Denervation and hyperinnervation in the nervous system of diabetic animals. II. Monoaminergic and peptidergic alterations in the diabetic encephalopathy

Insulin effects on core neurotransmitter pathways involved in schizophrenia neurobiology: a meta-analysis of preclinical studies. Implications for the treatment

Impairment of insulin action and metabolic dysregulation have traditionally been associated with schizophrenia, although the molecular basis of such association remains still elusive. The present meta-analysis aims to assess the impact of insulin action manipulations (i.e., hyperinsulinemia, hypoinsulinemia, systemic or brain insulin resistance) on glutamatergic, dopaminergic, γ-aminobutyric acid (GABA)ergic, and serotonergic pathways in the central nervous system. More than one hundred outcomes, including transcript or protein levels, kinetic parameters, and other components of the neurotransmitter pathways, were collected from cultured cells, animals, or humans, and meta-analyzed by applying a random-effects model and adopting Hedges'g to compare means. Two hundred fifteen studies met the inclusion criteria, of which 180 entered the quantitative synthesis. Significant impairments in key regulators of synaptic plasticity processes were detected as the result of insulin handlings. Specifically, protein levels of N-methyl-D-aspartate receptor (NMDAR) subunits including type 2A (NR2A) (Hedges' g = -0.95, 95%C.I. = -1.50, -0.39; p = 0.001; I2 = 47.46%) and 2B (NR2B) (Hedges'g = -0.69, 95%C.I. = -1.35, -0.02; p = 0.043; I2 = 62.09%), and Postsynaptic density protein 95 (PSD-95) (Hedges'g = -0.91, 95%C.I. = -1.51, -0.32; p = 0.003; I2 = 77.81%) were found reduced in insulin-resistant animal models. Moreover, insulin-resistant animals showed significantly impaired dopamine transporter activity, whereas the dopamine D2 receptor mRNA expression (Hedges'g = 3.259; 95%C.I. = 0.497, 6.020; p = 0.021; I2 = 90.61%) increased under insulin deficiency conditions. Insulin action modulated glutamate and GABA release, as well as several enzymes involved in GABA and serotonin synthesis. These results suggest that brain neurotransmitter systems are susceptible to insulin signaling abnormalities, resembling the discrete psychotic disorders' neurobiology and possibly contributing to the development of neurobiological hallmarks of treatment-resistant schizophrenia.

The neuropeptide substance P/neurokinin-1 receptor system and diabetes: From mechanism to therapy

Diabetes is a significant public health issue known as the world's fastest-growing disease condition. It is characterized by persistent hyperglycemia and subsequent chronic complications leading to organ dysfunction and, ultimately, the failure of target organs. Substance P (SP) is an undecapeptide that belongs to the family of tachykinin (TK) peptides. The SP-mediated activation of the neurokinin 1 receptor (NK1R) regulates many pathophysiological processes in the body. There is also a relation between the SP/NK1R system and diabetic processes. Importantly, deregulated expression of SP has been reported in diabetes and diabetes-associated chronic complications. SP can induce both diabetogenic and antidiabetogenic effects and thus affect the pathology of diabetes destructively or protectively. Here, we review the current knowledge of the functional relevance of the SP/NK1R system in diabetes pathogenesis and its exploitation for diabetes therapy. A comprehensive understanding of the role of the SP/NK1R system in diabetes is expected to shed further light on developing new therapeutic possibilities for diabetes and its associated chronic conditions.

Understanding the relevance of herb-drug interaction studies with special focus on interplays: a prerequisite for integrative medicine

Integrative medicine refers to the blending of conventional and evidence-based complementary medicines and therapies with the aim of using the most appropriate of either or both modalities for ultimate patient benefits. One of the major hurdles for the same is the chances of potential herb–drug interactions (HDIs). These HDIs could be beneficial or harmful, or even fatal; therefore, a thorough understanding of the eventualities of HDIs is essential so that a successful integration of the modern and complementary alternative systems of medicine could be achieved. Here, we summarize all the important points related to HDIs, including types, tools/methods for study, and prediction of the HDIs, along with a special focus on interplays between drug metabolizing enzymes and transporters. In addition, this article covers future perspective, with a focus on background endogenous players of interplays and approaches to predict the drug–disease–herb interactions so as to fetch the desired effects of these interactions.

