The functional significance of biochemical alterations in streptozotocin-induced diabetes

Activation of 5-HT1A Receptors Normalizes the Overexpression of Presynaptic 5-HT1A Receptors and Alleviates Diabetic Neuropathic Pain

Neuropathic pain is a well-documented phenomenon in experimental and clinical diabetes; however, current treatment is unsatisfactory. Serotoninergic-containing neurons are key components of the descending autoinhibitory pathway, and a decrease in their activity may contribute at least in part to diabetic neuropathic pain (DNP). A streptozotocin (STZ)-treated rat was used as a model for type 1 diabetes mellitus (T1DM). Pain transmission was evaluated using well-established nociceptive-based techniques, including the Hargreaves apparatus, cold plate and dynamic plantar aesthesiometer. Using qRT-PCR, Western blotting, immunohistochemistry, and HPLC-based techniques, we also measured in the central nervous system and peripheral nervous system of diabetic animals the expression and localization of 5-HT1A receptors (5-HT1AR), levels of key enzymes involved in the synthesis and degradation of tryptophan and 5-HT, including tryptophan hydroxylase-2 (Tph-2), tryptophan 2,3-dioxygenase (Tdo), indoleamine 2,3-dioxygenase 1 (Ido1) and Ido2. Moreover, spinal concentrations of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA, a metabolite of 5-HT) and quinolinic acid (QA, a metabolite of tryptophan) were also quantified. Diabetic rats developed thermal hyperalgesia and cold/mechanical allodynia, and these behavioral abnormalities appear to be associated with the upregulation in the levels of expression of critical molecules related to the serotoninergic nervous system, including presynaptic 5-HT1AR and the enzymes Tph-2, Tdo, Ido1 and Ido2. Interestingly, the level of postsynaptic 5-HT1AR remains unaltered in STZ-induced T1DM. Chronic treatment of diabetic animals with 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), a selective 5-HT1AR agonist, downregulated the upregulation of neuronal presynaptic 5-HT1AR, increased spinal release of 5-HT (↑ 5-HIAA/5-HT) and reduced the concentration of QA, decreased mRNA expression of Tdo, Ido1 and Ido2, arrested neuronal degeneration and ameliorated pain-related behavior as exemplified by thermal hyperalgesia and cold/mechanical allodynia. These data show that 8-OH-DPAT alleviates DNP and other components of the serotoninergic system, including the ratio of 5-HIAA/5-HT and 5-HT1AR, and could be a useful therapeutic agent for managing DNP.

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.

Sympathectomy Effects on Intra-Abdominal Organ Catecholamine Levels in a Streptozotocin-Induced Diabetic Rat Model

Diabetes mellitus (DM) is a metabolic disorder whose prevalence has continuously increased worldwide and is associated with dysfunction of the autonomic nervous system and, in particular, that of the sympathetic nervous system (SNS). The objective of this study was to analyze the interaction of DM and the SNS, building a model of sympathectomized diabetic rats to determine alterations in the content of CA (catecholamines) in different intra-abdominal organs. Sympathectomy was conducted with guanethidine (GNT). Additionally, DM was induced with STZ (Streptozotocin). Treatment with GNT decreased norepinephrine (NE) content in all analyzed tissues, with significant differences found in the paraganglia, liver, pancreas, duodenum, and heart compared to the control group. With respect to epinephrine (E), which was only found in the liver, pancreas, and heart, presenting significant differences (p < 0.05) in the heart, a decrease in its concentration was observed for all of the experimental groups with respect to the control. The decrease in dopamine (DA) content due to the GNT−STZ treatment was 30.1% in the heart with respect to the diabetic (STZ) group. The amount of CA in the adrenal medulla indicates the effect of sympathectomy on the GNT group where there was a significant reduction (p < 0.05) of DA. These findings suggest that the elimination of the sympathetic nervous system in diabetic organisms contributed to a decrease in blood glucose; likewise, an alteration in the levels of CA was observed in the different selected organs, possibly attributed to the severity, duration, and pathogenesis of the complications of acute and chronic DM.

Posttraumatic stress disorder-type behaviors in streptozotocin-induced diabetic rats can be prevented by prolonged treatment with vitamin E

Anxiety and stress disorders, such as posttraumatic stress disorder (PTSD) have been described as debilitating comorbidities of diabetes. In the present study, we aimed to investigate anxiety-like behavior and the extinction and generalization of aversive memories in fear conditioning using a streptozotocin-induced model of diabetes (DBT). Moreover, considering that DBT animals present increased oxidative stress in brain areas related to anxiety and memory, we aimed to evaluate the effect of prolonged treatment with antioxidant vitamin E on behavioral parameters of anxiety and fear memory and on the diabetic condition. It was observed that DBT animals showed a deficiency in extinguishing the aversive memory in a fear conditioning test, along with a generalization of the fear memory. They also present a more pronounced anxiety-like behavior in the elevated plus maze test. VIT E treatment (300 mg/kg, p.o.) was not able to reduce hyperglycemia; however, it was able to block the anxiogenic-like behavior, also improving the deficit in the extinction of the aversive memory as well as blocking the generalization of such memory in a different context. Taken together, our data suggest that DBT animals are prone to extinction deficits and generalization of fear memories, behaviors which are observed in models of PTSD. Lastly, prolonged VIT E supplementation may be effective in the treatment of anxiety, extinction deficit and generalization of fear memories induced by the diabetic condition.

