Histamine-induced, central nervous system-mediated hyperglycemia is suppressed by atropine in the brain

Effects of mepyramine and famotidine on the physostigmine-induced antinociception in the formalin test in rats

In this study, the effects of mepyramine (H1-receptor antagonist), famotidine (H2-receptor antagonist), physostigmine (a cholinesterase inhibitor) and atropine (muscarinic-receptor antagonist) have investigated on the formalin-induced nociception in rats. The effects of mepyramine and famotidine have also examined on nociceptive changes induced by physostigmine and atropine. Nociception was induced by intraplantar injection of formalin (50 microL, 1%) into the right hind paw and the time spent licking and biting of the injected paw, was taken as a measure of pain. Formalin induced a marked biphasic (first phase: 0-5 min and second phase: 15-45 min) pain response. The used drugs did not change the first phase of formalin-induced pain. Subcutaneous injection of physostigmine significantly (p<0.05) suppressed pain. Subcutaneous injection of atropine alone did not change the intensity of pain, but pretreatment with atropine significantly (p<0.05) prevented physostigmine-induced antinociception. Intraperitoneal injections of mepyramine and famotidine significantly (p<0.05) decreased pain response. Mepyramine did not significantly change, but famotidine significantly (p<0.05) prevented analgesic effect of physostigmine on pain. Atropine did not inhibit the antinociceptive effects of both mepyramine and famotidine on formalin-induced nociception. These results indicate that physostigmine through muscarinic cholinergic receptors suppresses the pain induced by formalin. Both H1 and H2 receptor antagonists produce antinociception. Histamine H2, but no H1 antagonists may be involved in physostigmine-induced antinociception.

Role of central neural mechanisms in the regulation of hepatic glucose metabolism

Central monoamine neurotransmitters affect blood glucose homeostasis. Activation of central cholinergic, noradrenergic histaminergic, and serotonergic neurons rapidly increase hepatic glucose output via the sympathetic nervous system. Acute hyperglycemia is mediated by three distinct pathways: the action of epinephrine on the liver, the action of glucagon on the liver, and the direct innervation of the liver. The relative contribution of these factors to hyperglycemia can be altered by diet and the kinds of neurotransmitters evoked in the central nervous system, but the magnitude of epinephrine secretion is closely related to the magnitude of hyperglycemia. On the other hand, neuropharmacological stimulation of central cholinergic muscarinic receptors, histaminergic H1 receptors, and serotonergic 5-HT2 receptors increases hypothalamic noradrenergic neuronal activity, which is associated with hyperglycemia. In contrast, central GABAA receptors play an inhibitory role in the regulation of hepatic glucose metabolism. Thus, central monoaminergic neurons could be linked together, and play a homeostatic role in the regulation of hepatic glucose metabolism.