Diabetes-induced changes in monoamine concentrations of rat hypothalamic nuclei

Impact of insulin and insulin resistance on brain dopamine signalling and reward processing- an underexplored mechanism in the pathophysiology of depression?

Type 2 diabetes and major depressive disorder (MDD) are the leading causes of disability worldwide and have a high comorbidity rate with fatal outcomes. Despite the long-established association between these conditions, the underlying molecular mechanisms remain unknown. Since the discovery of insulin receptors in the brain and the brain's reward system, evidence has accumulated indicating that insulin modulates dopaminergic (DA) signalling and reward behaviour. Here, we review the evidence from rodent and human studies, that insulin resistance directly alters central DA pathways, which may result in motivational deficits and depressive symptoms. Specifically, we first elaborate on the differential effects of insulin on DA signalling in the ventral tegmental area (VTA) - the primary DA source region in the midbrain - and the striatum as well as its effects on behaviour. We then focus on the alterations induced by insulin deficiency and resistance. Finally, we review the impact of insulin resistance in DA pathways in promoting depressive symptoms and anhedonia on a molecular and epidemiological level and discuss its relevance for stratified treatment strategies.

Roles of Pancreatic Islet Catecholamine Neurotransmitters in Glycemic Control and in Antipsychotic Drug-Induced Dysglycemia

Catecholamine neurotransmitters dopamine (DA) and norepinephrine (NE) are essential for a myriad of functions throughout the central nervous system, including metabolic regulation. These molecules are also present in the pancreas, and their study may shed light on the effects of peripheral neurotransmission on glycemic control. Though sympathetic innervation to islets provides NE that signals at local α-cell and β-cell adrenergic receptors to modify hormone secretion, α-cells and β-cells also synthesize catecholamines locally. We propose a model where α-cells and β-cells take up catecholamine precursors in response to postprandial availability, preferentially synthesizing DA. The newly synthesized DA signals in an autocrine/paracrine manner to regulate insulin and glucagon secretion and maintain glycemic control. This enables islets to couple local catecholamine signaling to changes in nutritional state. We also contend that the DA receptors expressed by α-cells and β-cells are targeted by antipsychotic drugs (APDs)-some of the most widely prescribed medications today. Blockade of local DA signaling contributes significantly to APD-induced dysglycemia, a major contributor to treatment discontinuation and development of diabetes. Thus, elucidating the peripheral actions of catecholamines will provide new insights into the regulation of metabolic pathways and may lead to novel, more effective strategies to tune metabolism and treat diabetes.

Guanfacine Normalizes the Overexpression of Presynaptic α-2A Adrenoceptor Signaling and Ameliorates Neuropathic Pain in a Chronic Animal Model of Type 1 Diabetes

Background: Diabetes is associated with several complications, including neuropathic pain, which is difficult to manage with currently available drugs. Descending noradrenergic neurons possess antinociceptive activity; however, their involvement in diabetic neuropathic pain remains to be explored. Methods: To infer the regulatory role of this system, we examined as a function of diabetes, the expression and localization of alpha-2A adrenoceptors (α2-AR) in the dorsal root ganglia and key regions of the central nervous system, including pons and lumbar segment of the spinal cord using qRT-PCR, Western blotting, and immunofluorescence-based techniques. Results: The data revealed that presynaptic synaptosomal-associated protein-25 labeled α2-AR in the central and peripheral nervous system of streptozotocin diabetic rats was upregulated both at the mRNA and protein levels. Interestingly, the levels of postsynaptic density protein-95 labeled postsynaptic neuronal α2-AR remained unaltered as a function of diabetes. These biochemical abnormalities in the noradrenergic system of diabetic animals were associated with increased pain sensitivity as typified by the presence of thermal hyperalgesia and cold/mechanical allodynia. The pain-related behaviors were assessed using Hargreaves apparatus, cold-plate and dynamic plantar aesthesiometer. Chronically administered guanfacine, a selective α2-AR agonist, to diabetic animals downregulated the upregulation of neuronal presynaptic α2-AR and ameliorated the hyperalgesia and the cold/mechanical allodynia in these animals. Conclusion: Together, these findings demonstrate that guanfacine may function as a potent analgesic and highlight α2-AR, a key component of the descending neuronal autoinhibitory pathway, as a potential therapeutic target in the treatment of diabetic neuropathic pain.

