The Retino-Hypothalamic Ultrastructure aspects of Traumaticoptic Neuropathy’s Pathogenesis and Treatment

Introduction

The possibility of the suprachiasmatic hypothalamus nucles activation using by light was shown by Bremer [1]. The peptides of supraoptic and paraventricular nucleus activate of the synthesis of nerve tissue growth factor [2, 3]. The mutation of this factor promotes growth differentiation of vegetative system’s elements and change its properties neurosecretory [4]. It is known else that suprachiasmatic nucleus regulates light depended corticosteroids’ secretion at night and day time [5, 6].

The neural secretion of hypothalamic nucleus activates due to phospin electric stimulation (PES). There was detected dose independence of PES influence for cerebral vessels’ to use and for neural secrete’s synthesis by magnocellular are neurons of the supraoptic hypothalamic nucleus. Course application of stimulation with current of 100 μA and 300 μA causes redistribution of the contents of different structural-functional types of neurons in the supraoptical nucleus of the hypothalamus [7, 8].

These mechanisms formed the basis of our assumption about the possibility of using retino- hypothalamic stimulation in traumatic optical neuropathy (TON) to ensure the development of endogenous cortecosteroids, which would reduce the dose of proven use of Methylprednisolone, which in the dose of 30 mg/ kg is a standard TON treatment [5]. This would have the ability to reduce the toxic effects of megadoses of corticosteroids, while preserving their neuroprotective effect. The purpose was to study the importance of retino- hypothalamic ultrastructural changes in traumatic optic neuropathy’s pathogenesis and treatment.

Materials and Methods

There experimental traumatic optic nerve crush by surgical clips was reproduced in 90 sexually mature rabbits of the chinchilla breed, according to the conclusion of the Bioethics Commission approved by the Ivano-Frankivsk National Medical University in 2016 [9].

Animal groups were as follows: intact (I), experimental (II) and 2 groups with different treatments (I and II) for 30 individuals in each (120 animals). Group III received (Methylprednisol) at a dose of 30 mg/kg for three days. Group IV received methylprednisolone 15 mg/kg with a combination of PES from the third till the 13thday (Figure 1) with a current of 800 mA on the side of the lesion and 300 mA on the opposite side.

Click to enlarge

The morphological analysis (electron microscopy of the semithin and ultrathin sections and morphometry) of the retina and suprachiasmatic (synonyms of supraoptic) nucleus of the hypothalamusin all groups after removing from the experiment (using guillotine)was done in one month after the trauma (in the electron microscopy laboratory of the Anatomy Department of Ivano- Frankivsk National Medical University). The maintenance of animals (up to 1 month after injury) and their remove from the experiment were performed in accordance with the "Requirements of Bioethics of the Helsinki Declaration on the Ethical Regulation of Medical Research". An analysis of the content of cortisol and adeno-corticotropic hormone (ACTH) in blood serum of experimental animals of all groups in the dynamics up to one month after injury was carried out at 9.00.

Result

In the retina of the side with crushed optic nerve II group of animals, there is find a significant thickening of the retina in comparison with the control group (I) from 178,5±11,47 μm to 246,85±23,69 μm. There is an increase

Note: * significant difference with I group, P<0,05.

Also in animals of group ІІ it was noted swelling in ONL, INL and GCL (Figure 2б, 2B). There were observed microcystal degeneration of ganglionic neurons and pericellular edema in the GCL. There was seen the significant decrease in the number of multipolar neurons in the GCL compared with the intact group of animals (Figure 2a). The area of these neurons increases compared with intact from 58,81±9,01 μm2 to 71,68±8,87 μm2 (P<0,01), whereas the core area does not significantly change and is 37,06±36,20 μm2 (intact group - 36,20±6,63 μm2), which leads to a decrease in nuclean- cytoplasmic index (NCI) from 1,14±0,36 to 1,14±0,36 (P<0,03). There are also thickening and enligtnment of NFL.

