Elsevier

Behavioural Brain Research

Volume 250, 1 August 2013, Pages 274-284
Behavioural Brain Research

Research report
Involvement of cannabinoid receptors in the amygdala and prefrontal cortex of rats in fear learning, consolidation, retrieval and extinction

https://doi.org/10.1016/j.bbr.2013.05.002Get rights and content

Highlights

  • Drug study on fear memory and cannabinoids in prefrontal cortex and amygdala.

  • Cannabinoids reduce fear learning in amygdala and prefrontal cortex.

  • Cannabinoid antagonists impair fear extinction in the prefrontal cortex.

Abstract

Cannabinoid receptors 1 (CB1R) have been shown to be a crucial part of the neuromodulatory endocannabinoid system which is involved in emotional learning and memory.

We here investigated in rats the role of CB1R in the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC) in different phases of fear learning, memory and extinction. We used the fear potentiated startle paradigm to measure the effects of local microinfusion of the CB1R agonist WIN 55,212-2 (WIN) or the CB1R antagonist AM251 on acquisition, consolidation, retrieval and extinction of fear.

No effects on fear acquisition of WIN or AM251 were found in the BLA or mPFC. WIN impaired fear retrieval in the BLA and in mPFC. Also, WIN reduced fear consolidation in the BLA but not in the mPFC. AM251 decreased fear consolidation after mPFC infusion. Likewise, fear extinction was impaired by AM251 infused into the mPFC.

Our data indicate that fear memory consolidation and retrieval, as well as extinction are regulated differentially by amygdaloid and cortical CB1R.

Introduction

Endocannabinoid signalling regulates transmitter release via cannabinoid receptors 1 (CB1R) that are located presynaptically on several transmitter systems in the brain [1], [2], [3]. CB1R inhibit transmitter release as heteroreceptors mainly on glutamatergic and GABAergic nerve terminals in the cerebellum and in the forebrain. Hence, CB1R and endocannabinoid signalling are in strategic positions to regulate a variety of cognitive functions, such as learning and memory. For example, enhancement of endocannabinoid signalling by the inhibition of its metabolizing enzyme modulates acquisition and extinction of spatial memory [4], the selective CB1R-antagonist AM251 has an amnestic effect in the inhibitory avoidance paradigm [5], and the synthetic CB1R agonist WIN 55,212-2 (WIN) impairs spatial memory retrieval [6]. In addition the genetic deletion of CB1R in mice impaired the extinction of conditioned fear [7]. Many recent studies support the important role of endocannabinoid signalling in mnemonic processes [8], [9], [10], [11], [12], [13], [14]. However, there are still some open questions concerning the involvement of CB1R with respect to different brain systems and different phases of learning and memory.

We here focus on fear conditioning and fear memory. Classical fear conditioning comprises different phases of learning and memory processes such as acquisition, consolidation, retrieval and extinction [15], [16]. Recently, different paradigms of fear conditioning were used to study the role of endocannabinoid signalling in fear conditioning. But the differences of for example olfactory fear conditioning [12], auditory fear conditioning [11], contextual fear conditioning [10], visual fear conditioning [17] and trace fear conditioning [13] make direct comparisons between these studies difficult. Furthermore, different species (mice or rats), knockout and wildtype animals and various drugs in different doses were used in these studies. Therefore, we here investigated in a systematic approach in rats the role of CB1R in the basolateral complex of the amygdala (BLA) and the medial prefrontal cortex (mPFC) in different phases of fear learning. We used the fear-potentiated startle (FPS) paradigm and tested the effects of the CB1R agonist WIN and the antagonist AM251 on acquisition, consolidation, retrieval and extinction of fear after local microinfusion of the drugs.

Section snippets

Subjects

A total of 265 adult male Wistar rats (Hannover strain, Harlan-Winkelmann, Borchen, Germany) weighing between 250 and 300 g were used. Animals were housed in groups of five in Macrolon cages (type IV) under standard conditions on a 12 h light-dark cycle with lights on at 7 o’clock. All experimental procedures were performed during the rats’ light cycle. They received free access to tap water and were maintained on their experimental body weight by controlled feeding of 12 g rodent chow per rat per

Histology

A total of 265 animals underwent stereotactic surgery. The target areas were missed in nine animals. Data from these rats were not included in the analysis. Three animals died during surgery. Fig. 1A–D shows the localization of the injection cannulae in the BLA. In 127 rats evaluation of thionine-stained brain sections (Fig. 2A and B) using light microscopy indicated that the target area of the IC microinjection was accurately hit. Fig. 3A–D illustrates the localization of the injection

Discussion

Cannabinoid 1 receptors (CB1R) in the amygdala and the prefrontal cortex play important roles in associative learning [12], [22], [23], [24], [25]. The results of the present fear-conditioning study support this notion and suggest that the various phases of learning and memory in the rat can be influenced differentially in the mPFC and BLA by the synthetic CB1R ligands WIN and AM251.

References (82)

  • V.C. Oropeza et al.