Effect of resveratrol on behavioral performance of streptozotocin-induced diabetic mice in anxiety tests

The aim of this study was to evaluate with anxiety tests the effect of resveratrol (RSV) on streptozotocin (STZ)-induced diabetic mouse behavioral performance at the second and fourth week of treatment. Confirmed diabetic mice (>250 mg/dl of glucose in blood after STZ injection) were treated with RSV (RDM, n=12) or control treated (DM, n=12) for 4 weeks. DM and RDM were tested in the Open Field Test (OFT) and Elevated Plus Maze (EPM). In the second week of RSV treatment, a higher grooming frequency (P<0.05) and a lower defecation and rearing frequency (P<0.05) were detected in the OFT in the RDM group compared with the DM. There was a higher grooming frequency (P<0.05) and higher percentage of entries in open arms (P<0.05) in the RDM group than in the DM group in the EPM. However, in the fourth week of RSV treatment, the only effect observed was a higher grooming frequency in the RDM group than in the DM group (P<0.05) in the EPM. In conclusion, RSV treatment in diabetic mice provoked anxiolytic-like effects in both tests (OFT and EPM), and these effects were observed in a short time window (2 weeks). It is suggested that RSV may help diabetic animals to adapt to new stressing and anxiety situations and thus to improve their welfare.

Decreased [3H] YM-09151-2 binding to dopamine D2 receptors in the hypothalamus, brainstem and pancreatic islets of streptozotocin-induced diabetic rats

In the present study dopamine was measured in the hypothalamus, brainstem, pancreatic islets and plasma, using HPLC. Dopamine D2 receptor changes in the hypothalamus, brainstem and pancreatic islets were studied using [3H] YM-09151-2 in streptozotocin-induced diabetic and insulin-treated diabetic rats. There was a significant decrease in dopamine content in the hypothalamus (P<0.001), brainstem (P<0.001), pancreatic islets (P<0.001) and plasma (P<0.001) in diabetic rats when compared to control. Scatchard analysis of [3H] YM-09151-2 in the hypothalamus of diabetic rats showed a significant decrease in Bmax (P<0.001) and Kd, showing an increased affinity of D2 receptors when compared to control. Insulin treatment did not completely reverse the changes that occurred during diabetes. There was a significant decrease in Bmax (P<0.01) with decreased affinity in the brainstem of diabetic rats. The islet membrane preparation of diabetic rats showed a significant decrease (P<0.001) in the binding of [3H] YM-09151-2 with decreased Kd (P<0.001) compared to control. The increase in affinity of D2 receptors in hypothalamus and pancreatic islets and the decreased affinity in brainstem were confirmed by competition analysis. Thus our results suggest that the decreased dopamine D2 receptor function in the hypothalamus, brainstem and pancreas affects insulin secretion in diabetic rats, which has immense clinical relevance to the management of diabetes.

Decreased alpha1-adrenergic receptor binding in the cerebral cortex and brain stem during pancreatic regeneration in rats

The purpose of this study was to investigate the role of brain alpha1-adrenergic receptor binding in the rat model of pancreatic regeneration using 60-70% pancreatectomy. The alpha1-adrenergic receptors kinetics was studied in the cerebral cortex and brain stem of sham operated, 72 h pancreatectomised and 7 days pancreatectomised rats. Scatchard analysis with [3H]prazosin in cerebral cortex and brain stem showed a significant decrease (P < 0.01), (P < 0.05) in maximal binding (Bmax) with a significant decrease (P < 0.001), (P < 0.01) in the Kd in 72 h pancreatectomised rats compared with sham respectively. Competition analysis in cerebral cortex and brain stem showed a shift in affinity during pancreatic regeneration. The sympathetic activity was decreased as indicated by the significantly decreased norepinephrine level in the plasma (P < 0.001), cerebral cortex (P < 0.01) and brain stem (P < 0.001) of 72 h pancreatectomised rats compared to sham. Thus, from our results it is suggested that the central alpha1-adrenergic receptors have a functional role in the pancreatic regeneration mediated through the sympathetic pathway.

Hypothalamic 5-HT functional regulation through 5-HT1A and 5-HT2C receptors during pancreatic regeneration

5-HT receptors are predominantly located in the brain and are involved in pancreatic function and cell proliferation through sympathetic nervous system. The objective of this study was to investigate the role of hypothalamic 5-HT, 5-HT1A and 5-HT2C receptor binding and gene expression in rat model of pancreatic regeneration using 60% pancreatectomy. The pancreatic regeneration was evaluated by 5-HT content, 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus of sham operated, 72 h and 7 days pancreatectomised rats. 5-HT content was quantified by HPLC. 5-HT1A receptor assay was done by using specific agonist [3H]8-OH DPAT. 5-HT2C receptor assay was done by using specific antagonist [3H]mesulergine. The expression of 5-HT1A and 5-HT2C receptor gene was analyzed by RT-PCR. 5-HT content was higher in the hypothalamus of 72 h pancreatectomised rats. 5-HT1A and 5-HT2C receptors were down-regulated in the hypothalamus. RT-PCR analysis revealed decreased 5-HT1A and 5-HT2C receptor mRNA expression. The 5-HT1A and 5-HT2C receptors gene expression in the 7 days pancreatectomised rats reversed to near sham level. This study is the first to identify 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus during pancreatic regeneration in rats. Our results suggest the hypothalamic serotonergic receptor functional regulation during pancreatic regeneration.

