Voluntary exercise and its effects on young SHR and stroke-prone hypertensive rats

To determine whether voluntary exercise would lower resting blood pressure in spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SP-SHR), two separate but interrelated investigations were undertaken. The studies were initiated when the animals were 28-35 days of age and after they were assigned to either activity or sedentary cages. The activity cages were connected to transducers and recorders that allowed the monitoring and calculation of frequency, duration, and running speed. The SHR group ran 3-7 km/day intermittently for 12 wk at high speeds (48-68 m/min), which resulted in heart rates in excess of 500 beats/min. When the SHR exercised, they seldom exceeded 33 revolutions/bout (37 m) with the majority being less than 22 revolutions/bout. This type of exercise training significantly lowered, but did not normalize, resting blood pressure by approximately 20 mmHg [nontrained (NT) = 185 +/- 5; trained (T) = 163 +/- 5 mmHg] while increasing maximum O2 consumption (VO2max) (NT = 78 +/- 2.6; T = 95 +/- 2.2 ml X min-1 X kg-1) and endurance run time (NT = 62 +/- 9.0; T = 286 +/- 15.0 min), respectively. Although SP-SHR exhibited comparable patterns of voluntary activity, the effects were not similar. First, after approximately 5 wk of consuming a special Japanese rat chow and a 1% NaCl drinking solution, cerebrovascular lesions occurred and deaths ultimately resulted in both exercising and sedentary groups. Second, although there was statistical evidence for a training effect (higher VO2max, longer VO2 test run times), voluntary exercise had no advantage in either male or female runners in lowering resting blood pressures or in improving their life-spans. Whereas voluntary activity wheel exercise or moderate forced treadmill exercise will lower resting blood pressures in young SHR populations, similar generalizations cannot be made with young SP-SHR rats.     

Chronic exercise and its hemodynamic influences on resting blood pressure of hypertensive rats.

Studies with male spontaneously hypertensive rats (SHR) were initiated to determine the hemodynamic relationships associated with the lower resting caudal artery systolic blood pressure (SBP) of endurance-trained SHR populations. After assignment into nontrained (NT, n = 38) and trained (T, n = 38) groups, the T animals were exercised 5 times/wk on a motor-driven treadmill for 12-16 wk at a moderate intensity that ranged from 40 to 70% of their maximum O2 consumption capacity (VO2max). SBP, VO2max, and treadmill run time were determined before the experimental period began and before the animals were instrumented for hemodynamic measurements. At the end of the study, the T rats exhibited significantly lower SBP (NT = 210 +/- 3, T = 200 +/- 3 mmHg) and significantly higher VO2max (NT = 75 +/- 2, T = 83 +/- 2 ml.min-1.kg-1) and run durations (NT = 11.4 +/- 0.4, T = 14.5 +/- 0.3 min). When the animals were anesthetized for insertion of catheters and microprobes for blood pressure and cardiac output (thermodilution) measurements, the T rats had lower values for body mass, heart rate, mean blood pressure, cardiac output, and cardiac index than the NT rats; however, only the body mass and heart rate differences were statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of oat bran on sucrose-induced blood pressure elevations in SHR

To determine whether oat fiber influences BP, we gave spontaneously hypertensive rats (SHR) a diet high in sucrose and low in protein (calories: sucrose 52%, protein 15%, fat 33%) or a diet low in sucrose and high in protein (calories: sucrose 13%, protein 52%, fat 35%). The amount of fat in these particular diets has not been shown to influence BP, so we modified the 2 diets by replacing fat with oat bran (10% w/w). Accordingly, we examined 4 groups of 5 rats consuming different diets: high sucrose, high sucrose + oat bran, low sucrose, and low sucrose + oat bran. Not unexpectedly, SHR consuming the diet high in sucrose had a significantly higher BP after 2 weeks than those consuming the diet low in sucrose. The significant difference in BP continued over the next 3 weeks. At the end of 6 week duration of study, we found the following BP: SHR ingesting the high sucrose diet, 217 mm Hg +/- 5 (SEM) vs SHR consuming the low sucrose diet, 187 mm Hg +/- 4 (SEM) p less than .0001]. SHR eating the low sucrose diet and consuming supplemental bran showed no significant change in BP after 6 weeks compared to SHR eating the basic diet alone, 188 mm Hg +/- 6 (SEM); however, 5 SHR consuming the high sucrose diet with added oat bran showed a significantly lower BP 200 mm Hg +/- 2 (SEM) than SHR ingesting the basic high sucrose diet devoid of oat bran [p less than .01]. We conclude that addition of oat bran to the diet can ameliorate sucrose-induced BP elevations in SHR.     

