Origin of ascending and spinal pathways from the nucleus tegmenti pedunculopontinus in the rat

Abstract

The distribution and collateralization of ascending and descending projections from neurons in the nucleus tegmenti pedunculopontinus (PPN) were studied in the rat by using retrograde transport of HRP, HRP/WGA, and fluorescent dyes. The PPN and its two subdivisions, the subnucleus compactus (PPNc) and subnucleus dissipatus (PPNd), were delineated on sagittal Nissl-stained sections by using cytoarchitectural features as guidelines. Large bilateral pressure injections of HRP and/or fluorescent dyes into the cervical cord retrogradely labeled moderate numbers of fusiform and polygonal PPN cells which ranged in size between 65 and 390 microns2. The labeled cells were scattered throughout the PPNd and were somewhat more numerous in the medial half of the subnucleus. The PPNc contained only occasional labeled cells in its ventralmost portion. Following single unilateral HRP/WGA injections in the striatum, globus pallidus, entopeduncular nucleus, subthalamus, or the substantia nigra, the distribution of the labeled cells was similar to that of the spinal cord-projecting PPN neurons. Multiple HRP injections were then made bilaterally in the substantia nigra and the entopeduncular nucleus and/or subthalamus in order to label the entire population of PPN neurons projecting to the basal ganglia. In this case, not only the PPNd but also the PPNc contained a substantial number of retrogradely labeled cells. The rostrally projecting PPN cells outnumbered 5.4 times those projecting to the spinal cord, and their somata were somewhat larger, ranging between 114 and 472 microns2. While both fusiform and polygonal shapes were encountered, the polygonal cell somata were more numerous. In the double-labeling experiments, Granular Blue and Diamidino Yellow Dihydrochloride were injected into the cervical cord and the entopeduncular nucleus or subthalamus. In general, these experiments confirmed the extensive overlap of forebrain- and spinal cord-projecting neurons within the PPNd and the quantitative preponderance of ascending neurons. They also demonstrated that these two projection systems originate largely from separate cell populations since the double-labeled cells always composed less than 5% of the labeled neurons. The results confirm the existence of a direct PPN projection to the spinal cord. This pathway originates mainly in the PPNd and appears to be quantitatively weaker than the PPN projections to the forebrain. The spinal cord-projecting cells are not spatially segregated from the cells projecting to the basal ganglia, but they represent a separate population of the PPN projection neurons.

Cholinergic Modulation of Synaptic Transmission and Postsynaptic Excitability in the Rat Gracilis Dorsal Column Nucleus

“…Interestingly, CTbpositive neurons and doubled-labeled cells could not be detected in the neuronal Ch5 and Ch6 cholinergic groups described by Mesulam et al (1983). These results agree with the description that cholinergic neurons of the laterodorsal and pedunculopontine tegmental nuclei project to prosencephalic structures, whereas noncholinergic neurons project in a descending pattern (Satoh and Fibiger, 1986;Goldsmith and van der Kooy, 1988;Spann and Grofova, 1989;Semba et al, 1990). Our results indicate that the cholinergic projections to the GN arise at the pontine and bulbar reticular formation in which cholinergic cells have also been described (Armstrong et al, 1983;Cuello and Sofroniew, 1984).…”

Cholinergic, GABAergic, and glutamate-enriched inputs from the mesopontine tegmentum to the subthalamic nucleus in the rat

“…The subject of the present study is the input to the STN derived from the MTg (Bowsher. 1975;Graybiel, 1977;Nomura et al, 1980;Saper and Loewy, 1982;Jackson and Crossman, 1983;Moon-Edley and Graybiel, 1983;Woolf and Butcher, 1986;Moriizumi et al, 1987;Lee et al, 1988;Spann and Grofova, 1989;Canteras et al, 1990;Lavoie and Parent, 1994a). The MTg has been reported to be involved in a multitude of functions including locomotion, sleep-wake mechanisms and arousal (see Garcia-Rill, 1991, andJones, 1993, for reviews) and its projection to the STN is one route through which this region could exert profound effects on movement.…”

“…The MTg has been reported to be involved in a multitude of functions including locomotion, sleep-wake mechanisms and arousal (see Garcia-Rill, 1991, andJones, 1993, for reviews) and its projection to the STN is one route through which this region could exert profound effects on movement. The exact origin and neurochemical nature of the mesopontine tegmental projection to the STN, and indeed to the basal ganglia in general, have been the subject of much debate (Woolf and Butcher, 1986;Rye et al, 1987;Lee et al, 1988;Spann and Grofova, 1989). It has been proposed that this projection arises almost exclusively from the cholinergic neurons of the pedunculopontine nucleus and the laterodorsal tegmental nucleus, or almost exclusively from the noncholinergic neurons of the MEA or from both sites (Woolf and Butcher, 1986;Lee et al, 1988;Spann and Grofova, 1989).…”

Altered neuronal activity relationships between the pedunculopontine nucleus and motor cortex in a rodent model of Parkinson's disease

“…The pedunculopontine nucleus (PPN) has robust connections with the basal ganglia Grofova, 1989, 1991;Parent, 1994a, 1994c;Shink et al, 1996Shink et al, , 1997, thalamus (Lavoie and Parent, 1994b), cerebellum (Hazrati and Parent, 1992), and spinal cord (Spann and Grofova, 1989) and has been suggested to play a key role in the control of posture and locomotion (Masdeu et al, 1994;Lee et al, 2000;Pahapill and Lozano, 2000). The PPN has also recently emerged as a target for deep brain stimulation (DBS) in Parkinson's disease (PD) and early DBS results show amelioration of medically intractable akinesia and gait abnormalities (Mazzone et al, 2005;Plaha and Gill, 2005;Stefani et al, 2007).…”