Edinger-Westphal nucleus: cholecystokinin immunocytochemistry and projections to spinal cord and trigeminal nucleus in the cat.

Immunocytochemical methods were used to determine the distribution of cells with cholecystokinin-like immunoreactivity (CCK-LI) in the cat Edinger-Westphal complex (EW). Numerous cells with CCK-LI are found throughout the length of EW. The distribution and frequency of such cells are similar to the pattern of EW neurons that show substance P-like immunoreactivity (SP-LI). Companion retrograde transport experiments reveal that EW neurons which project to spinal cord or the region of the caudal trigeminal nucleus are found throughout the length of EW, and that some EW neurons which project to spinal cord also show CCK-LI.

Pontomedullary raphe neurons: intracellular responses to central and peripheral electrical stimulation.

The responses of pontomedullary raphe neurons to electrical stimulation of the medullary reticular formation (MRF) and the mesencephalic ventral periaqueductal gray region (PAG) were studied using intracellular methods in chloralose-anesthetized cats. Single shock stimulation of PAG at the level of the trochelear nucleus evoked short latency, monosynaptic excitatory postsynaptic potentials (EPSPs) in antidromically identified raphe-spinal neurons. Similar large EPSPs were produced by medullary reticular stimulation of either side. The large majority of raphe-spinal neurons responded to sciatic nerve shock, and most responded to tooth pulp or forepaw shock as well; these responses were always bilateral. The responses of cells that could not be antidromically invaded from spinal cord were similar to those of raphe-spinal neurons, but tended to be more variable. Intracellular injection of horseradish peroxidase into electrophysiologically characterized cells revealed that most recordings were made from large and medium sized raphe neurons. These findings are discussed in the context of a potential role for pontomedullary raphe neurons in nociception.

The distribution of substance P-containing neurons in the cat Edinger-Westphal nucleus: relationship to efferent projection systems.

The light microscopic localization of substance P-like immunoreactivity (SPLI) was examined in the cat Edinger--Westphal complex using the peroxidase--antiperoxidase method. A high density of cell bodies and processes staining for SPLI were found in the caudal part of the Edinger--Westphal complex (EWc) capping the somatic divisions of the oculomotor nucleus. This distribution continued rostrally into the anteromedian nucleus (AM). Cells labeled with SPLI were also found arranged in a thin layer dorsally capping the oculomotor nucleus, and scattered cells were found in the periaqueductal gray region at the same level. This distribution of SPLI-positive cells was then compared with the distribution of cells in EWc and AM that are retrogradely labeled by horseradish peroxidase or Nuclear Yellow injections into spinal cord, cerebellum, or ciliary ganglion. Injections of horseradish peroxidase into both cervical and lumbar cord labeled a large number of cells throughout the length of EWc and the more rostral AM. A similar pattern of labeling was seen following injections of Nuclear Yellow into the deep cerebellar nuclei. In contrast, cells innervating the ciliary ganglion were found predominantly outside of the Edinger--Westphal complex in AM, the rostral periaqueductal region, and the tegmentum ventral to the oculomotor complex. The distribution of cells projecting to spinal cord or cerebellum and the pattern of SPLI staining was found to closely overlap, evidence that substance P may be contained in cells that give rise to the central projections of the Edinger--Westphal complex.

Edinger-Westphal neurons that project to spinal cord contain substance P.

Combined retrograde transport and immunocytochemical methods were used to determine whether Edinger-Westphal neurons projecting to spinal cord also demonstrate substance P-like immunoreactivity (SPLI). Large injections of horseradish peroxidase (HRP) into cervical and lumbar enlargements retrogradely labeled cells throughout the length of the Edinger-Westphal complex (EW). Nearly all HRP-labeled EW neurons also stained for SPLI, evidence that EW is the origin of a direct substance P pathway linking rostral mesencephalon with spinal cord.

The oculomotor internuclear pathway: a double retrograde labeling study.

To determine whether oculomotor internuclear neurons (INOs) establish unilateral or bilateral connections with the abducens nucleus (nVI), horseradish peroxidase (HRP) and either DAPI or Nuclear Yellow (NY) were injected into nVI and the oculomotor complex (nIII) examined for retrogradely labeled cells. Such injections resulted in retrograde labeling of a large number of INOs within and just dorsal to nIII in the ventral periaqueductal gray; approximately 10% of HRP-positive cells were also labeled with a fluorescent marker. Within the conditions of the experiment, this frequency of double-labeling was largely independent of the amount of HRP or fluorescent label injected or the degree of spread of label at the injections sites. It was also independent of which fluorochrome was used as a second label. Individual double-labeled cells were scattered within and immediately dorsal to nIII within the distribution of single-labeled INOs. These findings provide strong evidence for a subset of nIII INOs that have bilateral projections to nVI; the low frequency of double-labeling, however, suggests that the population of INOs projecting to both nVI may be small.

The vestibulothalamic pathway: contribution of the ascending tract of Deiters.

Axoplasmic transport techniques were used to determine the contribution of the ascending tract of Deiters (ATD) to the vestibulothalamic projection in cats. Large injections of HRP into the thalamus centered on the border region between the ventrobasal complex and the caudal ventrolateral nucleus resulted in bilateral retrograde labeling of cells in the vestibular nuclear complex and the nucleus prepositus hypoglossi (PH). Similar thalamic injections were also made in animals with extensive bilateral lesions of the medial longitudinal fasciculus (MLF) and the brachium conjunctivum (BC). HRP-positive neurons in these cases were localized principally to the ventral lateral vestibular nucleus and adjacent superior vestibular nucleus ipsilateral to the thalamic injection, evidence that vestibulothalamic neurons in these nuclei may project to the thalamus over the unlesioned ATD. Injections of [35S]methionine into the rostral vestibular nuclear complex in animals with MLF and BC lesions confirmed these findings, demonstrating orthograde transport of radiolabel in the ATD with termination in thalamus. These experiments document a contribution of the ATD to the ipsilateral vestibulothalamic projection; other sources of the vestibulothalamic pathway (PH, Y group) likely travel through projection systems destroyed in the lesions made in the present study.