Subthalamic Nucleus: Neuroanatomical Review

Discovered in 1865 by Jules Bernard Luys, the subthalamic nucleus is a set of small nuclei located in the diencephalon, inferior to the thalamus and superior to the substantia nigra, that can be visualized in a posterior coronal section. Histologically, it consists of neurons compactly distributed and filled with a large number of blood vessels and sparse myelinated fibers. This review presents an analysis of this anatomical region, considering what is most recent in the literature. Subthalamic neurons are excitatory and use glutamate as the neurotransmitter. In healthy individuals, these neurons are inhibited by nerve cells located in the side globus pallidus. However, if the fibers that make up the afferent circuit are damaged, the neurons become highly excitable, thus causing motor disturbances that can be classified as hyperkinetic, for example ballism and chorea, or hypokinetic, for example Parkinson disease (PD). The advent of deep brain stimulation has given the subthalamic nucleus great visibility. Studies reveal that the stimulation of this nucleus improves themotor symptoms of PD.

Morphology and synaptic organization of non-dopaminergic nigral projections to the medio dorsal thalamic nucleus of the rat, a study by anterograde transport of PHA-L

Mediodorsal [MD] thalamic nucleus, which is considered to take place between extra pyramidal and limbic feedback circuit, receives projective fibers from ventrolateral neurons of reticular part of substantia nigra [SNr]. In order to better understand the influence and chemical reaction of these fibers upon MD nucleus, the morphology and synaptology of them were examined in the present study. Phaseolous vulgaris-leucoagglutin [PHA-L] was injected into substantia nigra pars reticulate. After 3-4 days, the sections of SNr injection site and MD nucleus were prepared. Then, we examined organization, morphology and, synaptology of PHA-L labeled SNr fibers that go to caudal and lateral part of MD thalamic nucleus. At the electron microscopic level, the SNr terminals made synapses predominantly with the medium to small dendrites and far less frequently with soma and large dendrites. These terminals were packed with polymorphic synaptic vesicles and formed symmetrical synapses; furthermore, it has been already recognized that cortico straital fibers from sensory-motor cortex go to region of the SNr that give rise to the nigrothalamic fibers. This data suggest that upon the synaptic organization, morphology and chemical nature of GABAergic, SNr fibers may have different inhibitory influence on MD neurons regulating the thalamic output from MD to cerebral cortex in the control of limbic and extra pyramidal feedback system

Enkephalinergic involvement in substantia nigra in the modulation of hypothalamically-induced predatory attack behavior.

The present study was carried out in five cats which did not attack the rats spontaneously. Predatory attack on an anaesthetized rat was elicited by electrical stimulation of lateral hypothalamus at a mean current strength of 650 microA. The attack was accompanied by minimal affective display and culminated in neck biting. Microinfusions of DAME (delta-alanine methionine enkephaline) in 500 ng dose in substantia nigra facilitated the predatory attack and there was a significant reduction in the threshold current strength for affective display as well as somatomotor components. Microinfusions of naloxone, an opioid antagonist in 1.0 microg dose when DAME effect was at its peak reversed the facilitatory effects and the threshold returned to the control levels within 10 minutes of naloxone infusion at the same locus. Microinfusions of naloxone alone in similar dosage completely blocked the predatory attack response as indicated by an increase in the threshold current strength for somatomotor as well as affective display components. The somatomotor were completely inhibited and could not be elicited even when the current strength was increased to 1000 microA. Control injections of saline in similar volumes (0.5 microl) failed to produce any response Microinfusions of naloxone in lower dose (250 ng) failed to produce any blocking effect. These findings indicate that hypothalamically elicited predatory attack is facilitated by enkephalinergic mechanisms operating at the midbrain level.

Deterioro de la microcirculación en la sustancia negra como causa de la enfermedad de Parkinson / Microcirculation deterioration in the substantia nigra caused by Parkinson's disease

Presentamos nuevos conceptos relativos a la etiología de la Enfermedad de Parkinson (EP). Basado en los hallazgos sobre la angio-arquitectura, relaciones neurono-vasculares y actividad metabólica de la zona compacta de la sustancia negra normal y parkinsoniana, nosotros creemos que una reducción subóptima en el flujo sanguíneo y su persistencia crónica a al sustancia negra, puede ser la clave en la patogénesis de la EP. Por el contrario, suponiendo que nuestra hipótesis es correcta, una revascularización de la sustancia negra podría detener o mejorar esta enfermedad.