Alterations in Physiologic Functions and in Brain Monoamine Content in Streptozocin-Diabetic Rats

In the present study, we used streptozocin (STZ) to induce diabetes in rats and observed alterations in several physiologic functions and in monoamine content of different brain regions. Rats with STZ diabetes displayed a thermoregulatory deficit in the cold. Both the body temperature and metabolic rate of the diabetic animals were reduced at ambient temperatures below 22°C. These diabetic animals had a higher level of the spontaneous pain threshold, but displayed a reduced sensitivity of analgesic responses to morphine injection. In addition, these diabetic animals had a lower level of spontaneous motor activity, but displayed an increased sensitivity of locomotor stimulant responses to amphetamine administration. Biochemical examination revealed that the diabetic animals had a lower serotonin level in both the hypothalamus and the brainstem without changes in the serotonin levels of the corpus striatum. These diabetic animals also had a lower catecholamine level in the hypothalamus, but a higher catecholamine level in the corpus striatum. The alterations in brain monoamine content and in the above-mentioned physiologic parameters were reversed after insulin replacement therapy. The data suggest that alterations in various autonomic, somatosensory, and motor neural functions of untreated STZ-diabetic rats correlated with a reproducible pattern of monoamine content in various brain regions (a pattern that differed from that observed in healthy control rats), and that both the altered neural function and the altered brain monoamine pattern were reversed after insulin therapy.