GABA-benzodiazepine receptor complex and drug actions

This short review describes the benzodiazepine receptors, their interplay with GABAergic transmission and chloride ionophore, the search for endogenous ligands, and the drug responses that can be evoked through these receptors. Benzodiazepine receptors offer a unique pathway through which opposite drug actions e.g., anxiogenic and anxiolytic effects can be exerted, and these actions can be inhibited with competitive receptor antagonists. The most plausible endogenous ligand for benzodiazepine receptors discovered so far, a polypeptide DBI, exerts actions opposite to those of the benzodiazepines used in clinical therapy. This has been the stimulus for a new look at the physiological role for these receptors.     

Oxidative stress correction by nicotinamide and nicotynol-GABA in diabetic neuropathy

Concentration of lipid peroxidation products and antioxidant enzyme activities in rat brain and erythrocytes and the effects of nicotinamide and nicotinoyl-GABA administration on these parameters were estimated on 21st day of streptozotocin-induced diabetes. It was demonstrated more then two-fold diabetes-induced accumulation of conjugated dienes and malondialdehyde in tissues studied. Superoxide dismutase and glutathione reductase activities of both brain homogenate and erythrocytes as well as catalase and glutathione peroxidase activities of brain homogenate were shown to decrease significantly in diabetic rats, meanwhile, catalase activity of erythrocytes was increased and glutathione peroxidase unchanged. So the correlation between changes in enzymatic antioxidant system in brain and erythocytes failed to be found. Alterations observed were virtually prevented by the course of nicotinamide and nicotinoyl-GABA treatment. The results suggested that the suppression of antioxidant system could be primary biochemical disturbance in diabetic neuropathy progression. It was shown that the antioxidant efficacy of nicotinoyl-GABA is lower than that of nicotinamide. It was suggested that the mechanism of antioxidant action of nicotinamide and its structural analogue consists of both scavenging of lipid peroxides and NAD biosynthesis that leads to activation and normalization of altered energy and lipid metabolism.     

The role of GABA-benzodiazepine receptor complex in affecting the anxiolytic effect of 3-hydroxypyridines--new non-benzodiazepine tranquilizers

The experiments on rats, using conflict situation method, have established that anxiolytic effect of 3-hydroxypyridine derivative is removed by bicucullin and picrotoxin, but not by Ro 5-3663, specific antagonist of benzodiazepine receptors Ro 15-1788 and inversive antagonist ethyl beta-carboline-3-carboxylate. The data obtained suggest that GABA-chloriontophor complex is involved into the realization of 3-hydroxypyridine anxiolytic effect.     

Neurotrophic action of nicotinamide and nicotinoyl-GABA in rat brain in experimental Parkinsonism]

It was established, that the content of nicotinamide adenine dinucleotides and the binding of NAD by isolated brain cortex synaptic membranes under experimental parkinsonism are impaired. Treatment of the experimental results in the Scatchard plots for binding of [U-14C]NAD to the brain cortex synaptic membranes demonstrated that binding capacities lowered, without changes of affinities. NAD-glycohydrolase involved in development of this pathology. The modulative effect of in vivo administered NAm and nicotinoyl-GABA supposes that NAm acts via NAD which binds specifically with synaptic membranes. Thus, NAm and nicotinoyl-GABA are involved in the regulation of the processes in the brain under experimental parkinsonism.     

Correction by nicotinamide and nicotinoyl-GABA of dopamine metabolism in rat brain in experimental Parkinson's disease

It was established, that serotonin and dopamine content and dopamine uptake by brain nerve endings under experimental parkinsonism are decreased. Nicotinamide nicotinoyl-GABA administration leads to normalization these parameters. It was shown that NAm was more effective on serotonin content while nicotinoyl-GABA on dopamine one. Dopamine uptake was impaired at experimental parkinsonism and partially was normalized by incubation with NAD (10(-6) M). Thus, NAm, nicotinoyl-GABA and NAD are involved in the regulation of brain neurotransmission under experimental parkinsonism and can be useful in treatment of Parkinson's disease.     

