Interleukin-1 stimulates hypothalamic inhibitory amino acid neurotransmitter release

Interleukin-1 (IL-1), a polypeptide cytokine, has been postulated as a chemical messenger between the immune and the neuroendocrine system. IL-1 receptors and immunopositive neurons have been visualized in the human and rat hypothalamus, suggesting that IL-1 can act as a neurotransmitter within the brain. In the hypothalamus IL-1 and the amino acid neurotransmitters are known to modulate several functions, such as fever, anorexia and the gonadal and adrenal axis. Since the hypothalamic actions of IL-1 on the amino acid neurotransmitter output are unknown, the aim of the present paper was to evaluate the effects of IL-1 on the hypothalamic release of both, the inhibitory taurine, glycine and GABA and the excitatory glutamate, amino acid neurotransmitters. Intact adult male rats were employed. The preoptic/mediobasal hypothalamic area was dissected and superfused with Earle's balanced salt solution. Superfusate fractions were collected after a 60-min stabilization period. Following 60 min of basal release, IL-1 was added to the superfusion medium over 30 min. GABA, taurine and glycine release were significantly (p < 0.05) increased in the superfusion medium, while glutamate was not modified compared with the control group. These observations show that IL-1 increased GABA, taurine and glycine release. These effects indicate that this cytokine can affect the hypothalamic inhibitory amino acid output, which may help us to understand the mechanism by which IL-1 exerts its effects.