Charles W.T Pilcher

Diabetes-induced suppression of IGF-1 and its receptor mRNA levels in rat superior cervical ganglia

Insulin-like growth factor-I (IGF-I) is implicated in the development, survival and maintenance of function of sympathetic and sensory neurons. These neurons are affected at an early stage during the course of diabetes. Reverse transcriptase polymerase chain reaction (RT-PCR) based assay revealed that rat superior cervical ganglia (SCG) express mRNA transcripts for IGF-I and its receptor. Moreover, specific membrane protein binding sites for IGF-I within the SCG have also been demonstrated using competition-inhibition and affinity cross-linking techniques. An induction of diabetes with streptozotocin (STZ, 55 mg/kg, i.v.) produced a marked decrease in the SCG levels of mRNA transcripts for IGF-I and its receptor. Concentrations of circulating IGF-I and its receptor protein within the SCG were also reduced in this disease state. Insulin treatment partially prevented diabetes-related alterations in circulating IGF-I and the SCG-IGF-I system. Overall, the data described in this study may be of value in understanding the pathogenetic mechanism(s) responsible for the development of diabetic sympathetic neuropathy.

Rhythmic nature of naloxone-induced aversions and nociception in rats

Taste conditioning procedures revealed a rhythmic fluctuation in the aversiveness of naloxone in opiate-naive rats. This rhythm exhibited two peaks during each 24-hour period. One peak was evident in the light phase and the second, which was more prominent occurred in the dark phase. Analgesia produced by morphine showed an essentially similar rhythm with heat and pressure as noxious stimuli. Although control nociceptive thresholds for heat also showed this rhythm, those for pressure showed only one broad peak through most of the dark phase. With noxious heat the hyperalgesic effect of naloxone also showed two peaks of activity but, as in control responding, this was not true for pressure. Opioid systems mediating nociception of different stimuli may show differential diurnal fluctuations.

Spinal cord noradrenergic dynamics in diabetic and hypercortisolaemic states

Disorders of pain sensation including spontaneous pain, allodynia and hyperalgesia are commonly seen in neuropathic diabetic patients. A wealth of evidence indicates that spinal monoamine systems are implicated in pain modulation but whether abnormalities in these systems underlay such disorders is unclear. The present study was therefore initiated to investigate spinal noradrenergic dynamics during diabetes. Spinal release of norepinephrine (NE) represented by 3-methoxy-4-hydroxyphenylglycol (MHPG)/NE ratio was markedly suppressed in 30-day streptozotocin (STZ)-treated diabetic male and female rats. The density of [3H] p-aminoclonidine binding sites and the level of expression of mRNA encoding for alpha2A-adrenoceptor subtype were also reduced as a function of diabetes. In contrast, an increase in the density of [3H] prazosin binding to spinal synaptosomal membranes was evident in these animals. Clonidine-induced elevation in nociceptive threshold was attenuated in diabetics. Control animals subjected to chronic treatment with a supraphysiological dose of glucocorticoid (GC) exhibited a neurochemical pattern which is similar in many respects to that produced by the diabetic state. Both insulin and the GC receptor blocker, RU 486, restored most of the neurochemical and behavioural abnormalities of diabetes. Overall, the present study supports the concept that a diabetes-related deficit in spinal noradrenergic dynamics may be a reflection of an overactivity of the hypothalamic-pituitary-adrenal axis.

Attenuation of IGF-1 antinociceptive action and a reduction in spinal cord gene expression of its receptor in experimental diabetes

&NA; Insulin‐like growth factor I (IGF‐1) is trophic to sensory, motor and sympathetic neurons. Intrathecal (i.t.) administration of IGF‐1 produced analgesic effects when tail flick/withdrawal latency was used as an indicator. This action was blocked by genistein (an inhibitor of tyrosine kinase) but not by atipamezol (an &agr;2 adrenoreceptor antagonist), naloxone (an opioid antagonist) or glibenclamide (a blocker of ATP sensitive K+ channels). Induction of diabetes with streptozotocin (STZ, 55 mg/kg, i.v.) impaired the ability of IGF‐1 to elevate nociceptive threshold. This phenomenon was not seen in normal animals rendered hyperglycemic with d‐glucose (20 mmol in 2.5 ml of saline, i.p.). PCR‐based assay revealed that the lumbar region of the spinal cord expresses mRNA transcripts for IGF‐1 and its receptor. The rates of expression of both of these transcripts were reduced during diabetes. The above behavioral and biochemical abnormalities induced by the diabetic state were partially restored following replacement therapy with insulin. Overall, our data suggest that a receptor‐linked tyrosine kinase mediates the antinociceptive effect of IGF‐1. Additionally, the attenuation in the ability of IGF‐1 to elevate nociceptive threshold may be a consequence of reduced gene expression of IGF‐1 receptor within the spinal cord.

Social crowding enhances aversiveness of naloxone in rats

If endorphins mediate various behavioural states including reactions to stress and social affect, then experimental manipulation of such states should alter the stimulus properties of opioid antagonists. The results of experiments in which the aversiveness of naloxone was increased by chronic environmental stress produced by rearing and maintaining male rats under conditions of severe social crowding, support this theoretical proposition. All rats acquired aversions to flavoured solutions that had been presented for 15 min immediately prior to a systemic injection of naloxone. The degree of the conditioned aversion was greater in rats maintained in crowded conditions. Transferring rats from crowded conditions to individual accommodation 3 weeks before the start of aversive conditioning did not attenuate the increased aversiveness of the antagonist. It is suggested that social interaction under conditions of chronic crowding induces a prolonged increase in the level of tonic activity in endorphinergic systems.