Decreased 5-HT1A receptor gene expression and 5-HT1A receptor protein in the cerebral cortex and brain stem during pancreatic regeneration in rats

The present study was to investigate the role of central 5-HT and 5-HT(1A) receptor binding and gene expression in a rat model of pancreatic regeneration using 60% pancreatectomy. The pancreatic regeneration was evaluated by 5-HT content and 5-HT(1A) receptor gene expression in the cerebral cortex (CC) and brain stem (BS) of sham operated, 72 h and 7 days pancreatectomised rats. 5-HT content significantly increased in the CC (P < 0.01) and BS (P < 0.05) of 72 h pancreatectomised rats. Sympathetic activity was decreased as indicated by the significantly decreased norepinephrine (NE) and epinephrine (EPI) level (P < 0.001 and P < 0.05) in the plasma of 72 h pancreatectomised rats. 5-HT(1A) receptor density and affinity was decreased in the CC (P < 0.01) and BS (P < 0.01). These changes correlated with a diminished 5-HT(1A) receptor mRNA expression in the brain regions studied. Our results suggest that the brain 5-HT through 5-HT(1A) receptor has a functional role in the pancreatic regeneration through the sympathetic regulation.

Decreased 5-HT2C receptor binding in the cerebral cortex and brain stem during pancreatic regeneration in rats

The purpose of this study was to investigate the role of central 5-HT2C receptor binding in rat model of pancreatic regeneration using 60-70% pancreatectomy. The 5-HT and 5-HT2C receptor kinetics were studied in cerebral cortex and brain stem of sham operated, 72 h pancreatectomised and 7 days pancreatectomised rats. Scatchard analysis with [3H] mesulergine in cerebral cortex showed a significant decrease (p < 0.05) in maximal binding (Bmax) without any change in Kd in 72 h pancreatectomised rats compared with sham. The decreased Bmax reversed to sham level by 7 days after pancreatectomy. In brain stem, Scatchard analysis showed a significant decrease (p < 0.01) in Bmax with a significant increase (p < 0.01) in Kd. Competition analysis in brain stem showed a shift in affinity towards a low affinity. These parameters were reversed to sham level by 7 days after pancreatectomy. Thus the results suggest that 5-HT through the 5-HT2C receptor in the brain has a functional regulatory role in the pancreatic regeneration.

Increased endogenous noradrenaline and neuropeptide Y release from the hypothalamus of streptozotocin diabetic rats

Noradrenaline and neuropeptide Y (NPY) in the hypothalamus regulate a number of important endocrine and autonomic functions. Alterations in brain neurotransmitter content have been described in type 1 diabetes but there is little understanding of whether these changes affect neurotransmitter release. This study examined for the first time, region-specific co-release of NPY and noradrenaline from the hypothalamus of male Sprague-Dawley rats treated intravenously with 48 mg/kg streptozotocin (STZ) or vehicle. Five weeks later, the release of endogenous noradrenaline and NPY was monitored by in vitro superfusion of ventral and dorsal hypothalamus slices under basal and potassium-stimulated conditions. STZ-diabetes induced significant increases in basal noradrenaline and NPY overflow from the ventral hypothalamus (P<0.05); only NPY overflow was increased in the dorsal hypothalamus (P<0.05). Noradrenaline overflow increased similarly to potassium depolarisation in vehicle and STZ-diabetic rats, whereas diabetic rats showed a significantly increased NPY overflow response to potassium depolarisation compared to vehicle rats. These region-specific increases in endogenous noradrenaline and NPY overflow from the hypothalamus in diabetes suggest increased neuronal activity at rest and enhanced responses under some conditions. Increased hypothalamic NPY and noradrenaline overflow most likely contributes to diabetic hyperphagia.

Simultaneous measurement of nitric oxide, blood glucose, and monoamines in the hippocampus of diabetic rat: an in vivo microdialysis study

The present study was undertaken to examine the relationships among the levels of nitric oxide (NO), monoamines, and blood glucose in the diabetic hippocampus. The levels of NO and monoamines (serotonin, 5-hydroxytryptamine [5-HT] and dopamine [DA]) were simultaneously measured in several experiments, using in vivo microdialysis techniques. We used both experimentally and spontaneously diabetic rats as the diabetic animal model, and compared the findings with those obtained from non-diabetic rats. The effects of the changed level of blood glucose due to insulin administration on the levels of NO, 5-HT, and DA were assessed. Total NO metabolite levels (NOx) were calculated as the sum of nitrite (NO2-) and nitrate (NO3-) levels. The results in the present study showed that: (1) the plasma levels of NOx in both diabetic rats were low compared to those in control rats, (2) the hippocampal NOx levels in both diabetic rats were almost the same as those in control rats, while the levels of 5-HT and DA were low in the diabetics, and (3) a sudden decrease in the plasma glucose level due to insulin administration reduced the NOx level as well as enhanced the 5-HT level in the diabetic hippocampus, a finding consistent with the results of 7 days administration of insulin. Taken together, these findings suggest that changes in the plasma glucose level cause, at least in part, the changes in the levels of NOx and monoamines in the diabetic brain.

