point for body temperature in open-field stressed animals does not vary with season. These data lend support to the hypothesis that something like stress fever may play some role in the higher body temperature observed in California ground squirrels living in the natural environment.

Fever response in laboratory-maintained and free-ranging chuckwallas (Sauromalus obesus).

The fever response was studied in laboratory-maintained and free-ranging chuckwallas. Five animals were used in a self-pairing laboratory experiment in which each animal was first injected with a sterile, pyrogen-free saline solution. Approximately 7 days later, each individual was injected with a solution of 4.75 x 10(9) Aeromonas sobria (formerly A. hydrophila). Saline-injected individuals had a mean preferred body temperature (MPBT) of 36.8 +/- 0.4 (SE) degrees C, whereas bacteria-injected animals had a MPBT of 39.1 +/- 0.6 (SE) degrees C (an increase of 2.3 degrees C). The within-animal variance associated with MPBT was significantly decreased in bacteria-injected animals. In the natural environment, 10 chuckwallas were divided into five pairs, so that both animals of a pair could be monitored simultaneously. One animal in a pair was given an injection of sterile, pyrogen-free saline, whereas the other animal received an injection of 4.75 x 10(9) A. sobria. On day 2, both the MPBT and the rate of heating were greater in bacteria-injected animals. The between-animal variation in fever MPBT was greater than the mean increase in MPBT of fever animals. Also, the absolute level of the MPBT during the fever response was related to time of the year, with spring-active animals having the highest fever MPBTs.

The effect of bacteria infection on mean selected body temperature in the common Agama, agama agama: a dose-response study.

1. The fever response was studied in 43 common agamas using a self-pairing experiment in which animals received an intraperitoneal injection of sterile saline and an injection of one of six dosages of dead Aeromonas sobria (1 x 10(6), 1 x 10(7), 1 x 10(8), 1 x 10(9), 1 x 10(10), and 1 x 10(11) total organisms). 2. The results demonstrated a significant increase in Tb (1.6-3.1 degrees C) above the mean selected body temperature (MSBT) of the saline injection animals over a bacteria infection range of three orders of magnitude. At 1 x 10(8) organisms, an increase was observed on bacteria day 1 while at dosages of 1 x 10(9) and 1 x 10(10) an increase was observed on bacteria days 1 and 2. 3. At dosages of 1 x 10(6) and 1 x 10(7) there was no difference between saline MSBT and bacteria MSBT. 4. At a dosage of 1 x 10(11), MSBTs on bacteria days 1 and 2 were below saline MSBT. 5. The average duration of the fever response is related to the level of infection; however, the magnitude of the fever is relatively independent of the level of infection.

Pre-existing bacterial infections, not stress fever, influenced previous studies which labeled Gerrhosaurus major an afebrile lizard species.

Early studies indicated that the Sudan plated lizard, Gerrhosaurus major, did not exhibit a febrile response when challenged with bacterial pyrogen. More recent results indicated that a 14-day antibiotic treatment regime produced a significant decrease (0.5 +/- 0.1 degree C) in the mean selected body temperature (MSBT) for this species (31.3 +/- 0.2-30.8 +/- 0.2 degrees C). The antibiotic treatment results suggested that G. major already had a fever caused by a pre-existing bacterial infection. The current study was designed first to determine if a sub-population of G. major, with a higher mean pre-antibiotic treatment MSBT would exhibit a greater decrease in MSBT after antibiotic treatment. A 14-day antibiotic treatment regime for G. major (N = 7) with MSBTs > or = 31.9 degrees C (mean 32.4 +/- 0.2 degrees C) produced a significant decrease of 1.7 +/- 0.4 degrees C in MSBT to 30.7 +/- 0.3 degrees C. Analysis of the combined antibiotic treatment MSBT data from [13] and the current study demonstrated that the magnitude of the change in MSBT after antibiotic treatment was dependent upon the pre-antibiotic treatment MSBT. These data imply that animals with a greater pre-treatment MSBT and greater MSBT change had a greater magnitude fever. In the second portion of this study the MSBT for individual lizards was measured during separate experiments using both indwelling cloacal thermocouples taped to the tail of the lizard and telemeters implanted into the peritoneal cavity of the lizard. This second study was designed to determine if measurement of Tb using thermocouples induced a stress fever which may have masked a portion of the pyrogen-induced fever. The MSBT measured using indwelling cloacal thermocouples (30.5 +/- 0.3 degrees C) was not significantly greater (T > 0.05) than the MSBT increased using telemeters (31.0 +/- 0.2 degrees C). The results of the experiments from this study demonstrate that the previously reported afebrile state for G. major was the result of animals having pre-existing bacterial infections. G. major does exhibit a febrile response similar to other lizard species.

Effect of bacterial pyrogen on three lizard species.

1. Three lizard species (Callopistes maculatus, Gerrhosaurus major, and Varanus exanthematicus) were tested for their response to intraperitoneal injection of alcohol-killed Aeromonas sobria. 2. A paired experimental design, in which each animal received an injection of sterile saline and 1 x 10(10) A. sobria, was utilized. 3. C. maculatus demonstrated a statistically significant increase in mean selected body temperature (MSBT) after bacteria injection. 4. G. major and V. exanthematicus did not demonstrate a statistically significant increase in MSBT. 5. C. maculatus is the first lizard species outside of the family Iguanidae to exhibit a febrile response to bacterial pyrogen.

