Neurons which exhibited vasoactive intestinal polypeptide (VIP) immunoreactivity identified with immunohistochemical techniques in the cat thoracic dorsal root ganglia (DRG, T8–T11) injected with colchicine 2 days prior to sacrifice. VIP-positive cells (5–40 cells per section) were small to medium size ranging from 14–41 μm in diameter. VIP-immunoreactivity was weaker in the thoracic DRG exposed to colchicine by topical administration. The neuropeptide could not be detected in the thoracic DRG (T1–T13) in the absence of colchicine. VIP-immunoreactivity was also identified in the superficial laminae (I and II) of the thoracic spinal cord. The findings indicate that VIP in afferent pathways in the cat is distributed more extensively than previously reported and is not restricted only to the lower lumbar and sacral levels of the spinal cord.

Splanchnic afferent projections to the spinal cord and gracile nucleus were labeled following the application of HRP to the central cut end of the major splanchnic nerve. Labeled afferent fibers were detected in the ipsilateral dorsal column, in Lissauer's tract (LT), in laminae 1, 5, 7, and 10, and in the dorsal gray commissure at T1-T13 levels of the spinal cord. Afferent projections were not identified in laminae 2-4. Collaterals from LT projected ventrally along the lateral and medial margins of the dorsal horn (called lateral and medial pathways, respectively). Afferents in the lateral pathway formed small bundles, spaced rostrocaudally at intervals of 300-1,000 microns, which passed medially at the base of the dorsal horn into laminae 5, 7, and 10 and to the contralateral spinal cord. Some afferents in the lateral pathway projected to the intermediolateral nucleus where labeled sympathetic preganglionic neurons were located. Afferents in the medial pathway entered the lateral aspect of the dorsal column and projected as a group near the midline rostrally to the medulla. The dorsal column pathway terminated in the ventral gracile nucleus in four or five clusters, each occupying a region ranging in size from 0.01-0.1 mm3 and separated in the rostrocaudal axis by distances of 400-800 microns. These clusters were concentrated in the middle and caudal portions of the nucleus below the obex. A comparison of the present results with those from earlier experiments on the central projections of afferent fibers from the heart, kidney, and pelvic organs demonstrates a consistent pattern of visceral afferent termination in the thoracolumbar and sacral segments of the spinal cord. This is not unexpected, since visceral afferent pathways to different organs perform similar functions, such as the transmission of nociceptive information and the initiation of autonomic reflexes.

Substance P immunoreactivity in the afferent pathways to the kidney of the cat was investigated by using combined retrograde fluorescent dye labeling and indirect immunofluorescent techniques. Substance P was identified in 24% of dye-labeled renal afferent neurons in the dorsal root ganglia from L1 to L3. By comparison, 29% of all cells in the lumbar ganglia were substance P-positive. These data indicate that substance P may be involved in the transmission of afferent input from the kidney to the central nervous system.

Retrograde and transganglionic transport of horseradish peroxidase (HRP) was used to trace afferent and efferent pathways in the left inferior cardiac nerve of the cat. Cardiac efferent and afferent neurons were located, respectively, in the stellate ganglion (average cell count per experiment: 2679) and in the ipsilateral dorsal root ganglia (DRG) from C8 to T9 (average cell count per experiment: 213). Labeled cardiac afferent projections to the spinal cord were most dense in segments T2–T6 where they were located in Lissauer's tract and in lamina 1 on the lateral border of the dorsal horn. Labeled affrent axons extended ventrally through lamina 1 into lamina 5 and the dorsolateral region of lamina 7 in proximity to the intermediolateral nucleus. A weak projection was noted on the medial side of the dorsal horn. These sites of termination are similar to projections by other sympathetic afferent pathways (i.e. renal, hypogastric and splanchnic nerves) to the lower thoracic and lumbar spinal cord, indicating that visceral afferents may have a uniform pattern of termination at various segmental levels. This pattern of termination in regions of the gray matter containing spinothalamic tract neurons and neurons involved in autonomic mechanisms is consistent with the known functions of sympathetic afferent pathways in nociception and in the initiation of autonomic reflexes.

