Histaminergic modulation of stress-induced analgesia and cognitive dysfunction

Physiological stress is known to produce analgesia and memory disruption. A large body of evidence favors the nonopiate mediation of stress-induced analgesia. It is suggested that brain histamine mediates nonopiate analgesia and participates in learning and memory in rodents. Histamine is released during stress, although the nature of histaminergic involvement in stress response is not clearly defined. Therefore, we studied the effect of L-histidine and histamine-receptor antagonists on antinociception and impaired retention induced by immobilization stress. In the present study, immobilization stress produced a naloxone-resistant analgesia that was potentiated by L-histidine and antagonized by pretreatment with the histamine receptor antagonists chlorpheniramine and cimetidine. L-histidine attenuated the memory disruption induced by immobilization stress, which was significantly reversed by chlorpheniramine but not by cimetidine. Thus the involvement of the central histaminergic system, through histamine H1- and H2-receptors, may be speculated in analgesia and cognitive deficit induced by immobilization stress.

Modulation of motor functions involving central dopaminergic system by L-histidine

There exists a possibility of interactions of histaminergic system with other neurotransmitters and their receptors in the central nervous system. Experimental evidences suggest a possible inhibitory influence of histaminergic system on the dopaminergic system. To elucidate the possible interaction between the histaminergic and dopaminergic pathways, we devised a strategy to study their effects on locomotor function and stereotypy behaviour. We investigated the effect of L-histidine, the precursor of histamine, on apomorphine-induced stereotypy and perphenazine-induced catalepsy. Histidine antagonised apomorphine-induced stereotypy. This inhibitory effect of histidine was abolished by both H1- and H2-receptor antagonists, chlorpheniramine and cimetidine, respectively. Perphenazine-induced catalepsy was potentiated by histidine and this effect was inhibited by chlorpheniramine alone but not by cimetidine. These results confirm a possible histamine-dopamine interaction in the modulation of motor functions by the central nervous system.

Prooxidant role of histidine in hypoxic stressed mice and Fe(3+)-induced lipid peroxidation

An attempt was made to study the effect of histidine on reactive oxygen species in a rodent model of hypoxic stress and in Fe(3+)-ascorbic acid-induced lipid peroxidation in mouse brain homogenates. The latency for onset of hypoxic stress-induced convulsions was decreased in histidine-treated animals with a concomitant rise in brain lipid peroxidation levels. In vitro, histidine potentiated Fe(3+)-ascorbic acid-induced lipid peroxidation in mouse brain homogenates while other antioxidants like B-HT and U-74500A inhibited the same. Moreover, Fe(3+)-histidine-induced lipid peroxidation could not be inhibited by preincubation of the system with high concentrations of ascorbic acid. Thus, it is concluded that histidine acts as a strong prooxidant potentiating the genesis of reactive oxygen species during hypoxic stress as well as during Fe(3+)-ascorbic acid-induced lipid peroxidation.