Effects Of Substantia Nigra Stimulation Research Articles

A cellular mechanism of reward-related learning.

Positive reinforcement helps to control the acquisition of learned behaviours. Here we report a cellular mechanism in the brain that may underlie the behavioural effects of positive reinforcement. We used intracranial self-stimulation (ICSS) as a model of reinforcement learning, in which each rat learns to press a lever that applies reinforcing electrical stimulation to its own substantia nigra. The outputs from neurons of the substantia nigra terminate on neurons in the striatum in close proximity to inputs from the cerebral cortex on the same striatal neurons. We measured the effect of substantia nigra stimulation on these inputs from the cortex to striatal neurons and also on how quickly the rats learned to press the lever. We found that stimulation of the substantia nigra (with the optimal parameters for lever-pressing behaviour) induced potentiation of synapses between the cortex and the striatum, which required activation of dopamine receptors. The degree of potentiation within ten minutes of the ICSS trains was correlated with the time taken by the rats to learn ICSS behaviour. We propose that stimulation of the substantia nigra when the lever is pressed induces a similar potentiation of cortical inputs to the striatum, positively reinforcing the learning of the behaviour by the rats.

Effects of substantia nigra stimulation on high- and low-threshold response in reticular neurons

The effects of electrical stimulation of the substantia nigra (NS) pars compacta on somatosensory response in pontine neurons (from n. reticularis pontis caudalis) and reticular cells (n. reticularis gigantocellularis) were investigated in chloralosed cats. These effects were found to be inhibitory and tended mainly towards high-threshold activation of reticular neurons: responses induced by activation of high-threshold somatic efferents were those mainly inhibited in 71% of test cells. Inhibition of low-threshold response induced by tactile stimuli emerged less clearly or not at all. Potential mechanisms and the functional significance of these SN influences on reticular neurons are discussed.

Effects of substantia nigra stimulation on hypothalamic rage reaction in cats

The effects of substantia nigra (SN) (pars compacta) stimulation on the rage reaction elicited by ventromedial hypothalamic nucleus (VMH) were investigated in the cat. The studied parameters of the rage reaction were: the current and the frequency threshold for the appearance of the hissing and the hissing latency. A facilitatory effect induced by the SN on the hypothalamic rage reaction was observed in the form of a decrease in the hypothalamic stimulus threshold for the hissing appearance and a decrease in the hissing latency. Moveover, when the VMH was stimulated with parameters below the threshold for the hissing display, simultaneous nigral activation determined its appearance. The excitatory influence exerted by the SN on the affective component of the aggressive behavior is discussed.

The role of the substantia nigra on the rage reaction elicited by hypothalamic stimulation, in the cat

The effects of substantia nigra stimulation on the rage reaction evoked by hypothalamic activation were studied. The reference value of the rage reaction was the latency of the hissing, which was constant in all animals when hypothalamic stimulation was performed with the same parameters. Simultaneous activation of substantia nigra and hypothalamus determined a significant decrease in hissing latency. The influence of the substantia nigra on the affective components of the aggressive behavior is underlined.

Effects of Substantia Nigra Stimulation on Electrical and Mechanical Activities of the Duodeno-Jejunal Loop, in the Cat

The effect of substantia nigra stimulation on duodeno-jejunal intraluminal pressure and electrical activity was analysed in the cat. An inhibitory influence was noted to occur on both the intestinal pressure and the electrical response activity (ERA): the effect seemed to be in correlation with the stimulus parameters employed. After bilateral vagotomy, the inhibition remained substantially unchanged. The possibility of the existence of a sympathetic pathway mediating the effect is emphasized.

Visual and oculomotor functions of monkey substantia nigra pars reticulata. II. Visual responses related to fixation of gaze.

Visual and oculomotor functions of monkey substantia nigra pars reticulata. II. Visual responses related to fixation of gaze.

Visual and oculomotor functions of monkey substantia nigra pars reticulata. III. Memory-contingent visual and saccade responses.

