Observations on the fine structure of the substantia nigra in the cat

Abstract

Summary. A light and electron microscopical investigation has been undertaken of the substantia nigra in the normal cat. The pars reticulata partly contains the arborization of dendrites whose cell bodies are located in the so-called pars compacta. There is a considerable overlap of the dendritic fields in the rostrocaudal direction, while the dendritic fields are very restricted in the mediolateral extension of the substantia nigra. The secondary and all subsequent branches of the dendrites of nigral ceils arc for considerable distances completely covered by boutons. Only few boutons contact the cell bodies. Three types of boutons are distinguished in the substantia nigra in the cat. Type I, about 90 ~ of the total, is of the terminal type, contains pleomorphic vesicles and establishes symmetrical synapses with nigral cell soma, dendritic trunks and spines. The type II bouton (about 10 % of the total number) is most commonly of the terminal type, contains spherical vesicles and establishes asymmetrical synapses with cell bodies and dendritic trunks of nigral cells. The type III bouton (about 2 ~o of the boutons) is always of the en passage type, contains pleomorphic vesicles and establishes symmetrical contacts with dendrites. All boutons in the cat's substantia nigra contain several large (700--1200 A) dense core vesicles. Occasional axo-axonic contacts between type I and type III boutons are observed. Type I bouton is invariably presynaptic to the other.The findings are discussed in relation to some relevant problems.

Morphology and electrophysiological properties of immunocytochemically identified rat dopamine neurons recorded in vitro

“…4C). In general, this morphology is consistent with morphological studies of identified dopaminergic neurons in these brain regions (Rinvik and Grofova, 1970;Gulley and Wood, 197 1;Schwyn and Fox, 1974;Bjorklund, 1974, 1978;Hijkfelt et al, 1976;Juraska et al, 1977;Groves and Linder, 1983).…”

Synapsin I (protein I), a nerve terminal-specific phosphoprotein. I. Its general distribution in synapses of the central and peripheral nervous system demonstrated by immunofluorescence in frozen and plastic sections.

“…These "railroad track" and circular images can be explained by the synaptic architecture of this region. The synaptic meshwork in the pars reticulata of the substantia nigra is predominantly constituted by long, poorly ramified dendrites of the nigral neurons and by the axons that extensively innervate them (43,45). Nerve endings on the surface of these dendrites form a regular and almost continuous sheath.…”

“…6), and in the main portion of the globus pallidus (not shown). In fact, these three regions are characterized by a similar synaptic architecture (20,40,43,45). Around this central region of Fig.…”

Balance of Increases and Decreases in Firing Rate of the Spontaneous Activity of Basal Ganglia High-Frequency Discharge Neurons

“…In contrast to this anatomical dominance of inhibitory input, physiological studies consistently report that most (60 -80%) of the pallidal neurons increase their firing rate in response to behavioral events (Brotchie et al 1991;Georgopoulos et al 1983;Jaeger et al 1995;Mink and Thach 1991;Mitchell et al 1987;Turner and Anderson 1997). Neurons of the SNr belong to the same morphological type as pallidal neurons (Fox et al 1974;Yelnik et al 1987), receive similar anatomical inputs Rinvik and Grofova 1970), and as in the pallidum their behavioral-related activity is not dominated by a decrease in firing rate (Handel and Glimcher 1999;Nevet et al 2007;Sato and Hikosaka 2002;Schultz 1986). Additionally, the soma of neurons in the GPi and the SNr (the output structures) as well as the GPe itself is innervated by GPe GABAergic synapses (Kincaid et al 1991;Sadek et al 2007;Smith and Bolam 1989).…”