Neuronal expression of fos protein in the forebrain of diabetic rats

We sought to identify the areas that have altered neuronal activity within the hypothalamus of diabetic rats by mapping neuronal expression of c-fos protein (Fos) and Fos-related antigens. After a standard PAP immunocytochemical protocol, Fos-like immunoreactivity was observed in the paraventricular nucleus (PVN), supraoptic nucleus (SON), median preoptic area (MnPO), anterior hypothalamus (AH) and posterior hypothalamus (PH) of control (vehicle; n=6) and diabetic rats (Sprague-Dawley rats injected with STZ 65 mg/kg/ip 4 weeks prior to the experiment; n=6). Blood glucose levels were significantly elevated in the diabetic group (370+/-8 mg/dl) compared to control group (104+/-3 mg/dl). Diabetic rats had a significantly higher number of Fos-positive cells in PVN (2.5x), SON (7x) and MnPO (2x) compared to the control rats. However, diabetic rats had significantly fewer Fos-positive cells in the AH (0.3x) and no difference was observed in the PH between the diabetic and control rats. Despite the elevated number of Fos-positive cells in the diabetic rats, dehydration (water withdrawal for 24 h) or hypertonic challenge (1.5 ml of 0.1 M NaCl i.p. injection) produced a further increase in the number of Fos-positive cells in the PVN, SON and MnPO. Dehydration did not alter the number of Fos-positive cells in the AH or PH, but hypertonic challenge produced a significant increase in the Fos-positive cells in both the AH and PH of diabetic rats. This study demonstrates that: (1) there is increased basal neuronal activity in the PVN, SON and MnPO, a decrease in neuronal activity in the AH and no change in neuronal activity in the PH as indicated by Fos staining in diabetic rats; and (2) dehydration or hypertonic challenge produces a further increase in the number of Fos-positive cells in the PVN, SON, and MnPO which is comparable to control rats. These data support the conclusion that vasopressin producing neurons in the PVN and SON and autonomic areas within the lamina terminalis and hypothalamus are activated during diabetes and may contribute to the elevated levels of vasopressin and autonomic dysfunction during diabetes.

Augmentation of drug reward by chronic food restriction: behavioral evidence and underlying mechanisms

Chronic food restriction and maintenance of low body weight have long been known to increase the self-administration and motor-activating effects of abused drugs. Using a lateral hypothalamic self-stimulation (LHSS) rate-frequency method, it is shown that chronic food restriction augments the rewarding (i.e., threshold lowering) effect of diverse drugs of abuse. Further, the effect is attributed to increased sensitivity of a neural substrate, rather than a change in drug bioavailability or pharmacokinetics, because it is preserved when drugs are injected directly into the lateral cerebral ventricle (intracerebroventricularly). The food restriction regimen that augments drug reward also increases the induction of c-fos, by intracerebroventricular amphetamine, in limbic forebrain dopamine (DA) terminal areas. The possibility of increased DA receptor function is suggested by findings that rewarding and motor-activating effects of direct DA receptor agonists are augmented by food restriction, and the augmented behavioral effects of amphetamine are reversed by an otherwise subthreshold dose of D-1 antagonist. Initial studies of DA receptor-mediated signal transduction, that are focused on the D-2 receptor, suggest increased functional coupling between receptor and G-protein (i.e., quinpirole-stimulated [(35)S]GTPgammaS binding) in dorsal striatum. Unlike behavioral sensitization induced by intermittent stress or psychostimulant treatment, which persist indefinitely following induction, the augmenting effect of food restriction abates within 1 week of restored ad libitum feeding and weight gain. The possible involvement of endocrine hormones and/or 'feeding-related' neuropeptides, whose levels change dynamically with depletion and repletion of adipose stores, is therefore under investigation. Initial tests have been limited to acute treatments aimed at attenuating the effects of hypoinsulinemia, hypoleptinemia and elevated corticosterone levels in food-restricted rats. None of these treatments has attenuated the behavioral effect of food restriction. While a melanocortin receptor agonist has been found to enhance drug reward, melanocortin receptors do not seem to mediate the augmenting effect of food restriction. Continuing investigations of endocrine adiposity signals, 'feeding-related' neuropeptides and dopaminergic signal transduction may further elucidate the way in which drugs of abuse exploit mechanisms that mediate survival-related behavior, and help explain the high comorbidity of drug abuse and eating disorders.