Sub-chronic treatment with cannabidiol but not with URB597 induced a mild antidepressant-like effect in diabetic rats

Depression associated with diabetes has been described as a highly debilitating comorbidity. Due to its complex and multifactorial mechanisms, the treatment of depression associated with diabetes represents a clinical challenge. Cannabidiol (CBD), the non-psychotomimetic compound derived from Cannabis sativa, has been pointed out as a promising compound for the treatment of several psychiatric disorders. Here, we evaluated the potential antidepressant-like effect of acute or sub-chronic treatment with CBD in diabetic rats using the modified forced swimming test (mFST). Also, to better understand the functionality of the endocannabinoid system in diabetic animals we also evaluated the effect of URB597, a fatty acid amide hydrolase inhibitor. Four weeks after the treatment with streptozotocin (60 mg/kg; i.p.; diabetic group-DBT) or citrate buffer (i.p.; normoglycemic group-NGL), DBT animals received an acute intraperitoneal injection of CBD (0, 0.3, 3, 10, 30 or 60 mg/kg), 1 h before the mFST, or URB597 (0, 0.1, 0.3 or 1 mg/kg) 2 h before the mFST. In another set of experiments, animals were sub-chronically treated with CBD (0, 0.3, 3, 30 or 60 mg/kg i.p.), 24, 5 and 1 h before the mFST or URB597 (0, 0.1, 0.3 or 1 mg/kg i.p.) 24, 5 and 2 h before the mFST. The NGL group was acutely treated with CBD (0, 30 mg/kg i.p.) or URB597 (0, 0.3 mg/kg; i.p.). Acute treatment with either CBD or URB induced an antidepressant-like effect in NGL rats, but not in DBT rats. However, sub-chronic treatment with CBD (only at a dose of 30 mg/kg), but not with URB597, induced a mild antidepressant-like effect in DBT animals. Neither body weight nor blood glucose levels were altered by treatments. Considering the importance of the endocannabinoid system to the mechanism of action of many antidepressant drugs, the mild antidepressant-like effect of the sub-chronic treatment with CBD, but not with URB597 does not invalidate the importance of deepening the studies involving the endocannabinoid system particularly in DBT animals.

A serotonergic deficit in the dorsal periaqueductal gray matter may underpin enhanced panic-like behavior in diabetic rats

It is known that diabetic (DBT) animals present dysregulation on the serotonergic system in several brain areas associated with anxiety-like responses. The aim of this study was to investigate the involvement of 5-HT1A receptors on dorsal periaqueductal gray (dPAG) in the behavioral response related to panic disorder in type-1 DBT animals. For this, the escape response by electric stimulation (ES) of dPAG in DBT and normoglycemic (NGL) animals was assessed. Both NGL and DBT animals were exposed to an open-field test (OFT) 28 days after DBT confirmation. The current threshold to induce escape behavior in DBT animals was reduced compared with NGL animals. No impairment in locomotor activity was observed when DBT animals were compared with NGL animals. An intra-dPAG injection of the 5-HT1A receptor agonist (±)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) increased the [INCREMENT] threshold in both DBT and NGL, suggesting a panicolytic-like effect. DBT animals presented a more pronounced panicolytic-like response compared with NGL as a higher [INCREMENT] threshold was observed after 8-OH-DPAT treatment, which could be a consequence of the increased expression of the 5-HT1A receptor in the dPAG from DBT animals. Our results are in line with the proposal that a deficiency in serotonergic modulation of the dPAG is involved in triggering the panic attack and the 5-HT1A receptors might be essential for the panicolytic-like response.