    Cannabinoid receptors are localized to noradrenergic axon terminals in the rat frontal cortex

    Brain Research

    (2007)
  • A.J. McDonald

    Cortical pathways to the mammalian amygdala

    Progress in Neurobiology

    (1998)
  • R.P. Vertes

    Interactions among the medial prefrontal cortex, hippocampus and midline thalamus in emotional and cognitive processing in the rat

    Neuroscience

    (2006)
  • F. Sotres-Bayon et al.

    Prefrontal control of fear: more than just extinction

    Current Opinion in Neurobiology

    (2010)
  • M. Pistis et al.

    Cannabinoids modulate neuronal firing in the rat basolateral amygdala: evidence for CB1- and non-CB1-mediated actions

    Neuropharmacology

    (2004)
  • J.R. Clarke et al.

    Posttraining activation of CB1 cannabinoid receptors in the CA1 region of the dorsal hippocampus impairs object recognition long-term memory

    Neurobiology of Learning and Memory

    (2008)
  • T.T. Yim et al.

    Post-training CB1 cannabinoid receptor agonist activation disrupts long-term consolidation of spatial memories in the hippocampus

    Neuroscience

    (2008)
  • M. Mackowiak et al.

    Activation of CB1 cannabinoid receptors impairs memory consolidation and hippocampal polysialylated neural cell adhesion molecule expression in contextual fear conditioning

    Neuroscience

    (2009)
  • N. Egashira et al.

    Intracerebral microinjections of delta 9-tetrahydrocannabinol: search for the impairment of spatial memory in the eight-arm radial maze in rats

    Brain Research

    (2002)
  • I. Ehrlich et al.

    Amygdala inhibitory circuits and the control of fear memory

    Neuron

    (2009)
  • A. Burgos-Robles et al.

    Consolidation of fear extinction requires NMDA receptor-dependent bursting in the ventromedial prefrontal cortex

    Neuron

    (2007)
  • C.J. Riebe et al.

    Fear relief-toward a new conceptual frame work and what endocannabinoids gotta do with it

    Neuroscience

    (2012)
  • T. Rubino et al.

    CB1 receptor stimulation in specific brain areas differently modulate anxiety-related behavior

    Neuropharmacology

    (2008)
  • M.V. Fogaca et al.

    The endocannabinoid and endovanilloid systems interact in the rat prelimbic medial prefrontal cortex to control anxiety-like behavior

    Neuropharmacology

    (2012)
  • M.R. Elphick et al.

    The neurobiology and evolution of cannabinoid signalling

    Philosophical Transactions of the Royal Society of London, Series B: Biological Sciences

    (2001)
  • D. Piomelli

    The molecular logic of endocannabinoid signalling

    Nature Reviews Neuroscience

    (2003)
  • S.A. Varvel et al.

    Inhibition of fatty-acid amide hydrolase accelerates acquisition and extinction rates in a spatial memory task

    Neuropsychopharmacology

    (2007)
  • A.L. de Oliveira et al.

    Amnestic effect of intrahippocampal AM251, a CB1-selective blocker, in the inhibitory avoidance, but not in the open field habituation task, in rats

    Neurobiology of Learning and Memory

    (2005)
  • N. Wegener et al.

    Effects of acute systemic and intra-cerebral stimulation of cannabinoid receptors on sensorimotor gating, locomotion and spatial memory in rats

    Psychopharmacology

    (2008)
  • G. Marsicano et al.

    The endogenous cannabinoid system controls extinction of aversive memories

    Nature

    (2002)
  • E. Mikics et al.

    The effects of cannabinoids on contextual conditioned fear in CB1 knockout and CD1 mice

    Behavioural Pharmacology

    (2006)
  • F.A. Pamplona et al.

    The cannabinoid receptor agonist WIN 55,212-2 facilitates the extinction of contextual fear memory and spatial memory in rats

    Psychopharmacology

    (2006)
  • S.R. Laviolette et al.

    Cannabinoids potentiate emotional learning plasticity in neurons of the medial prefrontal cortex through basolateral amygdala inputs

    Journal of Neuroscience

    (2006)
  • C. Reich et al.

    Endocannabinoid modulation of fear responses: learning and state-dependent performance effects

    Journal of Psychopharmacology

    (2008)
  • J.P. Chhatwal et al.

    Enhancing cannabinoid neurotransmission augments the extinction of conditioned fear

    Neuropsychopharmacology

    (2005)
  • G. Paxinos et al.

    The rat brain in stereotaxic coordinates

    (1998)
  • M. Roche et al.

    The effect of CB(1) receptor antagonism in the right basolateral amygdala on conditioned fear and associated analgesia in rats

    European Journal of Neuroscience

    (2007)
  • S.C. Azad et al.

    Circuitry for associative plasticity in the amygdala involves endocannabinoid signaling

    Journal of Neuroscience

    (2004)
  • H. Tan et al.

    Integrated cannabinoid CB1 receptor transmission within the amygdala-prefrontal cortical pathway modulates neuronal plasticity and emotional memory encoding

    Cerebral Cortex

    (2010)
  • S.A. Varvel et al.

    Disruption of CB(1) receptor signaling impairs extinction of spatial memory in mice

    Psychopharmacology

    (2005)
  • S.C. Azad et al.

    Activation of the cannabinoid receptor type 1 decreases glutamatergic and GABAergic synaptic transmission in the lateral amygdala of the mouse

    Learning and Memory

    (2003)
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