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Cannabinoid-mediated inhibition of recurrent excitatory circuitry in the dentate gyrus in a mouse model of temporal lobe epilepsy.

Bhaskaran MD, Smith BN - PLoS ONE (2010)

Bottom Line: Cannabinoids appear to be anti-convulsive in patients and animal models of TLE, but the mechanisms of this effect are not known.Agonist effects were blocked by the cannabinoid type 1 receptor (CB1R) antagonist AM251.This suggests a mechanism for the anti-convulsive role of cannabinoids aimed at modulating receptors on synaptic terminals expressed de novo after epileptogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America.

ABSTRACT
Temporal lobe epilepsy (TLE) is a neurological condition associated with neuron loss, axon sprouting, and hippocampal sclerosis, which results in modified synaptic circuitry. Cannabinoids appear to be anti-convulsive in patients and animal models of TLE, but the mechanisms of this effect are not known. A pilocarpine-induced status epilepticus mouse model of TLE was used to study the effect of cannabinoid agonists on recurrent excitatory circuits of the dentate gyrus using electrophysiological recordings in hippocampal slices isolated from control mice and mice with TLE. Cannabinoid agonists WIN 55,212-2, anandamide (AEA), or 2-arachydonoylglycerol (2-AG) reduced the frequency of spontaneous and tetrodotoxin-resistant excitatory postsynaptic currents (EPSCs) in mice with TLE, but not in controls. WIN 55,212-2 also reduced the frequency of EPSCs evoked by glutamate-photolysis activation of other granule cells in epileptic mice. Secondary population discharges evoked after antidromic electrical stimulation of mossy fibers in the hilus were also attenuated by cannabinoid agonists. Agonist effects were blocked by the cannabinoid type 1 receptor (CB1R) antagonist AM251. No change in glutamate release was observed in slices from mice that did not undergo status epilepticus. Western blot analysis suggested an up-regulation of CB1R in the dentate gyrus of animals with TLE. These findings indicate that activation of CB1R present on nerve terminals can suppress recurrent excitation in the dentate gyrus of mice with TLE. This suggests a mechanism for the anti-convulsive role of cannabinoids aimed at modulating receptors on synaptic terminals expressed de novo after epileptogenesis.

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Inhibitory effect of anandamide (AEA) on sEPSCs.A. Spontaneous bursts of EPSCs observed in a granule cell from a pilocarpine-treated mouse that survived SE. A1 and A2 are expanded segments of the events indicated by the arrows. B. AEA (10 µM) suppressed the epileptiform bursts of activity. B1 and B2 are examples of individual events from B. C. Bursts were reinstated after 20 minute wash to normal ACSF. C1 and C2, expanded segments of C. Asterisks indicate currents preceding the largest amplitude EPSCs in some cases. The recordings were made in the absence of Mg2+ and the presence of bicuculline (30 µM). D. Cumulative graph of normalized sEPSC frequency from control mice and pilocarpine-treated mice that survived SE and developed TLE before and after application of AEA. Asterisk in D indicates significant reduction in frequency by AEA (P<0.05). In mice with TLE, the effect of AEA was prevented by preapplication of the CB1 receptor antagonist AM-251 (10 µM). Number of cells for each experiment is in parentheses.
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pone-0010683-g004: Inhibitory effect of anandamide (AEA) on sEPSCs.A. Spontaneous bursts of EPSCs observed in a granule cell from a pilocarpine-treated mouse that survived SE. A1 and A2 are expanded segments of the events indicated by the arrows. B. AEA (10 µM) suppressed the epileptiform bursts of activity. B1 and B2 are examples of individual events from B. C. Bursts were reinstated after 20 minute wash to normal ACSF. C1 and C2, expanded segments of C. Asterisks indicate currents preceding the largest amplitude EPSCs in some cases. The recordings were made in the absence of Mg2+ and the presence of bicuculline (30 µM). D. Cumulative graph of normalized sEPSC frequency from control mice and pilocarpine-treated mice that survived SE and developed TLE before and after application of AEA. Asterisk in D indicates significant reduction in frequency by AEA (P<0.05). In mice with TLE, the effect of AEA was prevented by preapplication of the CB1 receptor antagonist AM-251 (10 µM). Number of cells for each experiment is in parentheses.

Mentions: In Mg2+-free ACSF containing bicuculline, application of AEA (1–10 µM) to recordings from granule cells in control animals resulted in no change in amplitude or frequency of sEPSCs (1.46±0.17 Hz control; 1.55±0.18 Hz AEA; P>0.05; n = 10). In granule cells from mice that survived pilocarpine-induced SE, application of AEA reduced the frequency of sEPSCs from 3.02±0.7 Hz in control ACSF to 1.80±0.35 Hz in AEA (Fig. 4; P<0.05; n = 8). In addition, the occurrence of sEPSC bursts was eliminated by AEA. Application of AEA thus suppressed EPSC bursting and frequency in these animals. The inhibitory effect of AEA was prevented by pre-application of the CB1R antagonist AM-251 (10 µM) (2.60±0.52 Hz to 3.06±0.67; P>0.05; n = 5; Fig 4D), indicating the involvement of CB1R in the response. No significant effect of AM-251 alone on sEPSC frequency was observed. Application of the synthetic cannabinoid agonist WIN 55,212-2 (1 µM) had similar effects on sEPSC bursts and reduced the frequency of sEPSCs from 2.77±0.67 Hz to 1.73±0.43 Hz (5 of 5 cells; P<0.05). Cannabinoid agonists acting at CB1R suppressed sEPSC bursts in pilocarpine-treated mice that survived SE, but had no effect on overall excitatory synaptic input in control mice.


