[Active avoidance training of rats with experimental diabetes mellitus]

Specific features of training the rats in a new form of defense behavior in insulin deficiency in animal body were under study. Experiments were carried out with 51 male Wistar rats, 24 of these with streptozotocin-induced diabetes. The method of bilateral active avoidance with acoustic signal stimulation, followed by electric stimulation of the skin, was employed. The curves of training, reflecting the time course of the number of effective behavioral acts, were analyzed, and the parameters of the shape of the individual curves of training estimated to classify the animals, making use of analysis of factors. A significant variability of the examined individual parameters of training was associated with the absence of noticeable differences in the approximated results of examinations of intact and streptozotocin-treated rats. Analysis of factors helped single out a group of rats with streptozotocin induced diabetes among the groups of animals that were characterized by similar training parameters, that could sooner learn a new habit after a longer latent period as against intact animals.

[Disorder of neuroendocrine regulation of sexual behavior of male rats with streptozotocin-induced diabetes]

The present paper presents studies of the sexual behavior characteristics and the associated changes of LH releasing factor and of sex hormone receptor concentrations in hypothalamic regions involved in the regulation of sexual behavior activity and hypophyseal gonadotropic function (the anterior preoptic and mediobasal regions) of rats with streptozotocin-induced diabetes. The activities of both motivational and copulative components of sex behavior of such rats were found reduced. These changes were parallelled by LH-RH reduction in the median eminence and in the synaptosomal fraction of the anterior preoptic and mediobasal regions. An increased concentration of estradiol nuclear receptors was found in the anterior preoptic region, that may be responsible for the male feminization in diabetes and for weaker male sexual activity parameters. Blood levels of LH and FSH in experimental rats were virtually the same as in the reference animals, whereas prolactin and testosterone levels were reduced in the presence of elevated estradiol content. The majority of the detected hormonal shifts and sexual behavior characteristics normalized after compensatory insulin therapy. The authors come to a conclusion on the neuroendocrine disorders at the level of the CNS in animals with experimental diabetes during the formation of the motivational and copulative components of sexual behavior.

Pain threshold in diabetic rats: effects of good versus poor diabetic control

Pain threshold was assessed via tail flick latency in streptozotocin diabetic rats following a 1-month period of either good or poor diabetic control. Additionally, tail flick latencies were determined under test conditions of euglycemia (60-120 mg/dl) and hyperglycemia (greater than 250 mg/dl) for both groups of diabetic rats. Conditions of hyperglycemia resulted in a significant decrease in tail flick latency in diabetic animals maintained in good as well as poor diabetic control. However, tail flick latencies for animals in the good but not in the poor diabetic control group increased when animals were euglycemic at the time of testing. Animals in the poor diabetic control group continued to have reduced tail flick latencies even after acute normalization of blood glucose levels. These results suggest that chronic states of hyperglycemia that attend prolonged periods of poor diabetic management may lead to persistent alterations in pain threshold. In contrast, the reduced pain threshold of rats maintained in good diabetic control was reversed by a normalization of blood glucose levels. These findings provide evidence for two patterns of hyperalgesia in diabetic rats: (1) a readily reversible form in well-maintained diabetic rats that is altered by reducing circulating blood glucose levels to control values and (2) a more persistent form found in poorly controlled diabetic rats that does not respond to acute normalization of blood glucose.

Morphine analgesia in normal and alloxanized mice

The analgesic response to 10 mg/kg of morphine hydrochloride, administered intraperitoneally, was examined in mice made diabetic by treatment with alloxan using the hot plate method. The hot plate base line latency of diabetic mice was significantly higher than that of normal mice. Morphine was found to possess an hyperglycaemic effect in both normal and diabetic mice. A decreased analgesic response to morphine was observed in diabetic mice. The decreased response seemed to be associated with plasma glucose levels, since multiple injections of insulin replacement abolished the decrease in morphine analgesia in diabetic mice. However, a single injection of insulin or glucose loading did not modify morphine analgesia. Naloxone was an effective antagonist of the analgesic and hyperglycaemic effects of morphine in both normal and diabetic mice, but induced a greater reduction of the plasma glucose level in diabetic than in normal mice. It is suggested that a supranormal dose of morphine may be needed in diabetics.

