Agonistic behavior patterns in mice with streptozotocin-induced diabetes mellitus

Depression-related behavioural and neuroendocrine changes in the Spontaneously Diabetic Torii (SDT) fatty rat, an animal model of type 2 diabetes mellitus

Depression is one of the most common psychiatric diseases and is commonly comorbid with type 1 or 2 diabetes mellitus (DM). However, the pathophysiology underlying the depressive state in DM remains poorly understood. Animal models are useful tools to investigate the association between depression and DM. In the present study we investigated whether the Spontaneously Diabetic Torii (SDT) fatty rat, a novel animal model of type 2 DM, shows depression-related features. We assessed depression-like behaviour, hyperactivation of the hypothalamic-pituitary-adrenal (HPA) axis, and neurotransmitter levels in the brain. Behaviour was evaluated using a forced swimming test, and the HPA axis was evaluated with changes in plasma corticosterone levels after a swimming stress exposure or dexamethasone challenge. In addition, serotonin (5-hydroxytryptamine; 5-HT), noradrenaline, glutamate and γ-aminobutyric acid (GABA) concentrations in the frontal cortex, hippocampus and brain stem were measured. In the forced swimming test, SDT fatty rats exhibited increased duration of immobility compared with control Sprague-Dawley (SD) rats. Moreover, basal corticosterone levels were significantly elevated in SDT fatty compared with control SD rats. However, there were no stress-induced increases or changes in dexamethasone-induced suppression of corticosterone in SDT fatty compared with control SD rats. Furthermore, there were significant changes in 5-HT concentrations in the prefrontal cortex, and in GABA and glutamate concentrations in the hippocampus in SDT fatty compared with controls. The results of the present study suggest that the SDT fatty rat may be an appropriate model for diabetes with comorbid depression associated with neurotransmitter impairments and aberrant basal HPA hyperactivity.

Anxiety correlates to decreased blood and prefrontal cortex IGF-1 levels in streptozotocin induced diabetes

It is well known that diabetes mellitus may cause neuropsychiatric disorders such as anxiety disorders. Diabetes may also cause reduced IGF-1 (insulin like growth factor-1) levels in brain and blood. The purpose of the present study was to investigate the relationship between diabetes induced anxiety and IGF-1 levels in diabetic rats. The anxiety levels of rats were assessed 2 weeks after intraperitoneal injection of streptozotocin. Diabetic rats had higher levels of anxiety, as they spent more time in closed branches in elevated-plus-maze-test and less time in the center cells of open-field-arena. Prefrontal cortex (PFC) IGF-1 levels and neuron numbers were decreased and apoptosis was increased in diabetic rats. Blood IGF-1 levels decreased in a time dependent fashion following streptozotocin injection while blood corticosterone levels increased. They had higher malondialdehyde levels and lower superoxide dismutase enzyme activity. Oxidative stress may negatively affect blood and PFC tissue IGF-1 levels. Reduction in IGF-1 may cause PFC damage, which may eventually trigger anxiety in diabetic rats. Therapeutic strategies that increase blood and brain tissue IGF-1 levels may be promising to prevent psychiatric sequelae of diabetes mellitus.

Diabetes as a chronic metabolic stressor: causes, consequences and clinical complications

Diabetes mellitus is an endocrine disorder resulting from inadequate insulin release and/or reduced insulin sensitivity. The complications of diabetes are well characterized in peripheral tissues, but there is a growing appreciation that the complications of diabetes extend to the central nervous system (CNS). One of the potential neurological complications of diabetes is cognitive deficits. Interestingly, the structural, electrophysiological, neurochemical and anatomical underpinnings responsible for cognitive deficits in diabetes are strikingly similar to those observed in animals subjected to chronic stress, as well as in patients with stress-related psychiatric illnesses such as major depressive disorder. Since diabetes is a chronic metabolic stressor, this has led to the suggestion that common mechanistic mediators are responsible for neuroplasticity deficits in both diabetes and depression. Moreover, these common mechanistic mediators may be responsible for the increase in the risk of depressive illness in diabetes patients. In view of these observations, the aims of this review are (1) to describe the neuroplasticity deficits observed in diabetic rodents and patients; (2) to summarize the similarities in the clinical and preclinical studies of depression and diabetes; and (3) to highlight the diabetes-induced neuroplasticity deficits in those brain regions that have been implicated as important pathological centers in depressive illness, namely, the hippocampus, the amygdala and the prefrontal cortex.