Cannabinoid-mediated inhibition of recurrent excitatory circuitry in the dentate gyrus in a mouse model of temporal lobe epilepsy.

Bhaskaran MD, Smith BN - PLoS ONE (2010)

Inhibitory effect of anandamide (AEA) on sEPSCs.A. Spontaneous bursts of EPSCs observed in a granule cell from a pilocarpine-treated mouse that survived SE. A1 and A2 are expanded segments of the events indicated by the arrows. B. AEA (10 µM) suppressed the epileptiform bursts of activity. B1 and B2 are examples of individual events from B. C. Bursts were reinstated after 20 minute wash to normal ACSF. C1 and C2, expanded segments of C. Asterisks indicate currents preceding the largest amplitude EPSCs in some cases. The recordings were made in the absence of Mg2+ and the presence of bicuculline (30 µM). D. Cumulative graph of normalized sEPSC frequency from control mice and pilocarpine-treated mice that survived SE and developed TLE before and after application of AEA. Asterisk in D indicates significant reduction in frequency by AEA (P<0.05). In mice with TLE, the effect of AEA was prevented by preapplication of the CB1 receptor antagonist AM-251 (10 µM). Number of cells for each experiment is in parentheses.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2871782&req=5

pone-0010683-g004: Inhibitory effect of anandamide (AEA) on sEPSCs.A. Spontaneous bursts of EPSCs observed in a granule cell from a pilocarpine-treated mouse that survived SE. A1 and A2 are expanded segments of the events indicated by the arrows. B. AEA (10 µM) suppressed the epileptiform bursts of activity. B1 and B2 are examples of individual events from B. C. Bursts were reinstated after 20 minute wash to normal ACSF. C1 and C2, expanded segments of C. Asterisks indicate currents preceding the largest amplitude EPSCs in some cases. The recordings were made in the absence of Mg2+ and the presence of bicuculline (30 µM). D. Cumulative graph of normalized sEPSC frequency from control mice and pilocarpine-treated mice that survived SE and developed TLE before and after application of AEA. Asterisk in D indicates significant reduction in frequency by AEA (P<0.05). In mice with TLE, the effect of AEA was prevented by preapplication of the CB1 receptor antagonist AM-251 (10 µM). Number of cells for each experiment is in parentheses.
Mentions: In Mg2+-free ACSF containing bicuculline, application of AEA (1–10 µM) to recordings from granule cells in control animals resulted in no change in amplitude or frequency of sEPSCs (1.46±0.17 Hz control; 1.55±0.18 Hz AEA; P>0.05; n = 10). In granule cells from mice that survived pilocarpine-induced SE, application of AEA reduced the frequency of sEPSCs from 3.02±0.7 Hz in control ACSF to 1.80±0.35 Hz in AEA (Fig. 4; P<0.05; n = 8). In addition, the occurrence of sEPSC bursts was eliminated by AEA. Application of AEA thus suppressed EPSC bursting and frequency in these animals. The inhibitory effect of AEA was prevented by pre-application of the CB1R antagonist AM-251 (10 µM) (2.60±0.52 Hz to 3.06±0.67; P>0.05; n = 5; Fig 4D), indicating the involvement of CB1R in the response. No significant effect of AM-251 alone on sEPSC frequency was observed. Application of the synthetic cannabinoid agonist WIN 55,212-2 (1 µM) had similar effects on sEPSC bursts and reduced the frequency of sEPSCs from 2.77±0.67 Hz to 1.73±0.43 Hz (5 of 5 cells; P<0.05). Cannabinoid agonists acting at CB1R suppressed sEPSC bursts in pilocarpine-treated mice that survived SE, but had no effect on overall excitatory synaptic input in control mice.

Bottom Line: Cannabinoids appear to be anti-convulsive in patients and animal models of TLE, but the mechanisms of this effect are not known.Agonist effects were blocked by the cannabinoid type 1 receptor (CB1R) antagonist AM251.This suggests a mechanism for the anti-convulsive role of cannabinoids aimed at modulating receptors on synaptic terminals expressed de novo after epileptogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America.

ABSTRACT
Temporal lobe epilepsy (TLE) is a neurological condition associated with neuron loss, axon sprouting, and hippocampal sclerosis, which results in modified synaptic circuitry. Cannabinoids appear to be anti-convulsive in patients and animal models of TLE, but the mechanisms of this effect are not known. A pilocarpine-induced status epilepticus mouse model of TLE was used to study the effect of cannabinoid agonists on recurrent excitatory circuits of the dentate gyrus using electrophysiological recordings in hippocampal slices isolated from control mice and mice with TLE. Cannabinoid agonists WIN 55,212-2, anandamide (AEA), or 2-arachydonoylglycerol (2-AG) reduced the frequency of spontaneous and tetrodotoxin-resistant excitatory postsynaptic currents (EPSCs) in mice with TLE, but not in controls. WIN 55,212-2 also reduced the frequency of EPSCs evoked by glutamate-photolysis activation of other granule cells in epileptic mice. Secondary population discharges evoked after antidromic electrical stimulation of mossy fibers in the hilus were also attenuated by cannabinoid agonists. Agonist effects were blocked by the cannabinoid type 1 receptor (CB1R) antagonist AM251. No change in glutamate release was observed in slices from mice that did not undergo status epilepticus. Western blot analysis suggested an up-regulation of CB1R in the dentate gyrus of animals with TLE. These findings indicate that activation of CB1R present on nerve terminals can suppress recurrent excitation in the dentate gyrus of mice with TLE. This suggests a mechanism for the anti-convulsive role of cannabinoids aimed at modulating receptors on synaptic terminals expressed de novo after epileptogenesis.

Show MeSH
Related in: MedlinePlus