Interactions of GABA and Cl ionophore-binding subunits of GABA-benzodiazepine receptor complex in the brain of inbred mice

The displacement curves of the effect of GABA on the S35-tert-butyl bicyclophosphorothionate binding to the brain membranes of inbred mice were analysed. It was revealed the lack of marked interstrain differences in dependent on the ionic force of incubation medium modification of IC50. After incomplete stimulation of Cl(-)-ionophore subunit (50 mM NaCl) reliable interstrain differences in the value of nHill were shown. Bicuculline in the same conditions prevented the inhibitory effect of GABA (10(-5) M). But submaximal concentrations of bicuculline (5 X 10(-6) M, 10(-6) M) stimulated the radioligand binding in the presence of GABA (10(-6) M). It was marked more expressed bicuculline stimulation effect on the membranes of C57Bl/6 mice, as compared to BALB/c mice.     

Antinociceptive effect of chrysin in diabetic neuropathy and formalin-induced pain models

ABSTRACT

Chrysin, a natural flavonoid, is the main ingredient of many medicinal plants, which shows potent pharmacological properties. In the present study, the antinociceptive effects of chrysin were examined in ICR mice. Chrysin orally administered at the doses of from 10 to 100?mg/kg exerted the reductions of formalin-induced pain behaviors observed during the second phase in the formalin test in a dose-dependent manner. In addition, the antinociceptive effect of chrysin was further characterized in streptozotocin-induced diabetic neuropathy model. Oral administration chrysin caused reversals of decreased pain threshold observed in diabetic-induced peripheral neuropathy model. Intraperitoneally (i.p.) pretreatment with naloxone (a classic opioid receptor antagonist), but not yohimbine (an antagonist of α2-adrenergic receptors) or methysergide (an antagonist of serotonergic receptors), effectively reversed chrysin-induced antinociceptive effect in the formalin test. Moreover, chrysin caused a reduction of formalin-induced up-regulated spinal p-CREB level, which was also reversed by i.t. pretreated naloxone. Finally, chrysin also suppressed the increase of the spinal p-CREB level induced by diabetic neuropathy. Our results suggest that chrysin shows an antinociceptive property in formalin-induced pain and diabetic neuropathy models. In addition, spinal opioid receptors and CREB protein appear to mediate chrysin-induced antinociception in the formalin-induced pain model.     

Study of the GABA-benzodiazepine receptor system of the human myometrium

A specific [3H] GABA and [14C] flunitrazepam binding sites have been identified in a membrane fraction of human myometrium. The specific binding of [14C] GABA was displaced by unlabelled GABA and bicuculline. It was shown that the binding of [3H] flunitrazepam to membrane preparations is enhanced in the presence of GABA. A similar reciprocal effect of benzodiazepines to enhance [14C] GABA binding has been demonstrated. The present results indicate that GABAA-BD receptors complexes may have a functional significance in human ovary.     

Antinociceptive effect of topiramate in models of acute pain and diabetic neuropathy in rodents

This study assesses the antinociceptive effect induced by different dosages of topiramate (TP), an anticonvulsant drug that is orally administered in models of neuropathic pain and acute pain in rats and mice, respectively. Orally administered TP (80 mg/Kg) in mice causes antinociception in the first and second phases of a formalin test, while in doses of 20 and 40 mg/Kg it was only effective in the second phase. TP (80 mg/Kg, p.o) also exhibited antinociceptive action in the hot plate test, however, it did not have an effect in the capsaicin test in mice, nor in the model of neuropathic pain in diabetic rats. The antinociceptive effect caused by TP (80 mg/Kg, p.o) in the formalin test was reversed by prior treatment with naloxone (opioid antagonist), but not with glibenclamide (antagonist of the potassium channel), ondansetron (antagonist of the serotonin 5HT3 receptor) or cyproheptadine (antagonist of the serotonin 5HT2A receptor).The data show that TP has an important antinociceptive effect in the models of nociception induced by chemical (formalin) or thermal (hot plate) stimuli, and that the opioid system plays a part in the antinociceptive effect, as shown by formalin.     

