Electrolytic lesion of the globus pallidus reduces the neurodegenerative effects of quinolinic acid lesion of the striatum in the rat

S49 gen balanced conditions may clarify brain metabolic and hemodynamic reserves as well as tissue viability. Supported by a grant from Committee for Research and Prevention in Occupational Safety and Health, Ministry of Labour and Social Affairs, and the Chief Scientist’s Office, Ministry of Health, Israel. THE EFFECT ON PHYSIOLOGICAL PROPERTIES OF SINGLE CELLS OF A SILVER ELECTRODE ACUTELY AND CHRONICALLY IMPLANTED IN THE VISUAL CORTEX OF CATS I. Spivak1, L. Yanko2 and U. Yinon1 Physiology. Lab1, Goldschleger Eye Research Institute, Tel-Aviv University. Fac. Med., Sheba Medical Center, Tel-Hashomer, Israel; The Michaelson Institute for the Prevention of Blindness2, Hadassah Medical Organization, Strauss Health Center, Jerusalem, Israel We have studied the responsiveness patterns of the cells in the primary visual cortex in the presence of a metal conductor. The experimental groups were 6 CHRONIC (n = 378 cells) and 5 ACUTE (n = 201) operated and implanted adult cats. The control groups were 7 OPERATED, but not implanted (n = 487) and 14 intact NORMAL adult cats (n = 429). A para-sagittal incision was unilaterally made in the primary visual cortex and a silver wire electrode (purity: 99.99%; dia: 0.5 mm; length: 4.5–5 mm) was implanted there. Single cells were extracellularly recorded in the pre- (afferented) and post- (deafferented) incision regions, following anesthesia and paralysis, immediately in the ACUTE group and 4–8 weeks following the implantation in the CHRONIC group. The responsiveness, ocular dominance, receptive field organization and orientation and direction selectivity of the cells were examined. The responsiveness was low in the pre-incision regions of all experimented groups (ACUTE: 40.3%; CHRONIC: 44.3%; OPERATED: 47.4%). It was consistently smaller in their post-incision regions (ACUTE: 23.9% CHRONIC: 35.4%; OPERATED: 36.3%). The responsiveness level in the NORMAL group was much higher (86.5%). Thus, an effect, although weak, is seen in the pre-incision region, attributed to the implant. The results of the other physiological parameters, in agreement with the above, showed no remarkable effect due to presence of the silver implant. Our findings thus show that a metal conductor implanted in the mammalian visual cortex, has a negligible effect on the efficiency of the cells there, and thus chemically inert metals may serve in the future as artificial conductors in the brain. Support: Michaelson Research Fund for the Prevention of Blindness; The Jewish Blind in Israel Association, London, UK. ROLE OF IMPULSES GENERATED ECTOPICALLY IN THE DRG IN NEUROPATHIC PAIN I. Sukhotinsky and M. Devor Dept. Cell & Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, Israel Abnormal discharge originating in the peripheral nervous system makes an important contribution to chronic pain states associated with neural injury and disease (neuropathic pain). The nerve injury site is a major source of this ectopic firing. Recently, evidence has begun to accumulate that sensory cell somata in the dorsal root ganglion (DRG) may be an additional source of ectopic impulses. The present work is designed to obtain direct evidence for a contribution of discharge originating in the DRG to neuropathic allodynia and hyperalgesia following incomplete peripheral nerve injury. Hindlimb allodynia was produced in rats by injuring the L5, or L5 and L6 spinal nerves (Chung model). A fine polyethylene catheter was implanted with its tip on the L5DRG. Ectopic DRG discharge was suppressed by injecting lidocaine through the catheter, and was enhanced by injecting a mixture of tetraethylammonium and 4-aminopyridine (TEA 10 mM, 4-AP 1 mM). Allodynia and hyperalgesia were estimated by measuring withdrawal latencies to heat and mechanical stimulation of the plantar surface of the hindpaw. Injection volumes were chosen to cover the DRG, without spread to the