Click to enlarge

in the thickness of the photosensory layer (PSL) by 70,8%, outer nuclear layer (ONL) by 54,9%, internal nuclear layer (INl) by 40,1%, ganglion cell layer (GCL) by 53%, and layer of nerve fibers (NFL), by 35% (Table 1).

There were number of neural cells (NC) with the phenomena of peripheral chromatolysis and hypochromic nuclei increases, "shadow cells" appear (Figure 3) in the hypothalamus suprachiasmatic nucleus (SN) in the experimental group (II) at the 30th day after injury the right optic nerve. There were found some NC with small vacuoles on the pericarp of the pericarion. There are karyopicnosis and somewhere carriolysisin majority NC. The area of pericarion SN in comparison with the intact group increases to 276, 59±38, 02 μm2 (P<0,05), whereas the area of the core field of nuclei does not significantly change 71,93±15.67 μm2 (P>0,05). NCI decreases to 0, 35±0,07 (P<0,01). This does not indicate NC’s functional activation. It means faster the swelling of the nucleus and cells and their destructive changes.

Click to enlarge

Click to enlarge

Notes: 1 - normochromic neurons with central chromatolysis, 2 - hyperchromic neurons, 3 – chiasmic fibers, 4 - glyocytes, 5 - shadow cells.

At the ultrastructural level, in the retina, there were observed neurons with dystrophic and destructive changes in the INL (Figure 4a). There were noted karyopicnose, invaginations of the nuclear shell, enlightenment and vacuolation of the cytoplasm. There were single neurons in the state of colicvative necrosis. In GCL, the great path of neurons has the cytoplasm with small vacuoles (Figure 4b). The nuclei acquire a triangular and irregular shape due to significant invasions of the nuclear shell, indicating reactive changes in the cell. The granular endoplasmic net tanks are expanded, some of them destroyed, others shortened, contain single attached ribosomes. A part of the mitochondria in the cell has a normal ultrastructural organization, other partially disorganized crystals and the rest - with a broken inner membrane. There were seen capillaries with significant edema of endothelial cells, which blocked the lumen of the vessel, were encountered in the NFL. Around these capillaries was found perivascular edema. In the part of nerve fibers of NFL there was observed axonal degeneration, which morphologically manifested itself: electron-transparent axoplasm, decrease in the number of neurofilaments on the background of the complete absence of microtubules; disorganization and destruction of mitochondrial crists.

Click to enlarge

Figure 4: The bipolar cell’s (а) and ganglion (б) neuron dystrophy and destructive changes for animal of II group at the 30th day after experiment Electronmicroscopy. Magn: а) x4800, б) x6400 Notes: 1 – neuron’snuclei, 2 – mitochondria, 3 – vacuole, 4 – granular endoplasmicnet, 5 – colicvativenecrosisofneuron, 6 – enlightenment of the axoplasm in NFL.

The cytoplasm, an expansion of the granular endoplasmic mesh tanks, illumination of the mitochondrial matrix and the destruction of crystals with the subsequent formation of vacuoles were found at the ultrastructural level in the majority of light NC of SN’s hypotalamus. An increase in the number of primary and secondary lysosomes, and the destruction of the Golgi complex are observed (Figure 5). Nucleis have low electron-optical density with minor invasions of the nuclear shell. There are isolated light NC with the phenomena of hydropic dystrophy. The volume density of NG in lightneurons is significantly reduced to 2,24±0,19% (P<0,02) compared to the intact group of animals (Table 2). The small vacuoles, lysosomes, an increase in the number and expansion of granular endoplasmic mesh tanks, multivascular corpses, and single NG are found in the neuroplasm of dark NCs. Their nuclei are electron- cubic with one or two nucleolis. The volumetric density of dark NG is significantly reduced to 1, 14±0,04% (P<0,02) compared with intact animals.

