Abstracts: Prof P. Redgrave
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Shehab, S., Guadagno, J., Ferguson, K., and REDGRAVE, P. (1997) |
| Previous experimental work has established that activation of sites in the dorsal midbrain can suppress tonic hindlimb extension in the electroshock model of epilepsy. The most sensitive region for this effect is centred on the intercollicular area and is referred to as the dorsal midbrain anticonvulsant zone (DMAZ). Subsequent experiments have shown that the ipsilateral descending projection from this region to the ventrolateral pens is critically involved in mediating its tonic seizure-suppressing properties. The purpose of the present investigation was to test whether direct anticonvulsanteffects in the electroshock model could be obtained from selective manipulation of DMAZ target regions in the ventrolateral pens. Animals were prepared with chronically implanted guide cannulae through which microinjections could bemade directly into the lateral pontine reticular formation, Animals received injections of saline or bicuculline (25-100 pmol) administered either bilaterally or unilaterally. The effects of these injections on the animals' behaviour were determined in an open arena, after which maximal electroshock (1 s, 40 mA, 50 Hz AC) was administered via ear-clip electrodesand the duration of tonic hindlimb extension was recorded. Bilateral injections of bicuculline (100 pmol) suppressed tonicseizures at a significantly higher proportion of sites centred on DMAZ target regions of the ventrolateral pens than surrounding areas. For injections centred on this region the suppressive effects of bicuculline were dose-related in the range 25-100 pmol. Unilateral injections of bicuculline into the ventrolateral pens also effectively suppressed tonic seizures in the electroshock model. Within the ventral pens there was a significant association between the behavioural andanticonvulsant effects of bicuculline; injections suppressing tonic seizures were associated with the induction of fast continuous locomotor activity. These data confirm that the DMAZrecipient region of the ventrolateral pontine reticular formation is part of a circuit which can suppress the manifestation of tonic hindlimb extension in the electroshock model. Whether this property is related to the participation ofthis region in normal locomotion and posture remains to be determined. |