Irving Nadelhaft

Organization of the sacral parasympathetic reflex pathways to the urinary bladder and large intestine.

Electrophysiological and horseradish peroxidase (HRP) techniques have provided new insights into the organization of the sacral parasympathetic reflex pathways to the large intestine and urinary bladder. The innervation of the two organs arises from separate groups of sacral preganglionic cells: (1) a dorsal band of cells in laminae V and VI providing an input to the intestine; and (2) a lateral band of cells in lamina VII providing an input to the bladder. These two groups of cells were separated by an interband region containing tract cells and interneurons. Neurons in the interband region received a visceral afferent input and exhibited firing correlated with the activity of intestine and urinary bladder. It seems reasonable therefore to consider the interband region as a third component of the sacral parasympathetic nucleus. Anterograde transport of HRP revealed that visceral afferents from the intestine and bladder projected into the parasympathetic nucleus. Most of the projections were collaterals from afferent axons in Lissauers tract that passed in lamina I laterally and medially around the dorsal horn. These afferent collaterals were located in close proximity to preganglionic perikarya and dendrites in laminae I, V and VI. The proximity of visceral afferents and efferents in the sacral cord probably reflects the existence of polysynaptic rather than monosynaptic connections since electrophysiological studies revealed that both the defecation and micturition reflexes occurred with very long central delays (45-70 msec). The reflex pathways mediating defecation and micturition in cats with an intact neuraxis were markedly different. Defecation was dependent upon a spinal reflex with unmyelinated (C-fiber) peripheral afferent and efferent limbs. On the other hand, micturition was mediated by a spinobulbospinal pathway with myelinated peripheral afferent (A-fiber) and efferent axons (B-fiber). Transection of the spinal cord at T12-L2 blocked the micturition reflex but only transiently depressed the defecation reflex. In chronic spinal cats the micturition reflex recovered 1-2 weeks after spinalization; however, in these animals bladder-to-bladder micturition reflexes were elicited by C-fiber rather than A-fiber afferents. The C-fiber afferent-evoked reflex was weak or undetectable in animals with an intact neuraxis. Transection of the spinal cord also changed the micturition reflex in neonatal kittens (age 5-28 days). In neonates with an intact neuraxis bladder-to-bladder reflexes occurred via a long latency spinobulbospinal pathway (325-430 msec). The long latency is attributable to the slow conduction velocity in immature unmyelinated peripheral and central axons. In chronic spinal kittens (3-7 days after spinalization) the long latency reflex was abolished and a shorter latency (90-150 msec) bladder reflex was unmasked. The emergence of this spinal pathway may reflect axonal sprouting and the formation of new reflex connections within the sacral parasympathetic nucleus.

Neurons in the rat brain and spinal cord labeled after pseudorabies virus injected into the external urethral sphincter

Male Sprague‐Dawley rats, with their pelvic and hypogastric nerves transected, were infected with pseudorabies virus (PRV) injected into the external urethral sphincter. Animals were sacrificed at 2, 2.5, 3, and 4 days postinfection. Spinal cord and brain tissue were sectioned and processed by immunohistochemical techniques with antisera against PRV and choline acetyl transferase (CAT). At 2 days postinfection, virus‐labeled neurons were found in the ventrolateral divisions of Onufs nucleus and in the dorsal gray commissure (DGC). At progressively later incubation times, labeled neurons were found in the intermediolateral regions, the superficial layer of the dorsal horn, and the brainstem, in particular, the pontine micturition center. PRV/CAT‐positive neurons were only found in Onufs nucleus. Preganglionic neurons in the L6‐S1 intermediolateral regions were CAT positive but PRV negative, thus suggesting that they are interneurons, not sacral parasympathetic preganglionic neurons. After 4 days, virus had spread to neurons in the paraventricular, preoptic, and even cortical regions. The distribution of these PRV‐labeled brain neurons strongly resembled that obtained after the injection of PRV into the urinary bladder (Nadelhaft et al. [1992] Neurosci. Lett. 143:271–274). In both cases, neurons were labeled in the DGC in the spinal cord. The data therefore suggest that neurons in the DGC may be involved in the integrated control of the bladder and the external urethral sphincter.

