Physiological role of the cannabinoid receptor 1 (CB1) in the murine central nervous system

Marsicano, Giovanni (2001). Physiological role of the cannabinoid receptor 1 (CB1) in the murine central nervous system. PhD thesis The Open University.



The cannabinoid system is involved in many functions of mammalian brain, such as learning and memory, pain perception and 'locomotion. The "brain type" cannabinoid receptor CB 1 is one of the key elements of the cannabinoid system. In this Thesis, some aspects of the neurobiology of mouse CB 1 are described.

CB 1 mRNA distribution was analysed by single and double in situ hybridization (ISH), revealing the expression of the receptor in specific neuronal subpopulations. This expression pattern suggests many putative functional cross-talks between the cannabinoid system and other signalling molecules in the brain, such as glutamate, GABA, cholecystokinin and nitric oxide (NO).

The putative functional interactions of the cannabinoid system with the NO pathway was studied by pharmacological treatment of neuronal NO synthase (nNOS) mutant mice with the CBI agonist A9-tetrahydrocannabinol (A9-THC). The results showed that nNOS is necessary for some central effects of A9-THC. Moreover, ISH analysis revealed. that nNOS-deficient mice contain levels of CBI lower than normal in selected brain regions.

A "conditional" targeting approach was developed to gain insights into the specific functions of CB 1 in mouse brain. By gene targeting experiments, two mutant lines were obtained. The "Flox CB 1" mouse line, containing the whole open reading frame of CB I flanked by two loxP sites will be the key tool for the generation of mouse mutants with a spatiotemporal-restricted deletion of CB I. The "CBN" mice, carrying a "null" mutation of CB 1, were used for a study aimed to clarify some aspects of the in vitro neuroprotective activity of cannabinoids and, in particular, the involvement of CB 1.

In vitro oxidative stress assays were performed on cell lines and on primary neuronal cultures derived from homozygous CBN/CBN mice and wild type littermates. The results indicate a differential protective activity of cannabinoids on cell lines and primary cultures. However, CBI does not appear to be involved in the in vitro leuroprotective effects of cannabinoids.

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