Sensory-motor processing in substantia nigra pars reticulata in conscious cats

The neostriatal mosaic. I. Compartmental organization of projections from the striatum to the substantia nigra in the rat

Combined neuroanatomical techniques were used to examine the organization of the striatal projection to the substantia nigra in the rat. Both double anterograde axonal tracing methods (Phaseolus vulgaris leuco-agglutinin (PHA-L) and 3H-amino acid tract tracing) and double fluorescent retrograde axonal transport tracing methods were used to examine the relationship among striatal neurons projecting to separate areas of the substantia nigra. Additionally, the distributions of retrogradely labeled striatonigral projection neurons were charted relative to the neurochemically distinct striatal "patch" compartment, identified by substance P- or leu-enkephalin-like immunoreactivity, and the complementary "matrix" compartment, identified by somatostatin-like immunoreactive fibers. These studies show two distinct types of organization in the striatonigral projections. One type is topographic in that the mediolateral relationships among these striatal efferent neurons are roughly maintained by their termination patterns in the substantia nigra, while the dorsoventral relationships are inverted. Projections from any part of the striatum, however, are distributed throughout the rostrocaudal axis of the substantia nigra. Despite their general topographic organization, the variable and dispersed nature of such projections from individual striatal loci results in partial overlap of afferent fields from separate striatal areas. The second type of organization is nontopographic and provides a different system for convergence of inputs from separated striatal areas that is superimposed on the rough topographic system. In this other projection system the mediolateral and dorsoventral relationships typical of the topographically ordered system are not maintained and are sometimes reversed. For example, PHA-L injected into the dorsal striatum labels a topographic (inverted relationship) projection to the ventral substantia nigra pars reticulata but also a smaller and separate projection to the dorsal pars reticulata and adjacent pars compacta. Retrograde tracer deposits in the pars compacta label neurons in the ventral striatum (the inverted relationship) but also clusters of neurons in the dorsal striatum. These clusters are in the neurochemically defined patch compartment whereas neurons in the matrix are labeled by injections into the pars reticulata. The dendrites of both retrogradely filled patch and matrix neurons are confined to the compartment containing their cell bodies, suggesting a restriction that would functionally segregate extrinsic striatal afferents shown in other studies to be confined to either patches or matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

Nigral reticulata neurons: potentiation of responsiveness to amphetamine with long-term treatment

Single-unit activity was recorded in the substantia nigra pars reticulata of rats in response to intravenous challenge injections of D-amphetamine. The animals were pretreated with saline or 5.0 mg/kg D-amphetamine twice daily for 6 consecutive days. Whereas the large majority of saline controls (6 of 8) showed no consistent responses to amphetamine at doses up to 2.0 mg/kg, amphetamine pretreated rats (7 of 10) responded with a progressive increase in firing rate. Both groups of animals responded to a subsequent injection of 5.0 mg/kg clozapine with a depression of firing rate. The remaining control rats were inhibited by amphetamine and this aberrant response was enhanced with long-term treatment. In these unusual cells, clozapine accelerated firing rate. Taken together, these results indicate that unlike dopaminergic neurons in the compacta region of the nigra, reticulata neurons increase their responsiveness to amphetamine with repeated administration.

Anticonvulsant action of 2-amino-7-phosphonoheptanoic acid in the substantia nigra

Focal injection of 2-amino-7-phosphonoheptanoic acid in the substantia nigra, pars reticulata or pars compacta, in rats produces a dose-dependent suppression of the tonic extensor seizure component in the electroshock test. Haloperidol pretreatment prevents stereotyped behaviour induced by 2-amino-7-phosphonoheptanoic acid, but does not change the effect on the electroshock test. This anticonvulsant effect of 2-amino-7-phosphonoheptanoic acid probably results from an antagonist action at a receptor site sensitive to N-methyl-D-aspartate leading to a decrease in activity in nigral efferent systems.

Non-dopaminergic neurones of the reticular part of substantia nigra can gate static fusimotor action onto flexors in cat

The effect on the fusimotor system of electrical stimulation of the reticular part of the substantia nigra or of the injection of the gamma-aminobutyric acid (GABA)-antagonist picrotoxin into this structure was studied in spindle receptors of pretibial flexors in cats anaesthetized with ketamine. Afferent activity of muscle spindle primary endings was recorded before and during these two forms of intranigral stimulation. Dynamic spindle sensitivity was assessed during both small- (100 microns) and large-amplitude (2 mm) sinusoidal stretching of the receptor-bearing muscles. From changes in spindle sensitivity after nigral electrical stimulation (eleven out of fourteen primary endings) or intranigral injection of picrotoxin (fifty-one out of sixty-seven primary endings) it is deduced that functional activation of neurones of the reticular part of substantia nigra, in this preparation, removed a normally present tonic static fusimotor action from the primary sensory endings of pretibial flexor muscle spindles. This effect, induced by picrotoxin (2 micrograms in 1 microliter), was reversed by a subsequent intranigral injection of the GABA-agonist muscimol (0.4 microgram in 1 microliters), but remained unchanged after subsequent intracaudate injections of haloperidol (12.5 micrograms in 5 microliters) or apomorphine (5 micrograms in 5 microliters). It is concluded that the C.N.S. can gate static fusimotor action onto flexor muscle spindle primary endings through non-dopaminergic output neurones of the reticular part of substantia nigra.