Effects of tryptophan on depression and aggression in STZ-D mice

Streptozocin-induced diabetic (STZ-D) mice have reduced brain concentrations of tryptophan, a precursor substance for 5-hydroxytryptamine, and show lengthened immobility in Porsolt's swim test, a putative animal model of depression. This study investigated whether tryptophan affects behavior in Porsolt's swim test in STZ-administered male National Institutes of Health Swiss mice. In addition, the effect of tryptophan on behavior in the resident-intruder test of aggression was studied. Tryptophan is effective in the treatment of mild depression and may reduce aggressive behavior. Diabetes was induced with injection of 200 mg/kg body wt i.p. STZ. Two weeks after STZ treatment, the mice received 0, 50, and 100 mg/kg i.p. tryptophan 60 min before the swim test. The STZ-administered mice exhibited lengthened immobility in the swim test, and tryptophan caused a dose-related shortening in their immobility times. The control and STZ mice, which were isolated for 1 wk before the resident-intruder test, did not show any difference in the time spent in social investigation or aggressive or defensive behaviors. However, 100 mg/kg i.p. tryptophan 60 min before the test reduced the social interaction and aggressive behavior of the STZ-D mice but increased these behaviors in controls. Results indicate that tryptophan shortens the increased immobility time and reduces social and aggressive behavior in STZ-D mice. Therefore, the reported reductions in the brain-tryptophan concentrations in STZ-D mice may participate in regulating their behavior.

Impact of environmental stress on the expression of insulin-dependent diabetes mellitus

To investigate the influence of environmental factors on inherited tendencies, the impact of chronic environmental stress on the expression of a genetically determined autoimmune disease was explored in the bio-breeding (BB) rat, which is an animal model for human autoimmune insulin-dependent diabetes mellitus. Animals assigned at random to the experimental group received a triad of stressors designed to model chronic moderate stress over a 14-week period. Animals from 25 to 130 days of age were weighed and tested for glycosuria twice weekly. Weekly blood sampling was performed on all animals. Diabetes was diagnosed on the basis of weight loss, 2+ glycosuria, and blood glucose levels of 250+ mg/dl. We found that in the BB rat chronic stress significantly increased the incidence of the phenotypic expression of the gene for Type I diabetes. Eighty percent of the male stress and 70% of the female stress animals developed diabetes, compared with 50% in both control groups. Stressed males developed manifest diabetes at the same time as their matched controls, whereas stressed females had significantly delayed onset in relation to controls.

Behavioral effects of an intrauterine or neonatal diabetic environment in the rat

Maternal diabetes during pregnancy may cause lasting effects on the psychoneurological development in the offspring. The aim of the present study was to investigate possible effects of an intrauterine or neonatal exposure to a diabetic environment on behavior during infancy and adulthood. On days 4 and 6 of age, offspring of streptozotocin-diabetic rats emitted higher numbers of ultrasound calls compared to control offspring. Neonatally streptozotocin-treated rats explored their environment by diminished sniffing and rearing intensity compared to control rats. However, in adult life neither of these rat groups displayed behavioral differences compared to their respective control group. The results suggest that development of basic behavioral patterns in the rat proceed almost normally despite exposure to a diabetic environment in the early embryonic period or in early infancy.