In vitro generation of secondary cell-mediated cytotoxic response against a syngeneic Gross virus-induced lymphoma in rats.

Cell-mediated cytotoxic responses against a syngeneic Gross virus-induced lymphoma, (C58NT)D, in W/Fu rats were generated in vitro by using mixed lymphocyte-tumor cell cultures. The source of responding cells was either spleens from normal rats or spleens from rats carrying or having rejected (C58NT)D tumors. Mitomycin C-treated (C58NT)D tumor cells were used as stimulating cells. The secondary anti-tumor cytotoxic response occurred more rapidly and reached higher levels than the primary response, and it was antigen specific. T cells, but nor B cells or macrophages, were essential for both the induction and the effector phases of the secondary anti-tumor responses. These data suggest that specific memory T cells persist for long periods of time in the lymphoid organs of (C58NT)D immune rats, which can rapidly become cytotoxic upon re-exposure to antigen.     

Alterations in plasma catecholamines and behavior during acute stress in spontaneously hypertensive and Wistar-Kyoto normotensive rats

The responsiveness of the sympathoadrenal system to stress was assessed in spontaneously hypertensive (SHR) and Wistar-Kyoto normotensive (WKY) rats at 6, 18, and 48 weeks of age. Two days after insertion of a tail arterial catheter, each rat was transferred from its home cage to a shock chamber, and after 5 min received 60 footshocks over a 5 min interval. Blood samples were taken from undisturbed rats when in the home cage, 3–5 min after transfer to the shock chamber, and at the end of shock. An additional group of naive SHR and WKY rats was exposed to footshock and behavioral responses were recorded. There were no strain differences in levels of norepinephrine (NE) or epinephrine (EPI) while rats were undisturbed in their home cages. Transfer to the shock chamber resulted in a greater increase in plasma levels of both catecholamines in SHRs of each age. A similar pattern was evident after footshock; SHR rats had significantly higher post-shock levels of plasma NE and EPI than age-matched WKY rats. During shock, SHR rats were more active and jumped and reared more frequently than WKYs. These results demonstrate that the sympathoadrenal system of SHR rats is more responsive than normotensive rats to stressful stimuli and that this hyper-responsitivity is independent of increases in blood pressure. The excessive discharge of NE and EPI into plasma during stress may contribute to the development and maintenance of high blood pressure in SHR rats.     

Selenium and blood pressure studies in young and adult normotensive,renal, and spontaneously hypertensive animals

With reports of either no change or reduction of blood pressure, the relationship between selenium and blood pressure has not been clear. Normal Se values are not available for the Sprague Dawley (SD) rat or in the young and adult rat with various models of experimental hypertension. This study measured serum Se levels in the young and adult normotensive (NT), Grollman renal hypertensive (RH), and Okamoto-Aoki spontaneous hypertensive rats (SHR). The young animals have statistically significant (P<0.001) lower Se values as measured by the fluorometric method than those found at adulthood. Selenium levels were found to be altered in the adult SHR animals when compared with the RH and NT animals. The serum Se value for the normotensive SD rat was found to be 65.0±3.5 μg/dL, and for the two experimental models, 63.7±4.6 μg/dL for the RH, whereas the SHR level was elevated to 75.04±4.8 μg/dL (P<0.001). Elevated serum Se values in the adult SHR animals suggests an altered metabolism in SHR animals.     

