Dorsal column-thalamic pathway is involved in thalamic hyperexcitability following peripheral nerve injury: a lesion study in rats with experimental mononeuropathy

A total of 68 neurons were recorded from the ventro-postero-lateral nucleus of thalamus (VPL) in rats with a unilateral chronic constriction injury (C CI) of the sciatic nerve (n = 20), sham operation (n = 24) and naive rats ( n = 24), and effects of the lesion of dorsal column (DC) pathway CDC lesion or DC + gracile nucleus lesions on VPL nucleus neuronal activities were st udied. In the VPL nucleus contralateral to the CCI (receiving input from th e injured nerve), response latencies of low threshold mechanoreceptive (LTM ) and wide dynamic range (WDR) neurons to electrical stimulation of the sci atic nerve were significantly longer than that in the contralateral VPL nuc leus receiving input from the sham-operated side (P < 0.05). In contrast, r esponse latencies of LTM and WDR neurons to DC stimulation were not differe nt between the sham operated and CCI sides (P > 0.05). Background activity of WDR neurons was significantly higher in the VPL nucleus contralateral to the CCI side when compared to neurons in the VPL nucleus contralateral to the sham operated side and in naive animals. Responses of LTM and WDR neuro ns to innocuous mechanical stimulation of the receptive fields were signifi cantly decreased after DC and DC + gracile nucleus lesions in all animals. However, the responses of WDR neurons to noxious stimuli were selectively r educed only in rats with CCI by DC and DC + gracile nucleus lesions (P < 0. 05). The decrease in noxious stimulus-evoked responses of WDR neurons in th e VPL nucleus contralateral to the CCI side after DC and DC + gracile nucle us lesions was greater than that in the VPL nucleus contralateral to the sh am operated side and naive animals. These results indicated that DC and DC + gracile nucleus lesions produced selective and stronger effect on noxious responses of VPL nucleus WDR neurons receiving input from the site of nerv e injury. The findings suggest that the gracile nucleus-thalamic pathway co nveys, or modulates, nociceptive information to the VPL nucleus following p eripheral nerve injury, resulting in an increase in VPL nucleus response to noxious stimuli that contributes to the development of mechanical hyperalg esia. (C) 2000 International Association for the Study of Pain. Published b y Elsevier Science B.V. All rights reserved.