c-Fos expression in GABAergic, serotonergic, and other neurons of the pontomedullary reticular formation and raphe after paradoxical sleep deprivation and recovery.

The brainstem contains the neural systems that are necessary for the generation of the state of paradoxical sleep (PS) and accompanying muscle atonia. Important for its initiation are the pontomesencephalic cholinergic neurons that project into the pontomedullary reticular formation and that we have recently shown increase c-Fos expression as a reflection of neural activity in association with PS rebound after deprivation in rats (Maloney et al. , 1999). As a continuation, we examined in the present study c-Fos expression in the pontomedullary reticular and raphe neurons, including importantly GABAergic neurons [immunostained for glutamic acid decarboxylase (GAD)] and serotonergic neurons [immunostained for serotonin (Ser)]. Numbers of single-labeled c-Fos+ neurons were significantly increased with PS rebound only in the pars oralis of the pontine reticular nuclei (PnO), where numbers of GAD+/c-Fos+ neurons were conversely significantly decreased. c-Fos+ neurons were positively correlated with PS, whereas GAD+/c-Fos+ neurons were negatively correlated with PS, suggesting that disinhibition of reticular neurons in the PnO from locally projecting GABAergic neurons may be important in the generation of PS. In contrast, through the caudal pons and medulla, GAD+/c-Fos+ cells were increased with PS rebound, covaried positively with PS and negatively with the electromyogram (EMG). In the raphe pallidus-obscurus, Ser+/c-Fos+ neurons were positively correlated, in a reciprocal manner to GAD+/c-Fos+ cells, with EMG, suggesting that disfacilitation by removal of a serotonergic influence and inhibition by imposition of a GABAergic influence within the lower brainstem and spinal cord may be important in the development of muscle atonia accompanying PS.