正常大鼠植入高血压大鼠肾脏后 动脉血压的变化

本实验对12周龄的自发性高血压大鼠(spontaneously hypertensive rat,SHR)及其对照组Wistar Kyoto (WKY)大鼠进行了肾脏移植的研究, 并观察受肾移植大鼠动脉血压的变化以及免疫抑制剂对动脉血压的影响。 用尾套法对接受同窝另一同胞WKY大鼠肾脏移植且存活5周的6只WKY大鼠(A组)及接受SHR肾脏移植且存活5周的6只WKY大鼠(B组)的尾动脉收缩压进行检测, 移植前A、 B两组受肾移植大鼠的尾动脉收缩压分别为18.0±0.93 和18.3±0.68 kPa,无统计学显著差异(P>0.05); 移植后3、 4、 5周时, B组大鼠的尾动脉收缩压显著高于A组大鼠, 移植后5周时, A, B两组大鼠的收缩压分别为19.0±0.71 和23.0±0.69 kPa (P<0.001); 所用剂量的免疫抑制剂CsA对双侧肾脏完整以及右侧肾脏切除的SHR、 WKY大鼠的动脉血压无显著影响。 以上结果表明, SHR的肾脏在高血压的形成中可能起重要作用。     

正常大鼠植入高血压大鼠肾脏后动脉血压的变化

本实验对12周龄的自发性高血压大鼠(spontaneouslyhypertensiverat,SHR)及其对照组WistarKyoto(WKY)大鼠进行了肾脏移植的研究,并观察受肾移植大鼠动脉血压的变化以及免疫抑制剂对动脉血压的影响。用尾套法对接受同窝另一同胞WKY大鼠肾脏移植且存活5周的6只WKY大鼠(A组)及接受SHR肾脏移植且存活5周的6只WKY大鼠(B组)的尾动脉收缩压进行检测,移植前A、B两组受肾移植大鼠的尾动脉收缩压分别为180±093和183±068kPa,无统计学显著差异(P>005);移植后3、4、5周时,B组大鼠的尾动脉收缩压显著高于A组大鼠,移植后5周时,A,B两组大鼠的收缩压分别为190±071和230±069kPa(P<0001);所用剂量的免疫抑制剂CsA对双侧肾脏完整以及右侧肾脏切除的SHR、WKY大鼠的动脉血压无显著影响。以上结果表明,SHR的肾脏在高血压的形成中可能起重要作用     

Choice behavior in spontaneously hypertensive rats: Variable vs. fixed schedules of reinforcement

Spontaneously hypertensive rats (SHR) and Wistar rats were evaluated in the successive-encounters procedure (an operant simulation of natural foraging) with the idea of assessing differences between them in their preference for variable schedules of reinforcement. In this procedure, after satisfying a schedule of reinforcement associated with search time, the subjects could “accept” or “reject” another schedule of reinforcement associated with handling time. Two schedules of reinforcement were available: a fixed interval (FI), and a variable interval (VI) with the same mean value. The results indicated preference for the variable schedule in both strains, as suggested by the observation that the VI was always accepted while the FI was often rejected. The difference in FI acceptability between strains was not statistically significant, a result which is relevant for the current debate of SHR as an adequate animal model of Attention Deficit Hyperactivity Disorder.     

