Serum from diabetic BB/W rats enhances calcium currents in primary sensory neurons.

We examined the hypothesis that exposure of nondiabetic rat dorsal root ganglion (DRG) neurons to sera from diabetic BB/W rats would produce an increase in calcium currents associated with impaired regulation of the inhibitory G protein-calcium channel complex. Acutely dissociated rat DRGs were incubated for 18-24 h in medium supplemented with sera (10% vol/vol) from either diabetic rats with neuropathy or age-matched, nondiabetic controls. Exposure of DRG neurons to sera from diabetic BB/W rats resulted in a surface membrane immunofluorescence pattern when treated with an anti-rat light-chain antibody that was not observed in neurons exposed to control sera. Calcium current density (IDCa) was assessed with the use of the whole cell variation of the patch-clamp technique. IDCa in neurons exposed to diabetic sera was significantly increased compared with neurons exposed to control sera. Guanine nucleotide-binding (G) protein regulation of calcium channel function was examined with the use of a two-pulse "facilitation" or IDCa enhancement protocol in the presence of activators [guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)] or antagonists [guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) and pertussis toxin (PTX)] of G protein function. Facilitation was significantly decreased in neurons exposed to diabetic sera. Intracellular diffusion of neurons with GDP beta s blocked facilitation, whereas dialysis with GTP gamma s increased facilitation to a similar magnitude in neurons exposed to either diabetic or control sera. Treatment with PTX resulted in a significant increase in IDCa and approximately 50% decrease in facilitation in neurons treated with control sera but no significant changes in neurons exposed to diabetic sera. We conclude that serum from diabetic BB/W rats with neuropathy contains an autoimmune immunoglobulin that impairs regulation of the inhibitory G protein-calcium channel complex, resulting in enhanced calcium influx. Regulation of the inhibitory G protein-calcium channel complex involves PTX-sensitive and -insensitive G proteins.

The effect of gabapentin on neuropathic pain.

OBJECTIVE: To evaluate the effects of gabapentin on pain scores and opiate use. DESIGN: Retrospective review of patients charts who received gabapentin for at least 30 days. Data were collected concerning patients' diagnosis, current drug use, concurrent drug use, gabapentin dose, pain scores, and patient-reported side effects. Patients were divided into three groups based on their pain diagnosis; low back, neuropathic, and myofascial pain. The neuropathic group was subdivided into postherpetic neuralgia, diabetic neuropathy, sympathetically maintained pain, and phantom pain. SETTING: Two tertiary referral teaching hospitals in southeastern Michigan. RESULTS: A total of 122 charts were reviewed and included in this study. A significant decrease in pain scores with gabapentin was seen in the neuropathic pain group (paired t-test, p < .0001) but not in the low back pain group. Of the neuropathic pain group, patients with postherpetic neuralgia had the greatest decrease in pain scores. Ten patients showed a > 75% decrease in pain scores, of these: nine had a direct nerve injury, and one had postherpetic neuralgia. Opiate use was unchanged in all groups. Patients who were taking opiates had significantly less benefit with gabapentin use in terms of pain score. Patient-reported side effects were similar to those reported in a nonchronic pain population. CONCLUSION: Gabapentin may be a useful adjunct for treating neuropathic pain with a minimum of side effects. Particular advantage may be gained with the use of this drug for postherpetic neuralgia and direct peripheral nerve injuries.

Failure of nimodipine to prevent or correct the long-term nerve conduction defect and increased neuronal Ca(2+)-currents in the diabetic BB/W-rat.

It has been suggested that L-type Ca2+ channel antagonists exert a beneficial effect on nerve conduction velocity (NCV) slowing in short-term experimental diabetic neuropathy. We examined the effects of long-term treatment with the L-channel blocker, nimodipine, on two aspects of neuronal function previously documented to be abnormal in the spontaneously diabetic BB/W-rat: nerve conduction velocity and calcium influx in dorsal root ganglion (DRG) neurons. Treatment with 20 mg/kg nimodipine i.p. every 48 h from onset of diabetes for 6 months led to a transient, non-significant (30%) improvement in NCV. Intervention with the same regimen from 3 to 6 months of diabetes had no corrective effect on the already established NCV defect. Voltage activated calcium currents were recorded in isolated DRG neurons from nimodipine-treated and untreated diabetic and non-diabetic age-matched BB/W control rats. The peak high-threshold calcium current density (IDCa, pA/pF) was significantly larger in non-treated diabetic rats compared with control rats (157 +/- 12 vs. 66 +/- 5.5 (P < or = 0.05)). Long-term treatment with nimodipine was associated with a non-significant (28%) decrease (112 +/- 29) in the IDCa compared with non-treated diabetic rats. We conclude that L-channel mediated perturbations of cytosolic Ca2+ levels are only of minor pathophysiologic significance in the development of chronic diabetic neuropathy.