Anandamide reverses depressive-like behavior, neurochemical abnormalities and oxidative-stress parameters in streptozotocin-diabetic rats: Role of CB1 receptors

The pathophysiology associated with increased prevalence of depression in diabetics is not completely understood, although studies have pointed the endocannabinoid system as a possible target. Then, we aimed to investigate the role of this system in the pathophysiology of depression associated with diabetes. For this, diabetic (DBT) male Wistar rats were intraperitoneally treated with cannabinoid CB1 (AM251, 1mg/kg) or CB2 (AM630, 1mg/kg) receptor antagonists followed by anandamide (AEA, 0.005mg/kg) and then submitted to the forced swimming test (FST). Oxidative stress parameters, CB1 receptor expression and serotonin (5-HT) and noradrenaline levels in the hippocampus (HIP) and prefrontal cortex (PFC) were also performed. It was observed that DBT animals presented a more pronounced depressive-like behavior and increase of CB1 receptor expression in the HIP. AEA treatment induced a significant improvement in the depressive-like behavior, which was reversed by the CB1 antagonist AM251, without affecting the hyperglycemia or weight gain. AEA was also able to restore the elevated CB1 expression and also to elevate the reduced level of 5-HT in the HIP from DBT animals. In addition, AEA restored the elevated noradrenaline levels in the PFC and induced a neuroprotective effect by restoring the decreased reduced glutathione and increased lipid hydroperoxides levels along with the decreased superoxide dismutase activity observed in HIP or PFC. Together, our data suggest that in depression associated with diabetes, the endocannabinoid anandamide has a potential to induce neuroadaptative changes able to improve the depressive-like response by its action as a CB1 receptor agonist.

Dopamine D1 receptor activity is involved in the increased anxiety levels observed in STZ-induced diabetes in rats

Epidemiological surveys have indicated that anxiety disorders are more frequent in diabetic patients than in the general population. Similar results have been shown in animal studies using the streptozotocin (STZ)-induced diabetes model. The mechanisms underlying this relationship are not clearly understood, but it has been suggested that alterations in the dopaminergic neurotransmission, which plays an important role in the amygdaloid modulation of fear and anxiety, may be involved. The aim of this study was to ascertain whether or not the amygdaloid DA D1 receptors are involved in the increase of anxiety-like behavior observed in "diabetic" animals. Adult Wistar male rats were injected with STZ (50mg/kg, i.p.) in two consecutive days and subjected to the Shock-Probe Burying Test 10days after the beginning of treatment. STZ-treated rats showed a significant increase in immobility/freezing behavior whereas no effects were elicited in latency to bury, burying behavior itself and the number of shocks received during testing as compared with non-diabetic controls. These results suggest the triggering of a passive coping response in the STZ-treated rats. Interestingly, immobility/freezing behavior was reversed following the intra-amygdaloid dopamine D1 receptor blockade by the local microinfusion of SCH23390 (100ng/side). Autoradiographic experiments showed a selective increase of [(3)H]-SCH23390 binding in the ventral intercalated paracapsular islands of STZ-treated rats when compared to the non-treated control group. Our results suggest that a hyperdopaminergic state involving DA D1 receptors within the amygdala may have a role in the increase of anxiety observed in diabetic rats.

Reestablishment of the hyperglycemia to the normal levels seems not to be essential to the anxiolytic-like effect induced by insulin

Diabetes is a chronic metabolic disease accompanied by several comorbidities, including neuropsychiatric conditions. Since the hyperglycemia appears to be the primary factor involved in diabetic conditions, we examined the effect of insulin treatment in diabetic rats on behavioral responses related to anxiety and aversive memory extinction. For this, normoglycemic (NGL) or streptozotocin-diabetic (DBT) rats were submitted to the elevated T maze (ETM) and the contextual conditioned fear (CCF) tests. Therefore, animals were subjected to the prolonged treatment with insulin (6 IU/day, s.c.) to investigate the effect of the treatment on distinct behaviors. When anxiety-like responses such as the inhibitory avoidance (IA) on the ETM and the time of freezing in the first session of the CCF test were evaluated, our data showed a more pronounced anxiogenic-like behavior in DBT animals when compared to NGL ones. In addition, an increased freezing time was observed in DBT animals exposed to the CCF test (sessions 2 and 3) when compared to the NGL group, suggestive of an impairment in the extinction of aversive memory. Insulin treatment induced an anxiolytic-like effect when IA and freezing time (session 1) was evaluated, but did not alter the impaired extinction of aversive memory (sessions 2 and 3). To better understand the involvement of a rigorous control of glycaemia, we also investigated the effect of a lower dose of insulin (3 IU/day, s.c.), unable to reestablish the hyperglycemia to the normal levels, on the same behavioral parameters. Our data show that independent of the dose of insulin, the same effects were observed when animals were evaluated in the ETM and CCF tests. However, only the highest dose of insulin was able to reduce the hyperglycemia to the normal levels. To conclude, our data suggest that a severe glycemic control by insulin treatment seems to be important, but not essential in improving diabetes-induced anxiety.

