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Synaptic Currents in Cerebellar Purkinje Cells

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Synaptic Currents in Cerebellar Purkinje Cells Proc. Nail. Acad. Sci. USA Vol. 87, pp. 2662-2665, April 1990 Neurobiology Synaptic currents in cerebellar Purkinje cells (climbing fiber/parallel fiber/glutamate receptors/brain slices/patch clamp) ARTHUR KONNERTH*, ISABEL LLANOt, AND CLAY M. ARMSTRONGt *Max-Planck-Institut fur Biophyikalische Chemie, Gottingen, Federal Republic of Germany; tLaboratoire de Neurobiologie, Ecole Normale Supdrieure, Paris, France; and tDepartment of Physiology, University of Pennsylvania, Philadelphia, PA 19104 Contributed by Clay M. Armstrong, January 22, 1990 ABSTRACT Cerebellar Purkinje cells are known to re- In addition to the excitatory inputs there are two inhibitory ceive strong excitatory input from two major pathways origi- inputs, the more powerful being from basket cells. A Purkinje nating outside the cerebellum and inhibitory input from two cell receives input from numerous basket cells. types of neurons in the cerebellar cortex. The functions and The changes in Purkinje cell membrane potential that synaptic strengths of these pathways are only partially known. follow activation ofthe excitatory inputs have been described We have used the patch-clamp technique applied to Purkinje in vivo and in cerebellar slices (3). We report here observa- cells in thin slices of rat cerebellum to measure directly the tions on the postsynaptic currents elicited by (i) climbing postsynaptic currents arising from the two major excitatory fibers, (ii) a second excitatory pathway probably involving pathways and one of the inhibitory inputs. Inhibitory synaptic mossy and parallel fibers, and (iii) an inhibitory input that currents occur spontaneously with high frequency and are arises from basket cells. variable in amplitude, ranging, in our recording conditions with'high internal Cl-, from less than 100 pA to more than 1 METHODS nA. These currents are blocked by the y-aminobutyrate type A antagonist bicuculline. One of the excitatory inputs is all or Experiments were performed on thin slices of cerebellum, none. For threshold stimulation, the synaptic current is either taken from rats 11-17 days after birth. The cerebellum was full amplitude, when the presynaptic fiber is successfully removed and placed in ice-cold saline within 2 min of stimulated, or completely absent. This synaptic current is often sacrificing the animal. The cerebellum was split at the midline larger than 1 nA and is virtually eliminated by 2 ImM 6- and glued in the appropriate orientation in the cutting cham- cyano-7-nitroquinoxaline-2,3-dione, a blocking agent thought ber ofthe slicer with cyanoacrylate glue. Slices, typically 140 to be specific for glutamate receptors that are not of the ,um thick, were prepared from the vermis with a vibrating N-methyl-D-aspartate type. Its all-or-none character identifies slicer. For all of the experiments reported here, the slice was it as arising from a climbing-fiber synapse. The other excitatory oriented parallel to the long axis ofthe folium (and the parallel input produces a synaptic current that is smoothly graded as a fibers). function of stimulus intensity. This response we believe arises After incubation for half an hour in oxygenated saline from the stimulation of mossy fibers or granule cells. The (bubbled throughout preparation and experimentation with synaptic current associated with this input is also 'largely 95% 02/5% C02), a slice was placed in the experimental eliminated by 2 ImM 6-cyano-7-nitroquinoxaline-2,3-dione. chamber and continuously superfused. A Purkinje cell was selected, using Nomarski optics with a x40 water-immersion A useful new technique (1) that makes possible the direct lens, and its upper surface was cleaned by gently blowing and measurement of synaptic currents in the central nervous sucking saline from a cleaning pipette with diameter of =8 ,um system has recently evolved from the application ofthe patch (1). A tight seal was formed using a Sylgard-coated patch clamp to thin slices of brain tissue. We have used this pipette of resistance 2-3 Mfl, and the membrane was then technique to record excitatory and inhibitory postsynaptic broken to achieve whole-cell configuration. Compensation currents from synapses on Purkinje cells of the cerebellar for series resistance was performed using the standard fea- cortex. tures of an EPC-7 patch clamp (List Electronics, Darmstadt, Cerebellar Purkinje cells receive excitatory synapses from F.R.G.). The cells under clamp changed very slowly and in two distinct pathways, as diagrammed in Fig. lA (2, 3). The favorable cases could be examined for many hours without first of these relays information arising from sensory recep- noticeable change in properties. tors in all parts of the body to the cerebellum, by way of Focal stimulation was applied from an