Visual and oculomotor functions of monkey substantia nigra pars reticulata. III. Memory-contingent visual and saccade responses.

The nigro-tectal pathway. An electrophysiological reinvestigation in the rat

Controversial data have been reported concerning the effect induced by stimulation of substantia nigra (SN) on the cells of the ipsilateral superior colliculus (SC) in the rat. Stimulation applied within SN activates not only the nigral neurons but also fibers passing through and in vicinity of SN, especially those of cerebral peduncle (Ped) and optic tract (OT). The effect of SN stimulation has therefore been reinvestigated on two types of preparation: firstly in animals whose Ped-OT fibers were transected rostral to SN; and secondly in rats whose nigral cells were destroyed by kainic acid injection. In normal animals, SN stimulation induced both inhibitory and excitatory responses in SC cells. After transection of Ped-OT fibers, SN stimulation no longer induced excitatory but only inhibitory effects. This observation clearly demonstrates that the nigro-tectal pathway is inhibitory. The excitatory responses observed in normal rats are related to activation of Ped-OT fibers at the level of SN. Indeed these excitation induced by SN stimulation still persist in kainic acid lesioned animals. Moreover, stimulation of Ped-OT fibers applied rostral to SN also produced these excitatory effects on SC cells. On the other hand, Ped-OT stimulation not only induces excitations but also inhibitory responses. These latter effects can still evoked by SN stimulation after kainic acid induced loss oof nigral cells. In conclusion the SC receives both excitatory and inhibitory input from Ped-OT fibers and only inhibitory input from nigral cells. This inhibitory nigral control is mainly exerted on cells of intermediate and deep collicular layers.

Effects of substantia nigra stimulation on suralis-evoked spinal reflex activity: Comparison with the effects of morphine and stimulation in the periaqueductal gray matter

The effects on spinal reflex activity of morphine and conditioning stimulation of the substantia nigra (SN) or the periaqueductal gray matter (PAG) were compared. Reflex activity was evoked by stimulation of various afferents in the sural nerve. In spinal rats. morphine (2 mg/kg, i.v.) did not significantly affect the ventral root short-latency reflex response to sural nerve stimulation but depressed the long-latency reflex response. Naloxone (0.2 mg/kg, i.v.) abolished this depressant effect of morphine. In rats with prenigral decerebration, trains of conditioning stimuli delivered to the SN or PAG (1) enhanced the short-latency reflex response to sural nerve stimulation, (2) depressed the long-latency reflex response to stimulation of the skin nerve and (3) evoked potentials in ventral and dorsal roots. The effects of stimulation of the SN or PAG were markedly reduced by lesioning of the dorsolateral funiculi. Morphine enhanced the potentials evoked in ventral and dorsal roots by brainstem stimulation with short trains of impulses, not those evoked by stimulation with long trains of impulses. Neither morphine nor naloxone exerted an effect on the unconditioned ventral root long-latency reflex response or on the conditioned long-latency reflex response in rats with prenigral decerebration and an intact spinal cord. Since, in rats with prenigral decerebration, SN stimulation depressed the C fibre evoked long-latency reflex response as well as did conditioning stimulation of the PAG, or as did morphine in spinal rats, it is concluded that the SN inhibits transmission of nociceptive impulses in the rat spinal cord.

The effect of substantia nigra stimulation and morphine on α-motoneurones and the tail-flick response

