Functional tolerance and blockade of long-term depression at synapses in the nucleus accumbens after chronic cannabinoid exposure

Alexander F. Hoffman, Murat Oz, Tara Caulder, Carl R. Lupica

Research output: Contribution to journalArticlepeer-review

169 Citations (Scopus)

Abstract

The rewarding properties of the psychoactive constituents of marijuana, termed "cannabinoids," may reflect actions on synaptic transmission in the nucleus accumbens (NAc). Furthermore, long-term changes in these synapses may support the addictive process. Excitatory and inhibitory synapses are acutely inhibited by cannabinoids in the NAc, and endogenous cannabinoids (endocannabinoids) play a critical role in the expression of long-term depression (LTD) of excitatory cortical afferents in this structure. Because humans often use marijuana for prolonged periods, we examined the impact of long-term cannabinoid exposure on synaptic processes in an animal model. Electrophysiological recordings in rat brain slices containing the NAc were performed after chronic exposure to vehicle solution, Δ9tetrahydrocannabinol (THC), or the cannabinoid agonist R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1, 4benzoxazin-6-yl]-(1-naphthalenyl)methanone mesylate (WIN55,212-2). Extracellular glutamatergic postsynaptic potentials and whole-cell GABAergic IPSCs were concentration-dependently inhibited by WIN55,212-2 in slices from naive or vehicle-treated animals. However, the sensitivity to WIN55,212-2 was diminished in chronic agonist-treated animals. In addition, cross-tolerance to the inhibitory effect of the μ-opioid agonist Tyr-D-Ala2,N-CH3-Phe4,Gly-ol-enkephalin was observed. Endocannabinoid-mediated LTD was initiated via electrical stimulation (5 min, 10 Hz) of glutamatergic afferents to the NAc and was completely blocked by the cannabinoid receptor antagonist SR141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3- carboxamide] in vehicle-treated animals. LTD was not observed in brain slices from rats chronically treated with Δ9-THC or WIN55,212-2. These data demonstrate that long-term exposure to the active ingredient of marijuana blocks synaptic plasticity in the NAc and reduces the sensitivity of GABAergic and glutamatergic synapses to both cannabinoids and opioids.

Original languageEnglish
Pages (from-to)4815-4820
Number of pages6
JournalJournal of Neuroscience
Volume23
Issue number12
DOIs
Publication statusPublished - Jun 15 2003

Keywords

  • Drug abuse
  • Marijuana
  • Nucleus accumbens
  • Synaptic plasticity
  • Tolerance
  • Δ-THC

ASJC Scopus subject areas

  • Neuroscience(all)

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