The concentrations of four neuropeptides in various brain areas of summer active and hibernating Spermophilus lateralis.

1. Twenty-six female golden-mantled ground squirrels were divided into four physiological stages; low weight summer, medium weight summer, high weight summer, and early hibernation period. 2. Sections of six brain regions from each animal were analyzed by radioimmunoassay for bombesin, cholecystokinin, neurotensin and somatostatin-like immunoreactivity. 3. Significant (P less than 0.05) between-stage differences were detected in thalamic bombesin, thalamic and hypothalamic neurotensin, and cerebellum somatostatin concentrations. 4. Significant (P less than 0.05) peptide concentration versus physiological stage correlations were found in cerebral cortex and hypothalamic cholecystokinin and hypothalamic somatostatin concentrations.

A positive fever response in Agama agama and Sceloporus orcutti (Reptilia: Agamidae and Iguanidae).

Three species of lizards (Agama agama, Mabuya perrotetii, and Sceloporus orcutti) were tested for a possible increase in mean selected body temperature (MSBT) in response to intraperitoneal injection of alcohol-killed Aeromonas sobria, a gram-negative bacterium known to be pathogenic to reptiles. A paired experimental design was utilized in which each animal was given an injection of sterile saline and 1.10(10) A. sobria. Body temperatures were monitored via indwelling cloacal thermocouples at 4-min intervals for one 12-h light period under saline injection and for two consecutive 12-h light periods under bacteria injection. Agama agama demonstrated a significant increase in MSBT on both day 1 and day 2 of bacteria injection with increases of 2.7 and 2.3 degrees C, respectively. The latency period on day 1 averaged 6.4 h. Sceloporus orcutti demonstrated a significant decrease in MSBT on day 1 of bacteria injection and a significant increase in MSBT of 1.0 degree C on day 2 of bacteria injection. No fever was evident in S. orcutti until the beginning of day 2. Mabuya perrotetii did not exhibit a significant change in MSBT on either day 1 or day 2 of bacteria injection. Agama agama (family Agamidae) is the first Old World reptile to exhibit a fever response to bacteria injection, and with these results fever has now been demonstrated in the lizard families Agamidae, Iguanidae, and Teiidae.

The acute phase response in the Sudan plated lizard, Gerrhosaurus major.

The Sudan plated lizard (Gerrhosaurus major), previously reported to be an afebrile species, was utilized in a series of experiments to test for various aspects of the acute phase response. Treatment of individuals with the antibiotic Baytril resulted in a slight (0.5 degree C) but significant reduction in mean selected body temperature (MSBT), while treatment with saline did not lower MSBT. Nonantibiotic treatment individuals had depressed plasma iron levels (86.6 +/- 22.4 micrograms Fe 100 ml-1 plasma) and treatment with Baytril produced a significant increase in plasma iron concentration (186.8 +/- 19.5 micrograms Fe 100 ml-1 plasma). Necropsy of randomly selected individuals indicated that animals obtained from the commercial supplier had Aeromonas, Arthrobacter, Pseudomonas and Salmonella infections and antibiotic treatment eliminated these infections. The growth rate of Aeromonas sobria is reduced when the bacteria are grown at 32 degrees C and reduced iron concentration compared to 34.5 degrees C and low iron concentration, which suggests that a fever response may not be beneficial in reducing bacterial growth. Saline injected, bacteria injected and antibiotic injected Gerrhosaurus major have high plasma zinc concentrations compared to the previously studied febrile species, Dipsosaurus dorsalis. This difference suggests that zinc concentrations in afebrile species deserve further study.

California ground squirrel body temperature regulation patterns measured in the laboratory and in the natural environment.

Body temperature (Tb) was measured by telemetry in both laboratory maintained and natural environment California ground squirrels, Spermophilus beecheyi. Laboratory animals had a mean diurnal Tb of 37.5 degrees C under conditions of LD 14:10, 20 degrees C and 36.5 degrees C under conditions of LD 10:14, 20 degrees C (P < 0.01). Nocturnal mean Tbs were 37.1 and 35.2 degrees C, respectively (P < 0.05). Mean diurnal Tbs for each animal in the natural environment ranged from 39.3 to 40.1 degrees C (mean = 39.6 degrees C) during both study seasons which included the hot season months of March through August and the cool season months of December through February. Natural environment hot season mean Tb was not significantly different from cool season mean Tb but both mean Tbs were significantly different from the diurnal mean Tbs measured in the laboratory (P < 0.05). California ground squirrels exhibit an open-field stress induced hyperthermia in the laboratory which can be extended for periods up to 6 h. The hyperthermic response is blocked by L-propranolol at a dosage of 15 mg kg-1. Laboratory animals do not habituate to repeated open-field exposures over a five consecutive day period. It is suggested that stress hyperthermia might be a normal component of thermoregulation in some free-living ground squirrels because of the openness of the habitat in which they exist.