Rats were used to study the effect of unilateral stimulation of the substantia nigra on the reflex discharge of α-motoneurones and on the reaction time of the tail-flick response. In preparations with prenigral decerebration, nigral stimulation facilitated monosynaptic α-reflex activity ehilst γ-reflex activity remained unchanged. The facilitation of monosynaptic α-reflex activity was reduced by naloxone (1 mg/kg); morphine (2 mg/kg) did not change the number of α-reflex discharges, but it reduced the α-reflex latency, enhanced the effect of nigral stimulation on the latency and abolished the effect of naloxone on nigral facilatation. Nigral stimulation prolonged the reaction time of the tail-flick response in rats with an intact brain and after prenigral decerebration. Naloxone did not influence the anti-nociceptive effect of nigral stimulation, whilst morphine enhanced it in rats with an intact brain. The anti-nociceptive effect exerted by morphine in animals with an intact brain was abolished by prenigral decerebration, and an additional spinalization restored it. Inactivating the nigral neurones by unilateral microinjections of procaine or GABA into the substantia nigra depressed the nociceptive reflex. It is concluded that (1) activation of nigral neurones influenced mono- and polysynaptic reflexes in a reciprocal fashion by a pathway descending via brain stem relays to the spinal cord, (2) inactivation of nigral neurones produced similar changes in reflex activity by altering the function of the nigro-striatal feedback system, the outlet from the system to the spinal cord not being the substantia nigra, (3) morphine influenced the nociceptive reflex by an action at different levels of the central nervous system.

Effect of substantia nigra stimulation on identified neurons in the VL-VA thalamic complex: Comparison between intact and chronically decorticated cats

The effects of substantia nigra (SN) stimulation on the activity of the nucleus ventralis lateralis of the thalamus (VL) have been studied. The VL cells were identified as relay or non-relay cells among the cerebellothalamocortical pathway on the basis of orthodromical activation from the cerebellum and antidromical activation from the cortex. Certaiin experiments were performed after wide pericruciate decortication in order to eliminate the response due to unavoidable activation of corticofugal fibers. These results show that nigrothalamic neurons exert an inhibitory effect on VL cells. This inhibition was observed on the relay as well as on non-relay cells and was strong enough to suppress the cerebellar monosynaptic excitatory input. Thus the SN can moduulate the information running along the cerebellothalamocortical pathway. The topographic localization of inhibited cells suggests that the SN controls the activity of the thalamic neurons which interfere with axial and proximal musculature.

Effect of substantia nigra stimulation on spontaneous unit activity in the caudate nucleus

A wide range of spontaneous unit activity (0.1–15 spikes/sec) was observed in the caudate nucleus of rats anesthetized with urethane. All units did not respond by driven activity following stimulation of the substantia nigra. However, 71% of this population responded by significantly increased or decreased firing rates. It is suggested that unit that exhibit spontaneous activity in the caudate nucleus and which respond to stimulation of the substantia nigra have polysynaptic connections, and those units which do not discharge spontaneously but respond to stimulation of the substantia nucleus by driven action potentials have monosynaptic connetion to the caudate nucleus.

Single-unit recording and stimulation in superior colliculus of the alert rhesus monkey.

RECENT SINGLE-UNIT recording studies of the alert rhesus monkey superior colliculus have disclosed that the deeper layers of this structure contain cells which discharge in association with eye movement (15-17, 23, 24). Such units fire selectively prior to saccades of a specific direction and size, irrespective of the position of the eye in orbit. Stimulation studies of the superior colliculus have so far produced conflicting results. Some reports suggest that in the alert cat stimulation brings the eye to a certain position in orbit irrespective of eye position prior to stimulation (1, 9, 19). Thus, the size and direction of elicited saccades is reported to vary as a function of initial eye position. By contrast, in the alert monkey it has recently been reported that stimulation produces conjugate saccades of a specific size and direction; these parameters are the same no matter where the eye is in the orbit prior to stimulation (12, 15, 16). The stimulation map of Robinson (12) shows a reasonable correspondence with the receptive-field map of the superior colliculus reported by Cynader and Berman (5). The aim of this study was to clarify the relationship between recording and stimulation data by using methods which allow a direct comparison. We used alert rhesus monkeys which had one eye immobilized for the mapping of visual receptive fields. The other eye was normal, thus permitting the study of eye movement. Stimulation and recording were carried out using the same low-resistance microelectrode; for each site sampled, records were obtained for both single-unit activity and for electrical stimulation.