Tricyclic antidepressants, thyroid function, and their relationship with the behavioral responses in rats

We first studied the effects of tricyclic antidepressants (TCAs) on thyroid function in rats in the learned helplessness paradigm. TCAs (clomipramine 32 mg/kg, desipramine 16, 24 mg/kg, or imipramine 8, 16, 32 mg/kg per day) were injected IP for 5 consecutive days. Blood samples were collected 1 hr after the last administration of the antidepressant for radioimmunoassay determination of triiodothyronine (T3) and thyrotropin. Whereas inducing helplessness did not result in any change in T3 and thyroid-stimulating hormone (TSH) levels, TCA therapy dose dependently decreased the T3 levels without changing TSH levels in helpless animals and in naive control rats. To further the investigation, the effects of TCAs on thyroid function were examined using two models of experimentation, one involving diabetes induction, the other using food deprivation; both are known to induce a resistance to TCAs that is reversible under T3 treatment. In both models, a decreased T3 level existed prior to the TCA administration. Although they had no effect on behavior, TCAs further decreased the T3 levels in diabetic and food-restricted rats. This study confirms that TCAs decrease thyroid function and suggests that the antidepressant effect of TCAs is not related to their T3 decreasing effects.

Behavior of streptozotocin-diabetic mice in tests of exploration, locomotion, anxiety, depression and aggression

The present study examined behavior of streptozotocin-diabetic mice in Porsolt's swim test, a putative animal model of depression, in the holeboard test of exploration and locomotor activity, in the plus maze test of anxiety, and in the resident-intruder paradigm of aggression. Two weeks after an IP injection of 200 mg/kg streptozotocin, which caused a 20% weight loss and increased fluid consumption and urination, male NIH Swiss mice were found to show lengthened duration of immobility in the swim test. One week of insulin treatment (0.1 IU/g/day) partially antagonized this change. The locomotor activity scores in the streptozotocin-treated mice were lower in the holeboard but higher in the plus maze than in the controls; therefore, the lengthened immobility was not likely to be due to a general motor impairment. No significant changes in the time spent in social interaction or aggressive behavior were found in the streptozotocin-treated mice. The results indicate that streptozotocin-treated mice show lengthened immobility in the swim test.

Dietary treatment ameliorates overt diabetes and decreased insulin secretion to glucose, induced by overeating in impaired glucose tolerant mice

Overt diabetes (NIDDM) was induced by overeating in neonatally streptozocin (60 mg/kg.BW) treated impaired glucose tolerant mice. We imposed a food restriction and a high fiber diet to evaluate the effects of dietary treatment in this NIDDM model mouse. Furthermore, insulin secretion after the dietary treatment was studied using the perfused pancreas technique. One group of IGT mice (SZ) was maintained on ordinary mouse chow during 6 to 14 weeks of age. The others received a cookie and chocolate mashed diet (C.C. diet) to induce overt diabetes during 6 to 10 weeks of age. Thereafter, the mice with induced overt diabetes were divided according to their diet treatment. The C.C. diet was continued in one group (SZC) for 4 weeks, and the others were divided into a food restriction group (SZR: 4 g/mouse/day of ordinary mouse chow, for 4 weeks) and a high fiber diet group (SZF: 20% W/W of cellulose in ordinary mouse chow, for 8 weeks). The mean caloric intake/mouse/day in SZC, SZR and SZF were 140, 80 and 98% of that in SZ, respectively. Amelioration of hyperglycemia and impaired glucose tolerance was noted in SZR and SZF. A better glycemic control was obtained in SZF with keeping a normal growth rate. On the pancreas perfusion, the insulin secretion to 30 mM glucose was improved in SZR and SZF. Furthermore, the incremental first phase peak insulin release to 30 mM glucose in SZF was significantly greater than that in SZC (SZF, 10.5 +/- 1.0 vs. SZC, 4.5 +/- 1.9 microU/min).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of intravesical volume upon contractile responses of the whole bladder preparation from streptozotocin-diabetic rats

