William DeGroat

Tracing of afferent and efferent pathways in the left inferior cardiac nerve of the cat using retrograde and transganglionic transport of horseradish peroxidase

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 Lissauers tract and in lamina 1 on the lateral border of the dorsal horn. Labeled afferent 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.

Influences of external urethral sphincter relaxation induced by alpha-bungarotoxin, a neuromuscular junction blocking agent, on voiding dysfunction in the rat with spinal cord injury

OBJECTIVES To determine whether external urethral sphincter (EUS) relaxation induced by alpha-bungarotoxin, a highly selective neuromuscular junction blocking agent, could ameliorate voiding dysfunction after spinal cord injury (SCI) in rats. METHODS The effects of intravenous alpha-bungarotoxin (333 microg/kg) were evaluated during cystometry in decerebrate, unanesthetized female Sprague-Dawley rats (250 to 300 g) with spinal cords chronically transected at T7-9 (n = 7) or with normal spinal cords (NSC) (n = 7). Parameters measured included voided volume (VV), residual volume (RV), volume threshold for inducing micturition (VT), voiding efficiency (VE), micturition pressure (MP), pressure threshold for inducing micturition (PT), bladder contraction duration (BCD), and compliance (CP). RESULTS In SCI rats, treatment with alpha-bungarotoxin improved voiding. The toxin increased VE (31%) and reduced RV (42%), MP (52%), BCD (14%), and VT (31%). VV, PT, and CP were not altered. In NSC rats, alpha-bungarotoxin decreased VE (23%), increased RV (63%), and decreased MP (36%), VV (38%), and VT (20%) but did not change BCD and CP. CONCLUSIONS The results of our study demonstrated that alpha-bungarotoxin improved voiding in SCI rats by reducing urethral outlet resistance. However, in NSC rats, the toxin reduced voiding, probably by suppressing high-frequency phasic sphincter activity, necessary for efficient urine elimination in normal animals. The present results provide further support for the view that drugs that depress striated muscle activity can be useful in the treatment of voiding dysfunction after SCI.

Changes in the biaxial viscoelastic response of the urinary bladder following spinal cord injury.

In order to gain a deeper understanding of bladder function, it is necessary to study the time-dependent response of the bladder wall. The present study evaluated and compared the viscoelastic behaviors of normal and spinal cord injured (SCI) rat bladder wall tissue using an established rat model and planar biaxial stress relaxation tests. Bladders from normal and spinalized (3 weeks) rats were subjected to biaxial stress (either 25 or 100 kPa in each loading direction) rapidly (in 50 ms) and subsequently allowed to relax at the constant stretch levels in modified Krebs solution (in the absence of calcium; with no smooth muscle tone) for 10,000 s. We observed slower and therefore less stress relaxation in the SCI group compared to the normal group, which varied with the stress-level. These experimental results were fitted (r2 > 0.98) to a reduced relaxation function. Furthermore, biochemical assays revealed that the collagen content of SCI rat bladders was significantly (p < 0.05) lower by 43%, while the elastin content was significantly (p < 0.001) higher by 260% than that of normal bladders. These results suggest that SCI and the associated urologic functional changes induce profound tissue remodeling, which, in turn, provided the structural basis for the alterations in the complex, time-dependent mechanical behavior of the urinary bladder wall observed in the present study.

Naloxone induced micturition in unanesthetized paraplegic cats.

In chronic spinal cats 2 to 10 weeks after transection of the spinal cord at the lower thoracic level (T12-T13), the administration of naloxone, an opiate antagonist, (32-500 micrograms./kg. i.p.), stimulated micturition. The total quantity of urine released after administration of naloxone ranged from 10 to 70 per cent, (mean 39 per cent) of the initial bladder volume. The response to the drug occurred 5 to 10 minutes after injection and was characterized by repeated periodic expulsion of small quantities of urine (5 to 10 ml.) which coincided with a pattern of hind-limb movement which resembled walking behavior. The effects of naloxone persisted for about 1 hour. The motor activity following administration of naloxone was dependent upon activation of bladder afferents since it did not occur when the bladder was empty. Naloxone also facilitated the release of urine induced by stimulation of somatic afferents. With repeated administration of naloxone, tolerance developed which was evident for several days. These observations suggest that an endogenous opiate may have a tonic inhibitory role in regulation of micturition. Pharmacologic manipulation of this putative inhibitory mechanism may facilitate management of neurogenic bladder dysfunction.

