The lateral hypothalamus (LH) is known to be involved in behavioral states control, in the regulation of energy homeostasis and in the regulation of the sympathetic outflow to several target organs. A central role in LH physiological functions is played by a cluster of hypocretinergic neurons sending widespread projections.

In anaesthetized rats, activation of LH neurons by local administration of GABAA antagonists has been shown to increase sympathetic outflow to the heart and to the brown adipose tissue. However, the widespread diffusion of GABA inputs to LH neurons makes it difficult to discriminate the contribution of the different neural populations within LH to this regulatory process. Recently, muscarinic receptors have been identified on a sub-population of hypocretinergic neurons.

Here we show preliminary observations on the effects of muscarinic receptors activation within LH in free behaving rats (n=3). The microinjection of the muscarinic agonist carbachol (100nl, 10mM) within LH significantly increased heart rate (HR) (+147±7 bpm) and hypothalamic temperature (Thy) (+1,40± 0,22°C) compared to the pre-injection baseline level. These effects are similar to those evoked by GABAA antagonism in the same area.

We conclude that the enhancement of the cardiovascular and thermogenetic sympathetic outflow which follows the activation of LH neurons is at least partly mediated by a population of neurons, probably hypocretinergic, expressing muscarinic receptors.