striatonigral

Striatonigral refers to the neural connections between the striatum (the caudate nucleus and putamen) and the substantia nigra, particularly the pars reticulata. In the traditional basal ganglia circuitry, striatonigral neurons are part of the direct pathway that transmits movement-promoting signals from the striatum to the output nuclei of the midbrain. These neurons are primarily GABAergic and express dopamine D1 receptors; they project to the substantia nigra pars reticulata (and to the internal segment of the globus pallidus in some species), where they exert inhibitory control.

Functionally, activation of the striatonigral (direct) pathway disinhibits thalamocortical circuits, facilitating movement. Dopamine from the substantia nigra pars compacta enhances this pathway by acting on D1 receptors, thereby promoting initiation and execution of voluntary movements. The indirect pathway, by contrast, involves different striatal neurons (often D2 receptor-expressing) that influence movement in the opposite direction. The balance between direct and indirect pathways modulates motor activity.

Striatonigral degeneration is a related but distinct term describing a neuropathology characterized by loss of neurons in both the striatum and the substantia nigra. It is most commonly associated with multiple system atrophy (MSA) presenting with parkinsonian features and autonomic dysfunction, and it helps explain some clinical differences from idiopathic Parkinson disease.

In summary, striatonigral describes a key motor pathway linking the striatum to the substantia nigra, as well as a neuropathological term referring to degeneration of these regions in certain disorders.