Indoleamine-2,3-Dioxygenase/Kynurenine Pathway as a Potential Pharmacological Target to Treat Depression Associated with Diabetes

Diabetes is a chronic disease associated with depression whose pathophysiological mechanisms that associate these conditions are not fully elucidated. However, the activation of the indoleamine-2,3-dioxygenase (IDO), an enzyme that participate of the tryptophan metabolism leading to a decrease of serotonin (5-HT) levels and whose expression is associated with an immune system activation, has been proposed as a common mechanism that links depression and diabetes. To test this hypothesis, diabetic (DBT) and normoglycemic (NGL) groups had the cytokines (TNFα, IL-1β, and IL-6) and 5-HT and norepinephrine (NE) levels in the hippocampus (HIP) evaluated. Moreover, the effect of the selective serotonin reuptake inhibitor fluoxetine (FLX), IDO direct inhibitor 1-methyl-tryptophan (1-MT), anti-inflammatory and IDO indirect inhibitor minocycline (MINO), or non-selective cyclooxygenase inhibitor ibuprofen (IBU) was evaluated in DBT rats submitted to the modified forced swimming test (MFST). After the behavioral test, the HIP was obtained for IDO expression by Western blotting analysis. DBT rats exhibited a significant increase in HIP levels of TNFα, IL-1β, and IL-6 and a decrease in HIP 5-HT and NA levels. They also presented a depressive-like behavior which was reverted by all employed treatments. Interestingly, treatment with MINO, IBU, or FLX but not with 1-MT reduced the increased IDO expression in the HIP from DBT animals. Taken together, our data support our hypothesis that neuroinflammation in the HIP followed by IDO activation with a consequent decrease in the 5-HT levels can be a possible pathophysiological mechanism that links depression to diabetes.

Neonatally induced mild diabetes: influence on development, behavior and reproductive function of female Wistar rats

BACKGROUND

Neonatal STZ treatment induces a state of mild hyperglycemia in adult rats that disrupts metabolism and maternal/fetal interactions. The aim of this study was investigate the effect of neonatal STZ treatment on the physical development, behavior, and reproductive function of female Wistar rats from infancy to adulthood.

METHODS

At birth, litters were assigned either to a Control (subcutaneous (s.c.) citrate buffer, n = 10) or STZ group, (streptozotocin (STZ) - 100 mg/kg-sc, n = 6). Blood glucose levels were measured on postnatal days (PND) 35, 84 and 120. In Experiment 1 body weight, length and the appearance of developmental milestones such as eye and vaginal opening were monitored. To assess the relative contribution of the initial and long term effects of STZ treatment this group was subdivided based on blood glucose levels recorded on PND 120: STZ hyperglycemic (between 120 and 300 mg/dl) and STZ normoglycemic (under 120 mg/dl). Behavioral activity was assessed in an open field on PND 21 and 75. In Experiment 2 estrous cyclicity, sexual behavior and circulating gonadotropin, ovarian steroid, and insulin levels were compared between control and STZ-hyperglycemic rats. In all measures the litter was the experimental unit. Parametric data were analyzed using one-way or, where appropriate, two-way ANOVA and significant effects were investigated using Tukey's post hoc test. Fisher's exact test was employed when data did not satisfy the assumption of normality e.g. presence of urine and fecal boli on the open field between groups. Statistical significance was set at p < 0.05 for all data.

RESULTS

As expected neonatal STZ treatment caused hyperglycemia and hypoinsulinemia in adulthood. STZ-treated pups also showed a temporary reduction in growth rate that probably reflected the early loss of circulating insulin. Hyperglycemic rats also exhibited a reduction in locomotor and exploratory behavior in the open field. Mild hyperglycemia did not impair gonadotropin levels or estrous cylicity but ovarian steroid concentrations were altered.

CONCLUSIONS

In female Wistar rats, neonatal STZ treatment impairs growth in infancy and results in mild hyperglycemia/hypoinsulinemia in adulthood that is associated with changes in the response to a novel environment and altered ovarian steroid hormone levels.

Brain insulin dysregulation: implication for neurological and neuropsychiatric disorders

Arduous efforts have been made in the last three decades to elucidate the role of insulin in the brain. A growing number of evidences show that insulin is involved in several physiological function of the brain such as food intake and weight control, reproduction, learning and memory, neuromodulation and neuroprotection. In addition, it is now clear that insulin and insulin disturbances particularly diabetes mellitus may contribute or in some cases play the main role in development and progression of neurodegenerative and neuropsychiatric disorders. Focusing on the molecular mechanisms, this review summarizes the recent findings on the involvement of insulin dysfunction in neurological disorders like Alzheimer's disease, Parkinson's disease and Huntington's disease and also mental disorders like depression and psychosis sharing features of neuroinflammation and neurodegeneration.

Imipramine treatment reverses depressive-like behavior in alloxan-diabetic rats

BACKGROUND

A growing body of evidence has shown an association between diabetes and depression, as well a role of brain-derived neurotrophic factor (BDNF) in diabetes and depression. The present study was designed to evaluate the behavioural and molecular effects of the anti-depressant imipramine in diabetic rats.

METHODS

To this aim, after induction of diabetes by alloxan (150 mg/kg), Wistar rats were treated with imipramine (30 mg/kg) once a day for 14 days and then subjected to behavioural tests. BDNF was then assessed in the prefrontal cortex, hippocampus and amygdala.