Painful neuropathy: Mechanisms

Painful neuropathy, like the other complications of diabetes, is a growing healthcare concern. Unfortunately, current treatments are of variable efficacy and do not target underlying pathogenic mechanisms, in part because these mechanisms are not well defined. Rat and mouse models of type 1 diabetes are frequently used to study diabetic neuropathy, with rats in particular being consistently reported to show allodynia and hyperalgesia. Models of type 2 diabetes are being used with increasing frequency, but the current literature on the progression of indices of neuropathic pain is variable and relatively few therapeutics have yet been developed in these models. While evidence for spontaneous pain in rodent models is sparse, measures of evoked mechanical, thermal and chemical pain can provide insight into the pathogenesis of the condition. The stocking and glove distribution of pain tantalizingly suggests that the generator site of neuropathic pain is found within the peripheral nervous system. However, emerging evidence demonstrates that amplification in the spinal cord, via spinal disinhibition and neuroinflammation, and also in the brain, via enhanced thalamic activity or decreased cortical inhibition, likely contribute to the pathogenesis of painful diabetic neuropathy. Several potential therapeutic strategies have emerged from preclinical studies, including prophylactic treatments that intervene against underlying mechanisms of disease, treatments that prevent gains of nociceptive function, treatments that suppress enhancements of nociceptive function, and treatments that impede normal nociceptive mechanisms. Ongoing challenges include unraveling the complexity of underlying pathogenic mechanisms, addressing the potential disconnect between the perceived location of pain and the actual pain generator and amplifier sites, and finding ways to identify which mechanisms operate in specific patients to allow rational and individualized choice of targeted therapies.

Sympathetic axonopathies and hyperinnervation in the small intestine smooth muscle of aged Fischer 344 rats

It is well documented that the intrinsic enteric nervous system of the gastrointestinal (GI) tract sustains neuronal losses and reorganizes as it ages. In contrast, age-related remodeling of the extrinsic sympathetic projections to the wall of the gut is poorly characterized. The present experiment, therefore, surveyed the sympathetic projections to the aged small intestine for axonopathies. Furthermore, the experiment evaluated the specific prediction that catecholaminergic inputs undergo hyperplastic changes. Jejunal tissue was collected from 3-, 8-, 16-, and 24-month-old male Fischer 344 rats, prepared as whole mounts consisting of the muscularis, and processed immunohistochemically for tyrosine hydroxylase, the enzymatic marker for norepinephrine, and either the protein CD163 or the protein MHCII, both phenotypical markers for macrophages. Four distinctive sympathetic axonopathy profiles occurred in the small intestine of the aged rat: (1) swollen and dystrophic terminals, (2) tangled axons, (3) discrete hyperinnervated loci in the smooth muscle wall, including at the bases of Peyer's patches, and (4) ectopic hyperplastic or hyperinnervating axons in the serosa/subserosal layers. In many cases, the axonopathies occurred at localized and limited foci, involving only a few axon terminals, in a pattern consistent with incidences of focal ischemic, vascular, or traumatic insult. The present observations underscore the complexity of the processes of aging on the neural circuitry of the gut, with age-related GI functional impairments likely reflecting a constellation of adjustments that range from selective neuronal losses, through accumulation of cellular debris, to hyperplasias and hyperinnervation of sympathetic inputs.

Quantifying nerve architecture in murine and human airways using three-dimensional computational mapping

The quantitative histological analysis of airway innervation using tissue sections is challenging because of the sparse and patchy distribution of nerves. Here we demonstrate a method using a computational approach to measure airway nerve architecture that will allow for more complete nerve quantification and the measurement of structural peripheral neuroplasticity in lung development and disease. We demonstrate how our computer analysis outperforms manual scoring in quantifying three-dimensional nerve branchpoints and lengths. In murine lungs, we detected airway epithelial nerves that have not been previously identified because of their patchy distribution, and we quantified their three-dimensional morphology using our computer mapping approach. Furthermore, we show the utility of this approach in bronchoscopic forceps biopsies of human airways, as well as the esophagus, colon, and skin.

