Brain CB₁ receptor expression following lipopolysaccharide-induced inflammation

Area of Science:

• Neuroscience
• Neuroimmunology
• Receptor Pharmacology

Background:

• Cannabinoid 1 receptors (CB1) are crucial for neurotransmitter release and their dysregulation is linked to neurological and psychiatric disorders.
• Peripheral inflammatory conditions are increasingly associated with depression and cognitive deficits.
• Lipopolysaccharide (LPS) administration in rodents models peripheral inflammation but its central effects on CB1 receptors require further investigation.

Purpose of the Study:

• To investigate the impact of peripheral LPS-induced inflammation on the central expression of CB1 receptors in the brain.
• To determine if LPS treatment alters CB1 receptor mRNA and protein levels in specific brain regions.

Main Methods:

• CD1 mice were administered varying doses of LPS intraperitoneally.
• Microglial activation was assessed using immunohistochemistry at 6 and 24 hours post-treatment.
• CB1 receptor mRNA and protein levels were quantified using real-time PCR and immunohistochemistry, respectively.
• Co-localization studies identified the specific neuronal terminals affected.

Main Results:

• LPS induced microglial activation in circumventricular organs at 6 hours and in broader brain regions, including the hippocampus, at 24 hours.
• LPS treatment increased CB1 mRNA levels in the hippocampus and brainstem.
• Immunohistochemistry revealed a decrease in CB1 receptor protein expression in the hippocampus, predominantly in the CA3 pyramidal layer.
• The reduction in CB1 receptors was specifically observed on glutamatergic terminals.

Conclusions:

• Peripheral LPS administration causes limited alterations in central CB1 receptor expression despite widespread microglial activation.
• The observed decrease in CB1 receptors on glutamatergic terminals in the hippocampus suggests a targeted effect of inflammation on neurotransmission.
• These findings contribute to understanding the neurobiological mechanisms linking peripheral inflammation to central nervous system disorders.