Morphological evidence for newly discovered double projection spinal neurons

Branching and/or collateral projections of spinal dorsal horn neurons

Branching and/or collateral projections of spinal dorsal horn neurons is a common phenomenon. Evidence is presented for the existence of STTm/STTl, STTc/STTi, STT/SMT, STT/SRT, SCT/DCPS, SST/DCPS, SCT/SST, STT/SHT, STeT/SHT, STeTs and other doubly or multiply projecting spinal neurons that have been anatomically and physiologically identified and named based on the locations of the cells of origin and their terminations in the brain. These newly discovered spinal projection neurons are characterized by a single cell body and branched axons and/or collaterals that project to two or more target areas in the brain. These novel populations of neurons seem to be a fuzzy set of spinal projection neurons that function as an intersection set of the corresponding single projection spinal neurons and to be at an intermediate stage phylogenetically. Identification strategies are discussed, and general concluding remarks are made in this review.

The target specificity of the extrinsic innervation of the rat small intestine

The target specificity of the extrinsic innervation of the rat small intestine was examined by simultaneously injecting the proximal and distal small intestine with either wheat germ agglutinin-horseradish peroxidase (HRP) or fast blue. The number of single- and double-labeled cells in the nodose, dorsal root and coeliac-superior mesenteric ganglia and the dorsal motor nucleus of the vagus were counted and expressed as percentages of total labeled cells. Cells containing both HRP and Fast blue projected to both regions of the intestine. We found that the nodose and mesenteric ganglia contained significantly fewer double-labeled neurons (approximately 3 and 9% respectively) than the dorsal motor nucleus (19%) or dorsal root ganglion (20%). Presumably, a large number of double-labeled afferent or efferent neurons would limit the ability of a given component of the extrinsic innervation to control the activity of restricted regions of the small intestine (but might be important in overall regulation of intestinal function). In a separate series of experiments we examined the topography of neurons in the dorsal motor nucleus of the vagus labeled with HRP injection into either the proximal or distal small intestine. Both of these injections labeled neurons in the entire rostro-caudal extent of the nucleus, though approximately 75% of the cells were located between 720 microns caudal and 720 microns rostral to the obex. Cells in the rostral regions were found primarily in the lateral pole of the nucleus, whereas caudal regions contained labeled cells in both the medial and lateral poles.

The morphology of cat spinal neurons projecting to both the lateral cervical nucleus and the dorsal column nuclei

Morphological features of physiologically characterized doubly projecting spinocervical tract-dorsal column postsynaptic (SCT-DCPS) neurons were examined following intracellular injections of horseradish peroxidase. Their cell bodies and majority of dendrites were located in laminae III-IV. The SCT-DCPS neurons have rostrocaudally elongated dendritic trees with spiny fine caliber dendrites, and issue local axon collaterals that are studded with varicosities. The results show that the doubly projecting SCT-DCPS neurons do not represent a morphologically distinct subset of the spinocervical tract (SCT) or dorsal column postsynaptic (DCPS) cells.