Conditioned Eyeblink Learning Is Formed and Stored Without Cerebellar Granule Cell Transmission
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Corrections NEUROSCIENCE. For the article ‘‘Conditioned eyeblink learning is published October 8, 2007; 10.1073͞pnas.0708165104), the formed and stored without cerebellar granule cell transmis- authors note that in Fig. 2a, the same trace was inadvertently sion,’’ by Norio Wada, Yasushi Kishimoto, Dai Watanabe, used for the electrophysiological records of RNB (DOX- Masanobu Kano, Tomoo Hirano, Kazuo Funabiki, and untreated) and RNB (DOX-withdrawn). This error does not Shigetada Nakanishi, which appeared in issue 42, October 16, affect the conclusions of the article. The corrected figure and 2007, of Proc Natl Acad Sci USA (104:16690–16695; first its legend appear below. Fig. 2. Action potential firing of Purkinje cells in awake WT and RNB transgenic mice. (a) Spontaneous activities of Purkinje cells consisted of simple spikes and complex spikes (red asterisks) in WT, DOX-untreated, and DOX-withdrawn RNB mice, but no simple spikes were evoked in DOX-treated RNB mice. (b) Traces of simple spikes shown in a were superimposed. (c) Interspike interval histogram of simple spikes shown in b.(d) Traces of five complex spikes were superimposed. (e and f) Mean Ϯ SEM of firing rates of simple spikes (e) and complex spikes (f) are shown with columns and bars, respectively. ***, P Ͻ 0.001 (comparison between DOX-treated RNB mice and all five other animals by the Scheffe´ test). (g) The extracellular recording site (red) was confirmed at the Purkinje cell layer by CORRECTIONS fluorescent Nissl staining. ML, molecular layer; PL, Purkinje cell layer; GL, granule cell layer. www.pnas.org͞cgi͞doi͞10.1073͞pnas.0711631105 www.pnas.org PNAS ͉ January 22, 2008 ͉ vol. 105 ͉ no. 3 ͉ 1097 Downloaded by guest on September 26, 2021 Conditioned eyeblink learning is formed and stored without cerebellar granule cell transmission Norio Wada*†, Yasushi Kishimoto‡§, Dai Watanabe†, Masanobu Kano‡, Tomoo Hirano¶, Kazuo Funabiki*, and Shigetada Nakanishi*†ʈ *Department of Systems Biology, Osaka Bioscience Institute, Suita, Osaka 565-0874, Japan; †Department of Molecular and System Biology, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan; ‡Department of Cellular Neuroscience, Graduate School of Medicine, Osaka University, Suita 565-0871, Japan; and ¶Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan Contributed by Shigetada Nakanishi, August 29, 2007 (sent for review August 15, 2007) Classical conditioning of the eyeblink reflex is elicited by paired responses (CRs) are properly evoked in response to CS by a presentation of a conditioned stimulus and an unconditioned timing signal from Purkinje cells (1, 3, 27, 28). Eyeblink condi- stimulus and represents a basic form of cerebellum-dependent tioning involves multiple learning processes, at least acquisition, motor learning. Purkinje cells and the deep nuclei receive conver- expression, and storage of motor learning. Once the expression gent information of conditioned stimulus and unconditioned stim- process of memory traces is impaired, it becomes difficult to ulus through the mossy fiber and climbing fiber projections, define the key neural circuits responsible for expression, forma- respectively. To explore the relative importance of these neural tion, and storage of memory traces. circuits and the underlying mechanism in associative eyeblink In this investigation, we adopted a novel reversible neuro- learning, we adopted a novel gene-manipulating technique, transmission blocking (RNB) technique to explore the role of termed reversible neurotransmission blocking (RNB). In this tech- Purkinje cells and the interpositus nucleus in associative eyeblink nology, cerebellar granule cells specifically expressed neurotrans- conditioning. In the RNB transgenic mice, the tetanus toxin light mission-blocking tetanus toxin in a doxycycline (DOX)-dependent chain is restrictedly expressed in granule cells under the control manner. Extracellular recording of Purkinje cells in awake RNB mice of a tetracycline-controlled reverse transactivator (rtTA) (29). revealed that DOX treatment and withdrawal reversibly turned off Tetanus toxin specifically cleaves synaptic vesicle VAMP2 (30), and on simple spikes elicited by granule cell inputs, respectively, resulting in blockade of transmitter release from synaptic vesicles without interference with complex spikes evoked by climbing fiber (Fig. 1b) (29). Consequently, granule cell inputs to Purkinje cells inputs. Blockade of granule cell inputs to Purkinje cells abolished are blocked and reversibly recovered by administration and eyeblink conditioned responses (CRs) in a DOX-dependent manner. omission, respectively, of doxycycline (DOX) (29). These RNB Importantly, when