1. The in vivo whole bladder preparation was used to correlate bladder volume with the ability of urinary bladders from control, sucrose-drinking, and diabetic rats to develop pressure in response to bethanechol or nerve stimulation. 2. Both streptozotocin-induced diabetes mellitus and sucrose-diuresis caused an increase in rat urinary bladder capacity and mass. 3. There were significant decreases in the ability of bladders from control rats to develop pressure in response to bethanechol at 1.0 ml intravesical volume, but no change in responsiveness of bladders from sucrose-drinking or diabetic rats at different intravesical volumes. Bladders from sucrose-drinking and diabetic rats developed significantly less pressure in response to bethanechol stimulation at low intravesical volumes than did bladders from control rats. 4. Bladders from diabetic rats developed significantly less pressure in response to 32 Hz stimulation at 0.2 ml intravesical volume compared to larger volumes, however, there were no differences in the responses of bladders from sucrose-drinking or control rats at any intravesical volume. 5. Bladders from control and sucrose-drinking rats had a reduced ability to empty in response to bethanechol and field stimulation at large intravesical volumes. 6. Bladders from 8-week streptozotocin-diabetic rats are able to contract and empty efficiently in response to nerve stimulation and bethanechol over a wide range of intravesical volumes.

Diabetes and a high-fat/low-carbohydrate diet enhance the acceptability of oil emulsions to rats

Acceptability of corn oil and coconut oil emulsions was examined in streptozotocin-diabetic (55 mg/kg, IP) and normal rats fed either a high-fat/low-carbohydrate (HF/LC) or low-fat/high-carbohydrate (LF/HC) diet. Intake of five concentrations of the emulsions (2.5, 5, 10, 20 and 40%) was measured in 30-min, one bottle intake tests. Diabetic rats consumed more of the oil emulsions than did normal rats. Emulsion intake by diabetic rats increased, then decreased across concentrations, whereas emulsion intake by normal rats showed little change across concentrations. No differences in the intake of corn and coconut oil emulsions were observed. Total oil consumption was higher in diabetic than in normal rats at the three highest emulsion concentrations. Total oil consumption was also higher in rats fed the HF/LC diet as compared to those fed the LF/HC diet. These findings suggest that the presence of diabetes or feeding a HF/LC diet can enhance oil emulsion intake of rats in short-term tests.

Helpless behavior (escape deficits) in streptozotocin-diabetic rats: resistance to antidepressant drugs

Using the learned helplessness model of depression in rats, the present study undertook to investigate the possibility of an impaired response to antidepressant drugs in diabetic animals. Experimental diabetes was induced by three intraperitoneal (IP) injections of streptozotocin (37.5, 37.5, 50 mg/kg, three days apart), four weeks before behavioral testing. Diabetic and non-diabetic rats were first exposed to 60 inescapable shocks. Forty-eight hours later and over three consecutive days, they were subjected to daily shuttle-box sessions for assessment of escape failures (helpless behavior). Twice daily (IP) injection of clomipramine (24 mg/kg), desipramine (24 mg/kg), imipramine (32 mg/kg) or clenbuterol (0.75 mg/kg) prevented escape deficits in the non-diabetic but not in the diabetic rats. However, this prevention was made possible in the diabetic rats by increasing the duration of the antidepressant treatment. Moreover, one week of insulin therapy restored operant escape responding to both the tricyclics and a beta-agonist. The inefficacy of clenbuterol (a central beta-agonist) in reversing helpless behavior in diabetic rats, along with the observation that triiodothyronine (T3) supplementation also restored the response to imipramine in the diabetic rats, suggests that thyroid-mediated alterations of central noradrenergic function might be a critical factor in the resistance or delayed response to antidepressants in experimental diabetes. These animal findings raise the possibility of a similar resistance to conventional antidepressants in depressed diabetic patients.

The psychoneuroendocrinology of diabetes mellitus in rodents

The metabolic-endocrine state of diabetes mellitus affects the brain and behavior of diabetic animals. Feeding, paradoxical sleep, analgesia, submissive behavior, and avoidance behavior, are generally increased in diabetic compared with nondiabetic rodents. In contrast, sexual behavior, aggressive behavior and sensitivity to the behavioral effects of amphetamine are decreased in diabetic rodents. This review examines behavioral changes in diabetes mellitus within the context of known disease-linked alterations in hypothalamo-pituitary relationships and brain monoamine metabolism.