Abnormalities of the thyroid hormone negative feedback regulation of TSH secretion in spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) are characterized by several neuroendocrine abnormalities including a chronic hypersecretion of thyrotropin (TSH) of unknown etiology. We hypothesized that the inappropriately high TSH secretion in SHR may be the result of an impaired thyroid hormone negative feedback regulation of hypothalamic thyrotropin-releasing hormone (TRH) and/or pituitary TSH production. To test this hypothesis, SHR or their normotensive Wistar-Kyoto (WKY) controls were treated with either methimazole (0.02% in drinking water) to induce hypothyroidism or administered L-thyroxine (T4) at a dose of 0.8 or 2.0 micrograms/100 g body weight/day to induce hyperthyroidism. All treatments were continued for 14 days after which animals were killed under low stress conditions. TSH concentrations in plasma and anterior pituitary tissue were 2-fold higher (P less than 0.01) in euthyroid SHR compared to WKY control rats while thyroid hormone (T3 and T4) levels were in the normal range. Hypothyroidism induced by either methimazole or thyroidectomy caused a significant (P less than 0.01) rise of plasma TSH levels in both WKY and SHR rats. However, relative to the TSH concentrations in control animals, the increase of plasma TSH in SHR was significantly blunted (P less than 0.01) in comparison to the WKY group. Hypothyroidism caused a significant depletion of TRH in stalk-median eminence (SME) tissue in both groups of rats. However, no differences between SHR and WKY rats were observed. The administration of thyroid hormone caused a dose dependent suppression of plasma TSH levels in both strains of rats. However, at both doses tested plasma TSH concentrations in SHR rats were significantly less suppressed (P less than 0.05) than those in WKY animals. Under in vitro conditions basal and potassium induced TRH release from SMEs derived from SHR was significantly (P less than 0.05) higher than that from WKY rats, whether expressed in absolute terms or as percent of content. These findings suggest that the thyroid hormone negative feedback regulation of TSH secretion may be impaired in SHR rats. Our data do not allow conclusions as to whether defects in the regulation of TSH production are located exclusively at the hypothalamic level. Since the overproduction of hypothalamic TRH and hypophysial TSH should lead to an increased thyroid hormone biosynthesis other defects in the hypothalamus-pituitary-thyroid-axis may contribute to the abnormal regulation of TSH secretion in SHR rats.     

Dietary obesity caused by a specific circadian eating pattern

The eating pattern is altered by high-fat diet-induced obesity. To clarify whether this is dependent on the fatty acid profile of the diet, the authors conducted two studies on adult female Sprague-Dawley rats fed normal-fat chow or high-fat diets with varying fatty acid composition. Eating pattern and body weight were assessed in rats fed canola-based (low in saturated fatty acids) or lard-based (moderate in saturated fatty acids) diets for 7 days, and in animals fed chow or canola- or butter-based diets (rich in saturated fatty acids) for 43 days. These parameters were also determined when restricted amounts of low-fat canola- or butter-based diets were consumed for 25 days. Early exposure to canola or lard high-fat feeding or prolonged access to canola- or butter-based fat-rich diets (relative to chow feeding) did not alter the normal light-dark distribution of food and energy intake. All animals ingested most of their food during the dark phase. However, feeding the high-fat canola- and butter-based diets produced an altered eating pattern during the light phase characterized by a smaller number of meals, longer intermeal interval, and enhanced satiety ratio, and consumption of shorter-lasting meals than chow-fed animals. Relative to canola or chow feeding, butter-fed animals consumed a lower number of meals during the dark phase and had a higher eating rate in the light phase, but ate larger meals overall. Only butter feeding led to overeating and obesity. When given a restricted amount of low-fat canola- or butter-based diet at the start of the light phase, rats ate most of their food in that phase and diurnal rather than nocturnal feeding occurred with restriction. These findings underscore the role of saturated fatty acids and the resulting eating pattern alteration in the development of obesity.     

Role of the renal nerves in blood pressure in male and female SHR

Female spontaneously hypertensive rats (SHR) have lower blood pressures than males. The renin-angiotensin system plays an important role in the sexual dimorphism of blood pressure in SHR. The sympathetic nervous system can stimulate renin release, and, therefore, the present study was performed to determine whether the renal sympathetic nerves play a role in the sexual dimorphism of blood pressure in SHR. Male and female SHR underwent bilateral kidney denervation or sham surgery, and, 2 wk later, mean arterial pressure (MAP) and pulse interval were recorded, and baroreflex sensitivity (BRS) was measured by the sequence technique. Left ventricle index (LVI) was also calculated. MAP was higher in sham-operated males than females (182 +/- 5 vs. 169 +/- 4 mmHg; P < 0.01), but, despite the higher MAP in males, LVI was significantly greater in female rats. BRS was not different between sham-operated male and female SHR. Following bilateral renal denervation, MAP was decreased by a similar percentage (8-10%) in males (169 +/- 2 mmHg) and females (152 +/- 3 mmHg), whereas LVI was reduced only in female SHR. BRS was not altered by renal denervation in either sex. These data indicate that renal nerves play a role in the control of blood pressure in SHR independent of sex, but do not play a role in mediating the sex differences in blood pressure.     