Anatomical and electrophysiological experiments have demonstrated a prominent projection from the sacral sympathetic chain via the pelvic nerve to postganglionic nerves on the surface of the urinary bladder and the large intestine of the cat. Retrograde labeling studies revealed that the pelvic nerve, which is generally believed to carry primarily parasympathetic axons, has a considerable population of sympathetic fibers originating mainly from the S1-S3 paravertebral ganglia. The number of sympathetic neurons projecting to the pelvic nerve (2,100) was about 75% of that projecting to the pudendal nerve (2,900), a somatic nerve which would be expected to carry a large sympathetic fiber constituent. Sympathetic neurons projecting to the pudendal nerve were located primarily in the L6-S2 ganglia. Electrophysiological studies confirmed the presence of a sympathetic pathway from the paravertebral ganglia to the pelvic viscera. Electrical stimulation (thresholds 1.5-3 V) of the lumbar sympathetic chain evoked firing in the pelvic nerve and in postganglionic nerves on the surface of the colon and bladder at latencies of 60-150 msec. The responses were unaffected by cutting the chain one segment rostral to the site of stimulation, but were abolished by the administration of a ganglionic-blocking agent (tetraethylammonium). The responses on the colon and bladder postganglionic nerves were also abolished by transection of the pelvic nerve. The conduction velocity in the sympathetic postganglionic axons was approximately 1 m/second. In summary, these studies indicate that the pelvic nerve, like somatic nerves, receives a prominent projection from the sympathetic chain ganglia. The function of this sympathetic paravertebral pathway and its relationship with prevertebral innervation of the pelvic organs remains to be established.

The segmental and central distributions of renal nerve afferents in adults cats and kittens were studied by using retrograde and transganglionic transport of horseradish peroxidase (HRP). Transport of HRP from the central cut ends of the left renal nerves labelled afferent axons in the ipsilateral minor splanchnic nerves and sensory perikarya in the dorsal root ganglia from T12 to L4. The majority of labeled cells (85%) were located between L1 and L3. A few neurons in the contralateral dorsal root ganglia were also labeled. Labeled cells were not confined to any particular region within a dorsal root ganglion. Some examples of bifurcation of the peripheral and central processes within the ganglion were noted. A small number of preganglionic neurons, concentrated in the intermediolateral nucleus, were also identified in some experiments. In addition, many sympathetic postganglionic neurons were labeled in the renal nerve ganglia, the superior mesenteric ganglion, and the ipsilateral paravertebral ganglia from T12 to L3. Transganglionic transport of HRP labeled renal afferent projections to the spinal cord of kittens from T11 to L6, with the greatest concentrations between L1 and L3. These afferents extended rostrocaudally in Lissauer's tract and sent collaterals into lamina I. In the transverse plane, a major lateral projection and a minor medial projection were observed along the outer and inner margins of the dorsal horn, respectively. From the lateral projection many fibers extended medially in laminae V and VI forming dorsal and ventral bundles around Clarke's nucleus. The dorsal bundle was joined by collaterals from the medial afferent projection and crossed to the contralateral side. The ventral bundle extended into lamina VII along the lateroventral border of Clarke's nucleus. Some afferents in the lateral projection could be followed ventrally into the dorsolateral portion of lamina VII in the vicinity of the intermediolateral nucleus. In the contralateral spinal cord, labeled afferent fibers were mainly seen in laminae V and VI. These results provide the first anatomical evidence for sites of central termination of renal afferent axons. Renal inputs to regions (laminae I, V, and VI) containing spinoreticular and spinothalamic tract neurons may be important in the mediation of supraspinal cardiovascular reflexes as well as in the transmission of activity from nociceptors in the kidney. In addition, the identification of a bilateral renal afferent projection in close proximity to the thoracolumbar autonomic nuclei is consistent with the demonstration in physiological experiments of a spinal pathway for the renorenal sympathetic reflexes.

Immunohistochemical and pharmacological studies were conducted to examine the origin and function of peptidergic nerves in the sacral autonomic system of the cat. Leucine-enkephalin (L-Enk) immunoreactivity was identified in nerve terminals in peripheral ganglia on the surface of the urinary bladder and in the parasympathetic nucleus in the sacral spinal cord. In colchicine-treated animals L-Enk was also detected in sacral preganglionic neurons (sPGN) identified by retrograde transport of a fluorescent dye. L-Enk terminals in bladder ganglia are believed to arise from sPGN since the terminals were eliminated by transection of the sacral ventral roots. Pharmacological studies indicated that exogenous as well as endogenously released enkephalins have an inhibitory action at both ganglionic and spinal sites in the sacral outflow to the urinary bladder. Peptides were also associated with afferents nerves in the sacral autonomic system. The distribution of substance P, VIP and cholecystokinin in the sacral dorsal horn paralleled the distribution of visceral afferent projections as demonstrated with HRP techniques. Dye labeling combined with immunohistochemistry revealed that some dorsal root ganglion cells projecting to the pelvic viscera contain substance P or VIP.

