TRPM8 thermosensation in poikilotherms mediates both skin colour and locomotor performance responses to cold temperature.

Thermoregulation is a homeostatic process to maintain an organism's internal temperature within a physiological range compatible with life. In poikilotherms, body temperature fluctuates with that of the environment, with both physiological and behavioral responses employed to modify body temperature. Changing skin colour/reflectance and locomotor activity are both well-recognized temperature regulatory mechanisms, but little is known of the participating thermosensor/s. We find that Xenopus laevis tadpoles put in the cold exhibit a temperature-dependent, systemic, and rapid melanosome aggregation in melanophores, which lightens the skin. Cooling also induces a reduction in the locomotor performance. To identify the cold-sensor, we focus on transient receptor potential (trp) channel genes from a Trpm family. mRNAs for several Trpms are present in Xenopus tails, and Trpm8 protein is present in skin melanophores. Temperature-induced melanosome aggregation is mimicked by the Trpm8 agonist menthol (WS12) and blocked by a Trpm8 antagonist. The degree of skin lightening induced by cooling is correlated with locomotor performance, and both responses are rapidly regulated in a dose-dependent and correlated manner by the WS12 Trpm8 agonist. We propose that TRPM8 serves as a cool thermosensor in poikilotherms that helps coordinate skin lightening and behavioural locomotor performance as adaptive thermoregulatory responses to cold.

The role of interindividual licking received and dopamine genotype on later-life licking provisioning in female rat offspring.

INTRODUCTION: Rat mothers exhibit natural variations in care that propagate between generations of female offspring. However, there is limited information on genetic variation that could influence this propagation. METHODS: We assessed early-life maternal care received by individual female rat offspring, later-life maternal care provisioning, and dopaminergic activity in the maternal brain in relation to naturally occurring genetic polymorphisms linked to the dopaminergic system. We also conducted a systematic analysis of other genetic variants potentially related to maternal behavior in our Long-Evans rat population. RESULTS: While we did not find a direct relationship between early-life licking received and later-life licking provisioning, this relationship was indirectly affected by dopamine levels in the nucleus accumbens and dependent on variation in the dopamine receptor 2 gene (rs107017253). More specifically, female rat offspring with the A/G genotype showed a positive relationship between average licking received and dopamine levels in the nucleus accumbens of the maternal brain; there was no relationship with female rat offspring with the A/A genotype. The higher dopamine levels in the nucleus accumbens corresponded with higher maternal licking provisioning from postnatal days 2-9. We also discovered and validated several new variants that were predicted by our systematic analysis. CONCLUSION: Our findings suggest that genetic variation influences the relationship between early-life maternal care received and the dopaminergic system of the maternal brain, which can indirectly influence later-life maternal care provisioning.

Type II Opsins in the Eye, the Pineal Complex and the Skin of Xenopus laevis: Using Changes in Skin Pigmentation as a Readout of Visual and Circadian Activity.

The eye, the pineal complex and the skin are important photosensitive organs. The African clawed frog, Xenopus laevis, senses light from the environment and adjusts skin color accordingly. For example, light reflected from the surface induces camouflage through background adaptation while light from above produces circadian variation in skin pigmentation. During embryogenesis, background adaptation, and circadian skin variation are segregated responses regulated by the secretion of α-melanocyte-stimulating hormone (α-MSH) and melatonin through the photosensitivity of the eye and pineal complex, respectively. Changes in the color of skin pigmentation have been used as a readout of biochemical and physiological processes since the initial purification of pineal melatonin from pigs, and more recently have been employed to better understand the neuroendocrine circuit that regulates background adaptation. The identification of 37 type II opsin genes in the genome of the allotetraploid X. laevis, combined with analysis of their expression in the eye, pineal complex and skin, is contributing to the elucidation of the role of opsins in the different photosensitive organs, but also brings new questions and challenges. In this review, we analyze new findings regarding the anatomical localization and functions of type II opsins in sensing light. The contribution of X. laevis in revealing the neuroendocrine circuits that regulate background adaptation and circadian light variation through changes in skin pigmentation is discussed. Finally, the presence of opsins in X. laevis skin melanophores is presented and compared with the secretory melanocytes of birds and mammals.