ORIGINAL PAPER J. V. Roughan á P. R. Laming Epicortical slow potential shifts and sensory-evoked potentials are related to seizure propensity in gerbils Accepted: 21 January 1998 Abstract Gerbils were assessed for behavioural ten- dency by scoring seizure severity and the amount of ambulatory and rearing activities in a novel `open-®eld' arena. Seizure-prone animals exhibited seizures on early open-®eld trials (1±2) and later performed more ambu- latory activity than non-seizure-prone animals. Two weeks later, two groups of both seizure prone and non- seizure prone animals were chronically implanted with six silver/silver chloride ball electrodes for recordings during behaviour. Electrodes were on the surfaces of the frontal, parietal and occipital cortices bilaterally. In one group these were used to record slow potential shifts; in the other, visual- and acoustic-evoked responses. Larger negative and positive slow shifts occurred in seizure- prone animals. Most evident were the larger positive right frontal shifts and negative left occipital shifts. Seizure tendency was related to the amplitude of these waveforms. Visual-evoked potential amplitudes were generally larger and latencies shorter in seizure-prone animals, especially in the right occipital and left parietal cortices. Seizure susceptibility was associated with in- creased visual-evoked potential amplitude in the right frontal and left occipital cortices, and with reduced la- tency of both auditory-and visual-evoked responses in the left occipital cortex. The discussion highlights a role for glia in slow shift generation and the association of large shifts with enhanced sensory-evoked responses, especially in seizure-prone animals. Key words Gerbil á Glia á Seizures á Evoked response Slow potential shift Abbreviations AEP auditory-evoked potential á EP evoked potential á EPSP excitatory post-synaptic potential á GABA gamma amino-butyric acid á IL initial latency á K   e the extracellular concentration of K + ions á MANOVA multivariate analysis of variance á NSP non-seizure-prone á PA peak amplitude á PCA principal components analysis á PL peak latency á SP seizure-prone á SPS slow potential shift á VEP visual-evoked potential Introduction Captive strains of Mongolian gerbils (Meriones un- guiculatus) frequently contain individuals that exhibit tonic-clonic seizures following novel experience (Thies- sen et al. 1968). Subsequent to introduction to an `open- ®eld', arousal in these animals can be measured quan- titatively by ambulatory activity (Nauman 1968) and attention by bipedal rearing (Kaplan 1981; Laming et al. 1989a). The latter work showed that on repeated pre- sentation with such an `open-®eld', non-seizure-prone (NSP) gerbils show a decline in ambulatory activity due to habituation, as the novelty of the arena is lost. Rearing activity increases for the ®rst three or four trials, but also habituates. Seizure-prone (SP) animals are so classi®ed as on the ®rst trial they exhibit seizures which may be graded for severity using a scale de®ned by Kaplan (1981), later modi®ed by Laming et al. (1989a). Following any seizure activity, these animals show ele- vated ambulatory activity and reduced rearing behav- iour compared to NSP animals. Slow potential shifts as measures of responsiveness Large slow potential shifts (SPSs) of up to 10 mV in surface brain potential of from ca. 2±30 s in duration J Comp Physiol A (1998) 182: 827±838 Ó Springer-Verlag 1998 J.V. Roughan (&) Comparative Biology Centre, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK, Tel.:+44-191 2226715; Fax: +44-191 2228688 or 2227140 e-mail: j.v.roughan@ncl.ac.uk P.R. Laming School of Biology and Biochemistry, Medical Biology Centre, The Queen's University of Belfast, Belfast BT9 7BL, UK Tel.: +44-1232 2243109; Fax: +44-1232 236505 e-mail: p.laming@qub.ac.uk