Packet theory of conditioning and timing

Packet theory is based on the assumption that the momentary probability of producing a bout or packet of responding is controlled by the conditional expected time function. Bouts of head entry responses of rats into a food cup appear to have the same characteristics across a range of conditions. The conditional expected time function is the mean expected time remaining until the next food delivery as a function of time since an event such as food or stimulus onset. The conditional expected time function encodes mean interval duration as well as the distribution form so that both the mean response rate and form of responding in time can be predicted. Simulations of Packet theory produced accurate quantitative predictions of: (1) the effect of reinforcement density (mean food-food interval) and distribution form on responding; (2) scalar variance in fixed interval responding; (3) CS-US and intertrial interval effects on the strength of conditioning; and (4) the effect of the ratio of cycle:trial time on the strength of conditioning.     

Analysis of nonstationarity in renal autoregulation mechanisms using time-varying transfer and coherence functions

The extent to which renal blood flow dynamics vary in time and whether such variation contributes substantively to dynamic complexity have emerged as important questions. Data from Sprague-Dawley rats (SDR) and spontaneously hypertensive rats (SHR) were analyzed by time-varying transfer functions (TVTF) and time-varying coherence functions (TVCF). Both TVTF and TVCF allow quantification of nonstationarity in the frequency ranges associated with the autoregulatory mechanisms. TVTF analysis shows that autoregulatory gain in SDR and SHR varies in time and that SHR exhibit significantly more nonstationarity than SDR. TVTF gain in the frequency range associated with the myogenic mechanism was significantly higher in SDR than in SHR, but no statistical difference was found with tubuloglomerular (TGF) gain. Furthermore, TVCF analysis revealed that the coherence in both strains is significantly nonstationary and that low-frequency coherence was negatively correlated with autoregulatory gain. TVCF in the frequency range from 0.1 to 0.3 Hz was significantly higher in SDR (7 out of 7, >0.5) than in SHR (5 out of 6, <0.5), and consistent for all time points. For TGF frequency range (0.03-0.05 Hz), coherence exhibited substantial nonstationarity in both strains. Five of six SHR had mean coherence (<0.5), while four of seven SDR exhibited coherence (<0.5). Together, these results demonstrate substantial nonstationarity in autoregulatory dynamics in both SHR and SDR. Furthermore, they indicate that the nonstationarity accounts for most of the dynamic complexity in SDR, but that it accounts for only a part of the dynamic complexity in SHR.     

Low‐intensity aerobic exercise improves cardiac remodelling of adult spontaneously hypertensive rats

We evaluated the influence of aerobic training on cardiac remodeling in untreated spontaneously hypertensive rats (SHR). Four experimental groups were used: sedentary (W‐SED, n=27) and trained (WEX, n=31) normotensive Wistar rats, and sedentary (SHR‐SED, n=27) and exercised (SHR‐EX, n=32) hypertensive rats. At 13 months old, trained groups underwent treadmill exercise five days a week for four months. Statistical analysis: ANOVA or Kruskal‐Wallis. Exercised groups had higher physical capacity. Hypertensive groups presented left ventricular (LV) concentric hypertrophy with impaired function. Left atrium diameter, LV posterior wall thickness and relative thickness, and isovolumetric relaxation time were lower in SHR‐EX than SHR‐SED. Interstitial collagen fraction and Type I‐Type III collagen ratio were higher in SHR‐SED than W‐SED. In SHR‐EX these parameters had intermediate values between W‐EX and SHRSED with no differences between either group. Myocardial matrix metalloproteinase‐2 activity, evaluated by zymography, was higher in SHR‐SED than W‐SED and SHR‐EX. TIMP‐2 was higher in hypertensive than normotensive groups. In conclusion, low intensity aerobic exercise reduces left atrium dimension and LV posterior wall thickness, and improves functional capacity, diastolic function, and metalloproteinase‐2 activity in adult SHR.     