isolated stimulus mossy fibers. In mature animals, a mossy fiber makes contact circuit by means ofa second pipette with a resistance ofabout with several hundred granule cells, each of which gives rise 1 Mfl. This pipette was moved about in the vicinity of the to a parallel fiber. The parallel fibers ascend through the Purkinje cell until the desired response was obtained. Stim- molecular layer, bifurcate, and synapse with Purkinje cells. ulus intensity is reported here in terms of volts applied to this Each Purkinje cell receives synaptic input from as many as pipette. The stimulating current can be approximated by 80,000 parallel fibers. The path thus is from mossy fibers to dividing this voltage by 1 Mfl. granule cells to Purkinje cells. The second input, the climb- The external saline was 125 mM NaCl/2.5 mM KCl/2 mM ing-fiber input, is strikingly different. A Purkinje cell receives CaCl2/1 mM MgCl2/1 mM NaH2PO4/26 mM NaHCO3/10 input from a single climbing fiber, and transmission in this mM glucose, pH 7.4. The usual internal solution was 120 mM pathway is one to one. The functional significance of these CsCI/20 mM tetraethylammonium chloride/4 mM NaATP/2 two inputs is not yet certain. An interesting hypothesis holds mM MgCl2/10 mM EGTA/10 mM Hepes, pH 7.3. We that a climbing fiber serves as "instructor" to alter the employed Cs' instead of K+ to facilitate the measurement of strength of parallel fiber synapses (4, 5). synaptic currents. Cs' blocks outward current through volt- age-sensitive K+ channels and thus simplifies interpretation The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" Abbreviations: CNQX, 6-cyano-7-nitroquinoxaline-2,3-dione; in accordance with 18 U.S.C. §1734 solely to indicate this fact. GABA, 'y-aminobutyrate. 2662 Downloaded by guest on September 27, 2021 Neurobiology: Konnerth et A Proc. NatL. Acad. Sci. USA 87 (1990) 2663 A B b a wn 500 pA MO7 9 200ms - L- L .. C >% 0 L 10liM bicuculline FIG. 1. (A) The major synaptic connections of a Purkinje cell (P) in the cerebellar cortex. The relevant inhibitory input is from numerous basket cells (13), which have synapses on the soma and the initial segment ofthe Purkinje cell axon. (Synaptic input to the basket cells is omitted for clarity.) In the mature animal, a single climbing fiber (CE) has multiple excitatory synapses on the soma and proximal dendrite ofthe Purkinje cell. The second excitatory input is the mossy fiber (MF) to granule cell (Gr) to Purkinje cell (P) path. A mossy fiber has synaptic contact with perhaps several hundred granule cells, and a Purkinje cell receives synaptic input from thousands of granule cells. (B) Spontaneous inward currents recorded from a Purkinje cell with high internal Cl (upper trace). The currents are completely eliminated by the y--aminobutyrate type A (GABAA) antagonist bicuculline (lower trace) and almost certainly arise from basket cell-Purkinje cell synapses. Holding potential, -60 mV. of the records. Experiments were performed at room tem- 0 mV), but in an unperfused cell the synapses would be perature, near 220C. inhibitory. Postsynaptic currents elicited by the two excitatory inputs RESULTS are illustrated in Fig. 2. The climbing fiber was stimulated by placing the stimulating electrode directly over the Purkinje All of the Purkinje cells that we examined had spontaneous cell, or in the granule cell layer 50-100 um away (Fig. 1A). currents similar to those illustrated in Fig. 1B, which ranged The electrode was moved about until the climbing-fiber from 50 pA to more than 1 nA. The peak of the current was response could be elicited with the minimum stimulus inten- 3-6 ms after its origin, and the current decayed to halfofpeak sity. An inward synaptic current elicited by the climbing fiber amplitude ==15 ms after the origin. These currents were was easily recognized by its large amplitude (2-3.4 nA at -60 reversibly blocked by 10 AM bicuculline (Fig. 18, lower mV) and its all-or-none characteristic: with stimulus intensity trace), a blocker of GABAA receptors. Thus the currents are near threshold, the response was either full amplitude or through GABAA channels and almost certainly arise from zero. It could be distinguished readily from an antidromic spontaneous activity in the numerous basket cells that form spike in the Purkinje cell axon, because the latter had a much inhibitory synapses on a Purkinje cell. The current is inward shorter latency, had a briefer duration, and could be inacti- in our recording conditions (high internal Cl-, with Vc, near vated by holding at -30 mV. A B 500 pA / loms 2000T l 500-- 15001- a 1000T a2) QO~ a) /~~~~~~ -UQ i E E 500-I- 0 500 n% U -- 1 T- 0 2 4 6 8 o0 2 4 6 8 10 stimulation strength (V) stimulation strength (V) FIG. 2. Two types of excitatory postsynaptic currents in Purkinje cells. (A) (Upper) The synaptic current elicited by a climbing fiber, stimulated with intensity of 1, 2, 3, 4, and 5 V.
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