EFFERENT CONNECTIONS FROM THE ANTERIOR PRETECTAL NUCLEUS TO THE DIENCEPHALON AND MESENCEPHALON IN THE RAT

The anterior pretectal nucleus has been described as part of the visua l pretectal complex. However, several electrophysiological and behavio ural studies showed that this area is involved in somatosensory modula tion, more specifically, antinociception. The efferents of the anterio r pretectal nucleus have not been identified taking into account the d ifferent function of this nucleus in relation to the rest of the prete ctal complex. In the study herein described, a sensitive anterograde t racer Phaseolus vulgaris leucoagglutinin was used to trace the mesence phalic and diencephalic efferents of the anterior pretectal nucleus in the rat. The majority of the connections were ipsilateral. Fibres wit h varicosities were observed in discrete areas of the thalamus (centra l lateral, posterior complex), hypothalamus (lateral, posterior and ve ntromedial), zona incerta, parvocellular red nucleus, intermediate and deep layers of the superior colliculus, central grey, deep mesencepha lon, pontine parabrachial region, and pontine nuclei. Fibres en passan t were detected in the medial lemniscus, from the level of the injecti on site to rostral medullary levels. Some labelled axons were seen cou rsing to the contralateral side through the posterior commissure and t he decussation of the superior cerebellar peduncle. These results show that the anterior pretectal nucleus projects principally to areas inv olved in somatosensory and motor control in a manner that permits sens ory modulation at higher and lower levels of the brain. These connecti ons may explain the antinociceptive and antiaversive effects of stimul ating the anterior pretectal nucleus in freely moving animals.