Reduced Ia-afferent-mediated Hoffman reflex in streptozotocin-induced diabetic rats.

In addition to reduced nerve conduction velocity, diabetic neuropathic patients often exhibit a reduction in the amplitude of the compound muscle action potential elicited by stimulation of the Ia-afferent-mediated reflex pathway (Hoffman or H wave) that can contribute to diminished or absent tendon reflexes. In contrast to nerve conduction velocity deficits, changes in H-wave amplitudes have not been reproduced in diabetic animal models. Using electrophysiological techniques developed for repeated recordings in individual animals, we report H-wave deficits in streptozotocin (STZ)-treated insulin-dependent diabetic rats. After 4 weeks of diabetes induced by STZ treatment, a 47% reduction in the H-wave amplitude was demonstrated by recording compound muscle action potentials in foot muscles after stimulation of Ia afferents. Interestingly, we also demonstrate that the H-wave amplitude gradually recovers to a 26% deficit after 12 weeks of experimental diabetes. The recovery of the H wave in STZ-treated rats distinguishes this deficit mechanistically from other STZ-induced electrophysiological changes and may model a similar recovery of the H wave reported in diabetic patients.     

Attenuation of the afferent limb of the baroreceptor reflex in streptozotocin-induced diabetic rats

Diabetic autonomic neuropathy is a common complication following prolonged diabetes. Alterations of cardiovascular reflexes contribute to the increased cardiovascular morbidity and mortality seen in diabetic patients. This study sought to better characterize these complications by investigating the afferent limb of the baroreceptor reflex in an experimental rat model of diabetes. Streptozotocin (STZ)-induced diabetic and euglycemic control rats were studied at 8- and 16-week time points after initiation of the experiment. Activation of the afferent limb of the baroreceptor reflex was assessed by measuring the numbers of c-Fos-immunoreactive (ir) neurons in the CNS site of termination of the baroreceptor afferent neurons, the nucleus of the solitary tract (NTS). Initial experiments established that baseline cardiovascular parameters and NTS expression of c-Fos-ir neurons were not different between diabetic and control rats at either time point. Phenylephrine (PE)-induced activation of baroreceptors resulted in a significant elevation in the numbers of c-Fos-ir neurons in the NTS of control rats. Although diabetic rats showed similar pressor responses to PE, the activation of c-Fos-ir neurons in the NTS of diabetic rats was significantly attenuated. At both 8 and 16 weeks, STZ-induced diabetic rats had significantly fewer c-Fos-ir neurons in the commissural NTS and in the caudal subpostrernal NTS when compared to the non-diabetic control animals receiving PE. These data suggest that STZ-induced diabetes, for a period of 8 and 16 weeks, results in reduced activity in the afferent baroreceptor input to the NTS, and are consistent with diabetes-induced damage to baroreceptor afferent nerves.     

Timing behavior in streptozotocin-induced diabetic rats

There is evidence of deterioration of spatial cognition in streptozotocin (STZ)-induced diabetic rats. Here, we evaluate a possible dissociation in the cognitive deficits due to diabetes by examining another crucial aspect of animal cognition: temporal perception. Timing behavior and temporal memory were evaluated in STZ-induced diabetic rats employing two timing tasks: the peak-interval procedure, with its Gap variant, and the interval bisection task. A spatial memory task, rewarded alternation in the T-maze, was also evaluated to explore spatial cognition. The two timing tasks employed coincide in the finding of a normal timing performance in STZ-induced diabetic rats. The peak-interval procedure provided results that suggest that the timing behavior is equally accurate and precise than in control subjects; in the Gap procedure, an equal change in peak time in both groups indicates that temporal working memory is also intact. In the interval bisection task, we analyzed the acquisition of a temporal discrimination and the sensitivity to changes in the duration of the stimulus; no differences were found in either the acquisition process or the sensitivity index. In contrast, in the rewarded alternation task, STZ-induced diabetic rats exhibited a significant deficit in spatial cognition. The cognitive processes involved in timing behavior and temporal memory are not deteriorated as a consequence of diabetes; the cognitive deficits associated to diabetes thus seem to be restricted to the spatial domain.     