spinal nerve neuroma (5–10 Pl). L5DRG injection of lidocaine 2% eliminated hindpaw allodynia, while injection of the TEA/4-AP exacerbated allodynia by triggering indicators of ongoing pain, hindpaw shaking and licking, and vocalization. Saline injection had no effect. These results support a role for ectopic firing in the DRG both in the generation of ongoing pain, due to ectopic activity in the L5DRG, and also allodynia by the central amplification of sensory input from the residual L4 innervation. EFFECTS OF MYO-INOSITOL AND LI+ AT THE CORTICOHIPPOCAMPAL CONNECTION A.E. Talpalar, R.H. Belmaker, and Y. Grossman Depts. Physiology and Psychiatry, Fac. Health Sciences, Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, BeerSheva, Israel Myo-inositol, a substrate of the phosphatidylinositol cycle, is effective in relieving depression and associated mood disorders. Li+, a blocker of inositol monophosphatase, an enzyme resynthesizing myoinositol, is a useful treatment for bipolar disease. We studied the cellular mechanisms underlying the therapeutic effects of these drugs. Field potentials were recorded in rat cortico-hippocampal slices. Population EPSP (pEPSP) and antidromic action potentials (AAP) were evaluated at the CA1 and the dentate gyrus. At 36°C, 50 min treatment with exogenous myo-inositol (1–2 mM) reduced the amplitudes of both pEPSP by 52% (n = 6, P < 0.0005) and the AAP by 47% (n = 6, P = 0.04). All these effects occurred only in electrically stimulated slices, suggesting use-dependence. Myo-inositol efficacy was significantly smaller at 24°C, suggesting the involvement of metabolic pathways. Li + (1– 10 mM) effects were dual. In nearly 50% of the slices pEPSP’s amplitude increased by 29% (n = 12, P = 0.014), whereas in the rest decreased by 28% (n = 15, P = 0.043). Similarly, AAP’s amplitude increased by 24% (n = 7, P = 0.029), while the rest were depressed by 18% (n = 7, P = 0.094). When myo-inositol (1–2 mM) was applied to previously LiCl (1–2 mM) – treated slices, it depressed the amplitudes of pEPSPs only by 30% (n = 13, P = 0.036) and AAP by 6% (n = 5, P = 0.1). Myo-inositol depressed synaptic and spike activity in the CA1 and the dentate gyrus in a use and temperature dependent manner. Li+ effects were dual, suggesting a double mechanism of action. The interaction between Li+ and myo-inositol suggested unspecific antagonism. Supported by the National Institute for Psychobiology in Israel. ELECTROLYTIC LESION OF THE GLOBUS PALLIDUS REDUCES THE NEURODEGENERATIVE EFFECTS OF QUINOLINIC ACID LESION OF THE STRIATUM IN THE RAT R. Tarrasch, D. Joel, J. Feldon and I. Weiner Dept. of Psychology, Tel-Aviv University, Tel-Aviv, Israel Huntington’s disease (HD) is an inherited progressive neurodegenerative disorder of mid-life onset. The first and most severely affected neurons are in the striatum, particularly those projecting to the external segment of the globus pallidus (GPe). The leading model of HD posits that loss of striatal innervation to GPe leads to overactivity of GPe which results in underactivity of the subthalamic nucleus, which in turn leads to underactivity of the internal segment of the globus pallidus and thus overactivity of the thalamus. Since progressive striatal degeneration characteristic of HD may depend on corticostriatal excitatory input, thalamic overactivity could contribute to the progressive striatal degeneration via its effects on the frontal cortex. Therefore, we hypothesized that GPe lesion may slow down the progressive striatal degeneration in this disease. We tested this suggestion in the leading rat model of HD, namely, striatal quinolinic acid (QA) lesion, which has been shown to most closely mimic the selective neuronal degeneration in the striatum of HD patients. The results showed that the extent of striatal degeneration in rats sustaining bilateral QA striatal lesion was greater compared with rats sustaining in addition a bilateral electrolytic lesion to the globus pallidus. Given that similar dysfunction of basal

S50 ganglia circuitry may subserve the progressive striatal degeneration seen in QA-lesioned rats and HD patients, the present results raise the possibility that lesion to the GPe may also slow down the progressive striatal degeneration characteristic of HD.

DOES CONDITIONED TASTE AVERSION (CTA) CONTRIBUTE TO APPETITE LOSS IN PARKINSON’S DISEASE ? L. Toister, S. Shamay, and B.D. Berger University of Haifa, Haifa, Israel Appetite loss and anorexia, commonly seen in Parkinson’s disease, often continues and may even worsen following drug therapy, even when other symptoms of the disorder improve. One conceivable explanation for this continued anorexia, is that the drugs used to treat Parkinson’s disease, might produce a generalized conditioned taste aversion (CTA), such that patients come to view many foods as aversive or unappetizing. If correct, one way to reduce or prevent anorexia clinically, would be to disassociate the antiparkinsonian drug therapy from meals, thus preventing the formation and maintenance of the hypothesized CTA. As a test of these ideas, it was first determined in a laboratory (rat) model, that drugs commonly used in the treatment of Parkinson’s disease, may indeed produce CTA. Results of these studies indicated that L-dopa, anticholinergic drugs, dopamine agonists, and MAO inhibitors, all produced CTA. In a clinical study, 20 drug treated Parkinson’s patients were offered novel tasting snack foods, either associated or disassociated with their regular medication. In a follow-up interview, the patients were asked which of the snacks they now preferred. Although CTA would predict less preference for the snack ingested in association with medication, the data did not support this hypothesis. One possibility is that latent inhibition or habituation to the noxious effects of the chronic medication prevented the formation of CTA in the patients, a result also observed in animals under laboratory conditions. We thank the Zevulun Clinic (Kiryat Bialik) and Beatrice Shacham, for their cooperation and collaboration.