Increased vasodilator response to acetylcholine of renal blood vessels from diabetic rats

The vasodilator effect of acetylcholine (ACh) and nitroprusside and the vasoconstrictor effect of noradrenaline was assessed in the perfused kidney of streptozocin diabetic rats. Compared with control animals injected with acidified saline, the renal vasoconstrictor effect of noradrenaline was increased in diabetic rats both in terms of the dose required to produce 50% of the maximal effect (EC50) and in the maximal response achieved. The renal vasodilator effect of ACh (but not nitroprusside) was similarly enhanced in diabetic animals. The effect of ACh (but not nitroprusside) in the perfused kidney of both control and diabetic rats was reduced or abolished by mepacrine (10 microM), metyrapone (10 microM) or methylene blue (100 microM) suggesting that ACh exhibits vasodilator activity in the rat kidney by virtue of releasing endothelium derived relaxing factor (EDRF). These results are in contrast to previous published reports demonstrating reduced biosynthesis of EDRF in the aorta of diabetic rats. The mechanism which underlies the increased renal vascular response to ACh is not known. However, increased endothelial cell turnover or cholinoceptor number, elevated activity of enzyme(s) which synthesis EDRF or hyperresponsiveness of vascular smooth muscle to released EDRF should all be considered.

The spontaneously diabetic Wistar-BB rat manifests altered grooming and catalepsy responses: implications of impaired dopamine function

1. The purpose of this study was to investigate the hypothesis that the grooming and catalepsy behaviors, believed to be mediated predominantly by the D1 and D2 dopamine receptor based mechanism(s), respectively, are altered in the Spontaneously Diabetic Wistar-BB Rat (SDR). 2. The insulin treated male SDR (5-6 months diabetic) and a genetically matched Non-Diabetic (NDR) control group were monitored for pharmacologically-induced catalepsy as well as stress-induced grooming. 3. Results obtained indicated that the SDR manifested an increased sensitivity to i) the cataleptogenic effects of haloperidol (0.3-1.0 mg/kg; s.c.) and ii) to the grooming response elicited by a mild stressor (novel environment), when compared to the NDR group. However, under more stressful conditions, the NDR groomed as much as the SDR. The altered behavioral sensitivity of the SDR may be a consequence of impaired dopaminergic neurotransmission and the subsequent upregulation of D1 receptors.

Promotion of diabetes onset by stress in the BB rat

The purpose of the present study was to address the question of whether environmental stress affects the age of onset and incidence of overt insulin-dependent diabetes mellitus in an animal model of human Type 1 (insulin-dependent) diabetes. Thirty-five diabetes prone BB rats of both sexes were divided into two groups: experimental animals were exposed to multiple, concurrent, and unpredictable environmental stressors, while littermate controls were exposed to a standard lab environment. Groups were housed in two separate, sound attenuated, independently ventilated, and restricted rooms. By age 150 days, experimental group animals had developed overt diabetes at a significantly earlier age.

Avoidance responding in mice with diabetes mellitus

In order to examine the behavioral concomitants of the neuroendocrine state of diabetes mellitus, the behavior of diabetic and normal male mice was compared in two behavioral paradigms. Diabetic mice were found to display significantly more passive avoidance to shock and significantly more submissive social behavior as compared to control mice. Furthermore, within the group of diabetic mice, mice showing the most passive avoidance also displayed the most submissive behavior. These findings suggest that diabetes mellitus may have effects on the neuroendocrine system that are manifested as changes in behavior.

