Synergistic effects of central glutamatergic and histaminergic systems on food intake in neonatal chickens: The role of NMDA receptors

Appetite modulation is a set of complex physiological mechanisms affecting different central nervous system areas. Glutamate and histamine play an important role in the central control of food intake in birds and reduce food intake in birds. The present study was conducted to investigate the synergistic effects of central glutamatergic and histaminergic systems on feeding behavior in neonatal chicks. 36 chickens were randomly divided into three experimental groups. Each experiment included a control group and 3 treatment groups (12 chickens in each group). In all experiments, after 3 hours of food deprivation (FD3), chicks received either control diluent or drug solution by intracerebroventricular (ICV) injection. Then the birds had ad libitum access to the ‎food and fresh water, and then cumulative food intake (gr) was measured based on the ‎percentage of the body (%BW) ‎. In the first experiment, glutamate (75 nmol), histamine (75 nmol), and histamine + glutamate was injected. In the second experiment, chlorpheniramine (H1 receptor antagonist, 300 nmol), MK-801 (NMDA glutamate receptor antagonist, 15 nmol), and chlorpheniramine + MK-801 was injected. In the third experiment, MK-801, α-FMH (histamine synthesis inhibitor, 250 nmol), and α-FMH + MK-801 was injected. The results showed that the injection of sub-effective doses of histamine with a dose of 75 nmol (sub-effective dose) and glutamate with a dose of 75 nmol (sub-effective dose) did not affect food intake (p > 0.05). However, co-injection of glutamate and histamine decreased food intake (p < 0.05). Injection of chlorpheniramine with a dose of 300 and MK-801 with a dose of 15 had no effect on food intake (p > 0.05). However, co-injection of chlorpheniramine and MK-801 increased food intake (p < 0.05). Injection of α-FMH with a dose of 250 and MK-801 with a dose of 15 did not influence food intake (p > 0.05). However, co-injection of α-FMHs and MK-801 increased food intake (p < 0.05). According to the results, there is probably a synergistic effect between histaminergic and glutamatergic systems in the control of food intake in neonatal chicks.