Acute reorganization of the forepaw representation in the rat SI cortex after focal cortical injury: neuroprotective effects of piracetam treatment

Immediate postlesion reorganization of the somatosensory cortical represent ation was examined in adult rats. Response properties of small clusters of neurons were recorded in the area of the primary somatosensory cortex (SI) devoted to the contralateral forepaw representation. Electrophysiological m aps were elaborated on the basis of the sensory 'submodality' (cutaneous or noncutaneous) and the location of the peripheral receptive fields (RFs) of layer IV neurons. Recordings were made prior to, and from 1 to 12 h after, induction of a focal neurovascular lesion to the SI cortex that initially destroyed a part (8.5%) of the cutaneous representation. Moreover, the infl uence of an anti-ischaemic substance (piracetam) on lesion-induced changes was analysed. The main observations were: (i) a gradual outward expansion o f the area of the functional lesion, which was smaller in the piracetam-tre ated (PT) rats than in the control, placebo-treated (PL) rats; (ii) a subst antial remodelling of the spared representational zones, both in cortical s ectors adjoining the site of injury and those remote from the site; (iii) a significant postlesion increase in the size of cutaneous RFs in the PT rat s, but not in the PL rats; (iv) a better preservation of RF submodality and topographic organization in the PT maps than in the PL maps; and (v) a dec rease in neuronal responsiveness to cutaneous stimulation which was less pr onounced in the PT than in the PL rats. Our results can be ascribed to a ra pid change in the balance of excitatory and inhibitory connections which le ads to unmasking of subthreshold inputs converging onto cortical neurons. O ur findings also indicate that acute piracetam treatment exerts a protectiv e function on the physiological response properties of cortical neurons aft er focal injury.