Total number of neurons in the neostriatal, pallidal, subthalamic, and substantia nigral nuclei of the rat basal ganglia: A stereological study using the cavalieri and optical disector methods

Abstract

The total number of neurons within six subdivisions of the rat basal ganglia was estimated using unbiased stereological counting methods and systematic random sampling techniques. Six young adult rats were perfuse-fixed, their right cerebral hemispheres were embedded in glycolmethacrylate, and a complete set of serial 40-mu m sections was cut through each hemisphere. After a random start, a systematic subset (e.g., every tenth) of these sections was used to estimate the total volume of each subdivision using Cavalieri's method. The same set of sampled sections was used to estimate the number of neurons in a known subvolume (i.e., the Nv) by the optical disector method. The product of the total volume and the Nv by these methods yields an unbiased estimate of the total number of neurons. It was found that the right basal ganglia consisted, on average, of 2.79 million neostriatal or caudate-putamen neurons (with a coefficient of variation of 0.07), 46,000 external globus pallidus neurons (0.11), 3,200 entopeduncular/internal globus pallidus neurons (0.10), 13,600 subthalamic neurons (0.10), 7,200 substantial nigra pars compacta neurons (0.15), and 26,300 substantia nigra pars reticulata neurons (0.07).

How laminar frontal cortex and basal ganglia circuits interact to control planned and reactive saccades

“…of about 300,000 fibers in the human (Oorschot, 1996;reviewed in Wickens, 1997), only a small fraction of the potential number of individual condition-action pairings that could be selected by the basal ganglia, given that these projections return to the entire frontal lobe via the thalamus.…”

Cholinergic interneuron characteristics and nicotinic properties in the striatum

“…In rats, the ratio of medium sized neurons (mostly spiny projection neurons) to large cells (mostly cholinergic interneurons) is about 100 to 1 or 2 (Oorschot, 1998), which would make the cholinergic cells about 10 -20% of all striatal interneurons (Graveland and DiFiglia,1985). The total number of neostriatum neurons on one side of a rat brain has been estimated to be about 2.8 million (Oorschot, 1996). Estimating that about 90% of the cells are spiny projection neurons, the number of cholinergic interneurons in a rat is ϳ40,000 per side.…”

Dopaminergic Modulation of Axon Collaterals Interconnecting Spiny Neurons of the Rat Striatum

“…How many come from axon collaterals? There are ϳ2840 striatal neurons inside the volume of a spiny dendritic tree (Oorschot, 1996;Kincaid et al, 1998). Most spiny neurons have their axon collaterals restricted to this volume (Kawaguchi et al, 1990).…”

“…This contamination should be small, because local stimulation of pallidal neurons with glutamate showed little effect on spiny neurons. Pallidal neurons are much less than neostriatal neurons (Oorschot, 1996), and only one-fourth of them innervate the neostriatum (Bevan et al, 1998;Kita and Kita, 2001): 1 of 240 spiny cells (Oorschot, 1996;Bevan et al, 1998). There are 800 intrastriatal boutons for each pallidal cell.…”

“…More than half of them (up to 80%) innervate interneurons (Bevan et al, 1998;Kita and Kita, 2001). Assuming that half of them (400) innervate spiny cells [4.6 ϫ 10 6 boutons; 2.6 ϫ 10 6 spiny cells (Oorschot, 1996)], the result is 2 boutons per spiny cell. Therefore, the probability of activating pallidostriatal terminals on spiny neurons instead of axon collaterals is low; however, a selective pallidostriatal innervation to certain spiny cells cannot be discarded.…”