Effects of Frontal Motor Cortex Ablation on the Ultrastructure of Cat Substantia Nigra

Abstract

3, 4 and 5 days after the removal by suction of the left motor and premotor cortex in cats, the presence of ultrastructural changes in the substantia nigra was investigated. Whereas after 3 days dark bouton degeneration was rare, after 4- and 5-day survival it was regularly found for a distinct type of synapse containing in its bouton densely packed small round vesicles and possessing an asymmetric synaptic junction with a dendrite. Often these darkly degenerated boutons contained dense bodies which were also observed in the same type of synapse not yet exhibiting a dark axoplasm. Various inclusions, especially glycogen depots, were present in these boutons suggesting that they were in the process of degeneration. The glial reaction was comparatively severe. In addition, darkly shrunken dendrites contacted both, by intact and by altered boutons were frequently encountered as well as single degenerated neuronal perikarya. The nature of this effect, i.e. whether transneuronal or retrograde, could not be clarified. All these alterations were found bilaterally after the unilateral cortex ablation, and were confined to the substantia nigra pars compacta along its whole anterior-posterior extent. In the pars reticulata, solely traversing myelinated axons in the process of degeneration were observed. Thus, the results are in agreement with the older studies and with evidence from primates demonstrating that the substantia nigra receives a bilateral projection from the motor and premotor cortex.

Synaptic innervation of midbrain dopaminergic neurons by glutamate-enriched terminals in the squirrel monkey

“…The existence of a direct connection from the cerebral cortex to the substantia nigra and the VTA was first suggested on the basis of results obtained in degeneration studies (Afifi et al, 1974;Usunoff et al, 1982;Nitsch et al, 1984). These data were further confirmed with retrograde (Bunney and Aghajanian, 1976;Gerfen et al, 1982) and anterograde (Beckstead, 1979;Sakai, 1988;Shook et al, 1991;Sesack and Pickel, 1992a;Naito and E t a , 1994) tracing techniques.…”

“…Early analysis at the electron microscopic level revealed that the cortical terminals are packed with round electronlucent vesicles and form mainly asymmetric synapses with SNc neurons Usunoff et al, 1982;Nitsch et al, 1984). More recently, the use of double immunocytochemical techniques at the electron microscopic level has allowed researchers to demonstrate that some of the VTA neurons that receive cortical inputs displayed TH immunoreactivity (Sesack and Pickel, 1992a).…”

Ibotenic acid lesions of the substantia nigra pars reticulata ipsilateral to a visual cortical lesion fail to restore visual orienting responses in the cat

“…All the anatomical, physiological and behavioral work suggesting that the nigrotectal projection is inhibitory and influences visuomotor behavior was done in animals with intact cortices, using acute methods of reversible activation and inactivation of the SNpr, not the chronic methods of permanent destruction used in the present study. Chronic manipulations such as cortical lesions have transsynaptic effects over time, altering the structural properties of neurons (Nitsch et al, 1984), altering gene expression and immunoreactivity (Uhl et al, 1988;Sommers and Beckstead, 1990;Chesselet, 1992, 1993) and altering the dynamics of neuronal activity (Garcia-Rill et al, 1979;Aldridge et al, 1990) throughout the basal ganglia. Changes are seen in the substantia nigra as well as in various afferents to the substantia nigra such as the striatum and the external segment of the globus pallidus.…”

Synaptic contacts in schizophrenia: Studies using immunocytochemical identification of dopaminergic neurons

“…However, as mentioned above, animal studies have demonstrated that most of the synaptic contacts on neurons of the substantia nigra are formed by terminals of GABAergic and substance P-ergic neurons of the striatum; several authors believe that innervation of dopaminergic neurons in the compact zone of the substantia nigra is characterized by a lower density on striatal input and a greater variety of sources [8]. Symmetrical contacts in the compact zone of the substantia nigra have been shown to form terminals belonging to neurons in the midbrain tegmental nuclei [16,21], to serotoninergic neurons in the cervical nuclei [18] and to cortical neurons [19]. This latter point, considering existing data on atrophy of the gray matter and "loss" of neurons in the frontal parts of the cortex in schizophrenia [4,5,10,23], is of particular interest from the point of view of putative lesions in the cortical regulation of subcortical dopaminergic formations [9,12,13].…”