This medical illustration comprises six sagittal-view diagrams of the human brain (a–f) detailing cholinergic pathways and the distribution of muscarinic receptor subtypes (M1–M5). Diagram (a) maps primary cholinergic inputs, illustrating projections from basal forebrain nuclei, including the medial septum (MS), diagonal band of Broca (DB), and nucleus basalis magnocellularis (nBM), toward the neocortex (frontal, parietal, occipital), amygdala (AMY), and hippocampus (Hc). Brainstem cholinergic projections from the pedunculopontine nucleus (PPN) and laterodorsal tegmentum (LDT) are shown targeting the thalamus and basal forebrain. Panels (b) through (f) utilize color-coded heatmaps to indicate the expression density of muscarinic receptor subtypes: M1 (purple) and M2 (green) show high cortical and hippocampal density; M3 (yellow) is localized primarily in the cortex and basal ganglia; M4 (red) exhibits strong expression in the striatum and neocortex; and M5 (cyan) displays more localized expression in the ventral tegmental area and substantia nigra. These diagrams facilitate understanding of cholinergic neurotransmission relevant to neurodegenerative diseases, epilepsy, and schizophrenia.

This composite educational graphic illustrates the effects of electro-acupuncture (EA) and MS/VDB-DG cholinergic circuit inhibition on muscarinic receptor expression in a 5xFAD mouse model of Alzheimer's disease. Panels A and B display representative immunofluorescence microscopy images of the hippocampal dentate gyrus (DG). Sections are stained for cell nuclei (DAPI, blue) and muscarinic receptors (M1 in Panel A; M2 in Panel B, red), with merged images provided. Comparisons are made across six groups: Wild-Type (WT), 5xFAD, 5xFAD+EA, and groups utilizing hM4Di DREADDs to inhibit cholinergic circuits. Visually, M1 receptor expression (red) is notably reduced in the 5xFAD group compared to WT, partially restored by EA treatment, and attenuated again following hM4Di-mediated circuit inhibition. In contrast, M2 expression appears more uniform across groups. Panels C and D provide quantitative bar graphs (mean ± SD) supporting these observations, showing statistically significant variations in M1+ cell counts across treatment groups, while M2+ cell counts remain stable. The data suggests that EA modulates cognitive function specifically through the M1 receptor pathway in the DG.

A composite figure consisting of a scatter plot and representative parametric PET brain images, illustrating research on Chronic Fatigue Syndrome (CFS). (A) A scatter plot displays the Antibody Index against muscarinic cholinergic receptors (mAChR) in serum for three groups: Normal Control (NC), CFS(-) patients, and CFS(+) patients. The CFS(+) group shows significantly higher antibody levels (p < 0.001) compared to NC and CFS(-) groups, with several individuals exceeding the 0.5 cut-off value. (B) Axial PET scan images demonstrate [11C](+)3-MPB binding, reflecting cholinergic receptor density across the same three cohorts. A color-coded Non-displaceable Binding Potential (BPND) scale (0 to 5) indicates receptor availability, where warmer colors (red/orange) represent higher binding. The PET images visually demonstrate a marked reduction in binding intensity and distribution in the CFS(+) group compared to the Control and CFS(-) groups, particularly within the central cortical regions and basal ganglia. This finding suggests a downregulation or blockage of cholinergic receptors associated with specific serum autoantibodies in a subset of CFS patients.

Educational comparison of neighboring coronal sections through the human occipital lobe, illustrating neuroanatomical architecture and molecular mapping. The left image is a receptor autoradiograph showing the distribution of cholinergic muscarinic M2 receptors. Density is represented by a pseudocolor scale (30–500 fmol/mg protein), with red/orange indicating high density in the primary visual cortex (V1), while areas such as V2d, V2v, V3d, V3A, and V4v show lower densities in green and blue. The right image is a corresponding cell body stained section (Nissl stain) displaying cytoarchitecture. Key landmarks like the calcarine sulcus (calc) and intraparietal sulcus (ips) are labeled. High-magnification insets (red and blue boxes) detail the laminar organization of V1 and V2v, distinguishing the supragranular (sg), granular (g), and infragranular (ig) strata. This visualization demonstrates how high-resolution histological staining is used to define cortical layer borders for subsequent mapping of receptor density profiles across specialized functional visual areas.