Temporal course of streptozotocin-induced diabetic polyneuropathy in rats

The temporal course of diabetic polyneuropathy in a rat model plays a critical role in studies on diabetic polyneuropathy treatment. In this study, the temporal course of neuropathic symptoms was investigated in diabetic rats induced by streptozotocin and evaluated by nerve conduction velocity and behavioral assays, including the von Frey test for mechanical allodynia and the hot plate test for hyperalgesia. The results revealed that both mechanical allodynia and heat hyperalgesia started on the 2nd week, while nerve conduction velocity significantly decreased from the 1st week. In addition, the severity of allodynia did not change after the 3rd week. Hyperalgesia and nerve conduction velocity progressively aggravated even to the 8th week. Transmission electron microscopy showed that loss of unmyelinated axons, loosening of the myelin structure, and thickening of the perineurium layer were visible from the 4th week and worsened on the 8th week. Differences in the temporal course of neuropathic symptoms are discussed.     

Ultrastructural changes in the atrioventricular valves of streptozotocin-induced diabetic rats

The present study describes ultrastructural changes in the atrioventricular (AV) valves of diabetic rats at 3, 6, 9 and 12 months. At 3 and 6 months of diabetes, the interstitial cells were characterized by an accumulation of vacuoles, lysosomes, electron-dense vesicles, mitochondria and cisternae of rough endoplasmic reticulum in the cytoplasm. There were numerous collagen fibres in the interstitial space. Unmyelinated axons were ensheathed by Schwann cells. Infiltration of macrophages was observed near the interstitial cells. Each macrophage showed a large round or oval nucleus containing heterochromatin masses at the periphery of the cell nucleus. At 9 and 12 months of diabetes, the interstitial cells contained numerous vacuoles, dilated mitochondria, agranular vesicles and a prominent multivesicular body in the cytoplasm. Degenerating unmyelinated nerve fibres were encountered near the interstitial cells. Phagocytic macrophages contained numerous vacuoles of various sizes, which occupied most of the cytoplasmic area. Several vacuoles and degenerated electron-dense granules (some of them appeared to be fragmented) were present in the cytoplasm of interstitial cells and macrophages. It is concluded that interstitial cells in the AV valves contribute to valvular dysfunction in the streptozotocin-induced diabetic rats.     

Enhanced menadione cytotoxicity in platelets isolated from streptozotocin-induced diabetic rats

To study whether chemically induced cytotoxicity occurs in diabetic platelets, platelets isolated from rats made hyperglycemic (diabetic) by a prior intravenous administration of streptozotocin were incubated with menadione and the cytotoxicity was assessed by the amount of lactate dehydrogenase (LDH) released from the menadione exposed platelets as a function of time. Platelets isolated from diabetic rats released greater amount of LDH in response to menadione than those from normal rats. Consistent with this finding, induction of menadione cytotoxicity was not dependent on glutathione depletion, but on greater generation of free radicals in diabetic platelets. Greater sensitivity of diabetic platelets to the menadione-induced cytotoxicity was accompanied by release of serotonin from dense granules, suggesting that this mechanism contributes to cardiovascular diseases in diabetic subjects.     

Signal transduction alterations in peripheral nerves from streptozotocin-induced diabetic rats

