Respiratory responses to microinjections of leptin into the solitary tract nucleus.

The regulatory peptide leptin has a respiratory stimulating effect along with its well known hypothalamic effects. The present study, performed on anesthetized rats, addressed respiratory responses to microinjections of 10(-10)-10(-4) M leptin into the solitary tract nucleus, which contains a high concentration of leptin receptors. Injections of 10(-8)-10(-4) M leptin led to stimulation of respiration, inducing a dose-dependent increase in the level of pulmonary ventilation and an increase in respiratory volume, accompanied by an increase in bioelectrical activity in the inspiratory muscles; 10(-6) M leptin also induced a transient increase in respiratory rate due to shortening of inhalation and exhalation. A characteristic feature of the response was the appearance of "sighs" - deep, prolonged inhalations accompanied by increased volley activity on the electromyograms of the inspiratory muscles and lengthening of the subsequent intervolley interval. These leptin effects, along with data on the high concentrations of specific leptin receptors (ObRb) in the solitary tract nucleus, suggested that endogenous leptin has a role in controlling respiration at the level of the dorsal segment of the respiratory center.