This dual-panel image provides an anatomical and histological overview of the basal ganglia and nigrostriatal systems. Panel A is a color-coded anatomical diagram of a coronal brain section illustrating basal ganglia circuitry. It depicts the direct pathway (red arrows), indirect pathway (black arrows), and dopaminergic (DA) projections (green arrows). Key labeled structures include the Caudate nucleus (Cd), Putamen (Pt), Thalamus (Th), Subthalamic Nucleus (STN), Globus Pallidus external (GPe) and internal (GPi) segments, Substantia Nigra pars compacta (SNc), Substantia Nigra reticulata (SNr), and Ventral Tegmental Area (VTA). Panel B is a coronal histological photograph of a monkey brain using Dopamine Transporter (DAT) immunostaining. The image shows intense white signal in the striatum (caudate and putamen) and the SNc, indicating high density of dopamine innervation compared to the darker surrounding cortical and thalamic tissue. This material is pedagogically significant for understanding Parkinson’s disease pathophysiology and the anatomical organization of motor control circuits.

This medical illustration presents a coronally sectioned schematic of the human brain, specifically detailing the functional neuroanatomy and pathways of the basal ganglia. The diagram categorizes the striatum (STR) into the dorsal striatum (DS) and ventral striatum (VS), the latter including the nucleus accumbens. Key subcortical structures identified include the Thalamus (Th), Globus Pallidus external (GPe) and internal (GPi) segments, Subthalamic Nucleus (STN), Hippocampus (HC), Substantia Nigra pars compacta (SNc), Substantia Nigra pars reticulata (SNr), and the Ventral Tegmental Area (VTA). The primary focus is the visual differentiation of motor and cognitive circuits via the direct and indirect pathways. Green arrows represent the direct pathway, illustrating excitatory projections that facilitate movement or cognitive gating, while red arrows denote the indirect pathway, representing inhibitory circuits. Dopaminergic modulation is highlighted by labeling D1 (excitatory) and D2 (inhibitory) receptors within the striatum, showing projections from the midbrain (VTA/SNc). This anatomical model is essential for understanding movement disorders like Parkinson’s disease and cognitive processes involving reward and habituation.

This pathophysiology diagram illustrates a hypothetical model of basal ganglia circuitry and the neurobiological effects of amphetamine-type stimulants (ATS). The top panel shows the normal state, detailing the balance between direct and indirect pathways. Key structures include the cortex, striatum (D1/D2 receptors), globus pallidus external (GPe) and internal (GPi), subthalamic nucleus (STN), substantia nigra pars compacta (SNc) and reticulata (SNr), and the thalamus. Neurotransmitter flow is color-coded: green for glutamate (excitatory), blue for GABA (inhibitory), and red for dopamine (DA). The bottom panel depicts the ATS-altered state, showing pathologically thickened lines representing enhanced dopaminergic and glutamatergic signaling. A detailed inset focuses on the striatal microenvironment, highlighting how ATS disturb the inhibitory influence of GABA interneurons on GABA projection neurons. This disruption leads to over-activation of the direct pathway and inhibition of the indirect pathway, ultimately resulting in increased glutamate release from the thalamus to the cortex. This model explains the polysynaptic mechanisms underlying ATS use disorders and neurotoxicity.

This medical illustration presents a pathophysiology diagram of the human brain in coronal section, focusing on the motor circuitry of the basal ganglia. The diagram maps the structural and functional relationships between the cerebral cortex, striatum (caudate nucleus and putamen), globus pallidus externa (GPe), globus pallidus interna (GPi), subthalamic nucleus (STN), substantia nigra (SN), and thalamus. Three primary signaling pathways are color-coded: the Direct Pathway (red), which facilitates movement; the Indirect Pathway (blue), which inhibits movement; and the Hyperdirect Pathway (green). The visual also utilizes distinct arrowheads to indicate neurotransmitter types: pointed arrows represent excitatory glutamatergic projections (e.g., from the cortex and STN), while T-shaped bars represent inhibitory GABAergic projections (e.g., from the striatum and globus pallidus). This anatomical model is essential for understanding neurodegenerative movement disorders such as Huntington’s Disease and Parkinsonism, specifically how striatal degeneration alters cortical excitation and inhibition loops.