[Show abstract][Hide abstract] ABSTRACT: The neostriatum (dorsal striatum) is composed of the caudate and putamen. The ventral striatum is the ventral conjunction of the caudate and putamen that merges into and includes the nucleus accumbens and striatal portions of the olfactory tubercle. About 2% of the striatal neurons are cholinergic. Most cholinergic neurons in the central nervous system make diffuse projections that sparsely innervate relatively broad areas. In the striatum, however, the cholinergic neurons are interneurons that provide very dense local innervation. The cholinergic interneurons provide an ongoing acetylcholine (ACh) signal by firing action potentials tonically at about 5 Hz. A high concentration of acetylcholinesterase in the striatum rapidly terminates the ACh signal, and thereby minimizes desensitization of nicotinic acetylcholine receptors. Among the many muscarinic and nicotinic striatal mechanisms, the ongoing nicotinic activity potently enhances dopamine release. This process is among those in the striatum that link the two extensive and dense local arbors of the cholinergic interneurons and dopaminergic afferent fibers. During a conditioned motor task, cholinergic interneurons respond with a pause in their tonic firing. It is reasonable to hypothesize that this pause in the cholinergic activity alters action potential dependent dopamine release. The correlated response of these two broad and dense neurotransmitter systems helps to coordinate the output of the striatum, and is likely to be an important process in sensorimotor planning and learning.
Preview · Article · Dec 2002 · Journal of Neurobiology
[Show abstract][Hide abstract] ABSTRACT: During the last four decades, extracellular single unit recordings have been performed within the neostriatum to investigate the firing properties and response characteristics of the neurons contained therein. Although there are numerous morphologically distinct classes of neostriatal cells, typically only two types of neurons are reported in unit recording studies. These two classes are discriminated on the basis of firing rate, firing pattern, extracellular action potential waveform and response to different aspects of movement tasks. One class, the so-called phasically active neurons (PANS), are believed to be the spiny projection cells and exhibit increases in firing in relation to movement. The other class which spike in a tonic, irregular fashion (TANs) are thought to be cholinergic interneurons and display changes in firing in relation to sensory stimuli which trigger a rewarded movement. Data from intracellular in vivo and in vitro studies have revealed that the intrinsic membrane properties of spiny cells and cholinergic interneurons are very different and provide a cellular basis for understanding the contrasting mechanisms underlying spike generation and patterning in these two populations of cells.