To clarify the peculiarities of the morphochemical organization of the substantia nigra SN of a human brain and to create a threedimensional model of pars compacta. Materials and Methods. Sections of the midbrain were stained by Nissl method and by an immunohistochemical method for localization of tyrosine hydroxylase — a marker of dopamine. In the SN pars compacta accumulations of neurons were identified in the form of 9 bands oriented in the rostrocaudal direction and including four areas: medial, lateral, dorsal and ventral.
Morphometric analysis detected significant differences in the density of neurons and in expression of tyrosine hydroxylase between the areas of SN. A model of cellular organization of SN pars compacta proposed by us on the basis of threedimensional reconstruction is characterized by a high degree of detalization as compared to similar works, and shows expressed spatial differentiation of the groups of neurons of SN which should be taken into consideration in pathomorphological examinations.
It is known that physiological ageing and Parkinson disease PD are manifested by morphological alterations of the substantia nigra SN of the brain. Here, age-related involution of SN is characterized by natural reduction in the amount of neurons [ 1 ], while Parkinson disease is associated with a selective death of dopamine neurons in pars compacta [ 2 ].
Intensity and uniformity of quantitative changes of neurons in the structures of SN both in physiological ageing and in pathology — PD — can be evaluated by a morphometric examination. Here, in-depth evaluation of quantitative changes of cell structures of SN is based on examination of the respective parameters of separate aggregations of neurons that make up this structure of the brain. In this context, different variants of division of SN to separate cellular structures were proposed. In one variant SN was divided to two zones — black pars compacta represented by 21 groups of pigmented neurons, and red pars reticulata , consisting of poorly pigmented cells [ 3 ].
Other authors combined dopamine neurons located in the region of the midbrain into 6 separate groups [ 4 ], and arranged dopamine neurons of substantia nigra into groups according to nigrosomes — zones of immunoreactivity of calbindin calcium-binding protein present in nigrostriatal afferent fibers and in cell neuropil [ 5 ]. Besides, there were proposed schemes for division of SN pars compacta of a human brain into regions accessible for studying by morphometric methods [ 6 ].
On the basis of similar schemes and classifications, distribution of cholinergic [ 7 ] and dopaminergic [ 8 ] neurons in SN of the brain was analyzed in laboratory animals, and models of spatial structural organization of SN were described. In the meanwhile, we did not find any information concerning similar three-dimensional models of organization of neuronal structures of SN pars compacta in a human brain in the available literature.
The aim of work was to clarify peculiarities of morphochemical organization of SN of a human brain and to obtain a spatial reconstruction of the structures of its pars compacta.
The average age was 71 years old. Binding of antibodies was determined using Thermo Fisher Ultra Vision set on the basis of the polymer system of detection with alkaline phosphatase. Staining was performed according to the protocols of antibody manufacturers. For three-dimensional reconstruction and morphometry, series of sections were selected from the caudal two thirds of SN with 0.
Stained brain sections were scanned using Plustek Opticfilm i slide-scanner China with dpi resolution. For three-dimensional reconstruction, the series of sections were aligned according to their anatomical landmarks and processed using Image J program free software, National Institutes of Health, USA.
The obtained images were used for localization of groups of cells in the examined structures. From the images of sections stained with cresyl violet, maps of distribution of neurons were obtained, with manual marking of neuron somas using Wacom graphic pad.
Images of sections stained for tyrosine hydroxylase, were segmented by brightness for identification of boundaries of dopaminergic structures. Using Free-D program ex-commercial software, Institut Jean-Pierre Bourgin, France [ 9 ], the areas with the highest local density of neurons in SN and boundaries of other structures of the midbrain were marked in the images, after which three-dimensional reconstruction was conducted on the basis of the obtained contours of cell aggregations.
The obtained three-dimensional model of SN was smoothed and its final image was created in Blender program free software, Blender Foundation, the Netherlands. The applied methods were described by us in more detail earlier [ 10 ]. Morphometric examination was carried out using Leica QWin Standart v. For this, neurons were counted in the field of microscope through the entire depth of the section, with recalculation of their number was per unit volume 0.
Besides, in the same structures the intensity of immunostaining for TH was evaluated in standard units from 0 to The work was carried out on 8-bit images obtained with x4 magnification of the objective, taking into account the background staining, with calculation of median values in the group at different levels along the rostro-caudal axis. The density of arrangement of neurons in the structures of pars compacta of SN was compared using Student test for comparison of groups with pairwise independent variants.
In unstained macropreparations — frontal sections of the midbrain — structures of SN were identified as a separate band of dark brown color Fig. With Nissl method of staining two zones of aggregations of neurons were distinguished Fig. The boundaries of SN were determined by localization of dopamine neurons and their processes Fig. In the obtained three-dimensional model of spatial organization of SN constructed on the basis of sections of the midbrain stained by Nissl method, pars compacta of SN Fig.