We have previously determined the presence of muscarinic receptors and the expression of several G proteins in homogenates and myelin fractions from ra sciatic nerves. In the present study we investigates whether changes in several signal transduction path ways in peripheral nerves might be responsible for some of the biochemical abnormalities (e.g., phosphoinositide metabolism) present in sciatic nerves from streptozotocin-induced diabetic rats. Sciatic nerves from 5 week diabetic rats that were prelabelled with [³H]-myo-inositol displayed a significant increase in the basal release of inositol mono-and bis-phosphate, while carbamylcholine-stimulated release was significantly smaller. Basal- and forskolinstimulated adenylyl cyclase activity was significantly decreased in sciatic nerve homogenates from diabetic animals. However, we were unable to detect any significant differences in the levels of cAMP in intact nerves or in nerve segments that were incubated in the presence or absence of forskolin. ADP-ribosylation experiments showed that in sciatic nerves from experimentally diabetic rats there was a significant increase in the ADP-ribosylation catalyzed by cholera and pertussis toxins. Measurements of the levels of a-subunits of G proteins revealed that the expression of G_q/11α, G_sα, and G_i-3α was increased by 30 to 50%. These results indicate that during the course of experimental diabetes, peripheral nerves exhibit an abnormal production of inositol phosphates and cAMP, together with an abnormal expression and/or function of G proteins. One of the consequences of such alterations is the diminished release of inositol phosphates triggered by muscarinic agonists in diabetic sciatic nerves. © 1995 Wiley-Liss, Inc.     

Motor conduction velocity and the Hoffman reflex in diabetes

The motor conduction velocity (MCV) and various parameters of the Hoffman reflex were studied in 55 diabetics compared to a control population of the same age. In the diabetics there were statistically significant alterations of the MCV, the Hmax/Mmax ratio and the H index, which are closely connected. These changes were more precise when there were clinical signs of neuropathy (absence of the Achilles reflex) but they still existed in the absence of signs. The older the diabetics, the more the electro-physiological parameters were altered. However, the H index is abnormal earlier than the Hmax-Mmax ratio or the MCV. Changes in the excitability cycle to double shock involve mainly phase IV of secondary facilitation and may be related to central disturbances.     

Effects of initial conditions on the Hoffman reflex

The Hoffmann reflex is a monosynaptic reflex elicited by electrical stimulation of afferent nerve fibres. The amplitude of the reflex response may be measured both by EMG recording from the muscle and by sensing the muscle twitch. These two effects are dependent, not only on the amplitude of the stimulus, but on the state of excitability of the afferent-efferent synaptic pools and on the mechanical state of the muscle. Voluntary control of the stimulated muscle influences these conditions but the effects on the EMG are quite different from those on the twitch. This paper discusses these effects under isometric conditions.     

Central nervous system protection by resveratrol in streptozotocin-induced diabetic rats.

The objective of the present study was to investigate the possible neuroprotective effect of resveratrol against streptozotocin-induced hyperglycaemia in the rat brain and medulla spinalis. Thirty adult male Wistar rats were divided into three groups as follows: control group, streptozotocin-induced diabetic-untreated group, and streptozotocin-induced diabetic resveratrol-treated group. Diabetes was induced by a single injection of streptozotocin (STZ) (60 mg/kg body weight). Three days after streptozotocin injection, resveratrol (10 mg/kg) was injected intraperiteonally daily over 6 weeks to the rats in the treatment group. Six weeks later, seven rats from each group were killed and the brain stem and cervical spinal cord were removed. The hippocampus, cortex, cerebellum, brain stem and spinal cord were dissected for biochemical studies (lipid peroxidation measuring malondialdehyde [MDA], xanthine oxidase [XO], nitric oxide [NO] and glutathione). MDA, XO and NO levels in hippocampus, cortex, cerebellum, brain stem and spinal cord in the streptozotocin-induced diabetic-untreated group increased significantly. Treatment with resveratrol significantly reduced MDA, XO and NO production and increased glutathione levels when compared to the streptozotocin-induced diabetic-untreated group. This study demonstrates that resveratrol is a potent neuroprotective agent against diabetic oxidative damage.     

