Neuroscience Letters, 154 (1993)9-12 9 © 1993 ElsevierScientificPublishers Ireland Ltd. All rights reserved0304-3940/93/$06.00 NSL 09467 Corpus callosotomy effects on cerebral blood flow and evoked potentials (transcallosal diaschisis) Russell J. Andrews a'c, John R. Bringas a'c, Gina Alonzo a'~, M. Shahriar Salamat b, Sami Khoshyomn a'c and Daniel S. Gluck a'c Departments ofaNeurological Surgery and b Pathology ( Neuropathology ), University of California at Davis, Medical Center, Davis (USA.) and cVeterans Affairs Medical Center, Martinez, CA (USA) (Received 12 November 1992; Revisedversion received 19 January 1993;Accepted21 January 1993) Key words: Brainretraction; Cerebral blood flow; Corpus callosum; Diaschisis; Evoked potentials; Focal cerebral ischemia The role of the corpus callosum in diaschisis was examinedthrough the acute effects of stereotacticcorpus callosumsectionon cerebralblood flow and somatosensoryor auditory evoked potentials bilaterallyduring unilateral brain retraction ischemia, using a previouslyreported swine model. Cerebral blood flowand evokedpotential amplitudecontralateral to retraction increasedduring retraction with the corpus callosumintact, compared with post-callosal section values. With retraction followingcallosat section, there was no increase in cerebral blood flow or evoked potential amplitude contralateral to retraction. Diaschisis during the early stages of a focal, unilateral injury takes the form of a contralateral disinhibition (as measured by cerebral blood flowand evoked potentials), an effectwhich is lost following callosal section. The term 'diaschisis' was first used by von Monakow in 1914 to describe distant changes in the nervous system following a focal injury [15]. He emphasized the impor- tance of neural connections: '...diaschisis represents an 'interruption of function' appearing in most cases quite suddenly.., which originates from a local lesion but has its points of impact...only at points where fibres coming from the injured area enter intact grey matter...' [15]. Most studies of diaschisis have considered distant effects hours or days after an insult (e.g. middle cerebral artery stroke) rather than during the initial stages [7, 12]. In our review of transhemispheric diaschisis, we found that the contralateral effects of a focal injury depended on the time after the injury at which the diaschisis was assessed [11. In our previously-described large animal model simu- lating operating room brain retraction ischemia [2, 3], we noted changes in the contralateral hemisphere during unilateral retraction [4]. There was an increase in cere- bral blood flow (CBF) and evoked potential (EP) ampli- tude contralateral to retraction. Given the abundant transcallosal connections between the somatosensory and auditory cortices, we have repeated our unilateral Correspondence: R.J. Andrews. Present address: VA Medical Center (Neurosurgery 112D), 3801 Miranda Avenue, Palo Alto, CA 94304, USA. Fax: (1) (415) 852-3430. retraction protocol with the corpus callosum sectioned in order to assess the importance of transcallosal connec- tions to the contralateral CBF and EP changes during focal unilateral ischemia. The animal model and techniques have been described elsewhere in detail [2, 3]; only a brief summary is pro- vided here. Eleven juvenile domestic swine (10 to 35 kg) were used. Following intramuscular injection of atropine sulfate (0.05 mg/kg) and fentanyl (0.4 mg/15 kg) plus droperidol (20 mg/15 kg) (Innovar-Vet 1 ml/15 kg), en- dotracheal intubation was performed, and femoral arte- rial and venous access established by cutdown. Mainte- nance anesthesia was isoflurane 1.5 to 2%. ThepCO2 was maintained at 40 mmHg. At the completion of the exper- iment (10 to 12 h of retraction-recovery recording se- quences), the animal was sacrificed by pentobarbital overdose. The head was placed in a stereotactic holder, and a wide bilateral craniectomy was performed as described previously [3]. The corpus callosum was sectioned ap- proximately one-half way through the recording period for each animal, to give similar numbers of retraction- release sequences both pre- and post-callosal sectioning. The stereotactic callosotomy technique described by Magni [10] and Fukuda [8] was employed. A 2-mm inci- sion was made in the dura approximately 2 mm lateral to the midline at a point 2 cm posterior to the frontal poles.