RESULTS

In diabetic rats treated with saline, we observed an increase in the immobility time, compared with control rats treated with saline. Treatment with imipramine decreased the immobility time in nondiabetic and diabetic rats, compared with both nondiabetic and diabetic rats treated with saline. In the open-field test, it was observed that treatment with imipramine reduced the number of crossings the diabetic rats performed, compared with nondiabetic rats treated with saline. The number of rearings did not alter in any of the groups. Diabetic rats injected with saline did not show altered BDNF levels in the prefrontal cortex, hippocampus or amygdala, but interestingly, the treatment with imipramine in diabetic animals increased BDNF levels in the prefrontal cortex.

CONCLUSIONS

In conclusion, this study demonstartes a link between diabetes and depression in rats and that imipramine exerted antidepressant effects in diabetic animals.

The streptozotocin-induced rat model of diabetes mellitus evidences significant reduction of myosin-Va expression in the brain

Diabetes mellitus is a disease characterized by increased glucose levels in the blood. Hyperglycemia causes damage to the brain tissue, and induces significant changes in synaptic transmission. In this investigation, we have found a significant alteration in the expression of the molecular motor involved in the synaptic vesicles transport, myosin-Va, and its distribution in rat brains of streptozotocin-induced diabetes model. Brains were removed after 20 days, homogenized and analysed by Western blotting, qRT-PCR and immunohistochemistry. Myosin-Va presented significantly lower levels of both mRNA and protein in diabetic than those observed in non-diabetic animals. Moreover, neuronal and glial cells of the occipital and frontal cortex exhibited decreased myosin-Va immunostaining in diabetic rat brains. In conclusion, diabetic rat brains displayed altered expression and distribution of myosin-Va, and these finding may contribute to the basic understanding about this myosin role in brain function related to diabetes.

Brain energy metabolism parameters in an animal model of diabetes

A growing body of evidence has indicated that altered mitochondrial function may be involved in mechanism for the development of diabetic complications. Thus, we investigated whether animal model of diabetes induced by alloxan alters energy metabolism parameters. Wistar rats received one single injection of alloxan (250 mg/kg) and after 15 days we evaluated mitochondrial respiratory chain complexes I, II, II-III and IV, creatine kinase and citrate synthase activities in prefrontal cortex, hippocampus and striatum. We observed that animal model of diabetes induced by alloxan increased complexes I and IV activities in hippocampus, complexes II and II-III activities in prefrontal cortex and striatum and complex IV in prefrontal cortex; however decreased complex IV activity in striatum. Moreover, diabetes rats decreased creatine kinase activity in striatum and increased citrate synthase activity in hippocampus. In conclusion, this study indicates that the alteration in mitochondrial function is probably involved in the pathophysiology of diabetes.

Oxidative stress parameters in diabetic rats submitted to forced swimming test: the clonazepam effect

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. We evaluated the oxidative stress from diabetic animals submitted to an experimental model of depression and the effects of clonazepam. Male Wistar rats were induced to diabetes with streptozotocin and submitted to forced swimming test. Clonazepam was administered 24, 5 and 1 h before test. The animals were sacrificed by decapitation, and plasma and erythrocytes were separated, as well as hippocampus, cortex and striatum. Reactive species of thiobarbituric acid (TBARS) and total antioxidant reactivity (TAR) as well as antioxidant enzyme activities catalase (CAT) and superoxide dismutase (SOD) were evaluated. Results showed a significant increase of TBARS and a significant decrease of TAR in plasma from diabetic animals, which was altered by clonazepam. There were no effects of CAT and SOD activities in erythrocytes from tested animals. The results observed in hippocampus showed a significant increase of TBARS from diabetic rats, altered by clonazepam, and no one alteration was verified in TAR. The significant increase of TBARS and the significant decrease of TAR in cortex from diabetic rats were not altered by clonazepam administration. There were no alterations of TBARS and TAR in striatum from tested animals. Besides, clonazepam reverses the immobility in diabetic rats. Considering the action of clonazepam, it is suggested that it could be an alternative therapeutic for depression to diabetic patients, once it could give a protection against free radicals.

Recognizing and treating depression in patients with diabetes

Diabetes doubles the risk for depression, which in turn may interfere with effective diabetes self-management, and is associated with hyperglycemia and with increased risk for diabetes complications. Despite its relevance to the course of diabetes and its chronic character, depression is recognized and treated appropriately in fewer than 25% of depressed diabetic patients. The authors discuss the use of screening tools to assist primary care providers in identifying depressed diabetic patients, as well as the application of a chronic care model of depression management. Data from controlled trials are limited but promising. They suggest that pharmacologic and psychological approaches are effective in the face of diabetes, and that successful treatment also produces improvements in glycemic control, overall functioning, and quality of life.