Increased levels of nerve growth factor in the urinary bladder and hypertrophy of dorsal root ganglion neurons in the diabetic rat

The level of nerve growth factor (NGF) in the streptozotocin (STZ)-diabetic rat was measured at approximately weekly intervals after STZ induction, using an ELISA assay technique. In addition, the area profiles of L6-S1, and L1-L2 dorsal root ganglion neurons (DRG), labelled by fast blue dye injected into the bladder, were measured at the same weekly intervals. Compared to control animals, the levels of NGF rose rapidly to a maximum at one week and then slowly declined over the next three weeks. The areas of the DRGs increased to a peak after which they also started to decline. The peak increase in DRG area profiles was delayed relative to the peak level of bladder NGF. The data suggest that bladder NGF is transported retrogradely to the DRG neurons where it transforms the cell economy to cause an increase in size.

The distribution with the spinal cord of visceral primary afferent axons carried by the lumbar colonic nerve of the cat

Horseradish peroxidase taken up by the sensory axons in the lumbar colonic nerves in 5 cats was observed in the dorsal root ganglia and in the spinal cord in segments L1 through L5. Reaction product was observed in Lissauers tract, the dorsal columns and laminae I, V, VII and X in a pattern typical of visceral primary afferents from other nerves. A small number of preganglionic neurons were also labeled.

Origin of sympathetic efferent axons in the renal nerves of the cat

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 horseradish 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 micrometers, 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.

Bilateral projections of the pontine micturition center to the sacral parasympathetic nucleus in the rat

Previous work has revealed that pontine micturition center (PMC) neurons send projections to the sacral parasympathetic nucleus (SPN) of the intermediolateral (IML) regions of L6-S1 spinal cord segments in rats. Although unilateral SPN injections will retrogradely label PMC neurons bilaterally, it is not known whether single PMC neurons project bilaterally to the SPN. There may be two different populations of PMC neurons on each side of the brainstem, with both groups independently connecting to the SPNs on opposite sides of the spinal cord. To verify one of these alternatives, a small injection of either rhodamine-labeled latex microspheres or a red fluorescent emulsion was made into the SPN on one side of the cord; a similar injection of either fluorescein-tagged microspheres or a green fluorescent emulsion was made into the other. After at least seven days, the rats were perfused. Inspection of 40 micron cord sections confirmed the similar placement of these injections along the rostrocaudal axis of the cord and that no tracer had spread across midline. Thirty-micron brain sections were examined for filled neurons. Red, green and double labeled neurons were found bilaterally in the PMC, subcoeruleus, and A5 regions. Although some red nucleus cells were also filled, they were only singly labeled and always located contralateral to the injection. Finally, immunohistochemical staining of dopamine-beta-hydroxylase (DBH) containing cells confirmed that some labeled cells were also noradrenergic. We therefore conclude that some PMC, subcoeruleus, and A5 neurons send axons to the SPN on both sides of the lumbosacral cord.

Conduction velocity distribution of afferent fibers in the female rat hypogastric nerve

Conduction velocities of single afferent fibers in the female rat hypogastric nerve were measured by stimulating dorsal rootlets and recording from the hypogastric nerve. A total of 344 units were identified and measured. They were distributed among dorsal roots T13 to L3 ipsilaterally (75%) and between L1 and L2 contralaterally (25%). Over 95% were found in the L1 plus L2 dorsal roots. Ninety-six percent of the units had conduction velocities less than 2 m/s; the average conduction velocity was 0.98 m/s. By way of contrast, afferents in the postganglionic nerves innervating the urinary bladder with conduction velocities less than 2 m/s constituted 65% of the afferents. We conclude that the overwhelming majority of afferents in the female rat hypogastric nerve are unmyelinated C-fibers.