NEW INDIRECT PATHWAYS SUBSERVING THE PUPILLARY LIGHT REFLEX - PROJECTIONS OF THE ACCESSORY OCULOMOTOR NUCLEI AND THE PERIAQUEDUCTAL GRAY TOTHE EDINGER-WESTPHAL NUCLEUS AND THE THORACIC SPINAL-CORD IN RATS

The pupillary light reflex (PLR) is under the control of retinal gangl ion cells projecting to the olivary pretectal nucleus (OPN). The OPN h as a major projection to the Edinger-Westphal (EW) nucleus, which exer ts its parasympathetic action on the iris musculature via the ciliary ganglion. The accessory oculomotor nuclei (AON) and the periaqueductal gray (PAG) receive input from the OPN and influence the PLR. The pres ent study in rats aimed to elucidate the possible projections from the AON and FAG to the EW nucleus. The anterograde tracer Phaseolus vulga ris leucoagglutinin (PHA-L) was iontophoretically injected into the in terstitial nucleus of Cajal (INC), the nucleus of the posterior commis sure (NPC), the nucleus of Darkschewitsch (ND) and the rostral part of the FAG. The projections were studied at the light and electron micro scopic level. The INC, NPC and ND have small projections to the EW nuc leus, whereas the rostral part of the FAG densely projects to the EW n ucleus. Without exception INC, NPC, ND and FAG varicosities are presyn aptic to dendritic profiles in the EW nucleus and contain electron den se mitochondria, round vesicles and make asymmetric synaptic contacts. In addition the ND and FAG project to the thoracic level of the spina l cord. The fibres are presynaptic to dendritic profiles and contain e lectron dense mitochondria, round vesicles and make asymmetric synapti c contacts. The present observations allow the conclusion that the par asympathetic preganglionic neurons in the EW nucleus are not only cont rolled by the OPN-EW pathway but also by indirect pathways running via the AON and FAG. Moreover light-sensitive information is also transfe rred via an OPN-PAG-spinal cord pathway to the sympathetic superior ce rvical ganglion (SCG) that innervates the iris, suggesting that the FA G may have an integrative function in the sympathetic and parasympathe tic control of the PLR.