Hypothesis: Intensive insulin therapy-induced mortality is due to excessive serotonin autoinhibition and autonomic dysregulation

Action to Control Cardiovascular Risk in Diabetes (ACCORD), The Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation and the Veterans Affairs Diabetes Trial were designed to study whether older patients with type 2 diabetes mellitus could reduce the risk of heart attacks and stroke and thereby prolong their lives by maintaining their blood glucose levels at near-healthy levels but failed to demonstrate the hoped-for benefit. Why the trials failed, though, and why ACCORD saw significantly more deaths due to increased rates of cardiovascular events in the intensive therapy arm of the study are not clear. These data have now been confirmed by the results of the recently concluded NICE-SUGAR Study which again revealed that intensive glucose control increased mortality among adults in intensive care units. I propose that the negative results noted in these trials are due to altered brain serotonin concentrations and autonomic dysregulation in addition to the low-grade systemic inflammation, decreased endothelial nitric oxide and enhanced free radical generation, diminished anti-oxidant defenses and altered metabolism of essential fatty acids present in patients with type 2 diabetes.

Concurrent activation of the somatosensory forebrain and deactivation of periaqueductal gray associated with diabetes-induced neuropathic pain

We combined behavioral testing with brain imaging using (99m)Tc-HMPAO (Amersham Health) to identify CNS structures reflecting alterations in pain perception in the streptozotocin (STZ) model of type I diabetes. We induced diabetic hyperglycemia (blood glucose >300 mg/dl) by injecting male Sprague-Dawley rats with STZ (45 mg/kg i.p.). Four weeks after STZ-diabetic rats exhibited behaviors indicative of neuropathic pain (hypersensitivity thermal stimuli) and this hypersensitivity persisted for up to 6 weeks. Imaging data in STZ-diabetic rats revealed significant increases in the activation of brain regions involved in pain processing after 6 weeks duration of diabetes. These regions included secondary somatosensory cortex, ventrobasal thalamic nuclei and the basolateral amygdala. In contrast, the activation in habenular nuclei and the midbrain periaqueductal gray were markedly decreased in STZ rats. These data suggest that pain in diabetic neuropathy may be due in part to hyperactivity in somatosensory structures coupled with a concurrent deactivation of structures mediating antinociception.

Potential mechanisms of neuropathic pain in diabetes

Abnormal sensations and pain are features of approximately 10% of all cases of diabvetic neuropathy and can cause marked diminution in the quality of life for these patients. The quality and distribution of pain are variable, although descriptions of burning pain in the hands and feet are commonly reported. Like other neuropathic pain states, painful diabetic neuropathy has an unknown pathogenesis and, in many cases, is not alleviated by nonsteriodal anti-inflammatory drugs or opiates. In the last decase, a number of behavioral and physiologic studies have revealed indices of sensory dysfunction in animal models of diabetes. These include hyperalgesia to mechanical and noxious chemical stimuli and allodynia to light touch. Animal models of painful diabetic neuropathy have been used to investigate the therapeutic potential of a range of experimental agents and also to explore potential etiologic mechanisms. There is relatively little evidence to suggest that the peripheral sensory nerves of diabetic rodents exhibit spontaneous activity or increased responsiveness to peripheral stimuli. Indeed, the weight of eveidence suggests that sensory input to the spinal cord is decreased rather than increased in diabetic rodents. Aberrant spinal or supraspinal modulation of sensory processing may therefore be involved in generating allodynia and hyperalgesia in these models. Studies have supported a role for spinally mediated hyeralgesia in diabetic rats that may reflect either a response to diminished peripheral input or a consequence of hyperglycemia on local or descending modulatory systems. Elucidating the affects of diabetes on spinal sensory processing may assist development of novel therapeutic strategies for preventing and alleviating painful diabetic neuropathy.

