Response properties of the auditory cortex and behavioral capabilities of the Syrian hamster (Mesocricetus auratus)

S30 GABA-INDEPENDENT DORSAL ROOT AFFERENT DEPOLARIZATION IN THE NEONATAL RAT SPINAL CORD E. Kremer and A. Lev-Tov Dept. of Anatomy and Cell Biology, The Hebrew University-Hadassa Medical School, Jerusalem, Israel Primary afferent depolarization (PAD) in the vertebrate spinal cord co-occurs with presynaptic inhibition. PAD is considered to be mediated by GABAA receptors and to contribute to the inhibitory mechanism. The present work describes GABAA-independent afferent depolarization in the isolated spinal cord preparation of the neonatal rat. The afferent depolarization is manifested by the appearance of prolonged dorsal root potentials (DRPs), by antidromic afferent discharge, and by prolonged increase in intraspinal afferent excitability in the absence of chloride, or in the presence of the GABAA receptor blocker, bicuculline. The afferent depolarization and antidromic firing persisted when the GABAA and GABAB receptors (by which presynaptic inhibition is considered to be mediated) were blocked by their specific antagonists, or when a mixture of antagonists of GABAA, GABAB, 5HT2, and the glutamate metabotropic group II and III presynaptic receptors, was added to the bath. It is suggested that the afferent depolarization under these conditions is produced by potassium transients which have been reported to reach a substantial level in the developing spinal cord, during neuronal activation. Possible implications of potassium transients in the developing and the adult mammalian spinal cord will be discussed. PROTEIN PHOSPHORYLATION IS MODULATED IN FETAL BRAIN PREPARATIONS AFTER EPISODES OF ISCHEMIA F. Kuperstein, E. Bercovici, R. Seger and E. Yavin Dept. of Neurobiology, Weizmann Institute of Science, Rehovot, Israel Stress-induced phosphorylation of proteins via diverse cellular signaling pathways constitute an important step in the pathological cascade leading to cell damage and death. We have examined protein kinase C (PKC)-dependent phosphorylation and MAP kinase activation signals in fetal brain preparations after in utero episodes of maternalfetal blood flow restriction (fetal global ischemia). Ischemic and matched controls of fetal rat brains at 20 days gestation were isolated and 105ug cytosolic and membrane subcellular fractions prepared. Endogenous PKC activity was abolished by heat inactivation, 45°C for 30 min, and aliquots of these preparations served as substrates for phosphorylation by exogenously added, partially purified PKC using J32P-ATP in the presence of Ca2+ and lipid activators. Two major radioactive bands of apparent MW of 80 and 43 kDa resembling MARCKS and GAP43 respectively, were identified. Brain preparations after 20 min restriction incubated with exogenous PKC showed reduced phosphorylation of the above protein bands; an effect which was reversed after 24 h reperfusion. Addition of o-vanadate (1 mM) and okadaic acid (1 PM), increased lipid dependent phosphorylation. Fetal global ischemia also resulted in changes in the phosphorylation kinetics of the MAPK/ERK subfamily (ERK1 and ERK2) in the fetal brain. After 20 min restriction the activation/phosphorylation of ERK1 (44 kDa) isoform was elevated whereas that of ERK2 (42 kDa) was not affected and remained low. This effect was PKC independent. These results suggest that intrauterine stress turns on independently the PKC and MAPK signaling cascades in the developing brain. DOES TRAINING LEAD TO AUTOMATICITY? R. Laiwand1, M. Ahissar2 and S. Hochstein3 Depts. of Neurobiology1,3 and Psychology2, and Center for Neural Computation, The Hebrew University of Jerusalem, Jerusalem, Israel Automaticity implies the ability to perform two tasks at the same time without interference. Are simple visual tasks performed automatically? Recently it was demonstrated that performance of a detection task degraded when subjects performed a second task at the same time.

We now ask whether substantial practice with simple detection leads to automaticity. We trained subjects in an orientation detection task (popout). Following prolonged systematic training, their performance dramatically improved. However, when a second, letter identification (T/L) task was added, performance was hampered immensely. Additional practice with the double task substantially improved performance. Thus, despite a lot of practice, pop-out detection does not become automatic: it can not be performed as well when attention is paid to a second task. Pre-training the subjects also with the second task improved performance on the first session with the double task, yet it was still worse than performance on either single task separately. There seems to be something about simultaneous performance of two tasks which can not be learned by separate practice of each task! In the next experiment, we first trained subjects separately with each of the two tasks, with two sets of stimulus orientations. We then trained subjects with the double task with one set of orientations, and finally tested them on double task performance using the second set. Performance regressed back to predouble task training levels and was improved by renewed training. This suggests that learning to perform the double task is also stimulus specific, and not the learning of a generalized skill. We conclude that training with each task and with their combination does not lead to automatic performance. RESPONSE PROPERTIES OF THE AUDITORY CORTEX AND BEHAVIORAL CAPABILITIES OF THE SYRIAN HAMSTER (MESOCRICETUS AURATUS) M. Lamish1, G. Koay2, R.S. Heffner2, H.E. Heffner2 and Z. Wollberg1 1 Dept. of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel; 2 Dept. of Psychology, University of Toledo, Toledo, Ohio, USA The goal of this study was to establish an experimental animal model to examine cross-modal neuroplasticity and auditory behavioral compensation in visually impaired mammals. To that end we initially determined, electrophysiologically, the boundaries of the auditory and visual cortices in intact Syrian hamsters (Mesocricetus auratus) and characterized some of the auditory cortex response properties. In addition we evaluated, behaviorally, some auditory capabilities of this rodent. The hamster was selected for this purpose mainly because its pups are born at a very early stage of neural development. Boundaries were determined on the basis of auditory field evoked potentials whereas response properties were evaluated on the basis of single and multi-unit responses to auditory clicks, noise bursts and pure tones. More than 90% of the 500 cells that were included in this sample responded to all the stimuli that we applied with a minimum latency ranging between 7.4 and 22.4 (mean ± SD = 10.8 ± 2.7 ms). Best frequencies in a sample of 60 cells ranged between 1.0 and 21.0 kHz, with minimum threshold intensities around 8.0–10.0 kHz. About 80% of these cells were narrowly tuned as evaluated by the Q10dB factor (Q10dB > 2). Using an arbitrary standard of the highest and lowest frequencies audible at an intensity of 60 SPL, the behavioral hearing range of the hamster extended from 96 Hz to 46.5 kHz with best sensitivity at 8.0 kHz which agrees well with the electrophysiological minimum thresholds. The minimum azimuthal audible angle, as determined by a conditioned avoidance task, ranged between 18 and 22 degrees. Supported in part by the United States-Israel Binational Science Foundation (BSF). MATERNAL DIABETES AFFECTS FETAL CEREBRAL GLUCOSE METABOLISM: 13C NMR ISOTOPOMER ANALYSIS A. Lapidot and S. Litvin Weizmann Institute of Science, Rehovot, Israel The brain is not usually thought to be a target of chronic diabetes complications. Utilization of glucose, and competition between glucose and other energy fuels in the diabetic fetal brain, have not yet been