Responses of lateral hypothalamic neurons to simulative hypogravic condition induced by body suspension

In unanesthetized rats, neuronal activity in the lateral hypothalamic area was recorded during horizontal and head-down tilt suspension. When the rat was raised in the horizontally suspended position, 21 of 44 neurons changed activity as follows: immediate increase (7/21, Type I), immediate decrease (3/21, Type II), and gradual decrease (11/21, Type III). When the rat was raised with a head-down tilt position, the responses were suppressed in about half of the neurons tested. These results showed that the LHA neurons altered their activity in response to low G simulation induced by body suspension. Possible signals which induce the changes in the LHA neuronal activity, and an involvement of the LHA in the autonomic reflexes under hypogravic condition are discussed.