Autoradiography and anterograde horseradish peroxidase transport were used to examine retinocollicular projections in normal hamsters and in animals subjected to ablation of the ipsilateral, posterior neocortex at 1, 3, 6, 10 or 120 days of age. The crossed retinotectal projections of all groups were quite similar. There did, however, appear to be a slight increase in the density of the projection to the lower portion of the stratum griseum superficiale in the neonatally brain-damaged hamsters.

Anterograde and retrograde tracing techniques were employed to delineate the organization of a visual cortical input to the deep layers of the hamster's superior colliculus which may be mediated by links in the striatum and substantia nigra. Autoradiographic experiments showed that areas 17, 18a, and the cortex medial to area 17 (areas 18b and 29) all projected to the dorsocaudal part of the ipsilateral striatum. This projection was organized so that the rostrocaudal axis of the visual cortex was represented along the antero posterior axis of the striatum. Large posterior neocortical injections which included all of these areas also revealed a weak, crossed corticostriatal pathway. Such injections also demonstrated clear discontinuities in the terminal distribution of the visual corticostriatal projection, similar to those which have been noted after injections of tracers into the motor and premotor cortices. Retrograde tracing experiments showed that the cells of origin of the visual cortical projections to the striatum were medium-sized pyramidal neurons located primarily in the upper portion of lamina V. Anterograde transport of [3H]-leucine and HRP showed that the portion of the striatum heavily innervated by the visual cortex projected to the part of substantial nigra, pars reticulata immediately adjacent to the cerebral peduncle. Injections in the rostral striatum labeled more medial portions of this nucleus. The cells of origin of the striatonigral pathway measured between 13 and 20 micrometers in diameter and they were located primarily in the dorsal and lateral parts of the striatum. Anterograde tracing after substantia nigra, pars reticulata injections revealed a projection to both superior colliculi. The uncrossed pathway terminated primarily as a series of patches throughout the mediolateral and rostrocaudal extents of the lower stratum griseum intermediale and stratum album intermedium. Labeling was also visible in the lateral portion of the stratum griseum profundum. The crossed nigrotectal pathway terminated primarily in the rostrolateral stratum griseum profundum. The cells of origin of the nigrocollicular pathway were fusiform or multipolar cells and were located primarily adjacent to the cerebral peduncle throughout the rostral half of the substantias nigra, par reticulata.

The fiber compositio of the left major splanchnic nerve was studed in cats by electron microscopy. Comparisons were made between normal and partically degenerated nerve specimens following ventral rhizotomy (T3‐L1), or spinal nerve division (T3‐L1). Normal, major splanchnic nerves contained 2,500–4,000 myelinated and 10,000–15,000 unmyelinated fibers. Preganglionic fibers included approximately 90% of the finely myelinated (1–7μm) and over 50% of the unmyelinated fibers. Removal of the sensory and preganglionic components by spinal nerve division revealed a third, postganglionic fiber category. This included 13–38 small myelinated (1–5μm) and 1,645‐7,619 unmyelinated fibers. Finally, a comparison of normal and partially degenerated nerve specimens of both groups (ventral rhizotomy and spinal nerve cut) indicated that splanchnic afferents are made up of virtually all of the 120–350 large myelinated (8‐14μm) and 10% of the small myelinated (1–7μm) fibers. A preliminary estimate indicated that about 10–20% of the unmyelinated fibers were sensory. The implications of these findings are discussed.

