Serotonergic function in diabetic rats: psychotherapeutic implications

Functional change of the auditory cortex related to brain serotonergic neurotransmission in type 1 diabetic adolescents with and without depression

The aim of this study was to determine whether diabetic patients who were depressed present a decrease of brain serotonergic activity compared to diabetic patients without depression or patients with depression but without diabetes. Determination was made with plasma free fraction of L-tryptophan (FFT) and intensity-dependent auditory-evoked potentials (IDAEPs). Thirty-seven adolescents were studied (20 type 1 diabetic subjects: nine with depression, 11 without depression), nine controls and eight subjects with only depression. FFT, glucose, glycated haemoglobin, free fatty acids, albumin and IDAEPs were determined. All diabetic patients showed a significant decrease of FFT. The group diabetic subjects with depression presented a steeper slope of the amplitude-intensity function of N1/P2 component, suggesting a higher reactivity of the auditory cortex in comparison to diabetic subjects without depression, subjects with only depression, and controls. This was associated with lower plasma FFT. Diabetic subjects with depression had a deficiency of metabolic control due to poor treatment adherence. These findings suggest an enhanced deterioration of brain serotonergic neurotransmission in diabetic subjects with depression with abnormal responses of the auditory cortex. The N1/P2 component of IDAEP is proposed as a non-invasive indicator of brain serotonergic tone that differentiates depressed from non-depressed diabetic patients.

Cerebral dysfunction in type 1 diabetes: effects of insulin, vascular risk factors and blood-glucose levels

Type 1 diabetes can lead to several well-described complications such as retinopathy, nephropathy and peripheral neuropathy. Evidence is accumulating that it is also associated with gradually developing end-organ damage in the central nervous system. This relatively unknown complication can be referred to as "diabetic encephalopathy" and is characterised by electrophysiological and neuroradiological changes, such as delayed latencies of evoked potentials, modest cerebral atrophy and (periventricular) white matter lesions. Furthermore, individuals with type 1 diabetes may show performance deficits in a wide range of cognitive domains. The exact mechanisms underlying this diabetic encephalopathy are only partially known. Chronic metabolic and vascular changes appear to play an important role. Interestingly, the differences in the "cognitive profile" between type 1 and type 2 diabetes also suggest a critical role for disturbances of insulin action in the central nervous system.

Cerebral function in diabetes mellitus

Diabetes mellitus is a common metabolic disorder associated with chronic complications such as nephropathy, angiopathy, retinopathy and peripheral neuropathy. Diabetes is not often considered to have deleterious effects on the brain. However, long-term diabetes results in a variety of subtle cerebral disorders, which occur more frequently than is commonly believed. Diabetic cerebral disorders have been demonstrated at a neurochemical, electrophysiological, structural and cognitive level; however, the pathogenesis is still not clear. Probably alterations in cerebral blood supply and metabolic derangements play a role, as they do in the pathogenesis of diabetic neuropathy. Furthermore, the brain is also affected by recurrent episodes of hypoglycaemia and poor metabolic control. We describe herein the cerebral manifestations of diabetes and discuss the putative pathogenetic mechanisms.

Risk factors for neuroleptic-induced movement disorders

Chronic neuroleptic therapy may be associated with the development of diverse movement disorders including Tardive dyskinesia (TD), Parkinsonism, dystonia, and akathisia in a subset of schizophrenic patients. It is presently unknown why only a proportion of neuroleptic-treated patients develop these movement disorders. In the following communication, we present a series of studies which demonstrate that the development of these movement disorders may be facilitated by certain risk factors including disturbances in pineal melatonin functions, diabetes mellitus, cognitive deficits, suicidal behavior, and disturbances in the functions of the choroid plexus. Recognition of these biological factors may prove useful in: (a) further understanding of the pathophysiology of these disorders, and (b) identifying patients at risk for these movement disorders.

Attenuation of central alpha 2 adrenergic action in diabetic rats

Molecular components in transmembrane signaling may be dysfunctional in insulin-deficient states. To investigate whether the alpha 2 adrenergic receptor-effector mechanism is functionally altered by insulin deficiency, we determined the hypnotic response to dexmedetomidine [(+)4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole, a highly-selective alpha 2 agonist, in streptozotocin-induced diabetic rats. The duration of the loss of righting reflex (sleep time) in response to dexmedetomidine, 0.25 mg.kg-1 IP, was measured in rats pretreated with streptozotocin, 50 mg.kg-1 IP. Dexmedetomidine sleep time was significantly shortened when tested 10 days (-25%), 3 (-29%), 6 (-35%) and 8 (-47%) weeks into the diabetic state. Supplementation of the diabetic rats with insulin normalized alpha 2 responsiveness. Acute hyperglycemia did not reduce dexmedetomidine-induced sleep time. Sleep time was also reduced when dexmedetomidine was administered via the intracerebroventricular (ICV) route at 4 (-21%) and 8 (-29%) weeks after streptozotocin. Thus the central nervous system response to the alpha 2 adrenergic agonist has become attenuated. The mechanism may involve a perturbation of an insulin-sensitive molecular component of the signal transduction pathway responsible for alpha 2 adrenoceptor-mediated anesthetic action.

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.

Distinguishing in vitro electrochemical signatures for norepinephrine and dopamine

An electrochemical method for the qualitative detection of dopamine and norepinephrine in the presence of serotonin and other purported contaminants in vitro is described. The method uses semidifferential electrochemistry in conjunction with a stearate graphite paste electrode. A method to distinguish electrochemical signatures for specific catecholamines is particularly important because catecholamines are known to have similar oxidation potentials for electrochemical detection. The findings may bear relevance to the interpretation of electrochemical signals from discrete brain nuclei in vivo.