Use of cortical circuits during focal penicillin seizures: an autoradiographic study with [14C]deoxyglucose

Autoradiography with [14C]deoxyglucose was used to study the architectural pattern of glucose utilization in the motor cortex of rats during focal penicillin seizures. The seizure focus was characterized by a well circumscribed area whose metabolic activity was increased 2-3 times normal. This was tightly surrounded by cortex that was normal or slightly depressed. The posterior third of the focus showed an increase in glucose utilization in a columnar pattern with particular accentuation of activity in lamina V. There was a loss of normal activity in lamina IV within the focus and in somatosensory and occipital cortex far behind the focus. This depression was particularly prominent in the ipsilateral barrel field. Increased metabolic activity was found in a small area in contralateral homotopic cortex, in lamina Vb with columns extending above this from lamina IV to the surface. Glucose utilization was accentuated 1.2-1.8 fold in the ipsilateral secondary somatosensory area, but was normal in the contralateral cortex. The intensity of focal seizures was increased by the intracortical injection of more penicillin or by giving intravenous metrazol. Both of these methods resulted in an increase in the size of the focus as determined with [14C]deoxyglucose. This was most prominent on the lateral border in lamina I-II and V. In addition, there was an accentuation of the columnar pattern in the posterior part of the focus, ipsilateral somatosensory cortex, and contralateral motor cortex. The architectural pattern of glucose utilization in the cortex during focal seizures is discussed with reference to corticocortical, commissural, and corticothalamic circuits that have been identified by others in anatomical studies. Superimposed on this structure are physiological principles of recurrent excitation, lateral spread, and surround inhibition that characterize basic electrophysiological mechanisms of epilepsy, and influence the intensity of activity within the architectural design.