Central Nervous System Associated With Light Perception and Physiological Responses of Birds

Environmental light that animal receives (i.e., photoperiod and light intensity) has recently been shown that it affects avian central nervous system for the physiological responses to the environment by up or downregulation of dopamine and serotonin activities, and this, in turn, affects the reproductive function and stress-related behavior of birds. In this study, the author speculated on the intriguing possibility that one of the proposed avian deep-brain photoreceptors (DBPs), i.e., melanopsin (Opn4), may play roles in the dual sensory-neurosecretory cells in the hypothalamus, midbrain, and brain stem for the behavior and physiological responses of birds by light. Specifically, the author has shown that the direct light perception of premammillary nucleus dopamine-melatonin (PMM DA-Mel) neurons is associated with the reproductive activation in birds. Although further research is required to establish the functional role of Opn4 in the ventral tegmental area (VTA), dorsal raphe nucleus, and caudal raphe nucleus in the light perception and physiological responses of birds, it is an exciting prospect because the previous results in birds support this hypothesis that Opn4 in the midbrain DA and serotonin neurons may play significant roles on the light-induced welfare of birds.

Neural activation in photosensitive brain regions of Atlantic salmon (Salmo salar) after light stimulation

Photoreceptive inputs to the teleost brain are perceived as image of the visual world and as photo-modulation of neuroendocrine and neuronal signals. The retina and pineal organ are major receptive organs with projections to various parts of the brain, but in the past decades deep brain photoreceptors have emerged as candidates for photoreceptive inputs, either independent or in combination with projections from light sensory organs. This study aimed to test the effects of narrow bandwidth light using light-emitting diodes technology on brain neural activity through putative opsin stimulation in Atlantic salmon. The expression of c-fos, a known marker of neural activity, was compared in situ between dark-adapted salmon parr and following light stimulation with different wavelengths. c-fos expression increased with duration of light stimulation and the strongest signal was obtained in fish exposed to light for 120 minutes. Distinct and specific brain regions were activated following dark to light stimulation, such as the habenula, suprachiasmatic nucleus, thalamus, and hypothalamus. The c-fos expression was overlapping with photoreceptors expressing melanopsin and/or vertebrate ancient opsin, suggesting a potential direct activation by light. Interestingly in the habenula, a distinct ring of vertebrate ancient opsin and melanopsin expressing cells is overlapping with c-fos expression after neural activation. Salmon exposed to different spectra had neural activation in similar brain regions. The most apparent difference was melanopsin expression in the lateral cells of the lateral tuberal nuclus in the hypothalamus, which appeared to be specifically activated by red light. Light-stimulated neuronal activity in the deep brain was limited to subpopulations of neurons, mainly in regions with neuronal modulation activity, retinal and pineal innervations and known presence of nonvisual photoreceptors. The overlapping expression patterns of c-fos and nonvisual opsins support direct light stimulation of deep brain photoreceptors and the importance of these systems in light induced brain activity.

Photoperiodic Regulation of Reproduction in Vertebrates

Organisms use changes in photoperiod for seasonal reproduction to maximize the survival of their offspring. Birds have sophisticated seasonal mechanisms and are therefore excellent models for studying these phenomena. Birds perceive light via deep-brain photoreceptors and long day–induced thyroid-stimulating hormone (TSH, thyrotropin) in the pars tuberalis of the pituitary gland (PT), which cause local thyroid hormone activation within the mediobasal hypothalamus. The local bioactive thyroid hormone controls seasonal gonadotropin-releasing hormone secretion and subsequent gonadotropin secretion. In mammals, the eyes are believed to be the only photoreceptor organ, and nocturnal melatonin secretion triggers an endocrine signal that communicates information about the photoperiod to the PT to regulate TSH. In contrast, in Salmonidae fish the input pathway to the neuroendocrine output pathway appears to be localized in the saccus vasculosus. Thus, comparative analysis is an effective way to uncover the universality and diversity of fundamental traits in various organisms.

Regulasi Fotodeteksi: Peran Cahaya Pada Performa Produksi Telur Unggas

Cahaya merupakan salah satu faktor lingkungan yang esensial bagi kehidupan aves. Signal cahaya yang diterima oleh hipotalamus dapat mengontrol sekresi gonadotropin releasing hormone (GnRH) yang berperan dalam menstimulasi pitutari melepaskan follicle stimulating hormone (FSH) dan luteinizing hormone (LH). Peningkatan konsetrasi dan waktu sekresi gonadotropin berpengaruh pada umur dewasa kelamin, siklus ovulasi, serta performa produksi telur pada aves. Tujuan dari ulasan artikel ini fokus pada peran cahaya yang melibatkan sistem sensori pada performa produksi telur unggas. Organ fotoreseptor vertebrata non-mamalia termasuk aves selain mata adalah organ pineal dan fotoreseptor otak bagian dalam (deep brain photoreceptors). Beberapa molekul fotoreseptor deep brain, yaitu rodopsin (RH), melanopsin (OPN4), dan vertebrate ancient (VA)-opsin, serta protein opsin 5 (OPN5 atau neuropsin). Paparan cahaya yang lebih lama pada siang hari yang panjang menstimulasi peningkatan ekspresi mRNA GnRH sehingga menginduksi dewasa (matang) kelamin unggas. Peningkatan performa reproduksi walaupun kecil tetap berpengaruh pada produksi telur. Lebih dari 33% peningkatan performa reproduksi dan produksi telur merupakan kontribusi dari penggunaan cahaya. Intisari dari ulasan ini adalah mengetahui peran fotoreseptor pada unggas.