RESUMEN
OBJECTIVES: This study compares the effects of constant current (CC) and constant voltage (CV) spinal cord stimulation (SCS) at various frequencies and intensities on standard nociceptive measurements in rats, the visceromotor reflex (VMR) and neuronal activity, during noxious visceral and somatic stimuli. MATERIALS AND METHODS: Abdominal muscle electromyographic activity changes were measured to indicate VMR, and extracellular activity of L6-S2 spinal neurons was recorded during somatic (pinching) and noxious visceral stimulation (colorectal distension [CRD], 60 mmHg) in anesthetized rats. A stimulating (unipolar ball) electrode at L2-L3 delivered CC- or CV-SCS at varied frequencies and intensities. RESULTS: CC-SCS reduced VMR evoked by CRD significantly more than CV-SCS (p < 0.05). For neuronal activity, high-frequency CC-SCS (40 and 100 Hz) and CV-SCS (100 Hz) effectively reduced intraspinal somatic nociceptive transmission more than low-frequency SCS (2 Hz). No significant differences were observed between the effects of CC- and CV-SCS on spontaneous activity and nociceptive responses of spinal neurons to noxious CRD following short- (five to ten minutes) or long-term (20-30 min) SCS. CONCLUSIONS: Although high-frequency CC- and CV-SCS may be more useful for the management of somatic pain, CC-SCS may be more effective for treating complex pain systems like visceral hypersensitivity.