The effect of 5-hydroxytryptamine (5-HT) on population primary afferent depolarisation (PAD) has been studied using in vitro spinal cord preparations from normal and capsaicin pre-treated (neonatal subcutaneous injection; 75 mg kg-1) rats aged 10-14 days. In preparations from untreated rats, the concentration-response curve for PAD in response to 0.1-100 μM 5-HT was bell-shaped but in the capsaicin pre-treated group, a non-saturating 5-HT- induced PAD concentration-response curve was generated. Quantitatively, the mean PAD responses to 0.1-10 μM 5-HT were of a greater amplitude in the control group compared to the capsaicin pre-treated group (p ≤ 0.05). For the highest 5-HT concentration of 100 μM, PAD values were significantly greater in the capsaicin pre-treated group (p ≤ 0.05). These data indicate that control of sensory afferent polarity may involve two 5-HT receptor types and that nociceptive and non-nociceptive afferents may be targets for released 5-HT.
- Nociceptive afferent
- Primary afferent depolarization
- Serotonin (5- HT)
- Spinal dorsal horn