Hyperglycemia and fight-flight behavior in nondiabetic and diabetic mice

Glycemic responses to a resident-intruder encounter and to the drawing of blood from the retro-orbital sinus were studied in diabetic and normal male Swiss Webster mice. The diabetes induced with streptozotocin was either borderline, overt, or severe. The resident-intruder encounter consisted of a brief exposure to another male mouse trained to be aggressive. The blood collected was not sufficient (3% blood volume) to cause significant volume depletion. Behavior during the resident-intruder encounter was videotaped and later quantified. Borderline diabetic, overtly diabetic and nondiabetic mice responded to both procedures with significant increases in plasma glucose. The glycemic response to the resident-intruder encounter in these groups was significantly greater than that to the bleeding trial. The severely diabetic mice did not experience increases in plasma glucose in either test. Fight-flight behavior of nondiabetic mice was significantly correlated with increases in plasma glucose. Total activity was negatively correlated with change in plasma glucose in the borderline diabetic mice. In overtly diabetic mice no relationship between either measure and glucose increases was observed. These results indicate that plasma glucose elevation in overtly and severely diabetic mice is not as specific to behavior as in nondiabetic mice.

Dietary self-selection in diabetic rats: an overview

The literature concerning dietary self-selection patterns of diabetic rats is reviewed and compared with new data. There is agreement among the various investigators as to the dietary choices observed following induction of diabetes, regardless of the diabetogenic treatment used. That is, moderately diabetic rats select a high fat, low carbohydrate diet, whereas more severely diabetic animals consume high protein, low carbohydrate diets with little change in fat consumption relative to nondiabetic controls. Even very midly diabetic rats reduce carbohydrate intake. Evaluation of metabolic status of diabetics suggests that with severe diabetes, the beneficial reduction of plasma glucose seen with consumption of a high fat diet may be offset by extreme elevations in ketone and triglyceride levels. Moreover, the hypothesis that diabetic rats are insensitive to carbohydrate calories seems weakened by evidence of reduced food intake following carbohydrate consumption either in solutions or as a gastric load. These findings are discussed in terms of "dietary wisdom" as first proposed by Richter.

Effects of dietary protein and tyrosine on behavior of diabetic rats

Streptozotocin-diabetic and nondiabetic control male rats were fed synthetic diets varying in macronutrient content (experiment 1) or diets with or without added tyrosine (experiments 2 and 3). All rats were evaluated for stereotyped behaviors after administration of apomorphine (1 mg/kg) and amphetamine (3 and 5 mg/kg). At the end of experiments 2 and 3, rates of tyrosine hydroxylation in hypothalamus, nucleus accumbens, and striatum were determined by measuring L-3,4-dihydroxyphenylalanine concentrations after decarboxylase inhibition. In experiment 3 the ratios of tyrosine to dopamine were also measured in striatum and nucleus accumbens. Diabetic rats fed a standard high-carbohydrate diet showed decreased stereotypy relative to controls. Neither systematic alterations of fat or protein content of the diet nor selective tyrosine enrichment affected this attenuation of stereotypy in diabetics. L-3,4-dihydroxyphenylalanine concentration in nucleus accumbens was increased by dietary tyrosine enrichment in experiment 2 but not in experiment 3. However, brain tyrosine levels were elevated in rats fed tyrosine-enriched diets. These results argue against a significant contribution of precursor elevation to catecholamine function and behavior in experimental diabetes.

Morphine dependence and diabetes. I. The development of morphine dependence in streptozotocin-diabetic rats and spontaneously diabetic C57BL/KsJ mice

Spontaneously diabetic (db/db) and nondiabetic (db/m+, m+/m+) C57BL/KsJ mice were made dependent by a 9-day exposure to increasing doses of morphine-admixed food. Radioimmunoassay for morphine demonstrated that diabetic mice had significantly greater brain accumulations of morphine than nondiabetic littermates after morphine-admixed food. Despite their greater brain levels of morphine, diabetic mice showed significantly fewer behavioral signs of withdrawal after naloxone, and lost significantly less weight at 60 min after naloxone than their nondiabetic littermates. Streptozotocin-diabetic and nondiabetic rats rendered dependent by a 6-day i.p. infusion of morphine had equal brain levels of morphine, but the diabetic rats showed significantly fewer behavioral signs of withdrawal than nondiabetic rats at 24 and 48 hr after the end of the infusion. These results indicate that spontaneously diabetic mice and streptozotocin-diabetic rats were both significantly less physically dependent upon morphine than their respective nondiabetic controls and support our conclusion that the development of physical dependence upon morphine is reduced in experimental models of diabetes.

