Intrinsic neuromuscular defects in the neurogenic bladder. 1. Short‐term ultrastructural changes in muscular innervation of the decentralized feline bladder base following unilateral sacral ventral rhizotomy

Abstract

The morphology of cholinergic and adrenergic muscular nerves of the feline bladder base was studied ultrastructurally 2, 3, and 4 weeks following its decentralization by unilateral sacral ventral rhizotomy. In all samples, there was widespread transsynaptic degeneration of cholinergic axon terminals and varicosities, with loss of neuroeffector junctions. This was associated with preservation of most adrenergic axons, and -especially in the 4-week samples-with concurrent early regeneration or sprouting in many cholinergic and adrenergic axons. The findings are discussed in relation to neural ultrastructure in other known models of axonal degeneration, and to the pathogenesis of neurogenic dysfunction of the parasympathetic-decentralized bladder. The concurrent degenerative and early regenerative axonal changes herein observed in such a bladder ( I ) suggest that the degeneration of cholinergic axons occurring shortly after rhizotomy is reversible, and probably is compensated for by developing adrenergic hyperinnervation; (2) support the existence of mutual peripheral cholinergic/adrenergic neurotrophism in the vesical muscularis; and (3) provide a probable structural basis for the altered motor and autonomic drug responses of the parasympathetic-decentralized bladder.Key words: neurogeuic bladder, parasympathetic-decentralized bladder, sacral ventral rhizotomy , transsynaptic axonal degeneration, cholinergicladrenerigc neurotrophism, adrenergic hyperinnervation INTRODUCTIONInterruption of efferent sacral parasympathetic neural pathways results in lowermotor-neuron dysfunction of the vesicourethral muscularis, associated with alteration of its neurogenic responses and autonomic drug sensitivity [ElmCr, 1973[ElmCr, , 1974[ElmCr, , 1975aSundin and Dahlstrom, 1973;Lapides, 1974;NorlCn, 1976 Ekstrom et al, 1978;Koyanagi, 1979; Ekstrom and ElmCr, 19801. This dysfunction has traditionally been attributed to loss of central cephalospinal control, according to the broad concept of micturition reflexes [Kuru, 1965; Mahony et al, 19771. Some recent experimental and clinical studies suggest, however, that motor dysfunction of the sacral-decentralized bladder may be due, largely, or in part, to changes in its intrinsic muscular innervation [Sundin and Dahlstrom, 1973; ElmCr, 1975, 1979; Norltn, 1976;Sundin et al, 1977; Dahlstrom, 19781. The present study was conducted to define the short-term ultrastructural changes in intrinsic cholinergic and adrenergic muscular innervation of the feline bladder base following unilateral sacral ventral rhizotomy. The findings will be discussed in the context of known neuroanatomical, neurophysiologic and neuropharmacologic principles in general, and neurogenic vesical dysfunction in particular. MATERIAL AND METHODSNine sexually mature male cats (10-12 months of age; 3-4.2 kg body weight) were used. Left sacral ventral rhizotomy was performed in all cats under intravenous pentobarbital anesthesia (30 mg/kg body weight). As recommended in earlier studies [Carlsson and Sundin, 1968; Sund...