Hypoinsulinemia may mediate the lowering of self-stimulation thresholds by food restriction and streptozotocin-induced diabetes

7 days beyond cessation of insulin treatment) elevation of threshold in ad libitum fed rats and, more transiently, reversed the threshold-lowering effect of food restriction. Acute insulin treatment (3 mU, 15 min prior) also elevated threshold in food-restricted rats. These results are consistent with the hypothesis that insulin modulates sensitivity of a brain reward system and that hypoinsulinemia may be the common factor in food restriction and diabetes that accounts for the enhancement of perifornical LHSS.

Alpha2 adrenergic and high affinity serotonergic receptor changes in the brain stem of streptozotocin-induced diabetic rats

The brain stems (BS) of streptozotocin (STZ)-diabetic rats were studied to see the changes in neurotransmitter content and their receptor regulation. The norepinephrine (NE) content determined in the diabetic brain stems did not show an increase, while epinephrine (EPI) content increased significantly compared with control. The NE to EPI turnover showed a significant increase. The alpha2 adrenergic receptor kinetics revealed that the receptor affinity was significantly reduced during diabetes. In insulin treated rats the NE content decreased while EPI content remained increased as in the diabetic state. Insulin treatment increased the Bmax for alpha2 adrenergic receptors significantly while the increase in Kd reversed to normal. Unlabelled clonidine inhibited [3H]NE binding in BS of control diabetic and insulin treated diabetic rats showed that alpha2 adrenergic receptors consisted of two populations of binding sites with Hill slopes significantly away from unity. In diabetic animals the ligand bound weaker to the low affinity site than in controls. Insulin treatment reversed this alteration to control levels. The displacement analysis using (-)-epinephrine against [3H]yohimbine in control and diabetic animals revealed two populations of receptor affinity states. In control animals, when GTP analogue added with epinephrine, the curve fitted for a single affinity model; but in the diabetic BS this effect was not observed. In both the diabetic and control BS the effects of monovalent cations on affinity alterations were intact. Our data thus show that alpha2 adrenergic receptors have a reduced affinity due to an altered post receptor affinity regulation The serotonin (5-HT) content in the brain stem increased. Its precursor (5-hydroxy) tryptophan (5-HTP) showed an increase and its breakdown metabolite (5-hydroxy) indoleacetic acid (5-HIAA) showed a significant decrease. This showed that in serotonergic nerves there is a disturbance in both synthetic and breakdown pathways which lead to an increased 5-HT. The high affinity serotonin receptor numbers remained unaltered with a decrease in the receptor affinity. The insulin treatment reversed these altered serotonergic receptor kinetic parameters to control level. Thus our study shows a decreased serotonergic receptor function. These changes in adrenergic and serotonergic receptor function were suggested to be important in insulin function during STZ diabetes.

Peripheral noradrenergic turnover in streptozotocin-induced diabetic rats

Our goal was to determine whether basal sympathetic tone to the kidney and various peripheral tissues is altered in conscious diabetic rats. Norepinephrine (NE) turnover was determined by measuring the decline in tissue NE concentration ([NE]) at 4 and 8 h after administering alpha-methyl-p-tyrosine to animals from each of three groups, diabetic (STZ injected 4 weeks prior to experimentation), diabetic + insulin (STZ injected; insulin injected; 2 U/day per rat for 4 weeks) and control (n = 18-20 per group). Various peripheral tissues (duodenum, left ventricle of the heart, kidney, skeletal muscle, left adrenal gland and liver) were examined. [NE] was significantly increased in the kidney and liver, but decreased in the duodenum of the diabetic compared to the control rats. In contrast to the changes in [NE], the rate constant, which provides an index of sympathetic tone, increased in the duodenum and liver, and a decreased in the adrenal gland. The turnover of NE, which is a composite of [NE] and rate constant, increased in the kidney and liver, and decreased in the adrenal gland of diabetic rats. Chronic treatment of diabetic rats with insulin normalized NE turnover in the liver, but not in the adrenal gland. Diabetic rats treated with insulin exhibited a reduced turnover of NE in the kidneys. These data demonstrate that there are differential changes in the [NE], rate constant, and turnover of NE in diabetic rats. Overall, these data indicate that there is increased noradrenergic activity to the kidney, possibly related to sodium retention, and a differential change in noradrenergic activation to various peripheral tissues in diabetic rats.