Elevated substance-P-like immunoreactivity levels in spinal dialysates during the formalin test in normal and diabetic rats

Pharmacologic studies implicate the involvement of substance P in spinal nociceptive processing during the formalin test. However, no direct measurement of the temporal changes in substance P levels within the spinal cord of conscious animals has been reported. Further, dissociation between substance P levels and formalin-evoked nocifensive behavior may exist in diabetic rats, as exaggerated hyperalgesic behavior coexists with reduced peripheral nerve substance P levels. The present study was performed to directly measure the appearance of substance-P-like immunoreactivity (SP-LI) in spinal CSF of conscious, unrestrained rats using microdialysis techniques following injection of formalin into the hindpaw. The effect of diabetes upon formalin-evoked SP-LI levels in spinal CSF dialysates was also determined. In control rats, SP-LI increased in spinal dialysates following formalin injection and levels were maximal 20-30 min after injection, rising to 325% of basal values (p<0.02). Diabetic rats exhibited reduced (p<0.05) SP-LI in their spinal roots, while basal levels in spinal CSF were not different from controls. Formalin-evoked nocifensive behavior was increased in diabetic rats but SP-LI levels in spinal CSF dialysates after paw formalin injection were significantly (p<0.05) attenuated, reaching a maximum of only 161% of basal levels. This was accompanied by attenuated swelling at the formalin injection site and increased thermal response latencies. While increased SP-LI in spinal CSF coincides with phase 2 behavior in the formalin test and may contribute to spinal nociceptive processing during this period, exaggerated spinal substance P release is unlikely to underlie the increased nocifensive behavior seen in diabetic rats.

The impact of diabetes on CNS. Role of bioenergetic defects

To address the problem of the pathogenesis in diabetic neuropathy, rats were made diabetic by streptozotocin administration, and discrete brain regions, such as cortex, cerebellum, brainstem, thalamus, and hypothalamus, were sampled for assay of activities of electron transport chain complexes I-IV at 1 and 3 mo after induction of diabetes. Significant decrease was seen in activities of dinitrophenylhydrazine DNPH-coenzyme Q reductase (complex I), coenzyme Q cytochrome-c reductase (complex III), and cytochrome-c oxidase (complex IV) from discrete brain regions with more pronounced changes in complex I. The decline in the complex I, III, and IV activity was more severe in the 3-mo group. Succinate dehydrogenase (SDH) coenzyme Q reductase (complex II), which is an enzyme shared by tricarboxylic acid (TCA) cycle and electron transport chain, showed a significant increase under the same set of conditions. These results suggest that the bioenergetic impairment has an important role in the pathophysiology of diabetes.

Exposure to perinatal morphine promotes developmental changes in rat striatum

This study shows that perinatal exposure to morphine promotes developmental changes (up to 8 months of life) in the striatum by up-regulating concentrations of substance P and met-enkephalin with changes of prometenkephalin A mRNA expression at the day of birth only. Dopamine metabolism (up to 60 days) is also increased as suggested by the reduced concentrations of dopamine and increased content of 3,4-dihydroxyphenylacetic acid. Tyrosine hydroxylase mRNA expression is selectively reduced only in the substantia nigra by perinatal morphine. Serotonin content is reduced only during the early postnatal days and is unaffected thereafter. Supplementation of naltrexone to morphine-exposed rats prevents monoaminergic and neuropeptidergic changes in the striatum, which directly implicates opioid receptors in the developmental changes caused by morphine. The data suggest that perinatal morphine may inhibit met-enkephalin release, causing accumulation of the peptide without corresponding changes in specific mRNA. Dopamine release may also be increased as indicated by a higher metabolism and consequent reduction of tyrosine hydroxylase mRNA expression in the substantia nigra.

