J. Feng et Jj. Kendig, SELECTIVE EFFECTS OF ALFENTANIL ON NOCICEPTIVE-RELATED NEUROTRANSMISSION IN NEONATAL RAT SPINAL-CORD, British Journal of Anaesthesia, 74(6), 1995, pp. 691-696
We have examined the effects of alfentanil on nociceptive-related neur
otransmission in isolated neonatal rat spinal cord, with particular at
tention to acute tolerance. Electrical stimulation of a lumbar dorsal
root was used to evoke the monosynaptic reflex (MSR), a slow ventral r
oot potential (sVRP), and the dorsal root potential (DRP). Alfentanil
(0.5 nmol litre(-)1 to 1 mu mol litre(-1)) depressed sVRP area by a ma
ximum of 85%; EC(50) was approximately 2 nmol litre(-1). The effects o
f alfentanil were selective for very slow, metabotropically mediated s
VRP components compared with faster NMDA receptor-mediated components.
The MSR was unaffected. Alfentanil depressed DRP area by a maximum of
50% at 1 mu mol litre(-1). Naloxone antagonized all alfentanil effect
s. Morphine depressed sVRP area with an approximate EC(50) of 90 nmol
litre(-1), giving an alfentanil:morphine potency ratio of 45:1. The ef
fects of alfentanil on sVRP showed no biphasic time dependence up to 6
0 min. Naloxone administered after alfentanil produced a significant r
ebound in sVRP area to a level of 143 (SD 21.3)% above control. Thus,
in this study there was no evidence for acute tolerance, as measured b
y a decrease in effectiveness over time, but there was evidence as mea
sured by rebound following naloxone.