Impaired response of experimental diabetic mice to tricyclics: a possible beta-adrenergic mechanism

Ethopharmacology of the antidepressant effect of clonazepam in diabetic rats

Diabetes-associated depression may occur due to changes in the quality of life imposed by treatment, or may be a consequence of the biochemical changes accompanying the disease. It was our objective to evaluate the behaviors of diabetic rats through an animal model of depression, and determine if a positive GABA modulator agent, clonazepam, is an effective antidepressant. Wistar male rats were submitted to the forced-swimming test after 26 days of the induction of diabetes with streptozotocin (60 mg/kg). Test and retest days analyzed with an ethological approach. Clonazepam (control, 0.25, 0. 5, and 1.0 mg/kg) was administered IP 24, 5, and 1 h before the retest. Diabetic rats presented longer immobility duration during test and retest of forced swimming. Diabetic rats dived significantly less during the test. Clonazepam 0.25 and 0.5 mg/kg decreased immobility of diabetic rats with no consequences on the behaviors of nondiabetic rats. These results demonstrate that diabetic rats present more intense depressive-like behavior, such as immobility and lack of interest in exploring the environment, when exposed to the forced-swimming test. It is possible that decreased GABA function is involved in depression associated with diabetes, because a benzodiazepine partially counteracts these changes without modifying blood glucose and glycogen parameters.

Impairment of albuterol-induced suppression of food intake in diabetes mellitus

Albuterol (salbutamol), a beta 2 adrenoreceptor agonist, produced a dose-dependent decrease in food intake in Sprague-Dawley male control rats. This phenomenon appeared to be impaired in streptozotocin (STZ) diabetic rats. The density of beta 2 adrenoreceptors in the ventromedial hypothalamic nucleus was increased as a function of diabetes. In contrast, a decrease in the ventromedial hypothalamic 5-hydroxyindoleacetic acid (5-HIAA) concentration, an indicator of serotonin (5-hydroxytryptamine; 5-HT) release or turnover rate, was observed in this disease state. Neither the beta 2 adrenoreceptor level nor 5-HT turnover rate was altered in the periventricular hypothalamic nucleus of STZ diabetic rats. The concentrations of 5-HT in both hypothalamic nuclei were unchanged in these animals. Neurochemical and behavioral abnormalities featured in the diabetic state were reversed with institution of insulin therapy. These data conclude that diabetes-related impairment in the anorexic action of albuterol may be due to derangements in ventromedial hypothalamic beta 2 adrenoreceptor function.

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.

Hypoaminoacidemia caused by imipramine but not by clenbuterol is dissociable from hyperglycemia and hyperinsulinemia

The effects of the tricyclic antidepressant imipramine (20 mg/kg) and the beta-adrenoceptor agonist clenbuterol (0.5 mg/kg) on the serum concentrations of tyrosine, tryptophan, glucose and insulin were compared 30 min after intraperitoneal injection. The drugs had nearly identical effects on serum tyrosine, which was reduced to 73% of control by both drugs, and on tryptophan, which was reduced to 72% by imipramine and to 66% by clenbuterol. In contrast, whereas clenbuterol raised serum glucose to 174% and insulin to 379% of control, imipramine had no significant effects on either glucose or insulin. The results clearly demonstrate that the effects of imipramine on blood amino acid levels are dissociable from effects on glucose and insulin. We conclude, therefore, that hypoaminoacidemia caused by imipramine is not mediated by stimulating insulin release.