Perinatal exposure to morphine: reactive changes in the brain after 6-hydroxydopamine

The effects of neonatal 6-hydroxydopamine treatment on the brain of control rats and of rats perinatally exposed to morphine were examined. Noradrenaline levels were increased in the pons-medulla, mesencephalon and caudate of 8-week-old control rats lesioned with neonatal 6-hydroxydopamine; perinatal morphine treatment prevented such an increase. In the caudate, there was a loss of dopamine and an increase of serotonin following the neurotoxic lesion; exposure to perinatal morphine prevented the serotonin increase. Brain expression of synapsin I mRNA was particularly abundant in cerebral cortex, hippocampus, dentate gyrus and olfactory bulb. In perinatal morphine-treated rats, the expression of synapsin I mRNA was significantly reduced; interestingly, the neonatal treatment with 6-hydroxydopamine normalized its expression. Therefore, brain-reactive neurochemical changes triggered by 6-hydroxydopamine were suppressed by perinatal morphine exposure whereas the association of morphine exposure and 6-hydroxydopamine lesion promoted the normal mRNA expression of the synaptic marker synapsin I.

Perinatal morphine II: changes in cortical plasticity

We have previously shown that perinatal exposure to morphine impairs reactive plasticity of serotonin (5-HT) neurons following selective neonatal lesion (Gorio et al., J Neurosci Res 34:462-471, 1993). This study shows that morphine inhibits also that the compensatory sprouting of intact axons after partial denervation. Neonatal 6-OHDA injection causes norepinephrine (NE) depletion in the frontal cortex, which triggers a compensatory increase of dopamine, serotonin (5-HT), and met-enkephalin content correlated by the increased density of tyrosine hydroxylase- and 5-HT-positive axons. In perinatal morphine-treated rats, no compensatory changes are observed after neonatal 6-OHDA depletion of NE in the frontal cortex.

Perinatal morphine. I: Effects on synapsin and neurotransmitter systems in the brain

We have previously shown that rat perinatal exposure to morphine causes dopaminergic and met-enkephalin (ME) and substance P (SP) changes in the striatum during the early postnatal period (Tenconi et al.: Int J Dev Neurosci 10: 517 - 526, 1992); in addition it increases the susceptibility to neurotoxic lesions and impairs regenerative capacity of the serotoninergic system (Gorio et al.: J Neurosci Res 34: 462 - 471, 1993). Our study shows that ME and SP levels increase postnatally in several areas of the rat brain, reaching the highest values between 30 and 60 days, after which the peptide content subsides to lower levels. Perinatal exposure to morphine increases such ME and SP levels during the early stages of postnatal life. No effect of morphine on 5-HT and NE is observed, while the dopaminergic system is mainly affected in the mesencephalon. The pre- and postnatal brain expression of synapsin I mRNA is gradually and progressively localized in discrete areas of the brain. In the brain of rats perinatally exposed to morphine, the abundance of synapsin I mRNA expression is markedly reduced. Therefore, perinatal exposure to morphine affects early postnatal synaptic development in the brain as shown by the altered peptidergic and monoaminergic content and by the reduced synapsin I mRNA expression.

Norepinephrine and epinephrine levels in the brain of alloxan diabetic rats

Thirty days after induction of experimental diabetes the brain catecholamines namely, norepinephrine (NE) and epinephrine (E) were studied in discrete brain regions (striatum, hippocampus, hypothalamus, midbrain, pons and medulla, cerebellum and cerebral cortex) in control, alloxan-diabetic untreated and insulin-treated diabetic rats. E showed significant increase in striatum, hippocampus and hypothalamus, whereas NE was increased in hypothalamus, and decreased in pons and medulla significantly in untreated diabetic rats. These effects were not seen in the insulin-treated diabetic rats.