Diabetes attenuates the antidepressant-like effect mediated by the activation of 5-HT1A receptor in the mouse tail suspension test

Several lines of evidence have indicated that the prevalence of depression in diabetic subjects is higher than that in the general population, however, little information is available on the effects of antidepressants in diabetes. In the present study, the antidepressant-like effect mediated by the activation of 5-HT(1A) receptors was examined using the tail suspension test in streptozotocin-induced diabetic mice. Long-lasting increases in 5-HT turnover rates were observed in the diabetic mouse midbrain and frontal cortex, but not in the hippocampus. Duration of immobility was significantly longer in diabetic than in nondiabetic mice in the tail suspension test. The 5-HT(1A) receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (3-30 microg/kg, i.p.) reduced the duration of immobility in nondiabetic mice, and this effect was completely antagonized by pretreatment with N-[2-[4-(2-methoxyphenil)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY-100635) (30 microg/kg, s.c.), a selective 5-HT(1A) receptor antagonist. In contrast, 8-OH-DPAT (3 microg/kg-3 mg/kg, i.p.) was ineffective in diabetic mice. The selective 5-HT reuptake inhibitor fluoxetine (3-56 mg/kg, i.p.) reduced the duration of immobility in both nondiabetic and diabetic mice. However, fluoxetine was less effective in diabetic mice than in nondiabetic mice. WAY-100635 (30 microg/kg, s.c.) reversed the suppression of the duration of immobility by fluoxetine (30 mg/kg, i.p.) in nondiabetic mice. On the other hand, the anti-immobility effect of fluoxetine (56 mg/kg, i.p.) was not antagonized by WAY-100635 (30 microg/kg, s.c.) in diabetic mice. The selective 5-HT(2) receptor antagonist 6-methyl-1-(1-methylethyl)-ergoline-8beta-carboxylic acid 2-hydroxy-1-methylpropyl ester (LY53,857) (30 microg/kg, s.c.) reversed the anti-immobility effect of fluoxetine in both nondiabetic and diabetic mice. Spontaneous locomotor activity in diabetic mice was not different from that in nondiabetic mice. 8-OH-DPAT (30 microg/kg, i.p.), but not fluoxetine, increased the spontaneous locomotor activity in both nondiabetic and diabetic mice. The number of 5-HT(1A) receptors in the mouse frontal cortex was unaffected by diabetes. Plasma corticosterone levels in diabetic mice were significantly higher than that in nondiabetic mice. These results suggest that the antidepressant-like effect mediated by 5-HT(1A) receptors may be attenuated by diabetes.

Clonazepam increases in vivo striatal extracellular glucose in diabetic rats after glucose overload

Hyperglycemia modulates brain function, including neuronal excitability, neurotransmitter release and behavioral changes. There may be connections between the GABAergic system, glucose sensing neurons and glucose in the neuronal environment that shed light on the mechanism by which GABA(A) agents influence depressive behavior in diabetic rats submitted to the forced swimming test. We aimed to investigate whether clonazepam (CNZ), a GABA(A) receptor positive modulator, modifies in vivo striatal extracellular glucose levels in diabetic rats under fasting condition or after oral glucose overload. Streptozotocin diabetic and nondiabetic rats were submitted to in vivo striatal microdialysis. Perfusate samples were collected at baseline, during fasting and following administration of CNZ (0.25 mg/kg) and oral glucose overload. Blood glucose and striatal extracellular glucose were measured simultaneously at several time points. Fasting striatal glucose levels were higher in diabetic than in nondiabetic rats and the differences between these animals were maintained after glucose overload. The increases in extracellular striatal glucose after glucose overload were around 40% and blood to brain transference was decreased in diabetics. CNZ treatment paradoxically increased striatal glucose after glucose overload in diabetic rats, which may mark the dysfunction in brain glucose homeostasis.

Prevalence of psychiatric disorders in an onset cohort of adults with type 1 diabetes

BACKGROUND

Previous studies indicate a high prevalence of psychiatric disorders in adults with type 1 diabetes mellitus. The aim of our study was to determine if newly diagnosed adults with type 1 diabetes already have an elevated rate of psychiatric disorders at the beginning of their physical illness.

METHODS

The authors consecutively recruited 313 newly diagnosed, adult inpatients with type 1 diabetes (age 17-40 years) from 12 hospitals. A national, representative population sample of 2046 persons of a similar age range served as the reference group. Psychiatric disorders were measured in both groups using structured interviews that provided diagnoses according to DSM-IV.

RESULTS

There was a point prevalence of 12.5% for psychiatric disorders in the sample. The most frequent conditions were anxiety and affective disorders. Subjects with type 1 diabetes demonstrated a rate of major depressive episodes twice that of the reference group (5.8% vs 2.7%, p < 0.003; corrected for confounders). Apart from this finding, there was no significantly increased prevalence of psychiatric disorders in the diabetes sample as compared to the general German population.