Streptozotocin-induced diabetes provokes changes in serotonin concentration and on 5-HT1A and 5-HT2 receptors in the rat brain

Since reduced levels of brain serotonin are known to cause behavioural abnormalities, to which diabetics are also prone, we investigated the effect, in rats, of chronic diabetes on brain serotonin concentration and on the numbers of 5-HT(1A) and 5-HT2 receptors in cerebral cortex and brainstem. Our data show that streptozotocin induces a longlasting hyperglicemia that is associated with a decrease in cerebral concentration of serotonin and with an accompanying increase in the maximum number of 5-HT(1A) and 5-HT2 receptors in the brain areas studied. Our results may suggest that changes in serotonergic transmission in the CNS play a role in diabetes-related behavioural abnormalities.

Indications of pre- and post-synaptic 5-HT1A receptor interactions in feeding behavior and neuroendocrine regulation

This bipartite study uses behavioral and biochemical means to explore the involvement of both pre- and post-synaptic 5-HT1A receptors in the control of food intake and neuroendocrine regulation. In the pharmacological study, the administration of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; 60 micrograms/kg b.wt., i.p.) to rats caused a significant increase in 2 h intake of a high carbohydrate (CARB)/sugar diet (P < 0.05) during the relatively inactive feeding period of the late light cycle. No significant change was detected in the intake of Purina laboratory chow at 2 h, or of the intake of either diet at 4 h and 24 h after 8-OH-DPAT administration. Injection of 8-OH-DPAT induced a drop in insulin levels in rats maintained on high CARB/sugar diets only (-90%; P < 0.05). It also caused an increase in circulating glucose levels in both high CARB/sugar (240%; P < 0.01) and chow fed (123%; P < 0.05) rats; it did so more intensely in high CARB/sugar-fed rats. In the biochemical study, radioligand binding techniques were used to assess 5-HT1A receptor density in the hypothalamus, as well as the relationship between 5-HT1A receptors and circulating levels of insulin and glucose. Chronic and acute administration (25 mg/kg b.wt./5 injections, and 50 mg/kg b.wt., respectively, i.p.) of the potent hypoglycemic agent tolbutamide (TOL) caused a significant increase in 5-HT1A receptor density (+243% and +132.6%, respectively; P < 0.05) in the medial hypothalamus but not in the lateral hypothalamus, as compared to vehicle-treated rats. Chronic glucose replacement therapy showed a trend towards reversing the depressed circulating glucose levels as well as the medial hypothalamic 5-HT1A receptor density to control levels. These studies indicate that the pre-synaptic mechanism of 8-OH-DPAT-induced hyperphagia may require specific circulating levels of insulin and glucose, which are regulated via post-synaptic 5-HT1A receptors.

Effects of insulin and acarbose alone and in combination in the female streptozotocin-induced diabetic rat

Diabetes is characterized by hyperphagia, polydipsia, polyuria, elevations in blood and urinary glucose, and alterations in the adrenergic nervous system. Insulin treatment is effective in reversing most of the adverse conditions of diabetes in the streptozotocin-treated rat. Acarbose (BAY G 5421), an intestinal alpha-glucosidase inhibitor, decreases postprandial glycemia by delaying carbohydrate absorption and also affords some beneficial effects in the diabetic animal. The purpose of this study was to evaluate the effects of chronic insulin (< or = 2 U/day) with and without acarbose treatment (20 mg/100 g of diet) on the metabolic and adrenergic parameters altered in streptozotocin (50 mg/kg, intravenously)-induced diabetes in female rats. Insulin dosage was changed weekly after the first 2 weeks of treatment in both insulin-treated groups in an attempt to maintain a level of blood glucose that was comparable to that achieved with acarbose treatment alone. Insulin dosage was reduced to a greater extent in the dual-treated group than in the group treated with insulin alone. Diabetic rats were hyperphagic, polydipsic, and polyuric within 1 week of streptozotocin treatment. Each treatment alone was effective in reducing these alterations. However, these reductions were more apparent in the combined therapy group. Only in this combined therapy group was glycated hemoglobin returned to normal. All treatments also prevented the significant weight loss observed in untreated diabetic animals. Adrenergic responses were assessed by monitoring the rise in tail skin temperature associated with administration of isoproterenol. Diabetic rats were less responsive than controls, and each of the treatments restored this response.(ABSTRACT TRUNCATED AT 250 WORDS)

Weak magnetic fields antagonize the effects of melatonin on blood glucose levels in Parkinson's disease