Diabetic neuropathy in the rat: 1. Alcar augments the reduced levels and axoplasmic transport of substance P

This study examined the sciatic nerve axonal transport of substance P-like immunoreactivity (SPLI) and its basal content in stomach, sciatic nerve and lumbar spinal cord of 8- and 12-week alloxan-diabetic rats, respectively. One group of diabetic rats received acetyl-l-carnitine (ALCAR) throughout the experimental period. Alloxan treatment caused hyperglycemia and reduced boy growth. Axonal transport of SPLI was studied by measurement of 24-hour accumulation at a ligature on the sciatic nerve. There was a marked reduction (from 50% to 100% according to the nerve segment examined) of anterograde and retrograde accumulation of SPLI in the constricted nerve of 8-week diabetic rats. In the sciatic nerve of ALCAR-treated diabetic rats, the accumulation of SPLI was comparable to control values. In the sciatic nerve, lumbar spinal cord and stomach of 12-week diabetic rats, there is a significant reduction of SPLI content. ALCAR treatment prevented SPLI loss in these tissues. Sciatic nerves showed the typical sorbitol increase and myo-inositol loss that were significantly counteracted by ALCAR. This study suggests that ALCAR treatment prevents diabetes-induced sensory neuropathy by improving altered metabolic pathways such as polyol activity and myo-inositol synthesis, and by preventing the reduction of synthesis and axonal transport of substance P.

Changes in glucose metabolism from discrete regions of rat brain and its relationship to reproductive failure during experimental diabetes

This study reports the effects of alloxan induced diabetes on glucose metabolism enzymes viz. Hexokinase, Lactate dehydrogenase, and Glucose-6-phosphate dehydrogenase from discrete brain regions. Enzymes activity was assayed from hypothalamic areas such as medial preoptic area and median eminence-arcuate region which have gonadotropin releasing hormone cell bodies and their terminals, respectively and other brain regions like septum, amygdala, hippocampus, and thalamus. In all the areas studied, induction of diabetes resulted in a significant decrease in particulate bound HK activity, whereas soluble HK, LDH and G6PDH activity showed increase at 3, 8, 15 and 28 days intervals. Insulin treatment of diabetic rats led to recovery in enzyme activity. Blood glucose levels increased significantly after induction of diabetes and recovery was seen after insulin treatment. The present results suggest that altered cerebral glucose metabolism may also be responsible for reproductive failure observed in diabetic rats.

Changes in sensory neuropeptides in dorsal root ganglion and spinal cord of spontaneously diabetic BB rats. A quantitative immunohistochemical study

This study examined the expression of the sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), in the lumbar 4 and 5 dorsal root ganglion (DRG) and spinal cord of spontaneously diabetic BB rats and non-diabetic controls using quantitative immunohistochemical analysis. In both animal groups immunoreactivities for CGRP and SP were widely distributed within the neurons of DRG and in nerve fibres of the dorsal spinal cord. Image analysis of each neuropeptide subpopulation in the DRG showed that in diabetic rats the cell diameter of immunostained CGRP neurons was significantly decreased compared with controls, while no difference could be found for SP-immunoreactive (IR) neurons. The decrease in the CGRP-IR cell diameter appeared to occur mainly in medium to large neurons (30-50 microns diameter; 2.2% controls, < 1% diabetes), this change being parallel to an increased frequency of small-size neurons (< 20 microns diameter) in diabetic rats (62% controls, 69% diabetes; P < 0.05). However, there was no statistical difference in the total number of cells immunostained for either CGRP or SP between control and diabetic rats. The ratio of CGRP or SP neurons compared to total cells in the ganglion was similar in control and diabetic groups. No difference could be observed for peptide immunoreactivity in the dorsal and ventral horns of either control or diabetic animals. The observed changes of perikaryal size in diabetic rats might relate to the reduced axonal calibre and conduction velocity observed in these animals, and indicate that subpopulations of sensory neurons are affected differently by diabetes.

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.

Effect of alloxan-induced diabetes on acetylcholinesterase activity from discrete areas of rat brain

The effect of experimental diabetes induced in rats was examined in brain areas like the septum, medial preoptic area, median eminence-arcuate region, amygdala, thalamus, hippocampus, pons and medulla. In all the areas studied, acute hyperglycemia caused an increase in the activity of acetylcholinesterase, the degradative enzyme of cholinergic system, whereas insulin administration reversed this effect. These findings suggest that the dysfunction of cholinergic system may also be involved in the diabetes associated CNS complications.

