GLUTAMATERGIC AND CHOLINERGIC PROJECTIONS TO THE PONTINE INHIBITORY AREA IDENTIFIED WITH HORSERADISH-PEROXIDASE RETROGRADE TRANSPORT AND IMMUNOHISTOCHEMISTRY

Previous studies in our laboratory have shown that microinjection of a cetylcholine and non-N-methyl-D-aspartate (NMDA) glutamate agonists in to the pontine inhibitory area (PIA) induce muscle atonia. The present experiment was designed to identify the PIA afferents that could be r esponsible for these effects, by use of retrograde transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP), glutamate immunohistochemistry and NADPH-diaphorase staining techniques. Experi ments were performed in both decerebrate and intact cats. Dense retrog rade WGA-HRP labelling was found in neurons in the periaqueductal gray (PAG) and mesencephalic reticular formation (MRF) at the red nucleus (RN) level, ventral portion of paralemniscal tegmental field (vFTP), r etrorubral nucleus (RRN), contralateral side of PIA (cPIA), pontis ret icularis centralis caudalis (PoC), and most rostral portion of the nuc leus parvicellularis (NPV) and nucleus praepositus hypoglossi (PH) at the level of the pontomedullary junction; moderate labelling was seen in pedunculopontine nucleus, pars compacta (PPNc), laterodorsal tegmen tal nucleus (LDT), superior colliculus (SC), MRF and PAG at the level caudal to RN, medial and superior vestibular nuclei, and principle sen sory trigeminal nucleus (5P); and light labelling was seen in dorsal r aphe (DR) and locus coeruleus complex (LCC). The projection neurons we re predominantly ipsilateral to the injection site, except for both vF TP and RRN, which had more projection cells on the contralateral side. Double labelled WGA-HRP/NADPH-d neurons could be found in PPNc and LD T. Double labelled WGA-HRP/glutamatergic neurons could be seen at high densities in MRF, RRN, vFTP, and cPIA, moderate densities in SC, LDT, PPNc, PoC, and NPV, and low densities in PH, 5P, DR, LCC, and PAG. No cells in LDT and PPNc were triple labelled with NADPH-d, glutamate an tibody and WGA-HRP. The mesopontine efferents identified here may medi ate the suppression of muscle tone in REM sleep and coordinate muscle tone during head and neck movements. (C) 1993 Wiley-Liss, Inc.