Intrathecal galanin alleviates allodynia-like behaviour in rats after partial peripheral nerve injury

We have previously suggested that the neuropeptides galanin and galanin mes sage-associated peptide (GMAP) may have an inhibitory role in spinal nocice ption. The present study examined the effects of intrathecal (i.t.) adminis tration of these two peptides on allodynia-like behaviours in response to m echanical and cold stimulation in rats after photochemically induced ischae mic peripheral nerve injury. I.t. galanin significantly alleviated the mech anical- and cold-allodynia-like behaviours in nerve injured rats, and was n ot associated with motor impairment or sedation. I.t. GMAP relieved mechani cal allodynia much less than galanin. I.t. M-35, a high-affinity galanin re ceptor antagonist, did not significantly alter the response of the rats to mechanical or cold stimulation. At 1 or 2 weeks postinjury, around 15% of d orsal root ganglion (DRG) neuron profiles showed galanin-like immunoreactiv ity. These profiles were mostly small sized. Although the number of galanin positive cells was thus increased in the DRG in the present model, the inc rease was substantially less than after complete sciatic nerve section, as previously shown. The present results showed that spinal administration of galanin inhibited some abnormal pain-like behaviours in rats after partial peripheral nerve i njury. These results further support an inhibitory function for galanin in nociception. However, endogenous galanin may not play a significant role in suppressing nociceptive input after partial ischaemic peripheral nerve inj ury, as the upregulation of galanin is moderate.