Effect of diabetes on levels of lipid peroxides and glycolipids in rat brain

The effects of diabetes on levels of lipid peroxides and glycolipids in brain were studied in alloxan (18 mg/100 g body weight) diabetic rats. Free fatty acid (FFA) and malondialdehyde (MDA) levels were increased in the brains of diabetic animals. On the other hand, activities of the antioxidative enzymes catalase and superoxide dismutase (SOD) were decreased. The study also showed elevated levels of most of the glycolipid fractions except gangliosides, which were found to decrease in diabetic brain. Administration of insulin to diabetic animals results in the restoration of these parameters to normal levels. These changes observed in diabetic brain may be responsible for the increased frequency of stroke in diabetes.

Perinatal morphine treatment inhibits pruning effect and regeneration of serotoninergic pathways following neonatal 5,7-HT lesions

Lesion of the serotoninergic system in neonate rats is an ideal model for assessing the activity of chemical substances capable of affecting neuronal plasticity and regeneration (Jonsson et al., Dev Brain Res 16: 171-180, 1984). Treatment of newborn rats within 6 hr from birth with the selective neurotoxin 5,7-dihydroxytryptamine causes degeneration of the most distal serotoninergic axons. In our experimental conditions we have observed that after such neurotoxic treatment there is spinal cord denervation, which is particularly remarkable in the lumbar segment. This degenerative event is followed by gradual regeneration of the lesioned axons, with good reinnervation of the entire cord within 8 weeks. The degeneration-regeneration process is correlated with a transient hyperinnervation of the pons-medulla and hypothalamus by the short collaterals (pruning effect), as evidenced by increased serotonin content. Perinatal morphine exposure markedly impairs serotonin regeneration in the spinal cord. In addition, opiate treated rats are more susceptible to lesions, as shown by the neurotoxin induced denervation of the cortex, pons-medulla, and hypothalamus, which does not occur in lesioned controls. Therefore, our observations suggest that perinatal exposure to morphine affects the plasticity and regeneration of the developing serotoninergic system by increasing its susceptibility to neurotoxic lesions and reducing its regenerative capacity.

Diabetes-induced alterations of central nervous system G proteins. ADP-ribosylation, immunoreactivity, and gene-expression studies in rat striatum

Previous studies from our laboratory have suggested that diabetes-associated central nervous system abnormalities are characterized by progressive alterations of neurotransmitters and of transductional Gi/Go proteins. In this study, we have further characterized these abnormalities in the striatum of alloxan-diabetic rats by means of adenosine 5'-diphosphate (ADP)-ribosylation, and Western and Northern blotting techniques. Fourteen weeks after diabetes induction, pertussis-toxin (PTX) catalyzed ADP-ribosylation of Gi/Go proteins was markedly reduced in diabetic animals, as shown by a clear decrease of 32P-ADPribose incorporation into G protein alpha subunits. In agreement with our previous pharmacological studies that showed a reduction of Gi-mediated modulation of adenylate cyclase activity only at this stage of diabetes, no changes in PTX-mediated ADP-ribosylation were observed earlier (5-wk diabetes). Immunoblotting studies performed by using antibodies selectively raised against Gi-2, Go, and Gs proteins did not reveal any differences between control and diabetic animals at any stage of diabetes. Similarly, the mRNAs corresponding to the alpha subunits of Gi-2, Go, and Gs proteins did not show any marked changes in chronic diabetic rats with respect to control animals. It is therefore concluded that diabetes is associated with development of a time-related alteration of cerebral Gi/Go proteins and that this defect is not owing to gross changes in either content of G proteins or mRNA level, but probably reflects modifications of G protein's structure or physiological status affecting the coupling with membrane effector systems and the sensitivity to PTX.