Amelioration of diabetic peripheral neuropathy by implantation of hematopoietic mononuclear cells in streptozotocin-induced diabetic rats

This study was performed in order to evaluate the angiogenic effect of implantation of either peripheral blood mononuclear cells (PBMNCs) or bone marrow mononuclear cells (BMMNCs) on diabetic peripheral neuropathy. Streptozotocin (50 mg/kg) was injected intravenously into 6-week-old male Lewis rats. Four weeks after the induction of diabetes, 6 x 10(7) of PBMNCs or 1 x 10(8) of BMMNCs were implanted into the left hindlimb muscle. Motor nerve conduction velocity (MNCV) was monitored before and after implantation. At the end of the experiment, bilateral nerve blood flow (NBF) was measured by laser Doppler and the number of vessels in the sciatic nerves quantified by Factor VIII staining of the sections. Diabetes resulted in an approximately 20% reduction (P < 0.01) in sciatic MNCV. Four weeks after implantation, MNCV was improved by 54% with PBMNCs and by 67% with BMMNCs (both P < 0.01). Moreover, the effects of implantation were almost abolished by administration of VEGF-neutralizing antibody. Sciatic NBF was reduced by approximately 50% by diabetes (P < 0.05). This reduction in perfusion was improved by 74% by implantation of PBMNCs and by 62% by implantation of BMMNCs (P < 0.05 and P < 0.01, respectively). These effects were observed only in the implanted limb. Immunohistochemical staining of sciatic nerve sections for Factor VIII showed no significant increase in the number of vessels in the sciatic nerve following implantation of either PBMNCs or BMMNCs. These data suggest that implantation of hematopoietic mononuclear cell fractions is associated with an improvement in MNCV as a result of arteriogenic effects in the sciatic nerve, and that VEGF may contribute to this effect. This improvement occurred in the absence of angiogenesis. Implantation of these cell fractions may therefore be a potential new therapeutic method for treating diabetic peripheral neuropathy.     

Insulin-like immunoreactivity persists in the spinal cord of streptozotocin-induced diabetic rats.

In both saline-injected control and streptozotocin-induced diabetic rats, insulin-like immunoreactivity was localized in the cervical, thoracic, lumbar and sacral segments of the spinal cord. This insulin-like immunoreactivity was consistently localized in the neurons and dendrites from control rats as well as from diabetic rats ranging from 1 month to 12 months after diabetes induction. In the neuronal cell bodies, the reaction product was predominantly localized in the cell nucleus and the proximal and distal dendrites. In the labelled cell nucleus, the reaction product was scattered throughout the cell cytoplasm and nucleoplasm, but not within the nucleolus. The inner and outer nuclear membranes were also labelled. In labelled dendrites, the reaction product was closely associated with the parallel arrays of neurotubules, plasma membranes and synaptic densities. Most of the labelled distal dendrites were postsynaptic to unlabelled axon terminals. A labelled dendrite often formed the central element of a synaptic glomerulus with several unlabelled axon terminals. It is hereby hypothesized that some of the neurons in the spinal cord of the diabetic rat are capable of synthesizing insulin-like substance(s), which appears to be involved in neurotransmission and neuromodulation.     

Impaired modulation of AMPA receptors by calcium-dependent processes in streptozotocin-induced diabetic rats

The mechanisms by which diabetes impairs cognitive function are not well-established. In the present study, we determined the electrophysiological and biochemical nature of disturbances in the mechanism of long-term potentiation (LTP) in diabetic rats. As previously reported, the administration of streptozotocin (STZ) was found to reduce the magnitude of LTP in the CA1 region of the hippocampus, while the same treatment did not interact with the capacity of the hippocampus to generate long-term depression induced by low-frequency stimulation. In addition, STZ treatment did not modify the component of excitatory postsynaptic potentials mediated by activation of the N-methyl-

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-aspartate (NMDA) subtype of glutamate receptors, suggesting that NMDA receptor function remained intact in STZ-treated slices. At the biochemical level, the capacity of calcium to increase [³H](RS)-α-amino-3-hydroxy-5-methylisoxazole propionic acid (³H-AMPA) binding to glutamate/AMPA receptors in rat brain tissue sections was markedly affected in most regions of the hippocampus of STZ-treated rats. Moreover, changes in ³H-AMPA binding properties elicited by both exogenous phospholipase A₂ and melittin, a potent activator of endogenous phospholipases, were also altered in synaptoneurosomes from diabetic rats. Taken together, the present data suggest that the loss of LTP maintenance in STZ-treated rats is more likely the result of disruption of calcium-dependent processes that are suspected to modulate postsynaptic AMPA receptors during synaptic potentiation. Understanding the biochemical factors participating in the impairment of AMPA receptor modulation might provide important clues revealing the very basis of memory deficits in diabetes.     