CONCLUSION

The rate of major depressive episodes in the new onset cohort of type 1 diabetes patients was double that of the population as a whole. However, the hypothesis, that newly diagnosed type 1 diabetes patients have more psychiatric disorders than the general population, was not confirmed.

Lower in vivo brain extracellular GABA concentration in diabetic rats during forced swimming

Diabetic rats are more immobile during the forced-swimming test (FST) and GABAergic drugs reverse this behavior. We investigated if there is in vivo changes of GABA levels of diabetic rats during the FST. In vivo basal striatal GABA levels of streptozotocin diabetic rats are similar to non-diabetic rats. Non-diabetic rats presented a significant increase in GABA levels after the FST while the increase was delayed and lower in diabetic rats. These results suggest that diabetes may change GABA homeostasis and modify behavioral responses in an animal model of depression.

Diabetes, the brain, and behavior: is there a biological mechanism underlying the association between diabetes and depression?

In summary, our review of the literature suggests that diabetes, especially type 1 diabetes, may place patients at risk for a depressive disorder through a biological mechanism linking the metabolic changes of diabetes to changes in brain structure and function. Further studies are warranted examining these relationships in order to better understand the impact of diabetes on brain functioning and structure as well as one potential manifestation of such changes--affective disorder. Moreover, such studies could play a useful role in better understanding mechanisms that commonly underlie the development of depression in individuals without diabetes but with other medical problems or conditions.

A review of 25 years of the social interaction test

The social interaction test of anxiety was developed 25 years ago to provide an ethologically based test that was sensitive to both anxiolytic and anxiogenic effects. It is sensitive to a number of environmental and physiological factors that can affect anxiety. It has detected anxiogenic effects of peptides such as corticotropin-releasing factor (CRF) and adrenocorticotropic hormone (ACTH), and anxiolytic effects of neuropeptide Y and substance P receptor antagonists. It has successfully identified neuropharmacological sites of action of anxiogenic compounds and drug withdrawal. Effects of compounds acting on the gamma-aminobutyric acid (GABA) and 5-hydroxytryptamine (5-HT) systems have been extensively investigated after both systemic administration and microinjection into specific brain regions. The use of this test has, thus, played a crucial role in unravelling the neural basis of anxiety. It is hoped that in the next 25 years, the test will play a crucial role in determining the genetic basis of anxiety disorders.

Treatment of depression in diabetes: impact on mood and medical outcome

Depression is prevalent as a co-morbid condition in diabetes. The efficacy of depression treatment with either pharmacological agents or psychotherapy has been demonstrated in the few available controlled trials. Depression has been associated with poor glycemic control and with accelerated rates of coronary heart disease in diabetic patients. Reported depression treatment trials demonstrate benefits of depression remission on glycemic control as well as mood and the potential for improvement in the course and outcome of diabetes. Because adverse effects of pharmacological agents on glycemic control have been observed, optimal therapies that improve both depression and measures of diabetes are still being sought. This review critically examines the efficacy of depression treatment in diabetes patients, the effects of depression treatment on the medical condition, and methodological issues important in the performance of treatment trials in the patient population.

Ageing and diabetes: implications for brain function

Diabetes mellitus is associated with moderate cognitive deficits and neurophysiological and structural changes in the brain, a condition that may be referred to as diabetic encephalopathy. Diabetes increases the risk of dementia, particularly in the elderly. The emerging view is that the diabetic brain features many symptoms that are best described as "accelerated brain ageing." The clinical characteristics of diabetic encephalopathy are discussed, as well as behavioural (e.g. spatial learning) and neurophysiological (e.g. hippocampal synaptic plasticity) findings in animal models. Animal models can make a substantial contribution to our understanding of the pathogenesis, which shares many features with the mechanisms underlying brain ageing. By unravelling the pathogenesis, targets for pharmacotherapy can be identified. This may allow treatment or prevention of this diabetic complication in the future. We discuss changes in glutamate receptor subtypes, in second-messenger systems and in protein kinases that may account for the alterations in synaptic plasticity. In addition, the possible role of cerebrovascular changes, oxidative stress, nonenzymatic protein glycation, insulin and alterations in neuronal calcium homeostasis are addressed.

