Background Melatonin (N-acetyl-5-methoxytryptamine), a significant indoleamine neuromodulator implicated in circadian rhythms and sleep patterns, regulates diverse rhythmic functions via activating its high-affinity G-protein-coupled receptors. However, the detailed cellular expression of the Mel1a receptor in the retina is still a research gap. Methods The expression of the Mel1a receptor in pigeon retina was assessed using Western blot analysis and immunofluorescent staining. The cellular localization of the Mel1a receptor was studied using double immunofluorescent staining and laser-scanning confocal microscopy. Results Our data suggested that the Mel1a receptor was extensively expressed in the outer segment of Rho4D2-labeled rod and L/M-opsin-labeled red/green cone and in the somata of the CB-labeled horizontal cell, TH-labeled dopaminergic amacrine cell, ChAT-labeled cholinergic amacrine cell, PV-labeled AII amacrine cell, Brn3a-labeled conventional ganglion cell, melanopsin-containing ganglion cell and CRALBP-labeled Müller glial cell. In addition, the Mel1a receptor was diffusely distributed throughout the full thickness of the inner plexiform layer. However, the outer segment of S-opsin-labeled blue cone, the somata of ChX-10-labeled bipolar cell and outer plexiform layer seemed to lack immunoreactivity of the Mel1a receptor. Conclusion The finding that multiple types of retinal cells express the Mel1a receptor provides a new neurobiological basis for the participation of melatonin in the regulation of retinal functions through activating the Mel1a receptor.

The Chinese government has not only been increasing investments in environmental protection, improving the quality of the ecological environment, but has also been focusing on curbing the excessive growth of medical and healthcare expenses so as to ease the economic burden of China's residents. Both aspects are significant concerns worldwide and have received much research attention individually, but the relationship between government environmental protection expenditure and residents' medical and healthcare expenditure remains unclear. Based on panel data from 31 provinces in China from 2007 to 2019, this paper empirically reveals that fiscal environmental protection expenditure is significantly negatively correlated with per capita medical and healthcare expenditure of residents (including outpatient expenditure and inpatient expenditure). This study shows that increasing the fiscal environmental protection expenditure can help curb the rising level of residents' medical and healthcare expenditure. In addition, the results of heterogeneity analysis indicate that the above relationship is stronger in provinces with a relatively low level of economic development or low proportion of the population over 65 years old. Management implications are discussed.

No abstract