Early alterations of Gi/Go protein-dependent transductional processes in the retina of diabetic animals

The early alterations of G-protein-dependent transductional mechanisms have been characterized in the retina of alloxan-treated diabetic rats. Five weeks after alloxan injection, pertussis toxin radiolabeling of Gi/Go proteins was markedly reduced in the retina of diabetic animals, suggesting either a reduced expression and/or the presence of some structural modification of these G-protein subtypes. The functional activity of Gs proteins, measured as stimulation of membrane adenylate cyclase by dopamine, did not seem to be impaired at this stage of the pathology; basal adenylate cyclase activity was indeed increased in diabetic rats, consistent with the observed reduction of Gi/Go inhibitory proteins. Such functional alterations of the cAMP producing system were causally related to diabetes induction, since they were reversed by treatment of diabetic animals with insulin. These results suggest that G-protein dependent transduction mechanisms are altered in the retina of diabetic animals, and that a defect of Gi/Go proteins could represent an early transductional damage in the development of diabetic retinopathy.

Denervation and hyperinnervation in the nervous system of diabetic animals: III. Functional alterations of G proteins in diabetic encephalopathy

G protein-mediated effects on cAMP production were evaluated in the corpus striatum of diabetic rats 5 and 14 weeks after alloxan injection by measuring both D1-receptor-induced stimulation and D2-receptor-mediated inhibition of adenylate-cyclase activity. At 5 weeks of diabetes, no obvious alterations of G protein functions were detected. Both dopamine-stimulated adenylate cyclase and bromocriptine-induced inhibition of enzyme activity were indeed similar in control and diabetic animals. Fourteen weeks after alloxan injection, profound alterations were observed. Dopamine-stimulated cAMP production was markedly increased in diabetic rats, whereas bromocriptine ability to reduce cAMP formation was almost abolished at this late stage of diabetes. Hypoactivity of Gi/Go proteins was also confirmed by the reduced ability of the GTP non-hydrolyzable analog GTP-gamma-S to inhibit forskolin-stimulation of adenylate cyclase. These results show an apparent functional imbalance between Gs and Gi/Go-mediated transduction mechanisms, with an increased efficacy of Gs activity likely due to the loss of Gi/Go inhibitory functions. Concomitantly with such transductional alteration detected in chronic diabetes, we observed a marked increase of the striatal content of met-enkephalin, which is known to utilize Gi/Go proteins for inhibition of adenylate cyclase. The measurement of other transmitters (vaso-active intestinal peptide, substance P, serotonin, noradrenaline, and dopamine) did not reveal any difference with respect to controls. The observed transductional defect in diabetic animals and the increased content and/or hyperinnervation by the metenkephalinergic system could be correlated as mutual compensatory mechanisms.

Denervation and hyperinnervation in the nervous system of diabetic animals. I. The autonomic neuronal dystrophy of the gut

Peripheral neuropathy is a correlate of experimental diabetes induced in rats by means of a single injection of alloxan. The autonomic and enteric innervation of the gut are profoundly affected in the small intestine of such animals. A complex process of denervation and hyperinnervation of the gut wall of diabetic animals is observed. It was previously reported that the cholinergic parasympathetic innervation of the intestine is markedly reduced. We have found that noradrenergic sympathetic axons hyperinnervate the duodenum of diabetic rats, whereas noradrenaline levels are significantly reduced in the jejunum. The putative enteric neurotransmitter dopamine is also present in higher levels in the duodenum. The intrinsic peptidergic neurons of the gut are deeply affected as well in diabetic rats. Substance P and met-enkephalin content are remarkably reduced throughout the small intestine, whereas vasoactive intestinal polypeptide levels (VIP) are significantly increased in the duodenum. Indeed, immunocytochemical staining of the ileum did reveal hypertrophy of VIP-positive axons in diabetic rats. The intrinsic serotoninergic innervation of the gut is apparently unaffected. Our results indicate that the changes of gut innervation observed in experimental diabetes are consistent with increased content and also likely with hyperinnervation by the neuronal systems involved in smooth muscle relaxation and decreased content and with denervation by those systems with smooth muscle contraction properties. Such a perturbed gut innervation may be responsible of the gastrointestinal dysfunctions that are among the most common complications of diabetes.