granule cell inputs recovered by removal of mice were thus used based on the following rationale: when DOX, normal CRs were immediately produced in the DOX-treated, granule cell inputs to Purkinje cells are selectively blocked, the CR-negative RNB mice from the beginning of reconditioning. This CS signal is not transmitted to Purkinje cells but still conveyed learning process in RNB mice during DOX treatment was com- to the interpositus nucleus via the direct mossy fiber pathway pletely abolished by bilateral lesion of the interpositus nucleus (Fig. 1a). The reversible blockade of granule cell transmission before eyeblink conditioning. These results indicate that the con- can thus delineate distinct roles of the direct mossy fiber- vergent information at the interpositus nucleus is critical for mediated information and the indirect granule cell-mediated acquisition and storage of learning in intimate association with the information in acquisition, expression, and storage of CRs in Purkinje cell circuit for expression of CRs in eyeblink conditioning. associative eyeblink conditioning. eyeblink conditioning ͉ interpositus nucleus ͉ Purkinje cell ͉ Results reversible neurotransmission blockade ͉ synaptic plasticity Specific and Reversible Blockade of Granule Cell Transmission. Our previous study showed that tetanus toxin was fully induced in lassical conditioning of the eyeblink reflex is elicited by RNB mice 5 days after DOX treatment and remained at maximal Cpaired presentation of conditioned stimulus (CS) with re- levels thereafter (29). This study showed that the tetanus toxin inforcing unconditioned stimulus (US) (1–4). This associative expression completely disappeared in RNB mice when DOX was motor learning is a basic form of cerebellum-dependent leaning. withdrawn for 14 days and that the toxin was restrictedly In eyeblink conditioning, the CS pathway includes the pontine expressed in granule cells and specifically cleaved VAMP2 nucleus and mossy fibers, whereas the US pathway includes the among neuronal proteins. In addition, the DOX-treated RNB inferior olive and the climbing fibers (1–5). The mossy fibers mice showed no abnormal motor behaviors such as ataxia or project directly to the interpositus nucleus and indirectly to the tremor under the ordinary condition, nor was there any alter- cerebellar cortex via granule cells (1–5). The CS and US signals ation in the cerebellar architecture with respect to the cell are thus conveyed to both the cerebellar cortex and the inter- positus nucleus (Fig. 1a). The localization and underlying mech- anisms of eyeblink conditioning have been extensively studied by Author contributions: N.W., Y.K., D.W., K.F., and S.N. designed research; N.W. and Y.K. performed research; N.W., Y.K., M.K., and T.H. contributed new reagents/analytic tools; different approaches including gene targeting (6–11), lesioning N.W., Y.K., and K.F. analyzed data; and N.W. and S.N. wrote the paper. (12–15), mutant analysis (16), and pharmacological inactivation The authors declare no conflict of interest. analyses (17–23). On the basis of these studies, one model Abbreviations: CR, conditioned response; CS, conditioned stimulus; US, unconditioned stim- proposes an essential role of the cerebellar Purkinje cell circuit ulus; RNB, reversible neurotransmission blocking; DOX, doxycycline; EMG, electromyogram. in memory traces (24–26). According to this model, convergence §Present address: Graduate School of Pharmaceutical Sciences, Tokushima Bunri University, of the CS and US signals induces long-term depression at the Sanuki 769-2193, Japan. parallel fiber–Purkinje cell synapses. Because Purkinje cells are ʈTo whom correspondence should be addressed at: Osaka Bioscience Institute, 6-2-4, inhibitory, long-term depression causes a disinhibition of the Furuedai, Suita, Osaka 565-0874, Japan. E-mail: [email protected]. interpositus nucleus and an increased input in the downstream This article contains supporting information online at www.pnas.org/cgi/content/full/ motor pathways. The other model proposes that the memory 0708165104/DC1. trace is located in the interpositus nucleus and that conditioned © 2007 by The National Academy of Sciences of the USA 16690–16695 ͉ PNAS ͉ October 16, 2007 ͉ vol. 104 ͉ no. 42 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0708165104 DOX-treated RNB mice [P Ͻ 0.001, cells of DOX-treated (n ϭ 6) vs. DOX-untreated (n ϭ 6) mice] (Fig. 2 a and e). When DOX was withdrawn for 14 days after 14-day DOX treatment, these simple spikes reversibly recovered to their normal levels in DOX-withdrawn mice (P Ͼ 0.99) (Fig. 2 a and e). Importantly, complex spikes remained unchanged in RNB mice, irrespective of administration and omission of DOX [P Ͼ 0.99, cells of WT (n ϭ 7) vs. RNB (n ϭ 6) mice] (Fig. 2 a and f). There was no difference