Genetic differences in the elevated plus-maze persist after first exposure of inbred rats to the test apparatus

The elevated plus-maze (EPM) is an anxiety model thought to assess different types of emotional states depending on whether or not the animals have been previously exposed to the test apparatus. Accordingly, benzodiazepine-treated rodents generally differ from controls in the first but not in the second EPM trial. Inbred Lewis and SHR rats of both sexes (N = 10) were submitted twice (test and retest) to the EPM with a 24 h interval between trials. Overall strain differences (Lewis < SHR) were observed in both males and females concerning anxiety-related measures (time spent and percent of entries in the open arms) regardless of previous maze experience. Moreover, prior exposure to the test apparatus produced an overall decrease in the approach towards the open arms in both strains and sexes. The fact that genetic differences did not diminish or disappear in the second trial, suggests that test and retest in the EPM are likely to share some common emotional components and that differences between naïve LEW and SHR rats are not similar to those observed between control and benzodiazepine-treated animals.     

Neuropeptide Y (NPY)-induced feeding behavior in female rats: comparison with human NPY ([Met17]NPY), NPY analog ([norLeu4]NPY) and peptide YY

Porcine neuropeptide Y (pNPY) administered into the third ventricle of the brain is known to elicit a powerful feeding response in steroid-treated ovariectomized and intact male rats. The present study compared the effects of pNPY and 3 structurally related peptides, human NPY (hNPY), an analog of NPY (NPY-A, [norLeu4]NPY) and peptide YY (PYY) on feeding behavior in intact female rats. Intraventricular administration of pNPY, hNPY, NPY-A and PYY over a dose range of 0.5 to 10 micrograms evoked feeding behavior to a varying extent. Cumulative food intake during 60 and 120 min was increased in a dose-related fashion at 0.5 and 2.0 microgram for the 4 peptides. Whereas the 10-micrograms dose of pNPY evoked a feeding response smaller than that seen after 2 micrograms, the responses to either 10 micrograms hNPY or 10 micrograms PYY were similar to that seen after 2 micrograms. The effects of these peptides on the time spent eating were quite different: while pNPY increased the time spent eating, this effect was not dose-related, whereas hNPY, NPY-A and PYY produced dose-related increments in the time spent eating. The most dramatic increment in local eating rate was observed after 2.0 micrograms pNPY, with lesser increments seen after 2.0 microgram hNPY and NPY-A. This increased local eating was apparently responsible for the highest cumulative food intake observed. These results demonstrate that (a) 2 micrograms pNPY is equally effective in stimulating feeding behavior in intact female rats as it is in steroid-primed ovariectomized female and intact male rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of 12-week nicotine treatment and dietary copper on blood pressure and indices of the antioxidant system in male spontaneous hypertensive rats

Nicotine treatment and copper (Cu) deficiency have been associated with an increased production of reactive oxygen species that may contribute to the development and/or progression of cardiovascular diseases (CVD). The present study investigated the influence of dietary Cu intake on the response to chronic nicotine treatment in spontaneous hypertensive rats (SHR) with respect to tissue trace mineral levels, several components of the oxidant defense system, and lipid peroxidation rates. SHR weighing 100–110 g were fed a Cu deficient diet (?Cu) (0.5 μg Cu/g) for 14 d prior to nicotine treatment. SHR were inserted with tablets that released nicotine at a rate of 75 μg/h or placebo (control). Following tablet insertion, rats were fed a control diet (+Cu) (12.0 μg Cu/g) or the ?Cu diet. Nicotine treatment lasted for 12 wk. Blood pressure (BP) was higher in nicotine-treated SHR than in control SHR at wk 3; BP was unaffected by diet. BP was higher in +Cu nicotine-treated SHR at wk 6 compared to ?Cu nicotine and control rats. BP was not affected by nicotine or diet at wk 2. Liver, heart, and brain Cu levels and liver, heart, and red cell CuZn superoxide dismutase and plasma ceruloplasmin oxidase activities were lower in the ?Cu SHR than in the +Cu SHR. Liver Fe levels were higher and plasma Fe levels were lower in the ?Cu rats than in the +Cu rats. Liver selenium-dependent-glutathione peroxidase (Se-GSH-Px) activity was lower in the ?Cu rats than in the +Cu rats; heart and thoracic aorta Se-GSH-Px activity was unaffected by ?Cu diet. Thoracic aorta, liver, and heart GSH-reductase activities were unaffected by treatments. Plasma thiobarbituric acid reactive substances (TBARS) were higher in the ?Cu than in the +Cu SHR. Liver and heart TBARS production was similar among the groups. These data show that nicotine can exacerbate the development of high BP in susceptible individuals; Cu deficiency did not exacerbate the effects of nicotine.     