胰岛素样生长因子与糖尿病神经病变

糖尿病神经病变给糖尿病患者造成严重危害,但其发生机制至今未明。最近研究表明：胰岛素样生长因子（ＩＧＦｓ）对感觉、运动及交感神经元具有支持营养作用;临床糖尿病患者及实验性糖尿病大鼠体内ＩＧＦｓ活性及ＩＧＦｓ ｍＲＮＡ表达水平下降;补充ＩＧＦｓ可减轻糖尿病神经损害程度。上述研究提示ＩＧＦｓ活性下降在糖尿病神经病变的发生中起重要作用。     

Childhood diabetic neuropathy: functional impairment and non-invasive screening assessment

Aim Sensory diabetic neuropathy, determined by nerve conduction studies, is common in children with Type?1 diabetes. Diabetic neuropathy diagnoses are rarely made in paediatric daily care because they are asymptomatic, vibration detection is mostly normal and nerve-conduction testing is impractical. The present study aims to: (1) describe somatosensory dysfunction in children with diabetes, (2) test whether diabetes duration and HbA(1c) are related to somatosensory dysfunction and (3) identify the best screening test for large-fibre dysfunction, as indicated by nerve conduction studies. Methods Forty-five children (age 13.2?±?2.5?years) with Type?1 diabetes for 6.7?±?2.5?years and matched control subjects were assessed by neurological examinations, nerve conduction tests and quantitative sensory testing on the feet using the protocol of the German Research Network on Neuropathic Pain. Abnormal nerve conduction was used as gold standard to define neuropathies. Results We found a high prevalence of mechanical (38%) and thermal (24%) hypoesthesia often associated with hyperalgesia (47%). Tactile hypoesthesia (33%) was more frequent than pallhypaesthesia (11%). Only cold detection and mechanical pain thresholds were related to HbA(1c) . Tactile hypoesthesia had the highest sensitivity (75%), specificity (89%) and positive (75%) and negative (89%) predictive values for neuropathies defined by nerve conduction tests (31% abnormal). Conclusions Almost half of the children with diabetes have subclinical large- and small-fibre neuropathies. Tactile detection was better than vibration for neuropathy assessment. Quantitative sensory testing is a valuable tool for assessment of neuropathy as well as a target of interventional studies in children with diabetes.     

Pupillary signs in diabetic autonomic neuropathy.

Pupillary function was investigated in 36 insulin-dependent diabetics and 36 controls matched for age and sex. About half of the diabetics had evidence of peripheral somatic or autonomic neuropathy, or both. The diabetic patients had abnormally small pupil diameters in the dark and less fluctuation in pupil size (hippus) during continuous illumination than the controls. They also had reduced reflex responses to light flashes of an intensity adjusted for individual retinal sensitivities. The pupillary findings were compared with results of five tests of cardiovascular function and five tests of peripheral sensory and motor nerve function. Almost all the patients with autonomic neuropathy had pupillary signs, which we therefore conclude are a common manifestation of diabetic autonomic neuropathy.     

Ghrelin reverses experimental diabetic neuropathy in mice

Ghrelin, an acylated peptide produced in the stomach, increases food intake and growth hormone secretion, suppresses inflammation and oxidative stress, and promotes cell survival and proliferation. We investigated the pharmacological potential of ghrelin in the treatment of polyneuropathy in uncontrolled streptozotocin (STZ)-induced diabetes in mice. Ghrelin or desacyl-ghrelin was administered daily for 4 weeks after STZ-induced diabetic polyneuropathy had developed. Ghrelin administration did not alter food intake, body weight gain, blood glucose levels, or plasma insulin levels when compared with mice given saline or desacyl-ghrelin administration. Ghrelin administration ameliorated reductions in motor and sensory nerve conduction velocities in diabetic mice and normalized their temperature sensation and plasma concentrations of 8-isoprostaglandin α, an oxidative stress marker. Desacyl-ghrelin failed to have any effect. Ghrelin administration in a mouse model of diabetes ameliorated polyneuropathy. Thus, ghrelin’s effects represent a novel therapeutic paradigm for the treatment of this otherwise intractable disorder.     

