Functional Redistribution of Hippocampal Cannabinoid Cb1 Receptors in the Rat Pilocarpine Model of Acquired Epilepsy

Cannabinoids, such as the marijuana derivative Δ9-THC, are known to have CBl receptor-mediated anticonvulsant effects in several animal models of seizures and epilepsy, including the rat pilocarpine model of acquired epilepsy. However, the distribution of CBl receptor expression and function in brains of epileptic rats has not been characterized. Therefore, this dissertation was initiated to evaluate the effect of epileptogenesis on the distribution and function of the endogenous CBI receptor system in the rat pilocarpine model, a well-established model of acquired temporal lobe epilepsy. Using immunohistochemistry, we demonstrated that chronically epileptic rats exhibit a unique, long-term, and specific redistribution of hippocampal CBl receptors when compared to controls, with concurrent layer-specific increases and decreases in CBl receptor expression within the hippocampus. In addition, studies in this dissertation demonstrated using [3H] WIN55,212-2 autoradiography and agonist-stimulated [35S]GTPγS autoradiography that this CBl receptor-specific reorganization results in corresponding functional changes manifested by alterations in CBl receptor binding and G-protein activation. These regionally selective changes were dependent on NMDA receptor activation during the initial insult of pilocarpine-induced status epilepticus (SE), and were independent of seizure suppression produced with phenobarbital administration in epileptic rats. Furthermore, time-course studies utilizing these techniques demonstrate that within a week following SE, a widespread loss of CBl receptor expression and function occurs throughout the hippocampus. The subsequent redistribution of CBl receptors that occurs temporally correlates with the emergence of spontaneous recurrent seizures, and is still observed up to 1 year following SE. Overall, the reorganization of cannabinoid receptors in epilepsy implicates the endocannabinoid system in modulating neuroexcitability in the epileptic state. This CBl receptor redistribution represents an essentially permanent neuronal plasticity change associated with epileptogenesis, and could account for the anticonvulsant effect of cannabinoids observed in this model.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Neurology

Year dc:date.available

2006

Author dc:creator

• Falenski, Katherine Winslow

Contributors dc:contributor

• Dr. Robert J. DeLorenzo

• anticonvulsant
• seizure
• epilepsy
• cannabinoid
• endocannabinoid
• Medical Specialties
• Medicine and Health Sciences
• Neurology

Statement dc:rights

• © The Author

Identifier

https://scholarscompass.vcu.edu/etd/1280

OAI identifier oai:identifier

oai:scholarscompass.vcu.edu:etd-2279