Primary preventive and secondary interventionary effects of acetyl-L-carnitine on diabetic neuropathy in the bio-breeding Worcester rat.

The abnormalities underlying diabetic neuropathy appear to be multiple and involve metabolic neuronal and vasomediated defects. The accumulation of long-chain fatty acids and impaired beta-oxidation due to deficiencies in carnitine and/or its esterified derivatives, such as acetyl-L-carnitine, may have deleterious effects. In the present study, we examined, in the diabetic bio-breeding Worcester rat, the short- and long-term effects of acetyl-L-carnitine administration on peripheral nerve polyols, myoinositol, Na+/K+ -ATPase, vasoactive prostaglandins, nerve conduction velocity, and pathologic changes. Short-term prevention (4 mo) with acetyl-L-carnitine had no effects on nerve polyols, but corrected the Na+/K+ -ATPase defect and was associated with 63% prevention of the nerve conduction defect and complete prevention of structural changes. Long-term prevention (8 mo) and intervention (from 4 to 8 mo) with acetyl-L-carnitine treatment normalized nerve PGE(1) whereas 6-keto PGF(1-alpha) and PGE(2) were unaffected. In the prevention study, the conduction defect was 73% prevented and structural abnormalities attenuated. Intervention with acetyl-L-carnitine resulted in 76% recovery of the conduction defect and corrected neuropathologic changes characteristic of 4-mo diabetic rats. Acetyl-L-carnitine treatment promoted nerve fiber regeneration, which was increased two-fold compared to nontreated diabetic rats. These results demonstrate that acetyl-L-carnitine has a preventive effect on the acute Na+/- K+_ATPase defect and a preventive and corrective effect on PGE1 in chronically diabetic nerve associated with improvements of nerve conduction velocity and pathologic changes.

Pharmacological characterization of dynorphin A (1-17)-induced effects on spinal cord-evoked potentials.

Dynorphin A (1-17) was applied directly onto the spinal cord of rats during electrophysiologic recording of the dorsal root potential (DRP) and the ventral root potentials (VRPs), i.e., monosynaptic reflex and polysynaptic reflexes. Dynorphin application resulted in a dose-dependent depression of the DRP (ED50, 4.5 nmol) which persisted for 30 to 50 min. This effect was not antagonized by nor-binaltorphimine, a kappa-opioid receptor antagonist. During this depression we observed a potentiation of the VRPs which persisted for 4 to 5 min and preceded depression of the VRPs (ED50, 4.0-4.9 nmol). The depression of the VRPs was antagonized competitively by nor-binaltorphimine, although the potentiation was not. beta-Funaltrexamine, a mu-opioid receptor antagonist, had no influence on dynorphin-induced changes of evoked potentials. These data indicate that dynorphin-induced depression of the VRPs is mediated by kappa-opioid receptor activity, whereas neither potentiation of the VRPs nor depression of the DRP appears to be mediated by an opioid receptor effect.

MK-801 blocks dynorphin A (1-13)-induced loss of the tail-flick reflex in the rat.

Dynorphin A (1-13) administered intrathecally to rats results in a dose-dependent loss of the tail-flick reflex. This effect is mediated, at least in part, by N-methyl-D-aspartate receptors. We examined the influence of pretreatment or post-treatment with MK-801 on this behavioral response. MK-801 administered i.p. 30 min prior to dynorphin provided dose-dependent protection against loss of the tail-flick reflex with an ED50 of 0.06 mg/kg. MK-801 administered after dynorphin had a dose- and time-dependent protective action. The dose of 0.06 mg/kg protected 63% of the animals from loss of the tail-flick reflex when injected 15 min after dynorphin. In contrast, 3 mg/kg did not protect animals when injected 15 min after dynorphin, but did protect 50% of the animals when injected 30 min post-dynorphin. Although we cannot exclude other effects mediated by MK-801, these data support our previous findings that dynorphin-induced loss of the tail-flick reflex involves the N-methyl-D-aspartate-receptor complex and support the contention that the process(es) initiated by dynorphin injection proceed rapidly (minutes rather than hours).