DEPOLARIZATION INCREASES THE SINGLE CHANNEL CONDUCTANCE AND THE OPEN PROBABILITY OF CRAYFISH GLUTAMATE CHANNELS O. Tour, H. Parnas and I. Parnas The Otto Loewi Center for Cellular and Molecular Neurobiology and the Dept. of Neurobiology, The Hebrew University of Jerusalem, Jerusalem, Israel We have studied the voltage-sensitivity of glutamate receptors in outside-out patches taken from crayfish muscles. Single channel conductance, measured directly at the single channel level, increases as depolarization rises. In particular, at holding potentials from −90 mV to about 20 mV the conductance is 109 pS. At holding potentials positive to 20 mV the conductance is 213 pS. This increase in single channel conductance was observed also in cell-attached patches. In addition, a complex voltage sensitivity was seen: desensitization, rise time and the dose-response curve were all affected by depolarization. To clarify further these multifaceted effects, we evaluated the kinetic properties of single channel activity recorded from cell-attached patches in hyperpolarization (membrane potential around −70 mV) and depolarization (membrane potential ~105 mV). We found that the glutamate dissociation rate constant (k-) was affected most significantly by membrane potential. It declined 6.5 fold under depolarization. The rate constant of channel closing (kc) was also significantly affected; it declined 1.8 fold. The rate constant of channel opening (k o) declined only 1.2 fold. We also examined the effect of altering the patch potential during the glutamate application in order to evaluate the time course of the potential effects.

CONTROL OF FLOOR PLATE GENE EXPRESSION BY THE TRANSCRIPTION FACTOR HNF3B V. Tzarfaty1, A. Frumkin1, Y. Feinstein1, U. Strahle2, M. Mendelshon3 and A. Klar1 1 Dept. of Anatomy and Cell Biology The Hebrew University Hadassah Medical School, Jerusalem, Israel, 2 IGBMC, CNRS, Illkirch, France, 3HHMI, Columbia University, New York, USA The notochord and the floor plate provide signals that contribute to the specification and allocation of cell types in the ventral spinal cord. Molecular and genetic evidence have demonstrated the contribution of several molecules in determining the fate of ventral neural tube cells:. the secreted signaling molecule sonic hedgehog (Shh), the cytoplasmatic signal transduction molecule, PKA, and the transcription factors HNF3β and GLI. We have identified an 80bp cis element of the floor plate gene F-spondin, that is sufficient to derive expression of a reporter gene inthe floor-plate of transgenic mice. By using EMSA (Electrophoresis Mobility Shift Assay), we were able to show specific binding of E14 floor-plate protein extract to the 80 bp region. Computer analysis of this region showed that it contains two known HNF3E sites. EMSA experiments with purified recombinant HNF3E protein, revealed one high affinity, and one low affinity binding site. Functional interaction between the 80 bp element and HNF3β was demonstrated in cellculture experiments. Co-transfection of 80 bp-CAT reporter plasmid with HNF3E expression vector showed increasing levels of CAT expression, in comparison to the CAT activity without HNF3E. In vivo, coinjection of the 80 bp-LacZ reporter construct and HNF3E into zebrafish embryos resulted in ectopic expression of LacZ. This demonstrates that both in vitro and in vivo F-spondin expression in the floor plate is controlled by HNF3E. CALCIUM APPETITE IN HUMANS L. Unger, D. Lugassy, *Y. Rudoy, T. Levin, J. Schulkin and M. Leshem Dept. of Psychology, Haifa University, and *Dialysis Unit, Carmel Hospital, Haifa, Israel Dialysis patients absorb calcium poorly and we investigated whether this influences their preference for calcium taste. Although they do receive calcium and/or vitamin D3 supplementation, we hypothesized that their electrolyte and hormonal status might bolster the appetite, so that they might discriminate calcium better in low concentrations and it would be more hedonic in high concentrations. 10 patients and 10 age and sex matched controls tasted 5 low concentrations of CaCl2 and sucrose (as a control tastant) that are difficult to discriminate. For the hedonic tests they were tested with 3 high (34–272 mM Ca2+) concentrations of CaCl2 in white cheese. There were no differences between patients and controls in concentration discrimination, preference or intensity ratings of calcium and sucrose solutions. However, dialysis patients clearly favored cheese with a higher concentration of Ca2+ than controls. This was not due to reduced taste acuity since patients did not differ on discrimination errors or intensity ratings for calcium in cheese. Most studies suggest that dialysis patients prefer lower concentrations of flavors, and find flavors less pleasant, but our results for calcium in cheese are different, suggesting that for dialysis patients calcium improves flavor. Moreover, the improvement is at very high concentrations (272 mM) that controls utterly reject. It is premature to determine whether this preference for calcium is a manifestation of calcium appetite in humans, but it suggests further research and it may be useful for improving taste and calcium acceptability in such patients. Supported by BSF grant No. 94–00206/1 to ML and JS. GLUTAMINE SYNTHETASE PROTECTS AGAINST NEURONAL DEGENERATION IN INJURED RETINAL TISSUE L. Vardimon, R. Gorovits, N. Avidan, N. Avisar and I. Shaked