Acute intracerebroventricular injections of the mast cell degranulator compound 48/80 and behavior in rats

Physiological responses to central and peripheral injections of compound 48/80 and histamine in chicks

Mast cells are a type of immune cell widely distributed in the body of vertebrates. Mast cells have many granules that contain several bioactive molecules such as histamine, and these molecules are released through degranulation when the mast cell receives certain stimuli. Because the number of mast cells increases during infection in chickens (Gallus gallus), the activity of mast cells might be related to non-specific symptoms such as anorexia under an infectious condition. Therefore, the purpose of the present study was to investigate whether intraperitoneal (IP) and intracerebroventricular (ICV) injections of compound 48/80, which induces degranulation of mast cells, affects feeding, voluntary activity, cloacal temperature, and the concentrations of plasma corticosterone (CORT) and glucose in chicks. The effect of histamine, which is found in mast cell granules, on these parameters was also investigated. IP injection of compound 48/80 significantly decreased food intake, voluntary activity, and cloacal temperature, and increased plasma CORT concentration in the chicks. While ICV injection of compound 48/80 also decreased food intake, it increased cloacal temperature and plasma glucose concentration. Both IP and ICV injections of histamine significantly decreased food intake, cloacal temperature, and plasma CORT concentration. However, only IP injection of histamine significantly decreased voluntary activity and increased plasma glucose concentration. The results suggest that degranulation of mast cells is related to non-specific symptoms in chicks, although the mechanism seems to be different between peripheral and central tissues. In addition, the effect of peripherally-injected compound 48/80 may be partly mediated by histamine.

Effects of drugs acting as histamine releasers or histamine receptor blockers on an experimental anxiety model in mice

Experimental anxiety in mice was evaluated using a light/dark test at 60 min after injection of various histaminergics. Thioperamide, a histamine H(3) receptor inhibitor (5-20 mg/kg, intraperitoneal [IP]), Compound 48/80, a mast cell degranulator (0.1-10 microg/2 microl, intracerebroventricularly [ICV]), mepyramine, a histamine H(1) receptor antagonist (0.1-10 microg/2 microl, ICV) or cimetidine, a histamine H(2) receptor antagonist (0.1-10 microg/2 microl, ICV) alone did not affect the locomotive activity, the time spent in the light zone, and number of shuttle crossings in the light/dark test. However, the time spent in the light zone and the number of shuttle crossings significantly decreased only when cimetidine (0.1-10 microg/2 microl, ICV) was co-treated with either thioperamide (10 mg/10 ml/kg, IP) or Compound 48/80 (1.0 microg/2 microl, ICV). The decrease in these behavioral parameters suggests induced experimental anxiety in mice. The experimental anxiety was antagonized by mepyramine (10 microg/2 microl, ICV). These results suggest that not only neuronal histamine release induced by thioperamide but also non-neuronal (mast cells) histamine release induced by Compound 48/80 play an important role in inducing experimental anxiety via post-synaptic H(1) and H(2) receptors. In addition, it is likely that the anxiety may be mediated by the stimulation of H(1) receptors, while H(2) receptors may inhibit the anxiety produced by the activation of H(1) receptors.

Role of histaminergic mechanisms in the regulation of some stress responses in rats

The involvement of histaminergic mechanisms in the regulation of some stress responses was studied in rats. The brain neuronal histamine (HA) depletor, alpha-fluoromethyl histidine (alpha-FMH), at doses (50 or 100 mg/kg) which markedly lower brain HA, significantly attenuated the gastric ulcer formation and the elevation in plasma corticosterone in response to cold restraint stress (CRS). alpha-FMH also appreciably reduced gastric mucosal HA content. The H1-antagonist, pheniramine (25 mg/kg), attenuated both the gastric mucosal and endocrine response to CRS, while the effects of the H2-antagonist, cimetidine (200 mg/kg), were on the plasma corticosterone levels. These results are discussed in light of complex HA-ergic mechanisms in the maintenance of physiological homeostasis during stress.