Hippocampal interneurons co-express transcripts encoding the alpha7 nicotinic receptor subunit and the cannabinoid...

Area of Science:

• Neuroscience
• Molecular Biology
• Neuroanatomy

Background:

• Emerging evidence suggests functional interactions between alpha7 nicotinic acetylcholine (alpha7 nACh) and cannabinoid systems.
• Both alpha7 nACh receptors and cannabinoid receptor 1 (CB1) are highly expressed in the hippocampus.

Purpose of the Study:

• To investigate the anatomical interactions between alpha7 nACh and cannabinoid systems in the rat hippocampus.
• To determine the distribution of neurons expressing alpha7 nACh mRNA in relation to CB1 mRNA.

Main Methods:

• In situ hybridization to detect mRNA distribution.
• Double in situ hybridization to identify co-expression of transcripts.
• Analysis of co-localization with glutamate decarboxylase (GAD) and cholecystokinin (CCK).

Main Results:

• Alpha7 nACh mRNA is diffusely expressed in principal neurons and highly in a subset of interneurons.
• Hippocampal interneurons co-expressing alpha7 nACh mRNA and GAD resemble those expressing CB1 mRNA.
• The majority of hippocampal interneurons expressing alpha7 nACh mRNA also exhibit high levels of CB1 mRNA.
• Alpha7 nACh/CB1 interneurons represent the major subpopulation of hippocampal interneurons expressing CB1 mRNA and half of CCK-containing neurons.

Conclusions:

• Most hippocampal alpha7 nACh-expressing interneurons possess CB1 mRNA.
• These alpha7 nACh/CB1 interneurons are a major subpopulation of hippocampal CB1 mRNA-expressing interneurons.
• These interneurons are likely the previously postulated hippocampal alpha7 nACh/5HT3/CB1/CCK interneurons that relay information about emotional and physiological states.