Differential c-fos expression in the rhinencephalon and striatum after enhanced sleep-wake states in the cat

In order to delimit the supra-brainstem structures that are activated durin g the sleep-waking cycle, we have examined c-fos immunoreactivity in four g roups of polygraphically recorded cats killed after 3 h of prolonged waking (W), slow-wave sleep (SWS), or paradoxical sleep (PS), following microinje ction of muscimol (a gamma-aminobutyric acid, GABA agonist) into the periaq ueductal grey matter and adjacent areas [Sastre et al. (1996), Neuroscience , 74, 415-426]. Our results demonstrate that there was a direct relationshi p between a significant increase in c-fos labelling and the amount of PS in the laterodorsalis tegmenti in the pens, supramamillary nucleus, septum, h ippocampus, gyrus cingulate, amygdala, stria terminalis and the accumbens n uclei. Moreover, in all these structures, the number of Fos-like immunoreac tive neurons in the PS group was significantly higher (three to 30-fold) th an in the SWS and W groups. We suggest that the dense expression of the imm ediate-early gene c-fos in the rhinencephalon and striatum may be considere d as a tonic component of PS at the molecular level and that, during PS, th e rhinencephalon and striatum are the main targets of an excitatory system originating in the pens.