Preference for high carbohydrate over various high fat diets by diabetic rats

Streptozotocin-diabetic male rats were hyperphagic relative to nondiabetic controls when offered only high carbohydrate (CHO) laboratory chow. Diabetics and controls ate about the same amount of high fat diets made from 67% w/w chow and 33% either coconut oil (saturated) or safflower oil (unsaturated). However, when offered a simultaneous choice of high fat diets and chow, nondiabetics and low dose (35 mg/kg) streptozotocin-diabetics showed a preference for the high fat diet: in contrast the high dose (65 mg/kg) streptozotocin diabetics developed a preference for chow. When pairs of isocaloric synthetic diets were offered, diabetics again preferred low fat/high CHO to high fat/low CHO diets, but the actual intake of fat was not constant across different diet pairs. Nondiabetics also selected away from the high fat diets in these synthetic diet pairs, even when saccharin was added to the high fat diet in an attempt to equate its sweetness with that of the paired low fat-high CHO diet. Plasma ketone levels of diabetics during obligatory high fat diet consumption were negatively correlated with their subsequent preference for the fat diet over simultaneously-offered chow. These data show that strong dietary preferences do not develop for fat in diabetics and suggest that high fat diets do not have net beneficial postingestional effects in these rats.

Environment modulates naloxone's suppressive effect on feeding in diabetic and non-diabetic rats

We evaluated the effect of environment on naloxone-induced suppression of feeding in streptozotocin rats and sham injected controls. Naloxone was administered to animals fasted for 24 hours and food intake was measured at 30, 60 and 120 minutes. Diabetic rats, in their home cages, were insensitive to naloxone's suppressive effect for the first 30 minutes and the 5 mg/kg dose suppressed feeding only at 120 minutes. In control rats, feeding was suppressed at 1 and 5 mg/kg naloxone during the first 30 minutes. In contrast, when animals were placed in novel plastic cages, control animals were insensitive to naloxone at all time points at doses as high as 5 mg/kg. In novel cages, diabetic rats responded to doses of 1 and 5 mg/kg during the first 30 minute period by lowering food intake. It should also be noted that basal food intake was suppressed (40-53%) when animals were placed in novel cages. These data suggest that stress of a novel environment alters the neuroregulatory system involved in inducing feeding. Lack of response of normal rats to naloxone's suppressive effect in a novel environment suggests that (1) a non-opioid feeding system operates under these conditions, or (2) opioid receptors are occupied as a result of the release of endogenous opioids due to stress. The opposite result observed in the diabetics indicates that glucose has a modulating effect on opioid effects.

Patterns of nutrient selection in rats with streptozotocin-induced diabetes

The effects of experimental diabetes on energy intake, patterns of nutrient selection, water intake, body weight and body composition were examined in male Sprague-Dawley rats given ground Purina Chow or a dietary self-selection regime. Following adaptation to dietary conditions, a portion of the animals in each diet group were made diabetic by the administration of 45 mg/kg streptozotocin (STZ). The remaining animals in each group served as vehicle-injected controls. STZ reliably produced diabetes in rats on both dietary regimes. Immediately after the induction of diabetes, rats on the self-selection regime increased carbohydrate and protein intakes and decreased fat intake. Approximately three weeks after STZ administration, diabetic rats reduced carbohydrate intake and increased fat intake. Diabetic animals in both diet groups were hyperphagic and polydipsic relative to non-diabetic controls. During the first three weeks following STZ injections, energy and water intakes of diabetic animals in the two dietary conditions were similar. However, after this initial period, energy and water intakes of diabetic rats given the self-selection regime were significantly lower than those of diabetic animals given Purina Chow.