Prolonged cannabinoid exposure alters GABA(A) receptor mediated synaptic function in cultured hippocampal neurons.
Laxmikant S Deshpande, Robert E Blair, Robert J DeLorenzo
Experimental Neurology June 2011 DOI: 10.1016/j.expneurol.2011.02.007 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | In vitro electrophysiological and immunochemical study Peer reviewed |
|---|---|
| Population | Cultured hippocampal neurons |
| Interventions | WIN 55 212-2 |
| Dose | 1 μM |
| Duration | 24 h |
| Measures | mIPSC frequency, mIPSC amplitude, GABA(A) channel number, surface staining for GABA(A) β2/3 receptor subunits, staining for presynaptic vesicular GABA transporter |
| Key points | Prolonged WIN 55,212-2 treatment downregulated CB1 receptors and increased neuronal excitability. It increased mIPSC frequency but reduced mIPSC amplitude and GABA(A) channel number, with decreased surface GABA(A) β2/3 staining and unchanged vesicular GABA transporter, suggesting hyperexcitability arises from altered presynaptic GABA release and postsynaptic GABA(A) receptor function. |
Abstract
Developing cannabinoid-based medication along with marijuana's recreational use makes it important to investigate molecular adaptations the endocannabinoid system undergoes following prolonged use and withdrawal. Repeated cannabinoid administration results in development of tolerance and produces withdrawal symptoms that may include seizures. Here we employed electrophysiological and immunochemical techniques to investigate the effects of prolonged CB1 receptor agonist exposure on cultured hippocampal neurons. Approximately 60% of CB1 receptors colocalize to GABAergic terminals in hippocampal cultures. Prolonged treatment with the cannabinamimetic WIN 55,212-2 (+WIN, 1 μM, 24 h) caused profound CB1 receptor downregulation accompanied by neuronal hyperexcitability. Furthermore, prolonged +WIN treatment resulted in increased GABA release as indicated by increased mIPSC frequency, a diminished GABAergic inhibition as indicated by reduction in mIPSC amplitude and a reduction in GABA(A) channel number. Additionally, surface staining for the GABA(A) β(2/3) receptor subunits was decreased, while no changes in staining for the presynaptic vesicular GABA transporter were observed, indicating that GABAergic terminals remained intact. These findings demonstrate that agonist-induced downregulation of the CB1 receptor in hippocampal cultures results in neuronal hyperexcitability that may be attributed, in part, to alterations in both presynaptic GABA release mechanisms and postsynaptic GABA(A) receptor function demonstrating a novel role for cannabinoid-dependent presynaptic control of neuronal transmission.