Experimental neurology
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Experimental neurology · Dec 1999
Effects of the serotonin synthesis inhibitor p-CPA on the expression of the crossed phrenic phenomenon 4 h following C2 spinal cord hemisection.
The present study assesses the effects of para-chlorophenylalanine (p-CPA), a serotonin-depleting drug, on the recovery of respiratory-related activity in the phrenic nerve induced by asphyxia 4 h following ipsilateral C2 hemisection in young adult rats. HPLC analysis was used to quantify levels of serotonin (5-HT), dopamine (DA), norepinephrine, and the 5-HT metabolite, 5-hydroxyindoleacetic acid, in the C4 segment of the spinal cord, all of which were significantly lower in p-CPA-treated hemisected rats compared to hemisected controls receiving saline. Hemisection alone was found to significantly increase 5-HT levels and significantly decrease DA levels compared to normal controls. ⋯ In addition, saline controls demonstrated significant increases in mean respiratory frequency and mean amplitude of contralateral phrenic nerve activity during asphyxia, compared to normocapnia. However, p-CPA-treated rats did not express significant differences in either mean respiratory frequency or mean amplitude of integrated respiratory wave-forms during asphyxia, compared to normocapnia. The results suggest that p-CPA treatment attenuates the recovery of respiratory-related activity in the phrenic nerve 4 h following ipsilateral C2 hemisection and attenuates asphyxia-induced increases in respiratory frequency and respiratory burst amplitude recorded from the contralateral phrenic nerve.
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Experimental neurology · Dec 1999
Effects of serotonin on crossed phrenic nerve activity in cervical spinal cord hemisected rats.
The present study investigates the effect of 5-hydroxytryptophan (5-HTP), a serotonin precursor, on crossed phrenic nerve activity (CPNA) in rats subjected to a left C2 spinal cord hemisection. Electrophysiological experiments were conducted on anesthetized, vagotomized, paralyzed, and artificially ventilated rats to assess phrenic nerve activity. ⋯ Specifically, in a group of eight animals, application of 5-HTP at 0.5, 1.0, and 2.0 mg/kg significantly increased CPNA by 102.2+/-18.5%, 200.8+/-58.1%, and 615.0+/-356.9% compared with predrug control values, respectively. 5-HTP-induced increases in CPNA were reversed by methysergide (2-6 mg/kg, i.v.), a serotonin receptor antagonist. The results suggest that serotonin is involved in the modulation of crossed phrenic nerve activity following spinal cord injury.