Academic achievement and the paired Hoffman reflex in students practicing meditation

The paired H reflex, considered to be the electrically evoked counterpart of the monosynaptic stretch reflex, provides a measure of motoneuron excitability under a variety of experimental and clinical conditions. It also offers a potentially useful tool in examining the neurophysiologic basis of alterations in reflex response in different states of awareness. This study investigated the relationship between the paired H reflex and academic achievement in students practicing the Transcendental Meditation program. The paired H reflex correlated significantly with grade point average, but not with SAT scores or any of three IQ measurements. These results suggest that the facilitation period of the paired H-reflex recovery curve may be a useful indicator of academic achievement, perhaps as a result of its relationship to awareness or wakefulness level.     

Impaired function and expression of P-glycoprotein in blood-brain barrier of streptozotocin-induced diabetic rats

The aim was to investigate the effect of diabetes mellitus (DM) on P-glycoprotein (P-GP) function and expression in rat blood-brain barrier (BBB). P-GP function in BBB was assessed by measuring the brain-to-plasma concentration ratios (Kp values) of rhodamine 123 (Rho123) and vincristine (VCR), two well-known P-GP substrates, in control rats and 5-week streptozotocin (STZ)-induced diabetic rats. Evans blue (EB) dye was used as a BBB integrity indicator for examining the extravasation from the blood into the brain. P-GP expression in the brain cortex was evaluated with Western blot. The uptakes of Rho123 and VCR by cultured rat brain microvessel endothelial cells (rBMECs) incubated in diabetic and control rat serum for 72 h were also used to examine P-GP function, respectively. It was found that the Kp value of Rho123 (0.022+/-0.005 vs. 0.016+/-0.002 ml/g brain, p=0.033) and VCR (0.072+/-0.028 vs. 0.023+/-0.006 ml/g brain, p=0.006) in diabetic rats was significantly higher than that in control rats. The uptakes of Rho123 and VCR by cultured rBMECs incubated in the diabetic rat serum were higher than that in the control rat serum, respectively. No significant difference of the EB concentration in the brain cortex was found between the diabetic rats and control rats. Electron microscope examination of the brain cortex did not show a clear damage to the endothelial cells of microvessel in diabetic rats. In addition, the protein level of P-GP in the brains of the diabetic rats examined was significantly lower than that of control rats. These results suggested that the function and expression of P-GP might be impaired in the BBB of STZ-induced diabetic rats.     

Neuropathological alteration of aquaporin 1 immunoreactive enteric neurons in the streptozotocin-induced diabetic rats

Long-term diabetic patients exhibit major clinical gastrointestinal problems, such as diarrhea and constipation. In recent years, water channel protein, aquaporin 1 (AQP1) has been identified in the enteric nervous system (ENS). We have examined the pathological changes in AQP1 immunoreactive (IR) neurons in streptozotocin-induced (STZ) diabetic rats. Eight-week-old Wistar rats were injected with streptozotocin, and artificial diabetes was induced. Sixteen-week-old STZ rats were then examined with double immunofluorescence staining and ABC immunohistochemical staining. AQP1-IR neurons in STZ rats were significantly increased compared with control rats (p<0.01). The ratio of AQP1 vs. HuC/D in STZ rats was also clearly increased as compared with control rats (p<0.05). It was apparent that thick AQP1-IR fibers were frequently observed in the secondary and tertiary myenteric plexus of STZ rats. The AQP1-IR fibers of STZ rats conspicuously showed many swollen varicosities. These swollen varicose fibers were also observed in the longitudinal and circular muscle layers. Streptozotocin-induced diabetic rats showed pathological changes in AQP1-IR neurons of the ENS. The alteration of AQP1-IR neurons may be possible contribute to diabetic gastrointestinal dysfunction in streptozotocin-induced diabetic rats.