In projection of this model on a plane, four areas in SN pars compacta were identified: medial, lateral, dorsal and ventral Fig. Morphometric examination of the density of neurons in the areas of SN pars compacta identified by us, showed higher density in the medial and ventral areas than in lateral and.
Localization of substantia nigra in the cross section of a human midbrain. Three-dimensional reconstruction of substantia nigra of a human midbrain. Groups of neurons of substantia nigra : medial area — 1,2; dorsal area — ; ventral area — ; lateral area — 9. Quantitative parameters of substantia nigra areas. Evaluation of the intensity of immunohistochemical staining for TH in these areas except for lateral area revealed the highest expression of TH in the medial area of SN Fig.
The conducted research permitted to clarify spatial localization of aggregations of groups of neurons in SN of the brain of elder individuals and to divide SN pars compacta to separate areas accessible for studying by methods of mathematical morphology. Three-dimensional reconstruction of sub-stantia nigra of the brain of rats and mice demonstrated similar cytoarchitectonic division of SN pars compacta of rodents into three or four regions depending on if authors identify the medial area [ 8 , 11 ].
Here, groups of dopamine receptors of SN of rodents were probably less differentiated in comparison to humans that was manifested by the absence of clearly discernable segmental division of parts of SN and was confirmed by the given work and by other authors [ 12 ].
According to the results of our work, the pars compacta of SN of humans consists of 9 bands aggregations of groups of neurons which, being compared with the literature data [ 13 ], correspond to the following segments: bands 1 and 2 — to ventromedial segment, band 3 — to intermediate segment, bands 4 and 5 — to ventrolateral segment, band 6 — to dorsomedial segment, bands 7 and 8 — to dorsolateral segment.
Band 9 corresponds to the lateral part of the dorsal area. Three-dimensional model of SN of the brain proposed by us does not show complete correspondence with other variants of SN organization [ 14 , 15 ] which is manifested by a higher specification of structures of this part of the brain identified by us.
This discrepancy is probably due to the fact that one of the above mentioned variants of division of SN suggested study of immu-noreactivity zones of calbindin, and both variants did not suggest use of methods of three-dimensional reconstruction.
Morphometric examination of SN pars compacta showed the higher density of neurons in the medial area than in other areas of SN pars compacta except for ventral area , and intensity of staining for TH was highest in the medial area which agrees with the results obtained by other authors [ 13 ].
In view of this it can be suggested that in elderly individuals involutional alterations to a lesser extent involve the medial area of this brain structure. According to literature data, different groups of dopamine neurons of the midbrain differ not only in location and connections, but also in vulnerability to damaging actions in experiment, in neurodegenerative pathology and in physiological ageing [ 16 ].
The causes of this are not completely clear, but it is suggested that the basis of selective resistance of separate groups of dopamine neurons is their different neurochemical profile that preconditions their susceptibility to oxidative stress [ 17 ].
Thus, the spatial structural morpho-chemical organization of SN of a human brain is characterized by aggregations of neurons along the full length of SN forming 9 bands oriented in rostro-caudal direction, which, being projected onto a horizontal plane, forms 4 areas: medial, lateral, dorsal and ventral.
Morphometric examination of these areas found that the medial area of SN is least susceptible to age-related involution. Author for correspondence. Email: neurolab yandex. Pavlov Russian Medical Biological Herald.
Menu Archives. Many of the dopamine neurons of the substantia nigra project to the striatum , another part of the basal ganglia that is made up of the caudate and putamen. In doing so they form a pathway called the nigrostriatal dopamine pathway that is thought to be crucial in the facilitation of movement. The influence of the substantia nigra on movement is made apparent by observing the symptoms of Parkinson's disease , which are associated with the death of dopamine neurons in the substantia nigra pars compacta.
Although it still isn't clear what exactly causes neurodegeneration in Parkinson's disease, when a significant number of these neurons have died, the individual will likely start to experience movement-related problems like tremors, rigidity, slowness of movement, and postural instability—all hallmark symptoms of Parkinson's disease. Being one of the major dopamine-producing areas of the brain, however, the substantia nigra has functions that extend beyond just motor control.
It is also thought to play important roles in a number of other functions and behaviors, including learning, drug addiction, and emotion. The Basal Ganglia. Principles of Neural Science, 5th ed. New York: McGraw-Hill. Know your brain: Basal ganglia. We experience these things every day, but how do our brains create them?
Your Brain, Explained is a personal tour around your gray matter. Dingman weaves classic studies with modern research into easily digestible sections, to provide an excellent primer on the rapidly advancing field of neuroscience. Louis , author, Origins of Neuroscience.
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