Kindling in the spinal cord: differential effects on mono- and polysynaptic reflexes and its modifications by atropine and naloxone.

We have used the kindling paradigm at the spinal cord level. In spinal, unanaesthetized, paralysed (gallamine 20 mg/kg) cats, the cutaneous afferent (sural) or the muscle afferent (gastrocnemius, tibial and peroneal) nerves were electrically stimulated at 20 min intervals with a 3 sec train (100 Hz, 2 msec pulse duration, 200-400 microA). Kindling was assessed by averaging 16 mono- or polysynaptic ventral root reflex responses produced by constant intensity single shocks. Atropine sulphate (0.5 mg/kg) and naloxone (0.4 mg/kg) effects were measured in the kindled preparation. Kindling induced a progressive increment of the amplitude, ipsilateral propagation and after-discharge frequency. This was greater in polysynaptic responses. When testing monosynaptic responses during the kindling of cutaneous afferents, a cumulative inhibitory effect was observed. In both types of kindled response, atropine had a transient inhibitory effect. Naloxone noticeably augmented the kindled polysynaptic reflexes.