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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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Western blot detection of cannabinoid type 1 receptor (CB1R) expression.A. Diagram of dentate gyrus illustrating the area that was micro-dissected (box) for analysis. B. Western blot showing CB1R expression in pilocarpine-treated mice that survived SE and developed TLE compared to untreated mice. Actin was used as the loading control, which did not change significantly. C. Graph showing cumulative (60%) increase in CB1R expression in mice with TLE versus controls (n = 6; p<0.05). * indicates significance. IML, inner molecular layer; GCL, granule cell layer; PML, polymorphic layer.
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pone-0010683-g008: Western blot detection of cannabinoid type 1 receptor (CB1R) expression.A. Diagram of dentate gyrus illustrating the area that was micro-dissected (box) for analysis. B. Western blot showing CB1R expression in pilocarpine-treated mice that survived SE and developed TLE compared to untreated mice. Actin was used as the loading control, which did not change significantly. C. Graph showing cumulative (60%) increase in CB1R expression in mice with TLE versus controls (n = 6; p<0.05). * indicates significance. IML, inner molecular layer; GCL, granule cell layer; PML, polymorphic layer.

Mentions: Since effects were seen in animals with mossy fiber sprouting but not control animals, we reasoned that the newly sprouted axon terminals expressed CB1R and this may result in an increase in CB1R protein expression in the dentate gyrus of pilocarpine-treated mice that survived SE. The dentate gyrus was microdissected to include the granule cell layer and the molecular layer in controls and pilocarpine-treated mice that survived SE. A discrete band at ∼56 kD, corresponding to the molecular weight of the CB1R receptor was identified by Western blot. Density analysis indicated that the protein binding in tissue from pilocarpine-treated mice that survived SE was increased by 60% over that observed in tissue from control mice (n = 6; p<0.05; Figure 8).


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)

Western blot detection of cannabinoid type 1 receptor (CB1R) expression.A. Diagram of dentate gyrus illustrating the area that was micro-dissected (box) for analysis. B. Western blot showing CB1R expression in pilocarpine-treated mice that survived SE and developed TLE compared to untreated mice. Actin was used as the loading control, which did not change significantly. C. Graph showing cumulative (60%) increase in CB1R expression in mice with TLE versus controls (n = 6; p<0.05). * indicates significance. IML, inner molecular layer; GCL, granule cell layer; PML, polymorphic layer.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2871782&req=5

pone-0010683-g008: Western blot detection of cannabinoid type 1 receptor (CB1R) expression.A. Diagram of dentate gyrus illustrating the area that was micro-dissected (box) for analysis. B. Western blot showing CB1R expression in pilocarpine-treated mice that survived SE and developed TLE compared to untreated mice. Actin was used as the loading control, which did not change significantly. C. Graph showing cumulative (60%) increase in CB1R expression in mice with TLE versus controls (n = 6; p<0.05). * indicates significance. IML, inner molecular layer; GCL, granule cell layer; PML, polymorphic layer.
Mentions: Since effects were seen in animals with mossy fiber sprouting but not control animals, we reasoned that the newly sprouted axon terminals expressed CB1R and this may result in an increase in CB1R protein expression in the dentate gyrus of pilocarpine-treated mice that survived SE. The dentate gyrus was microdissected to include the granule cell layer and the molecular layer in controls and pilocarpine-treated mice that survived SE. A discrete band at ∼56 kD, corresponding to the molecular weight of the CB1R receptor was identified by Western blot. Density analysis indicated that the protein binding in tissue from pilocarpine-treated mice that survived SE was increased by 60% over that observed in tissue from control mice (n = 6; p<0.05; Figure 8).

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