Diabetes attenuates the response of the lumbospinal noradrenergic system to idazoxan

Allodynia is a common feature of painful diabetic neuropathy. This phenomenon appears to be under endogenous noradrenergic control and can be ameliorated effectively by alpha(2)-adrenoceptor agonists. Accordingly, diabetic lumbospinal noradrenergic dynamics was evaluated using high performance liquid chromatography with electrochemical detector (HPLC-ECD), in vitro ligand binding and RT-PCR-based techniques. Streptozotocin (STZ)-treated and Goto-Kakizaki (GK) diabetic rats were included, respectively, as models for type I (insulin-dependent) and type II (non-insulin-dependent) diabetes mellitus. The data from these studies revealed that lumbospinal norepinephrine (NE) release, as indicated by the 3-methoxy-4-hydroxyphenyl glycol (MHPG)/NE ratio, was decreased as a function of diabetes. Similarly, the binding density of [3H] p-aminoclonidine and the level of expression of mRNA transcripts encoding for the alpha(2A)-adrenoceptor subtype and noradrenergic transporter were also reduced in this disease state. Analogous findings were obtained in non-diabetic Wistar rats rendered hypercortisolemic by the subcutaneous implantation of slow releasing pellets containing a supraphysiological dose of glucocorticoid (GC). Tactile allodynia was consistently observed in STZ- and GC-treated animals. The responsiveness of alpha(2)-adrenoceptors to idazoxan (alpha(2)-adrenoceptor antagonist) indicated a dose-dependent enhancement of noradrenergic transmission in lumbar segments of normal spinal cord. In stark contrast, this neurochemical action of idazoxan was attenuated in diabetic and hypercortisolemic animals. The institution of insulin therapy ameliorated diabetes-related abnormalities in lumbospinal noradrenergic dynamics. Overall, the current finding suggests that diabetic and hypercortisolemic allodynic symptoms may stem from, at least in part, down-regulation of alpha(2)-adrenoceptors in these disease states.

Effects of naloxone and Mr 1452 on stress-induced changes in nociception of different stimuli in rats

The effects of naloxone and Mr 1452 on nociceptive responding to heat and pressure following restraint stress were examined. Thresholds for heat and pressure were determined using standard tail immersion and paw pressure tests. Restraint produced significant analgesia to heat but hyperalgesia to pressure. Naloxone reduced this heat analgesia but had no effect on stress-induced hyperalgesia to pressure. Mr 1452 also attenuated the heat analgesia but in contrast to naloxone it potentiated the hyperalgesia to pressure. These results suggest a differential involvement of mu- and k-opioid systems in the mediation of stress-induced changes in nociception.

Antinociceptive action of intrathecally administered IGF-I and the expression of its receptor in rat spinal cord

mRNA transcripts for insulin-like growth factor I (IGF-I) and its receptor are expressed in the lumbar region of the spinal cord. Accordingly, we examined the involvement of IGF-I in nociceptive transmission. An intrathecal injection of IGF-I (200-1000 ng) produced a dose-dependent elevation in nociceptive threshold as indicated by tail flick/withdrawal latency. In contrast, comparable doses of insulin had no significant effect. The time-response curve (15-75 min) revealed that the peak for IGF-Is antinociceptive effect is attained at 30 min. Our data provide evidence that the IGF-I system within the spinal cord may serve as a target for novel analgesics.

Insulin-dependent attenuation in α2-Adrenoreceptor-mediated nociception in experimental diabetes

Diabetes mellitus is associated with abnormalities in central noradrenergic dynamics, a system that appears to be involved in the regulation of nociception in both humans and experimental animals. To this end, we investigated the responsiveness of nociceptive threshold to the actions of clonidine (an alpha 2-adrenoreceptor agonist) and yohimbine (an alpha 2-adrenoreceptor antagonist) during diabetes. The induction of diabetes was achieved by the administration of streptozotocin (STZ) (55 mg/kg, intravenously). Nociceptive threshold, as indicated by the tail-flick latency of the tail immersion test, was progressively elevated as a function of the duration of diabetes. Systemic administration of clonidine and yohimbine respectively produced dose-dependent analgesic and hyperalgesic effects in control animals. Both of these phenomena were impaired in chronically diabetic animals. In contrast, insulin-treated diabetics displayed supersensitivity to clonidines antinociceptive effect, especially at low doses. Acute hyperglycemia did not interfere with the alpha 2-agonist-mediated elevation in nociceptive threshold. Attenuation in clonidine antinociceptive effect was also observed following its intrathecal administration to diabetic animals. Overall, these data suggest that the impaired responsiveness of diabetic rats might be due to a central alpha 2-adrenoreceptor desensitization and/or biochemical defect in the postreceptor events.

On substance abuse in Kuwait (1992–1997): Evidence from toxicological screening of patients

PURPOSE To assess preference for different psychoactive substances and time trends in Kuwait. METHODS Analysis of urine and blood samples of specimens sent by attending physicians to the only public health reference laboratory for toxicological screening in the country. RESULTS A total of 28,548 tests were performed on 3781 samples. Cannabinoids were positive in 40% of the tested samples, opiates in 24%, ethanol in 10%, and amphetamines in 5%. Elevated concentrations of methadone, cocaine, and phencyclidine did not exceed 0.1%. About 40% of samples was positive for benzodiazepines, but their therapeutic use obscures the informativeness of this finding. There was a significant increase in the proportion of positive results for ethanol, amphetamines, and benzodiazepines. IMPLICATIONS It is high time to implement a modern and comprehensive preventive and control program. The tendency to blame the Iraqi invasion for drug addiction has hampered efforts to recognise and address the problem in its entirety.