Treatment with picoTesla magnetic fields recently has been reported to attenuate symptoms of Parkinson's disease (PD). The mechanisms by which weak magnetic fields ameliorate Parkinsonian symptoms are unknown. There is evidence that the pineal gland is a "magnetosensor" in the brain since in experimental animals exposure to external magnetic fields alters the firing rate of pineal cells and induces inhibition of melatonin secretion. Hence, the clinical effects of weak magnetic fields in PD likewise may involve the mediation of the pineal gland. Animal data indicate that the pineal gland is involved in the regulation of glucose metabolism and that exogenous administration of melatonin induces an hyperglycemic effect. To investigate the hypothesis that the pineal gland mediates the therapeutic properties of weak magnetic fields in PD, I studied the effects of orally administered melatonin (3.0 mg) followed by a 6 minute application of low intensity external weak magnetic fields (7.5 picoTesla) on blood glucose levels in two Parkinsonian patients. In both patients melatonin challenge produced a moderate hyperglycemic effect which was reversed by subsequent stimulation with weak magnetic fields. These findings support the hypothesis that weak magnetic fields inhibit melatonin secretion and that the antiParkinsonian properties of weak magnetic fields are mediated partially via the inhibition of melatonin secretion. Furthermore, these data suggest that melatonin receptor antagonists could be beneficial as an adjunctive treatment in PD and highlight the importance of the pineal-hypothalamic axis in the pathophysiology of the disease as well as in the mechanisms of action of antiParkinsonian drugs.

Effects of peripheral hormones on memory and ingestive behaviors

This article explores the mechanisms by which peripheral gastrointestinal hormones produce central nervous system effects on memory and feeding. Cholecystokinin produces its satiety effects and memory-enhancing effects by stimulating ascending vagal fibers. Hyperglycemia has been demonstrated to be a cause of memory dysfunction in persons with diabetes mellitus. A number of other hormones, such as amylin and bombesin, modulate both memory processing and feeding. The causes of the anorexia of aging are briefly reviewed.

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.

Hypothalamic osmoregulation for vasopressin release in streptozotocin-diabetic rats in vivo and in vitro

The central osmoregulation mechanism for vasopressin (VP) release was studied in the streptozotocin diabetic (STZ-DM) rat. Electrical activities of the VP-producing cell in the supraoptic nucleus (SON) were recorded extracellularly and compared with those in the control rat both in vivo and in vitro. Neuronal activities in the periventricular area (PVA) were also recorded in the in vitro experiment. Hyperosmolar stimulation which was done with an intraperitoneal injection of 1.0 M NaCl (4 ml/kg) resulted in an increase in plasma osmolality both of STZ-DM (increased by 14 +/- 2 mOsml/kg H2O) and control rats (15 +/- 3 mOsmol/kg H2O). Increased plasma osmolality caused significant increase in the mean discharge rate of VP-producing cells in the control animals, but only an insignificant change in STZ-DM rats. In the hypothalamic slice preparations incubated in the artificial cerebrospinal fluid (301 +/- 2 mOsml/kg H2O), VP-producing cells in control rats increased their discharge rate linearly as the osmolality (310 +/- 2 and 320 +/- 1 mOsmol/kg H2O) or concentration (10(-8) and 10(-6) M) of angiotensin II (AGII) of the perfusate was increased stepwise, but there was no change in response to either stimulus in STZ-DM rats. On the other hand, there was no difference in sensitivity to osmolality and AGII of PVA neurons in both animal groups. These data indicate that lower sensibility to osmotic change of VP-producing cells in STZ-DM rats may depend, at least partially, upon the disturbance of osmo- and AGII-sensitivity in VP-producing cells themselves, and that these changes seem to be restricted to SON VP-producing cells.

Dysregulation of the hypothalamo-pituitary-adrenal axis and duration of diabetes

We compared insulin-dependent diabetic outpatients with and without retinopathy for plasma indices of hypothalamo-pituitary-adrenal (HPA) axis activity. Diabetic patients with moderate-to-severe retinopathy had significantly higher postdexamethasone plasma levels of adrenocorticotropic hormone than patients with minimal or no retinopathy. However, when duration of diabetes was taken into account this difference was no longer significant. These data suggest that dysregulation of the HPA axis and retinal microvascular complications found in diabetic patients may both be a function of duration of diabetes.

Alterations in brain hexokinase activity associated with streptozotocin-induced diabetes mellitus in the rat