Fluctuations in central and peripheral temperatures associated with feeding behavior in rats

We examined the pattern of temperature fluctuations in the nucleus accumbens (NAcc), temporal muscle, and skin, along with locomotion in food-deprived and nondeprived rats following the presentation of an open or closed food container and during subsequent eating or food-seeking behavior without eating. Although rats in food-deprived, quiet resting conditions had more than twofold lower spontaneous locomotion and lower temperature values than in nondeprived conditions, after presentation of a container, they consistently displayed food-seeking behavior, showing much larger and longer temperature changes. When the container was open, rats rapidly retrieved food and consumed it. Food consumption was preceded and accompanied by gradual increases in brain and muscle temperatures ( approximately 1.5 degrees C) and a weaker, delayed increase in skin temperature ( approximately 0.8 degrees C). All temperatures began to rapidly fall immediately after eating was completed, but NAcc and muscle temperatures returned to baseline after approximately 35 min. When the container was closed and rats were unable to obtain food, they continued food-seeking activity during the entire period of presentation. Similar to eating, this activity was preceded and accompanied by gradual temperature increases in the brain and muscle, which were somewhat smaller than those during eating ( approximately 1.2 degrees C), with no changes in skin temperature. In contrast to trials with eating, NAcc and muscle temperatures continued to increase for approximately 10 min after the container was removed from the cage and the rat continued food-seeking behavior, with a return to baselines after approximately 50 min. These temperature fluctuations are discussed with respect to alterations in metabolic brain activity associated with feeding behavior, depending upon deprivation state and food availability.     

Plasma lipids and other factors in the LA/N corpulent rat in the presence of chronic exercise and food restriction

The effects of regular exercise and food restriction were studied in the LA/N corpulent rat up to age 9 months. This congenic strain of the Lister and Albany rat is normotensive, corpulent, and hyperlipidemic when homozygous for the corpulent (cp) gene derived from the Koletsky strain. Food restriction of corpulent animals to the intake of matched lean rats caused body weight to be significantly lower, although not as low as that of the lean animals. Plasma total cholesterol in freely eating sedentary corpulent animals was significantly higher (210 mg/100 mL) than in food-restricted rats (165 mg/100 mL), in which plasma cholesterol was considerably elevated compared with lean rats (80 mg/100 mL). Exercise caused a modest but significant increase in both total and high density lipoprotein cholesterol in both corpulent and lean rats. The rise was greater in corpulent rats and, in food-restricted exercising corpulent rats, the cholesterol concentrations were equivalent to those of freely eating corpulent animals. Systolic blood pressure in lean rats fell slowly from 146 mmHg at 8 weeks to 132 mmHg at 36 weeks and was not affected by exercise. Sedentary corpulent rats showed a rapid rise in systolic pressure from 107 mmHg at 7 weeks to 128 mmHg at 11 weeks. This rise was reduced by food restriction and completely prevented by the combination of food restriction and exercise. Thus, in this strain of rats exercise was associated with higher plasma cholesterol concentrations, while food restriction had limited effects.