Learning and memory in streptozotocin-induced diabetic rats in a novel spatial/object discrimination task

Diabetes mellitus is associated with disturbances of cognitive functioning. The aim of this study was to examine cognitive functioning in diabetic rats using the 'Can test', a novel spatial/object learning and memory task, without the use of aversive stimuli. Rats were trained to select a single rewarded can from seven cans. Mild water deprivation provided the motivation to obtain the reward (0.3 ml of water). After 5 days of baseline training, in which the rewarded can was marked by its surface and position in an open field, the animals were divided into two groups. Diabetes was induced in one group, by an intravenous injection of streptozotocin. Retention of baseline training was tested at 2-weekly intervals for 10 weeks. Next, two adapted versions of the task were used, with 4 days of training in each version. The rewarded can was a soft-drink can with coloured print. In a 'simple visual task' the soft-drink can was placed among six white cans, whereas in a 'complex visual task' it was placed among six soft-drink cans from different brands with distinct prints. In diabetic rats the number of correct responses was lower and number of reference and working memory errors higher than in controls in the various versions of the test. Switches between tasks and increases in task complexity accentuated the performance deficits, which may reflect an inability of diabetic rats to adapt behavioural strategies to the demands of the tasks.

Experimental diabetes in rats causes hippocampal dendritic and synaptic reorganization and increased glucocorticoid reactivity to stress

We report that 9 d of uncontrolled experimental diabetes induced by streptozotocin (STZ) in rats is an endogenous chronic stressor that produces retraction and simplification of apical dendrites of hippocampal CA3 pyramidal neurons, an effect also observed in nondiabetic rats after 21 d of repeated restraint stress or chronic corticosterone (Cort) treatment. Diabetes also induces morphological changes in the presynaptic mossy fiber terminals (MFT) that form excitatory synaptic contacts with the proximal CA3 apical dendrites. One effect, synaptic vesicle depletion, occurs in diabetes as well as after repeated stress and Cort treatment. However, diabetes produced other MFT structural changes that differ qualitatively and quantitatively from other treatments. Furthermore, whereas 7 d of repeated stress was insufficient to produce dendritic or synaptic remodeling in nondiabetic rats, it potentiated both dendritic atrophy and MFT synaptic vesicle depletion in STZ rats. These changes occurred in concert with adrenal hypertrophy and elevated basal Cort release as well as hypersensitivity and defective shutoff of Cort secretion after stress. Thus, as an endogenous stressor, STZ diabetes not only accelerates the effects of exogenous stress to alter hippocampal morphology; it also produces structural changes that overlap only partially with those produced by stress and Cort in the nondiabetic state.

Differential effects of restraint stress on hippocampal 5-HT metabolism and extracellular levels of 5-HT in streptozotocin-diabetic rats

Streptozotocin (STZ)-elicited diabetes reduces central serotonin (5-hydroxytryptamine, 5-HT) synthesis/metabolism, but whether this reduction leads to decreased release of 5-HT has only scarcely been investigated. We have thus analysed the impact of STZ diabetes on hippocampal extracellular 5-HT levels both under basal conditions and during restraint stress, a procedure known to stimulate hippocampal 5-HT synthesis/metabolism and release. The pretreatment with STZ (3 weeks beforehand) and the 1 h restraint session respectively decreased and increased hippocampal 5-HT metabolism, as assessed by tissue analysis of 5-HT and 5-hydroxyindoleacetic acid. On the other hand, hippocampal microdialysis revealed no difference in basal levels of extracellular 5-HT levels in (conscious) vehicle- and STZ-pretreated rats, but a differential effect of restraint. Thus, extracellular 5-HT levels increased throughout restraint (maximal increase: 194%) in vehicle-, but not in STZ-pretreated rats. In the latter rat group, plasma corticosterone levels were, however, increased, thus indicating a significant aversiveness to stress. Lastly, because anxiety-related behaviours may be affected by hippocampal serotonergic systems, resting and restrained vehicle- and STZ-pretreated rats were compared (immediately after stress) in an elevated plus-maze of anxiety. Pretreatment with STZ reduced the percent number of open arm entries and the number of closed arm entries, indicating increased anxiety and reduced locomotor activity, respectively. Restraint tended to increase anxiety-related behaviours in all rats, but this trend never reached significance. Our results confirm that gross analyses of 5-HT metabolism do not yield information on 5-HT release, and suggest that the prevalence of diabetes among patients suffering affective disorders could be related to the lack of hippocampal serotonergic response to aversive stimuli.

The reduction of antinociceptive effect of morphine administered intraventricularly is correlated with the decrease of serotonin release from the spinal cord in streptozotocin-induced diabetic rats

1. The antinociceptive effect of morphine (25 micrograms) administered into the 3rd ventricle was significantly attenuated in streptozotocin-induced diabetic rats as measured by the tail-flick assay. 2. The release of serotonin (5-HT; 5-hydroxytryptamine) from the spinal cord caused by intraventricular injection of morphine (25 micrograms) was significantly reduced in streptozotocin-induced diabetic rats. 3. No differences of 5-HT contents of the spinal cord (lumbar cord) between streptozotocin-induced diabetic- and vehicle-treated rats were found. 4. It is concluded that the reduction of antinociception produced by intraventricular injection of morphine in streptozotocin-induced diabetic rats might be, at least partly, due to the decrease of 5-HT release from the spinal cord.