Shigetada Nakanishi’s research while affiliated with Osaka Bioscience Institute and other places

In the early postnatal period, cerebellar granule cells exhibit an activity-dependent downregulation of a set of immaturation genes involved in cell growth and migration and are shifted to establishment of a mature network formation. Through the use of a granule cell culture and both pharmacological and RNA interference (siRNA) analyses, the present investigation revealed that the downregulation of these immaturation genes is controlled by strikingly unified signaling mechanisms that operate sequentially through the stimulation of AMPA and NMDA receptors, tetrodotoxin-sensitive Na(+) channels and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). This signaling cascade induces the Etv1 transcription factor, and knockdown of Etv1 by a siRNA technique prevented this activity-dependent downregulation of immaturation genes. Thus, taken into consideration the mechanism that controls the upregulation of maturation genes involved in synaptic formation, these results indicate that Etv1 orchestrates the activity-dependent regulation of both maturation and immaturation genes in developing granule cells and plays a key role in specifying the identity of mature granule cells in the cerebellum.

Fear is induced by innate and learned mechanisms involving separate pathways. Here, we used an olfactory-mediated innate-fear versus learned-fear paradigm to investigate how these pathways are integrated. Notably, prior presentation of innate-fear stimuli inhibited learned-freezing response, but not vice versa. Whole-brain mapping and pharmacological screening indicated that serotonin-2A receptor (Htr2a)-expressing cells in the central amygdala (CeA) control both innate and learned freezing, but in opposing directions. In vivo fiber photometry analyses in freely moving mice indicated that innate but not learned-fear stimuli suppressed the activity of Htr2a-expressing CeA cells. Artificial inactivation of these cells upregulated innate-freezing response and downregulated learned-freezing response. Thus, Htr2a-expressing CeA cells serve as a hierarchy generator, prioritizing innate fear over learned fear.

Significance The nucleus accumbens (NAc) is a key neural substrate that controls aversive learning through D1 receptor-expressing direct pathway neurons and D2 receptor-expressing indirect pathway neurons. We explored how aversive learning is controlled by intracellular PKA signaling in these two types of neurons in the NAc. We approached this issue not only by pathway-specific inhibition of PKA in either direct or indirect pathway neurons, but also by microendoscopic analysis of FRET responses of the PKA biosensor distinctly expressed in the two types of neurons. We obtained consistent findings from these two different approaches, and demonstrate that activation of PKA in the indirect pathway neurons plays a pivotal role in both the formation and the retention of aversive memory.

Significance Selection of actions that allow the seeking of rewards and avoidance of uncomfortable environments is a fundamental animal behavior. Here, we report an in vivo method, in which the activities of PKA and ERK were optically recorded by microendoscopy of Förster resonance energy transfer responses of biosensors in distinct D1 and D2 dopamine receptor-expressing neurons of the dorsal striatum. The PKA and ERK were coordinately but reciprocally regulated not only by rewarding and aversive stimuli but also between the two parallel projection neurons. Importantly, the cell type-specific regulation of PKA and ERK was causally linked to active and indifferent mating reactions of male mice. The dynamic modulation of PKA and ERK in the striatum underlies the selection of alternative actions.

The nucleus accumbens (NAc) plays a pivotal role in reward and aversive learning and learning flexibility. Outputs of the NAc are transmitted through 2 parallel routes termed the direct and indirect pathways and controlled by the dopamine (DA) neurotransmitter. To explore how reward-based and avoidance learning is controlled in the NAc, we developed the reversible neurotransmission-blocking (RNB) technique, in which transmission of each pathway could be selectively and reversibly blocked by the pathway-specific expression of transmission-blocking tetanus toxin and the asymmetric RNB technique, in which one side of the NAc was blocked by the RNB technique and the other intact side was pharmacologically manipulated by a transmitter agonist or antagonist. Our studies demonstrated that the activation of D1 receptors in the direct pathway and the inactivation of D2 receptors in the indirect pathway are key determinants that distinctly control reward-based and avoidance learning, respectively. The D2 receptor inactivation is also critical for flexibility of reward learning. Furthermore, reward and aversive learning is regulated by a set of common downstream receptors and signaling cascades, all of which are involved in the induction of long-term potentiation at cortico-accumbens synapses of the 2 pathways. In this article, we review our studies that specify the regulatory mechanisms of each pathway in learning behavior and propose a mechanistic model to explain how dynamic DA modulation promotes selection of actions that achieve reward-seeking outcomes and avoid aversive ones. The biological significance of the network organization consisting of 2 parallel transmission pathways is also discussed from the point of effective and prompt selection of neural outcomes in the neural network. This article is part of a Special Issue entitled: [Ventral Tegmentum & Dopamine].

Significance Dopamine (DA) neurons in the ventral tegmental area (VTA) react to aversive stimuli mostly by transient silencing. It remains unclear whether this reaction directly induces aversive responses in behaving mice. We examined this question by optogenetically controlling DA neurons in the VTA and found that the inactivation of DA neurons resulted in aversive response and learning. The nucleus accumbens (NAc), the major output nuclei of VTA DA neurons, was considered to be responsible for this response, so we examined which of the fundamental pathways in the NAc was critical to this behavior by using knockdown of D1 or D2 receptor, and found that the D2 receptor-specific pathway was crucial for this behavior.

Significance Purkinje cells and vestibular nuclei receive optokinetic and retinal slip signals that induce optokinetic motor learning. The role of multiple cerebellar circuits in the adaptive optokinetic response (OKR) was investigated by selective and reversible blockade of granule-cell transmission to Purkinje cells. This blockade abrogated both short-term and long-term OKR adaptation, but adaptive OKRs were immediately induced when the granule-cell transmission was recovered in pretrained, adaptive OKR-negative mice. Eye movement by electrical stimulation of the flocculus was elevated by long-term but not by short-term OKR training. Simultaneous flocculus and OKR stimulation produced normal OKR adaptation in adaptive OKR-negative mice. This study demonstrates that vestibular nuclei serve as a critical circuit responsible for formation and storage of OKR adaptation.

Bussey, Peter J (ed.) ; Knowles, Ian G (ed.) Imprint Bristol : IOP, 1995 - 2 v. ISBN 0750301236 (This book at Amazon) 0750301244 (This book at Amazon) 0750301252 (This book at Amazon)