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Contribution of C-fiber afferent nerves and autonomic pathways in the urinary bladder to spinal c-fos expression induced by bladder irritation

1998; Taylor & Francis; Volume: 15; Issue: 1 Linguagem: Inglês

10.1080/08990229870916

1369-1651

LORI A. BIRDER WILLIAM C. DE GROAT,

Veterinary Pharmacology and Anesthesia

AbstractPrevious studies have revealed that chemical irritation of the urinary bladder and urethral mucosa increases the expression of the immediate-early gene, c-fos, in the lumbosacral spinal cord of the rat. The present experiments were undertaken to determine whether drugs known to suppress bladder reflex pathways or spinal nociceptive mechanisms would influence c-fos expression induced by chemical irritation of the lower urinary tract (LUT). Capsaicin (100 mg/kg subcutaneous (sc), 7 days prior to the experiment) which does not block bladder reflexes but does desensitize C-fiber afferents, reduced (89%) the number of Fos-positive cells in the lumbosacral spinal cord induced by acetic acid-induced irritation of the LUT. Morphine (2.5 mg/kg, intravenous (iv)) or a low dose of baclofen, a GABAB agonist, both of which markedly suppressed reflex bladder activity, did not alter spinal c-fos expression induced by LUT irritation. However, a larger dose of baclofen (10 mg/kg, iv) reduced by 45% the number of Fos-positive cells. Clonidine (200 mug/kg, iv), an alpha2 adrenergic agonist, depressed bladder reflexes but produced only a small decrease (25%) in c-fos expression in lateral laminae V-VII of the cord. The ganglionic blocking agent, hexamethonium, which blocks autonomic but not afferent pathways to the LUT, decreased c-fos expression by 50%. The results indicate that certain drugs can differentially affect reflex bladder activity and c-fos expression and that analgesic drugs which suppress somatic nociceptive pathways do not necessarily affect the c-fos expression induced by visceral nociceptive input.KeywordsKey Words: Lower Urinary Tract, Nociception, c-fos, Capsaicin-sensitive Afferents, Mechanoreceptor Afferents, Autonomic Pathways