Click to enlarge

Click to enlarge

Click to enlarge

Notes: 1 – PSL, 2 – ONL, 3 – ORL, 4 – INL, 5 – IRL, 6 – GCL, 7 – NFL, 8 – pigment layer.

They are respectively 60,03±11,7 μm2 (P<0,01), 36,33±8,69 μm2 (P<0,01), 1,70±0,79 (P<0,05). Such quantitative indices of ganglionic neurons of the IV group of rabbits do not significantly different from intact animals (in all cases, P<0,05). There was a recovery of SN’s hypotalamus structure in rabbits III and IV groups, who received treatment during a month. There are central chromatolysis neurons. Most of the neurons had diffusely located tigroid granules (a sign of regeneration) in animals of the IV group. Such NCs were single in animals of the group III.

The area of pericarions in animals of groups III and IV significantly decreased to 232,14 ± 56,81 μm2 (P<0,04) and 224,25±58.26 μm2 (P<0,05) compared with the pathology(II) and were not significantly differed from the intact (I) group of animals (P<0,05).It indicates as edema. The nuclei in animals of groups III and IV did not significantly change and amounted to 63,46±14,38 μm2 and 76,51±16,54 μm2 (in all cases, P<0,05) compared to pathology and intact animals. The NCI significantly increased to 0, 56±0,23 (P<0,03) compared to the pathology and did not differ significantly from intact animals (P>0,05)in the animals in the IV group. There is not significantly different from the animals in the III and II group. The NCI of the group III is 0,39±0,09 (P>0,05). It is statistically significantly lower than intact animals (P<0,03).

In animals, after treatment at the ultrastructural level, traces of regenerative processes in the retina (Figure 7). There is an enlightenment of the neuroplasia of the individual pericarions, the disorganization of the mitochondria in the neurons of the INL. In the GCL of III group most of the neurons are in a state of vacuolic dystrophy, in some cases phenomena of apoptosis are observed. There are compensatory regeneration processes in the ganglionic neurons of the IV group. They characterized by: hypertrophy of the granular endoplasmatic mesh tanks and an increase in the surface of the attached ribosomes; restoration of fine-grained neuroplasm of moderate electron density; the appearance in the pericarion of new electron-density mitochondria with densely packed crystals. Nucleuses of round-shaped ganglionic neurons with diffusely located granules of euchromatin.

Click to enlarge

Figure 7: Ganglionic cell of III (а) and IV (б) groups of animals Electromicroscopy. Magn.: а) x4800, б)x6400 Notes: 1 – neuron’snuclei, 2 – new mitochondria, 3 – vacuole, 4 – endoplasmaticnet, 5 – neuron with vacuole dystrophy indirect sign of more intensive activation of neurosecretory processes under the action of combined treatment using PES, in comparison with monotherapy with corticosteroids.

Click to enlarge

Click to enlarge

Notes: 1 - nucleus of the neuron, 2 - GEN, 3 - Golgi complex, 4 - lysosomes, 5 - mitochondria, 6 - vacuoles, 7 - autophagosomes, 8 – NG There were also observed recovery processes in dark NC. The confirmation of this is an increase in volumetric density of NG in dark NC, there were compared with animals without treatment, in animals of the group III to 1, 40±0,13% (P<0,01), in animals of the group IV to 1,71±0,17 (P<0,003), But these data was remained statistically significantly lower than in intact rabbits (in all cases P>0,05) (Table 2). It should be noted that the volume density of NG in the animal of the group IV was significantly higher than in IIІ (P<0,01), which also confirms the more pronounced activation of neurosecretory processes under the influence of combined treatment with the use of PES, than with monotherapy with corticosteroids. The "pycnomorphic" neurons are observed along with the dark NCs with regeneration processes. They are at the final stages of their life cycle [10, 11].

