Abstracts: Prof P. Redgrave
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Wang, S. and REDGRAVE, P. (1997) |
| An important reaction in rodent models of persistent pain is for the animal to turn and bite/lick the source of discomfort (autotomy). Comparatively little is known about the supraspinalpathways which mediate this reaction. Since autotomy requires co-ordinated control of the head and mouth, it is possible thatbasal ganglia output via the superior colliculus may be involved; previously this projection has been implicated in thecontrol of orienting and oral behaviour. The purpose of the present study was therefore, to test whether the striato-nigro-tectal projection plays a significant role in oral responses elicited by subcutaneous injections of formalin. Behavioural output from this system is normally associated with the releaseof collicular projection neurons from tonic inhibitory input from substantia nigra pars reticulata. Therefore, in the present study normal disinhibitory signals from the basal ganglia were blocked by injecting the GABA agonist muscimol into different regions of the rat superior colliculus. c-Fos immunohistochemistry was used routinely to provide regional estimates of the suppressive effects of muscimol on neuronal activity.Biting and licking directed to the site of a subcutaneous injection of formalin (50 mu 1 of 4%) into the hind-paw were suppressed in a dose-related manner by bilateral microinjections of muscimol into the lateral superior colliculus (10-50 ng: 0.5 mu 1/side); injections into the medial superior colliculus had little effect. Bilateral injections of muscimol 20 ng into lateral colliculus caused formalin-treated animals to re-direct their attention and activity from lower to upper regions of space. Muscimol injected unilaterally into lateral superior colliculus elicitedipsilateral turning irrespective of which hind-paw was injectedwith formalin. Oral behaviour was blocked when the muscimol andformalin injections were contralaterally opposed; this was alsotrue for formalin injections into the front foot. Interestingly, when formalin was injected into the perioral region, injections of muscimol into the lateral superior colliculus had no effect on the ability of animals to make appropriate contralaterally directed head and body movements tofacilitate localization of the injected area with either front-or hind-paw.These findings suggest that basal ganglia output via the lateral superior colliculus is critical for responses to noxious stimuli which entail the mouth moving to and acting on the fool, but not when the fool is the active agent applied to the mouth. The data also suggest that pain produces a spatiallynon-specific facilitation of units throughout collicular motor maps, which can be converted into a spatially inappropriate signal by locally suppressing parts of the map with muscimol. |