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CB1 knockout mice display impaired functionality of 5-HT1A and 5-HT2A/C receptors
Susana Mato1, Ester Aso, Elena Castro
1Department of Physiology and Pharmacology, University of Cantabria, Cantabria, Spain.
Abstract:
Interaction between brain endocannabinoid (EC) and serotonin (5-HT) systems was investigated by examining 5-HT-dependent behavioral and biochemical responses in CB(1) receptor knockout mice. CB(1) knockout animals exhibited a significant reduction in the induction of head twitches and paw tremor by the 5-HT(2A/C) receptor selective agonist (+/-) DOI, as well as a reduced hypothermic response following administration of the 5-HT(1A) receptor agonist (+/-)-8-OH-DPAT. Additionally, exposure to the tail suspension test induced enhanced despair responses in CB(1) knockout mice. However, the tricyclic antidepressant imipramine and the 5-HT selective reuptake inhibitor fluoxetine induced similar decreases in the time of immobility in the tail suspension test in CB(1) receptor knockout and wild-type mice. No differences were found between both genotypes with regard to 5-HT(2A) receptor and 5-HT(1A) receptors levels, measured by autoradiography in different brain areas. However, a significant decrease in the ability of both, the 5-HT(1A) receptor agonist (+/-)-8-OH-DPAT and the 5-HT(2A/C) receptor agonist (-)DOI, to stimulate [(35)S]GTPgammaS binding was detected in the hippocampal CA(1) area and fronto-parietal cortex of CB(1) receptor knockout mice, respectively. This study provides evidence that CB(1) receptors are involved in the regulation of serotonergic responses mediated by 5-HT(2A/C) and 5-HT(1A) receptors, and suggests that a reduced coupling of 5-HT(1A) and 5-HT(2A) receptors to G proteins might be involved in these effects.
Insights
Cannabinoid CB1 receptors regulate brain serotonin (5-HT) system responses. CB1 knockout mice show altered 5-HT receptor signaling, impacting behavior and G protein coupling.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- The endocannabinoid (EC) and serotonin (5-HT) systems are crucial for brain function.
- Understanding their interaction is key to deciphering complex neurological processes.
- CB1 receptors play a significant role in modulating neurotransmitter systems.
Purpose of the Study:
- To investigate the interaction between brain EC and 5-HT systems.
- To examine 5-HT-dependent behavioral and biochemical responses in CB1 receptor knockout mice.
- To elucidate the role of CB1 receptors in regulating 5-HT receptor-mediated signaling.
Main Methods:
- Utilized CB1 receptor knockout mice and wild-type littermates.
- Administered selective 5-HT receptor agonists ((+/-) DOI, (+/-)-8-OH-DPAT) to assess behavioral and physiological responses.
- Measured receptor levels via autoradiography and G protein coupling via [(35)S]GTPgammaS binding assays.
Main Results:
- CB1 knockout mice showed reduced head twitches and paw tremor in response to 5-HT(2A/C) agonist DOI.
- A diminished hypothermic response to the 5-HT(1A) agonist 8-OH-DPAT was observed in knockout mice.
- Enhanced despair responses in the tail suspension test were noted in CB1 knockout mice, but antidepressant treatments showed similar efficacy.
- Autoradiography revealed no genotypic differences in 5-HT(1A) and 5-HT(2A) receptor levels.
- Significantly reduced G protein coupling of 5-HT(1A) and 5-HT(2A/C) receptors was detected in specific brain regions of knockout mice.
Conclusions:
- CB1 receptors are integral to regulating serotonergic responses mediated by 5-HT(1A) and 5-HT(2A/C) receptors.
- Reduced coupling of these 5-HT receptors to G proteins in CB1 knockout mice may underlie observed behavioral alterations.
- This suggests a critical role for cannabinoid-serotonin system crosstalk in neurological function and behavior.