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.

Sympathetic innervation of the cornea from the superior cervical ganglion. An HRP study in the cat

Horseradish peroxidase (HRP) was applied to the cornea in cats using a variety of methods. Small numbers of labeled neurons were observed in the superior cervical ganglion (SCG), the majority were located in the rostral half. This confirms previous histofluorescence data which indicated the SCG was the likely source of adrenergic fibers to the cornea.

EFFECT OF INTRAVESICAL CAPSAICIN AND VEHICLE ON BLADDER INTEGRITY IN CONTROL AND SPINAL CORD INJURED RATS

PURPOSE To determine the acute effect of intravesical capsaicin on bladder mucosal integrity in normal and spinal cord injured (SCI) rats. MATERIALS AND METHODS Intravesical reagents were instilled in 5 groups of age and weight matched female rats: 1) control + normal saline solution (NSS), 2) control + ethanol (EtOH), 3) control + capsaicin/EtOH, 4) SCI + NSS, 5) SCI + capsaicin/EtOH. Intravesical instillations were performed 4 weeks after a standard T10 SCI. Intravesical capsaicin (1 mM.) was dissolved in 30% EtOH/NSS. The animals (n = 3 each group) were sacrificed at 30 minutes, 24 hours, 72 hours, and 7 days after intravesical instillation. Whole bladders were harvested, fixed in 10% buffered formalin, and paraffin embedded. Tissue blocks were blind coded and sectioned (5 microns thickness) for histopathological analysis. All sections were initially stained with hematoxylin and eosin (H & E). Specific staining for mucin carbohydrate moieties included periodic acid-Schiff (PAS) and alcian blue. Also, immunohistochemical staining for GP51 (a urinary glycoprotein) was performed. RESULTS Control and SCI rats exhibited similar bladder mucosal histology by H & E and mucin specific stains. Instillation of saline demonstrated no effect on bladder histology, whereas instillation of intravesical capsaicin induced a profound acute effect of thinning of the epithelium, submucosal edema, and diminished presence of GP51. EtOH produced similar pathological findings, but to a lesser degree than capsaicin. Intravesical capsaicin demonstrated a similar effect in both control and SCI animals. The peak effect was seen after 30 minutes and continued for 24 hours. Partial recovery was noted after 72 hours and complete recovery was evident by 1 week. CONCLUSIONS The control and SCI rats demonstrated a histologically similar mucosa and glycosaminoglycan layer. The effect of saline instillation on the mucosa was negligible. Intravesical capsaicin dissolved in 30% ethanol/NSS had a profound effect on the bladder urothelium submucosa that was more pronounced than that seen with the ethanol vehicle alone in normal animals.

Enkephalinergic Modulation of Cholinergic Transmission in Parasympathetic Ganglia of the Cat Urinary Bladder

Dense networks of enkephalin containing nerve terminals have been identified in mammalian sympathetic and parasympathetic ganglia (1, 12, 20–22, 25, 35). Evidence from various sources indicates that enkephalins are contained in, and released by axons that arise from neurons extrinsic to the ganglia, and that enkephalins have an inhibitory effect on ganglionic transmission (2, 12, 23, 25, 26, 30, 36, 39).

Organization of corneal afferent axons in the trigeminal nerve root entry zone in the cat

SummaryExperiments were carried out in cats to learn the location of sensory axons from the cornea in the trigeminal nerve root just prior to its entry into the brainstem. HRP injected into the cornea labelled these axons and indicated they were not restricted to the ophthalmic division of the nerve root as had been indicated from previous studies. These findings, if representative of other branches of this nerve, offer a partial explanation for the variable preservation of function following transection of an entire division of the trigeminal nerve root in cases of trigeminal neuralgia.