Distribution and Function of CB1 Cannabinoid Receptor and VGLUT3 in the Human Cerebral Cortex

Background

Cannabinoid receptor 1 (CB1) regulates synaptic transmission through presynaptic receptors in nerve terminals, and its physiological roles are of significant clinical relevance. However, the cellular sources and synaptic targets of CB1-expressing nerve terminals in the human cerebral cortex remain unclear. This study aims to reveal the distribution, synaptic targets, and cellular origins of CB1-expressing nerve terminals in the human cerebral cortex, particularly in relation to GABAergic neurons. CB1 receptors are among the most abundant presynaptic receptors in the brain, activated by endocannabinoids such as 2-arachidonoylglycerol (2-AG), and regulate neurotransmitter release. Investigating the distribution and function of CB1 in the human cerebral cortex helps to understand its neurobiological significance in health and disease.

Source of the Paper

This paper was authored by Peter Somogyi and his team, with members from the Department of Pharmacology, University of Oxford, Kawasaki Medical School, Institute of Experimental Medicine, Hungary, and other institutions. The paper was published in 2025 in the European Journal of Neuroscience, titled “Synaptic targets and cellular sources of CB1 cannabinoid receptor and vesicular glutamate transporter-3 expressing nerve terminals in relation to GABAergic neurons in the human cerebral cortex.”

Research Process and Results

1. Research Process

The study was conducted in the following main steps:

a) Sample Collection and Slice Preparation

The study used human cortical tissue samples obtained from neurosurgical procedures at the John Radcliffe Hospital, University of Oxford. The samples were from patients undergoing treatment for brain tumors or temporal lobe epilepsy. The tissue samples were preserved in ice-cold artificial cerebrospinal fluid (ACSF) and sliced into approximately 350 μm thick sections. The slices were stored at room temperature until electrophysiological recordings were performed.

b) Electrophysiological Recordings

Whole-cell patch-clamp techniques were used to record the electrophysiological activity of neurons in cortical layers 1-3. During the recordings, neurons were filled with biocytin for subsequent immunohistochemical analysis. The recorded data included membrane potential, membrane time constant, and action potential parameters.

c) Immunohistochemical Analysis

After recording, the neuronal slices were fixed and subjected to immunohistochemical staining to detect the expression of molecules such as CB1 receptor and VGLUT3 (vesicular glutamate transporter 3). Multiple antibodies were used for multiplex immunofluorescence staining, and the results were observed using confocal microscopy.

d) Electron Microscopy Analysis

To determine the synaptic targets of CB1- and VGLUT3-positive nerve terminals, electron microscopy was used to analyze immunostained nerve terminals. Serial sectioning techniques allowed the identification of synapse types (type 1 or type 2) and their targets (dendritic shafts, dendritic spines, or cell bodies).

2. Main Results

a) Synaptic Targets of CB1-Positive Nerve Terminals

Electron microscopy analysis revealed that CB1-positive nerve terminals primarily formed type 2 synapses (inhibitory synapses), with the majority of targets being dendritic shafts (69%), followed by dendritic spines (20%) and cell bodies (11%). These results indicate that CB1 mainly regulates inhibitory inputs to dendritic shafts.

b) Co-expression of CB1 and VGLUT3

The study found that approximately 25% of CB1-positive GABAergic nerve terminals also expressed VGLUT3, suggesting that these neurons may co-release GABA and glutamate. This co-transmission phenomenon was particularly prominent on dendritic shafts.

c) Synaptic Targets of VGLUT3-Positive Nerve Terminals

Among VGLUT3-positive nerve terminals, 60% formed type 1 synapses (excitatory synapses), primarily targeting dendritic spines (80%) and dendritic shafts (20%). Additionally, 52% of VGLUT3-positive nerve terminals also expressed VGLUT1, indicating that these terminals may originate from intracortical glutamatergic neurons.

d) Cell Type Identification

Through electrophysiological recordings and immunohistochemical analysis, the researchers identified various types of GABAergic interneurons expressing CB1 and/or VGLUT3, including rosehip cells, neurogliaform cells, and basket cells. These cell types exhibited distinct electrophysiological properties and synaptic connectivity patterns in the human cerebral cortex.

3. Conclusions and Significance

The study revealed the distribution of CB1 receptors in the human cerebral cortex and their role in regulating GABAergic synaptic transmission. CB1-positive nerve terminals primarily target dendritic shafts, regulating GABA release, with some neurons exhibiting co-transmission of GABA and glutamate. Furthermore, the analysis of synaptic targets of VGLUT3-positive nerve terminals suggests that these terminals may originate from intracortical glutamatergic neurons or serotonergic neurons.

This research provides new insights into the function of CB1 receptors in the human cerebral cortex, particularly in regulating inhibitory synaptic transmission and neural circuits. The findings have potential applications in developing drugs targeting CB1 receptors, especially for treating neurological disorders related to GABAergic dysfunction, such as epilepsy, anxiety, and schizophrenia.

4. Research Highlights

• Synaptic Targets of CB1-Positive Nerve Terminals: For the first time, the study detailed the synaptic targets of CB1-positive nerve terminals in the human cerebral cortex, highlighting their crucial role in regulating inhibitory inputs to dendritic shafts.
• Co-transmission of GABA and Glutamate: The discovery that some CB1-positive neurons co-express VGLUT3 suggests that these neurons may co-release GABA and glutamate, offering a new perspective on neurotransmitter co-transmission.
• Origins of VGLUT3-Positive Nerve Terminals: Through immunohistochemistry and electron microscopy, the study revealed multiple sources of VGLUT3-positive nerve terminals, including intracortical glutamatergic neurons and serotonergic neurons.

Summary

This study, employing multidisciplinary approaches (electrophysiology, immunohistochemistry, and electron microscopy), revealed the distribution and function of CB1 receptors and VGLUT3 in the human cerebral cortex. The findings not only enhance our understanding of the role of CB1 receptors in neural circuits but also provide new directions for developing drugs targeting CB1 receptors.