The above morphological changes in the structure of the hypothalamus there were occurred on the background of changes in the concentration of hormones in the blood. The content of cortisol decreases from 92, 31±3, 26 μg/dl to 11,79±0,12μg/dl (P<0,05) in the II group in comparison with I. The content of ACTH decreases from 11, 64±0, 43 pg/ml to 6,91±0,09 pg/ml (P<0,05) in the II group in comparison with I. The cortisol’s level increases to 290,12±6,72 μg/dl and the ACTH values decreases to 0,32±0,13 pg/ml (P<0,05) in the group III compared with I group of animals. The content of cortisol was reduced to 6, 93±0.14 μg/dl in the group IV compared to the I group and the III group (P<0,05). The ACTH’ scontent in the group IV (6,13±0,12 pg/ml)was higher than in the group III (P<0,05).

Discussion

Thus, in the retina of the eye after traumatic orbital part optic nerve crush, are observed dystrophic and destructive changes. Mainly they were found in the neurons of the INL, GCL and in nerve fibers of the NFL. There are reactive axonal reaction in ganglionic neurons. Bipolar neurons have vacuolic dystrophy due to disturbance of the blood supply to the retina.

In that time, it was seen reactive edema and destructive changes in the suprachioscular nucleus of the hypothalamus. This leads to a decrease in the production of corticosteroids. Among the dark NCs there are cells of all groups with pronounced destructive changes that do not contain NG, but only lysosomes. A number of authors relate these hypothalamic neurons to pycnomorphic cells that are in the final stages of their life cycle [12, 13]. A characteristic feature of them is high osmophilia and total shrinkage of cells in general. Other researchers, like us, are isolated in the population of dark neurons "chromatophilic" and "pycnomorphic" [10, 11]. The chromatophilic neurons are characterized by a high level of RNA in the nucleus and nucleolis, and the absence of irreversible destructive changes, from which the authors conclude that these cells are more functionally active. The pycnomorphic neurons are in the final stages of cellular destruction. We, like other researchers, tend to attribute these neurons to functionally active, which are characterized by a high level of RNA in the nucleus and nucleoli, and the absence of irreversible destructive changes [10, 11]. These authors conclude that these cells are more functionally active than light, but according to our research, the volumetric density of NG in light cells is significantly higher than that of dark ones.

The treatment led to a partial restoration of the morphological parameters of the ipsilateral retina. The neuroprotective therapy contributes to the development of regenerative processes of the nucleus (more pronounced in combination with PES than with corticosteroid monotherapy). There becomes changing of retinal and hypothalamus architectonics. The number of neurosecretory granules increases. This can be morphological sign of the neurohumoral processes activation. The most optimal treatment is with the use of phosphine electro stimulation, which according to our research leads to compensatory regeneration processes, also described in the works of other researchers, which are characterized by: reduction of the thickness of the retina, restoration of cytokaryometric indices and regenerative processes in bipolar and ganglionic neurons [3].

The peripheral blood ACTH’ scontent decrease with cortisol’s content increase in the group III apparently become due to the use of corticosteroid mega doses. This is likely to result in a disturbance of feedback between hormones. This may be a sign of the depletion of the suprachiasmic nucleus of the hypothalamus. This is confirmed by the presence of pycnomorphic neurons that are not capable to product of hormones. The content of hormones is more closely related to the group without treatment in the group II. Therefore, obviously, it is more physiological, because it corresponds to endogenous processes of the organism. A lot of authors point out such a rearrangement of the hypothalamic NC under different pathological conditions [1, 7, 12].

Conclusion

Thus, retino-hypothalamic neurohumoral dysfunction is an important mechanism of pathogenesis of damage and possible negative consequences of treatment in traumatic optical neuropathy. Contralateral phosphine electric stimulation leads to activation of the neurosecretory processes of the suprachiosmic nucleus of the hypothalamus and the normalization of the content of cortisol and ACTH, which ensures the development of restorative processes in more physiological conditions, compared with monotherapy of corticosteroid mega doses, reducing their toxic effects and retaining retinal neuroprotective properties.