Medial arterial calcification and diabetic neuropathy.

X-ray examinations of the feet, knees, and hands were performed on 20 diabetics with severe neuropathy and 20 diabetics with no evidence of neuropathy but with a similar mean age and duration of diabetes. All were under 53 years old with no clinical evidence of peripheral vascular disease. Medial arterial calcification was much more common and extensive in the patients with neuropathy, occurring in the feet in 15 and in the hands in eight compared with in four (p less than 0.001) and none (p less than 0.001) of the controls respectively. Although there was some correlation between calcification and both proteinuria (p less than 0.05) and proliferative retinopathy (p less than 0.02), the association between calcification and neuropathy (p less than 0.001) was much stronger. Neuropathy, with sympathetic denervation of the smooth muscle of the tunica media, may be important in the aetiology of medial arterial calcification.     

Therapy with antioxidants in human diabetic neuropathy

Increased oxidative stress has been implicated in the pathogenesis of diabetic polyneuropathy (DPN). Antioxidant treatment with alpha-lipoic acid (ALA) has been shown to prevent or ameliorate experimental diabetic neuropathy, providing the rationale for treatment in humans. A recent meta-analysis including four controlled clinical trials provided evidence that treatment with ALA (600 mg/day i.v.) over 3 weeks is safe and significantly improves both neuropathic symptoms and deficits to a clinically meaningful degree in patients with symptomatic DPN. Moreover, oral treatment for 4–7 months tends to ameliorate neuropathic deficits and cardiac autonomic neuropathy. Clinical and postmarketing surveillance studies have revealed a highly favorable safety profile of this drug. Based on these findings, a pivotal long-term multicenter trial of oral treatment with ALA (NATHAN 1 Study) is under way aimed at slowing the progression of DPN.     

Early painful diabetic neuropathy is associated with differential changes in the expression and function of vanilloid receptor 1

Diabetes mellitus is associated with one or more kinds of stimulus-evoked pain including hyperalgesia and allodynia. The mechanisms underlying painful diabetic neuropathy remain poorly understood. Previous studies demonstrate an important role of vanilloid receptor 1 (VR1) in inflammation and injury-induced pain. Here we investigated the function and expression of VR1 in dorsal root ganglion (DRG) neurons isolated from streptozotocin-induced diabetic rats between 4 and 8 weeks after onset of diabetes. DRG neurons from diabetic rats showed significant increases in capsaicin- and proton-activated inward currents. These evoked currents were completely blocked by the capsaicin antagonist capsazepine. Capsaicin-induced desensitization of VR1 was down-regulated, whereas VR1 re-sensitization was up-regulated in DRG neurons from diabetic rats. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate blunted VR1 desensitization, and this effect was reversible in the presence of the PKC inhibitor bisindolylmaleimide I. Compared with the controls, VR1 protein was decreased in DRG whole-cell homogenates from diabetic rats, but increased levels of VR1 protein were observed on plasma membranes. Of interest, the tetrameric form of VR1 increased significantly in DRGs from diabetic rats. Increased phosphorylation levels of VR1 were also observed in DRG neurons from diabetic rats. Colocalization studies demonstrated that VR1 expression was increased in large myelinated A-fiber DRG neurons, whereas it was decreased in small unmyelinated C-fiber neurons as a result of diabetes. These results suggest that painful diabetic neuropathy is associated with altered cell-specific expression of the VR1 receptor that is coupled to increased function through PKC-mediated phosphorylation, oligomerization, and targeted expression on the cell surface membrane.