IMMUNOCYTOCHEMICAL STUDY OF THE CLIP ACTH-IMMUNOREACTIVE NERVE-FIBERSIN THE DORSAL RAPHE NUCLEUS OF THE RAT/

The injection of corticotrophin-like intermediate lobe peptide (CLIP) in the lateral ventricle or in the dorsal raphe nucleus (DRN) of the r at is followed by a significant increase in the amount of paradoxical sleep. In the DRN, CLIP would act through a somatic and/or dendritic r elease of serotonin. To establish the anatomical basis of these effect s, the nerve fibres immunoreactive for CLIP/ACTH were labelled and the ir fine anatomical relationships with the neuronal elements of the DRN were studied at the ultrastructural level. Half of the profiles of la belled varicosities were 'free' in the neuropile, the other half was i n close contact with dendrites, either shafts or spines. It was intere sting to note that few contacts with dendritic shafts were under the f orm of a synapse, whereas a large number of the contacts with spines w ere synaptic. The chemical nature of these dendritic targets remains t o be determined but preliminary results indicate that they are partly serotoninergic.