The intercollicular pathway of the hamster was studied by means of a combination of horseradish peroxidase (HRP), autoradiographic, and double-labeling (nuclear yellow-HRP) techniques. Small deposits of HRP marked significant numbers of cells in the contralateral colliculus only when the injection site included the laminae ventral to the stratum opticum. Anterior deposits labeled many more neurons than injections into the caudal part of the tectum. Of the cells labeled by our injections, 18.2% were located in the superficial collicular laminae (stratum griseum superficiale and stratum opticum), and the remainder (81.8%) were in the deep layers. A wide variety of morphological cell types contributed axons to the intercollicular projection, and in a given animal the loci of the labeled neurons were generally symmetrical with the injection site. Small deposits of [3H]-leucine resulted in contralateral labeling only when the injection included the deep collicular laminae. The transported label was most dense in the stratum griseum intermediale and stratum griseum profundum, and its location was generally homotopic with the injection site. Experiments in which collicular HRP deposits were combined with large cervical spinal or pontine reticular injections of Nuclear Yellow indicated that intertectal neurons did not, in most cases, contribute axon branches to the spinal or pontine reticular projections of the colliculus. Receptive field data obtained at the time of the HRP and/or [3H]-leucine deposits demonstrated that the collicular representations of the ipsilateral and at least 45 degrees of the contralateral hemifields were encompassed by intercollicular connections. This was also true for the somatosensory representation of the entire head and a portion of the neck.

The origin of efferent axons in the renal nerves of the cat was examined using retrograde transport of horseradish peroxidase (HRP). Nerves on the surface of the left renal blood vessels were dissected 5–7 mm proximal to the medial margin of the kidney, transected and the central cut ends exposed to HRP. Labeled neurons were typically identified in three locations: (1) centrally along the renal nerve, (2) in the superior mesenteric ganglion, and (3) in the ipsilateral sympathetic chain ganglia (T12-L3). HRP was not detected in preganglionic neurons in the thoracolumbar spinal cord. Labeled cells ranged in size from 15 to 50 μm, with those in the renal nerve at the smaller end of the spectrum and those in the superior mesenteric ganglion at the larger end. In the superior mesenteric ganglion labeled cells were typically localized to a small region in the caudal pole of the ganglion around the origin of the renal nerve. The results show that the sympathetic efferent innervation of the kidney is derived from both paravertebral and prevertebral ganglia. In the latter (superior mesenteric ganglion), renal efferent neurons exhibited a topographic distribution.

A significant number of sympathetic neurons in the lower thoracic paravertebral ganglia (lateral chain ganglia) were retrogradely labeled when the central cut end of the ipsilateral major splanchnic nerve was exposed to horseradish peroxidase (HRP) in the cat. HRP-labeled perikarya were found in all ganglia of that region of the chain from which the splanchnic nerve has its origin but they are most numerous in the last thoracic paravertebral ganglion, that adjacent to the T13 segment of the cord. The number of HRP-positive cell diminished rapidly in more rostral ganglia. Labeled cell bodies of postganglionic splanchnic neurons in the paravertebral ganglia were fusiform to oval in shape with cell diameters averaging between 25 to 45 micrometer. These results demonstrate that the splanchnic nerve contains, in addition to visceral afferents and preganglionic sympathetic constituents, many postganglionic fibers with cell bodies in the paravertebral ganglia. These splanchnic postganglionic axons pass through the coeliac ganglion and continue into distal coeliac nerves.

The organization of visceral sensory neurons in thoracic dorsal root ganglia (DRG) was studied by retrograde transport of horseradish peroxidase (HRP) from the central cut end of the left major splanchnic nerve of the cat. The majority of HRP-labeled cells were concentrated between T5 and T11. Within a DRG, labeled splanchnic neurons were found in all sectors. There was no consistent pattern of localization within the ganglion although clustering of visceral cell bodies was apparent. It may be that each clustered group of cells innervates individual viscera or reflects a degree of functional segregation.

Spinal nerves were transected at selected thoracic levels on the left side and the central cut end of the left major splanchnic nerve was exposed to horseradish peroxidase (HRP) in order to study the preganglionic sympathetic organization in the spinal cord of the cat. In three animals, a total of 4235 HRP labeled neurons were observed (uncorrected counts) in five regions: intermediolateral nucleus (IML) (82.8%), lateral funiculus (LF) (14.7%), intercalatus nucleus (IC) (2.1%), central autonomic (CA) (0.3%) and the anterior horn (AH) (0.1%). The neuronal distribution indicates that sympathetic preganglionic neurons in the thoracic spinal cord are segmentally organized.