Investigating complex basal ganglia circuitry in the regulation of motor behaviour, with particular focus on orofacial movement.

ABSTRACT

Current concepts of basal ganglia function have evolved from the essentially motoric, to include a range of extramotoric functions that involve not only dopaminergic but also cholinergic, γ-aminobutyric acid (GABA)ergic and glutamatergic mechanisms. We consider these mechanisms and their efferent systems, including spiralling, feed-forward striato-nigro-striatal circuitry, involving the dorsal and ventral striatum and the nucleus accumbens (NAc) core and shell. These processes are illustrated using three behavioural models turning-pivoting, orofacial movements in rats and orofacial movements in genetically modified mice. Turning-pivoting indicates that dopamine-dependent behaviour elicited from the NAc shell is funnelled through the NAc-nigro-striato-nigro-pedunculopontine pathway, whereas acetylcholine-dependent behaviour elicited from the NAc shell is funnelled through the NAc-ventral pallidum-mediodorsal thalamus pathway. Cooperative/synergistic interactions between striatal D1-like and D2-like dopamine receptors regulate individual topographies of orofacial movements that are funnelled through striatal projection pathways and involve interactions with GABAergic and glutamatergic receptor subtypes. This application of concerted behavioural, neurochemical and neurophysiological techniques implicates a network that is yet broader and interacts with other neurotransmitters and neuropeptides within subcortical, cortical and brainstem regions to 'sculpt' aspects of behaviour into its topographical collective.