Stress symptoms induced by repeated morphine withdrawal in comparison to other chronic stress models in mice

The present study was aimed at evaluating chronic stress models in mice with special attention to morphine treatment. We hypothesized that repeated periods of drug withdrawal induce chronic stress. To verify this hypothesis, mice were made dependent on morphine and then subjected to several types of repeated withdrawal. Body weight reduction, thymus involution, adrenal gland enlargement and activation of the hypothalamo-pituitary-adrenal axis were used as signs of chronic stress. The changes were compared to those induced by 'laboratory' models of chronic stress (2 weeks of repeated restraint or rat exposure) and to a disease model of streptozotocin-induced diabetes mellitus (STZ-DM). Mice were made dependent using increasing doses of morphine three times a day for 3 days (10-20-40 mg/kg s.c.). Thereafter, withdrawal was induced either spontaneously (morphine 40 mg/kg injected at 24- or 72-hour time intervals for 2 weeks) or repeatedly precipitated by naloxone (10 mg/kg s.c.) injected daily 3 h after morphine. The results show that repeated periods of spontaneous drug withdrawal (24 or 72 h) in morphine-dependent mice represent a mild stress load. Repeated withdrawal precipitated by naloxone induced clear chronic stress-like changes. Changes observed in the naloxone-precipitated withdrawal model were even more pronounced than those found in laboratory models, namely repeated restraint or exposure to the rat. The most severe chronic stress state developed in mice during untreated STZ-DM. Thus, naloxone-precipitated withdrawal in mice seems to be an appropriate model of chronic stress.

Alteration of antioxidant status in diabetic rats by chronic exposure to psychological stressors

Antioxidant status was measured in heart, liver, kidney, lung, and erythrocytes of 2-week streptozotocin-diabetic male Wistar rats exposed to chronic intermittent psychological stress consisting of 1 h of restraint twice daily for 14 days. Diabetes reduced erythrocyte and heart and liver susceptibility to hydrogen peroxide-induced glutathione depletion. Susceptibility to peroxide-induced thiobarbituric acid reactive substance (TBARS) formation increased in erythrocytes, liver, kidney, and lung but decreased in heart. Significant changes also occurred in glutathione levels (increased in heart and decreased in liver) and in the activities of catalase (reduced in liver and kidney), glutathione reductase (elevated in heart and liver), and glutathione peroxidase (decreased in liver and lung), but not Cu,Zn-superoxide dismutase. Stress potentiated diabetes-associated hyperglycemia and attenuated diabetes-induced hyperlipidemia. In addition, the reduction in peroxide-induced glutathione depletion in heart and liver and the increased TBARS formation in kidney and lung were reversed. Similarly, the diabetes-induced induced increase in liver glutathione reductase and decreases in liver and lung glutathione peroxidase activities were abolished by stress. Thus, the relative resistance of antioxidant systems to stress can be modified under pathologic conditions in which antioxidant alterations are present.

Diabetes mellitus: stress, neurochemistry and behavior

Neurochemical alterations in several rodent models of insulin-dependent diabetes are compared and their relevance to behavioral and physiological pathology in the clinical disorder is discussed. In the majority of rodent models, reductions in metabolism of norepinephrine (NE), dopamine (DA) and serotonin (5HT) in the central nervous system (CNS) have been reported. While there are two reports of increased 5HT turnover in CSF or post-mortem brains of diabetic humans experiencing severe ketoacidosis, these patients were receiving insulin therapy. Insulin appears to have effects on monoamines opposite to that of chronic hyperglycemia. Both in rodent models and in clinical populations, there is widespread evidence of enhanced hormonal and behavioral responsiveness to stress. There are findings in rodent models indicating that hormonal responses to stress are related to CNS monoamine activity. The mechanisms responsible for both hormonal and CNS alterations in diabetes, as well as their involvement in behavioral pathology, can best be investigated further using animal models.

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.

Circadian rhythm of corticosterone in diabetic rats

We proposed that the circadian rhythm of corticosterone in diabetic rats would have a different pattern than that in non-diabetic control rats. To test this hypothesis, 20 male Sprague-Dawley rats were given ad libitum access to a stock diet and housed individually in a light and temperature controlled room. Ten rats were made diabetic by two subcutaneous injections of streptozotocin. Ten rats which were not injected served as controls. Thirteen days after induction of the diabetes, tail blood samples were taken every 4 h for 24 h. Plasma corticosterone levels were significantly higher in diabetic rats than in control rats at 3 time points during the light cycle; however, concentrations were similar during the dark cycle. We speculate that diabetes may cause alterations in the steroid feedback mechanism to the hypothalamus and/or pituitary, resulting in an abnormal circadian rhythm of plasma corticosterone.

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.