Neuroscience Letters 588 (2015) 1–6.
Is a neuronal chain between the pineal body and the retina in rats and hamsters? Transneural tracing studies.
Ágnes Csákia, Béla Vígha, Zsolt Boldogkőib, Viktoria Vereczkia, Ágoston Széla, Katalin Kövesa*
a Department of Anatomy, Histology and Embryology, Semmelweis University, Budapest, Hungary; bDepartment of Medical Biology, Faculty of Medicine, University of Szeged, Hungary
Neuronal chains between the retina and the pineal body were investigated. Transneuronal tracers, retrograde spreading pseudorabies virus (labeled with green fluorescent protein, memGreen-RV) and virus spreading in both ante- and retrograde directions (labeled with red fluorescent protein, Ka-VHS-mCherry-A-RV) were injected into the right eye of vitreous body of intact or bilaterally sympathectomized Wistar male rats. Intact golden hamsters also received memGreen-RV into the eye and Ka-VHS-mCherry-A-RV into the pineal body. Four-five days later the animals were sacrificed. Frozen sections were prepared from the removed structures. In intact rats memGreen-RV resulted in green fluorescent labeling in the trigeminal and the superior cervical ganglia, the lateral horn of the spinal cord, the paraventricular and the suprachiasmatic nuclei, the perifornical region, the ventrolateral medulla, the locus ceruleus, and the raphe nuclei. In sympathectomized rats the labeling was missing from the brainstem but further existed in the hypothalamus. This observation indicates that the hypothalamic labeling is not mediated by the sympathetic system. One labeled neuron in the pineal body was only observed in 2/13 rats. It was independent from the sympathectomy. When the animals received Ka-VHS-mCherry-A-RV the distribution of the labeling was very similar to that of the intact group receiving retrograde virus. In golden hamsters the memGreen-RV labeled structures were seen in similar places as in rats, but virus labeled nerve cell bodies were always seen in the pineal body. Injection of Ka-VHS-mCherry-A-RV into the pineal body of hamsters resulted in labeling of the retina at both sides. It was concluded that the retinopetal neuronal chain in golden hamsters is always present but in rats it is stochastic. © 2014 Published by Elsevier Ireland Ltd.
KEYWORDS: Confocal microscopy; Golden hamster; Sympathectomy; Virus labeling; Wistar rat
It was accepted for a long time that the pineal body sends only hormonal signals to other organs including the eye. Rhythmic secretion of melatonin influences the photoperiodicity (Reiter et al, 1991). Allopregnanolone is produced by the brain and the the pineal organ as well. The pineal allopregnanolone production is protective for cerebellar Purkinje cells and maintains the circadian rhythm of locomotor activity. Pinealectomy induces apoptosis of the Purkinje cells (Tsutsui 2008). Allopregnanolone potentiates the activity of GABAA receptors (Carver and Raddy, 2013) and has also neuroprotective properties in vitro (Ishikawa et al, 2014) and in vivo in the retina.
The pinealofugal neuronal connection between the pineal body and the retina was not demonstrated beforehand. With the use of intravitreal injection of a retrograde spreading virus we were able to show labeled neurons in the pineal body in adult hamsters, but not in adult rats. Injection of an anterograde spreading virus in the pineal body of hamsters resulted in labeling in the retina at both sides. These results clearly show that a pinealofugal neuronal chain exists in hamsters. Later we have observed that neurons are also observed in young prepubertal rats; however, these neurons diasppear by the adult age. The first three postnatal weeks are critical period in the development of the nervous system of rats. In this moment it is not clear, why the neurons disappear, and what is the function of the pinealofugal visual system in mammals.
Fig. 1. Microphotographs demonstrate neurons in the pineal body of adult hamsters 4 days after the retrogradelly spreading GFP labeled virus injection in the vitreous body (A and B). Green fluorescence shows the labeled neurons (indicated by white arrows). Two examples of the injection site of an anterogradelly spreading Cherry labeled virus into the pineal body (C and D) indicated by red arrows. Scale: 10 µm in A and B, 250µm in C, 25µm in D.
Fig. 2. Microphotographs demonstrate retinal labeling 4 days after the Cherry labeled anterogradelly spreading virus injection into the pineal body. Red labeling showed characteristic distribution. The labeled neurons were arranged in columns in both right and left retinas. Arrows show labeled columns in A-C. Arrowheads show labeled ganglion, bipolar or amacrine cell in D, E and F, respectively. Scale: 50µm in A-C, and 25µm in D-F.
Fig. 3. Microphotographs show labeled neurons in the pineal body of prepubertal rats 4 days after the intravitreal injection of a retrogradelly spreading GFP labeled virus. The animals were inoculated when they were 3 (A), 8 (B), 14 (D) or 20 day-old (E) and they were sacrificed 2 days after the virus inoculation. F shows pineal body of adult rat where the labeling is missing. Arrows show labeled cells in the pineal body, arrowhead show a labeled cell in the optic chiasm of 14-day-old rat. Scale: 50µm in A and 100µm in C-F.
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Contact: Prof. Katalin Köves, M.D., Ph.D., D.Sc.
Dept of Anatomy, Histology and Embryology
Faculty of Medicine
Tűzoltó u 58. H-1094