Lesions of the caudal pontine reticular nucleus reduce spontaneous behavioural activity of rats differently in dorsal and ventral parts of the nucleus.

Four groups of 8 adult male hooded rats of the Long-Evans strain were investigated before and after lesions of the dorsal or the ventral subdivisions of the caudal pontine reticular nucleus (RPC) in an open field test (OF) and in a neurological test program. After dorsal (d) RPC lesions all labyrinthine reflexes were extremely slowed, tactile and visual placing responses strongly reduced and the startle reflex abolished, whereas ventral (v) RPC lesions did not alter the neurological status. The dRPC rats showed strongly reduced drinking from water bottles, did not eat pellets in their home cages and lost 5% of their body weight per day. This could be prevented by a supply with a cornflake pap. The ventral RPC lesion revealed no influence on food and water intake. Ambulatory activity in the OF was strongly reduced by dorsal lesions but not by ventralones. The habituation quotient increased only after ventral RPC lesions. Both lesion types increased the duration of immobilization. Exploratory activity was also reduced after both lesion types, but significantly stronger after dorsal lesions. In a centrophobia test the dRPC rats were 6 times slower than before lesion, whereas vRPC rats remained unchanged compared with their preoperative values. The negativism-test revealed strong enhancement after dRPC lesions, but not so strong after vRPC lesions. The results indicate specialized subdivisions of the pontine reticular formation controlling differently spontaneous behaviour.