Is a neuronal chain between the pineal body and retina in rats and hamsters? Transneural tracing studies

Significance Statement

The aim of the experiment was to identify the neuronal chain between the retina and the pineal body in Wistar male rats and golden hamsters. Transneuronal tracers, retrograde spreading pseudorabies virus (memGreen-RV) were injected into the vitreous body of right eye of intact or bilateral sympathectomized rats. Golden hamsters also received memGreen-RV. Four days later the animals were sacrificed. Frozen sections were prepared from the right trigeminal ganglion, the forebrain (including the pineal body), brain stem, and the last cervical and upper three thoracic segments of the spinal cord. The virus labeling was visualized under fluorescence microscope. Four days after inoculation in intact rats memGren-RV resulted in labeling in the trigeminal ganglion, lateral horn of the spinal cord, paraventricular and suprachiasmatic nuclei, perifornical region, ventrolateral medulla, locus ceruleus, raphe nuclei. In sympathectomized rats the labeling was missing from the brain stem. One labeled neuron in the pineal body were only observed in 2/14 rats. In golden hamsters the labeled structures were seen in similar places to rats, but labeled neuronal cell bodies were always seen in the pineal body. It was concluded that not in Wistar rats, but in golden hamsters, the retinopetal neuronal chain between the pineal body and the retina is very common. Because labeled neuronal cell bodies were seen only in hamsters virus spreading in both ante- and retrograde directions (memRed-A-RV) were injected to the pineal body and labeled cell were looked for int he retina to confirm the connection between the two organs. Microphotographs demonstrate labeled neurons in the pineal body after the injection of a GFP conjugated retrograde spreading virus into the vitreous body of the eye (A and B). Arrows indicate labeled neurons. Injection of an anterograde virus into the pineal body (C) (double arrow indicates the injection site) resulted in labeling in the retina at both sides. The labeled cells were arranged in columns (D). In E arrowhead indicate a labeled amacrine cell, in F and G arrowheads show labeled bipolar cells. These results clearly show the presence of a retinopetal (pinealofugal) connection between the pineal body and the retina.

Journal Reference

Neurosci Lett. 2015 Feb 19;588:1-6.

Csáki Á¹, Vígh B¹, Boldogkői Z², Vereczki V³, Szél Á¹, Köves K⁴.

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¹Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.

²Department of Medical Biology, Faculty of Medicine, University of Szeged, Hungary.

³Department of Anatomy, Histology and Embryology, Semmelweis University, Budapest, Hungary.

⁴Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary. Electronic address: [email protected]

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Abstract

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 brain stem 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.

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