The effects of streptozotocin-induced diabetes mellitus on the activity of discrete regions of the brain were studied with histochemical localization and photodensitometric quantification of the metabolic enzyme, hexokinase. Two weeks after a single injection of streptozotocin (65 mg/kg, i.p.), plasma glucose and osmolarity levels were elevated, and plasma sodium concentrations were depressed. These changes were reversed in diabetic rats treated with insulin. Accompanying these symptoms of diabetes were significant increases in hexokinase activity in the magnocellular division of the paraventricular nucleus of the hypothalamus (mPVH, 12.1%), the medial subdivision of the nucleus of the tractus solitarius (mNTS, 15.5%), and the commissural subdivision of the NTS (cNTS, 10.9%). An increase, though just below the level of significance, was also observed in the supraoptic nucleus of the hypothalamus (SON, 11.5%). The increases in hexokinase activity were completely reversed in the cNTS (and SON) and only partly reversed in the mPVH and mNTS of insulin-treated diabetic rats. No changes in hexokinase activity were seen in the subfornical organ, medial preoptic area, parvocellular division of the PVH, locus coeruleus, or dorsal motor nucleus of the vagus of diabetic rats. These results reinforce the idea that the brain is not exempt from changes associated with diabetes mellitus and suggest that metabolic alterations in the mPVH (and SON) and two divisions of the NTS are likely related to changes in vasopressin production and blood volume, respectively.

Hypothalamic-pituitary-adrenal axis dysregulation among diabetic outpatients

We compared insulin-requiring diabetic outpatients (n = 49) with normal controls (n = 42) for indices of hypothalamic-pituitary-adrenal (HPA) axis activity. Diabetic patients showed significantly elevated 9 a.m. plasma levels of cortisol as well as significantly elevated plasma levels of cortisol and adrenocorticotropic hormone (ACTH) at both 4 p.m. before and 4 p.m. after dexamethasone. Also, there was a significant correlation between postdexamethasone plasma levels of ACTH and duration of diabetes. These results suggest that HPA-axis dysregulation is found among diabetic outpatients. The possible psychiatric implications are discussed.

Alpha 2-adrenoceptor-mediated modulation of noradrenaline release is decreased in vas deferens but not in cerebral cortex of diabetic rats

In the present study, a superfusion method was used to investigate the alpha 2-adrenoceptor mediated modulation of the electrically evoked release of radiolabeled noradrenaline in vas deferens and cerebral cortex slices of streptozotocin-diabetic and control rats 8-10 weeks after the induction of diabetes. Stimulation of alpha 2-adrenoceptors led to a significantly smaller inhibition of radiolabeled noradrenaline release in the vas deferens of diabetic rats as compared to control rats. In the cerebral cortex no such difference was detected. It is concluded that these effects could be due to a decrease in the number of presynaptic alpha 2-adrenoceptors in the vas deferens of diabetic rats. The results of this study show that the superfusion technique offers a simple possibility to obtain information about the functional integrity of noradrenergic neurons in the peripheral nervous system and central nervous system in diabetes mellitus. Moreover, the results provide an indication for a different time scale in the development of neuropathy in the peripheral and central nervous system of streptozotocin-diabetic rats.

Tetrahydrobiopterin metabolism in the streptozotocin induced diabetic state in rats

Streptozotocin induced diabetes has been shown to have associated changes in the metabolism of tetrahydrobiopterin. De novo biosynthesis of tetrahydrobiopterin in the brain was reduced as was dihydropteridine reductase activity. Consequently there is a shift from fully reduced biopterins to more oxidised species. Both can cause reduced levels in the cofactor pool and may cause reduced levels of the associated neurotransmitters and neurological deficits.

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.

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

Diabetes is reportedly associated with alterations in peripheral and central noradrenergic systems. The latter might be involved in the antidepressant effects of imipramine-like drugs in both humans and animals. Therefore, it is possible that diabetics show an impaired responsiveness to tricyclics. To test this possibility the effects of streptozotocin (STZ)-induced experimental diabetes in mice were assessed in two psychopharmacological tests: 1) the reversal of apomorphine- (16 mg/kg) induced hypothermia and 2) the hypoactivity induced by a direct beta-agonist (clenbuterol 0.06 mg/kg). At day 15 after STZ or vehicle treatment, imipramine (4 mg/kg) antagonized the apomorphine-induced hypothermia in diabetic (D) and nondiabetic (ND) mice and clenbuterol produced hypoactivity in both groups. At day 30 and 45, the ability of imipramine (1, 2, 4, 8, 16 mg/kg), clomipramine (8 mg/kg) and desipramine (2 mg/kg) to reverse apomorphine-induced hypothermia disappeared at the same time that clenbuterol lost its ability to induce hypomotility in D mice. These impaired responses on both tests were corrected by a short period of insulin therapy. These two tests may reflect central beta-adrenergic functions. Therefore, these data suggest that the impaired responsiveness of diabetic mice might be due at least in part to a noradrenergic dysfunction. Possibly, in diabetes, a beta-adrenoceptor desensitization identical to that observed at the peripheral level occurs in the central nervous system. The possibility that a thyroid hormone deficiency may be involved was also tested. Decreased T3 plasma levels were found in D mice concomitant with the impaired pharmacological responses and T3 supplementation turned these responses to normal.(ABSTRACT TRUNCATED AT 250 WORDS)