Daily changes in light and food availability are major time-cues influencing circadian timing 1 . Little is known, however, about the circuits integrating these time-cues to drive a coherent circadian output 1 – 3 . Here, we investigated whether retinal inputs modulate the entrainment to non-photic cues, such as time-restricted feeding. Photic information is relayed to the suprachiasmatic nucleus (SCN), which houses the central circadian pacemaker, and the intergeniculate leaflet (IGL) through intrinsically-photosensitive retinal ganglion cells (ipRGCs) 4 . Adult mice lacking ipRGCs since early-postnatal stages displayed impaired entrainment to time-restricted feeding, whereas ablating ipRGCs at later stages had no effect. Early-postnatal ipRGC innervation influences neuropeptide Y (NPY)-expressing IGL neurons, guiding the functional IGL NPY -SCN circuit assembly. Moreover, silencing the IGL NPY neurons in adult animals mimicked the deficits induced by early-postnatal ipRGC ablation, and acute inhibition of IGL NPY terminals in the SCN decreased food-anticipatory activity. Thus, early-postnatal ipRGC innervation tunes the IGL NPY -SCN circuit to allow entrainment to time-restricted feeding.

No abstract

Chemogenetic strategies have emerged as reliable tools for remote control of neuronal activity. Among these, designer receptors exclusively activated by designer drugs (DREADDs) have become the most popular chemogenetic approach used in modern neuroscience. Most studies deliver the ligand clozapine-N-oxide (CNO) using a single intraperitoneal injection, which is suitable for the acute activation/inhibition of the targeted neuronal population. There are, however, only a few examples of strategies for chronic modulation of DREADD-controlled neurons, the majority of which rely on the use of delivery systems that require surgical intervention. Here, we expand on two non-invasive strategies for delivering the ligand CNO to chronically manipulate neural population in mice. CNO was administered either by using repetitive (daily) eyedrops, or chronically through the animal’s drinking water. These non-invasive paradigms result in robust activation of the designer receptors that persisted throughout the CNO treatments. The methods described here offer alternatives for the chronic DREADD-mediated control of neuronal activity and may be useful for experiments designed to evaluate behavior in freely moving animals, focusing on less-invasive CNO delivery methods.

We investigated whether circannual rhythms underlying annual testis maturation and moult cycles are independent of duration and frequency of the light period and circadian clock control in non-photoperiodic spotted munia. Birds were subjected to an aberrant light-dark (LD) cycle (3.5 h L:3.5 h D; T7, where T is the period length of the LD cycle) and continuous light (LL, 24 h L:0 h D), with controls on 12 h L:12 h D (T24, 24 h LD cycle). We measured the behavioural activity pattern of the birds and 24 h mRNA oscillations of circadian clock genes (, ,, ,) in the hypothalamus, the putative site of seasonal timing. Diurnal munia were rhythmic in behaviour with the period of the activity-rest cycle matched to T7 and T24, and became behaviourally arrhythmic with activity scattered throughout 24 h under LL. Similarly, exposure to 3.5 h L:3.5 h D and LL caused arrhythmicity in 24 h clock gene expression, suggesting disruption of internal circadian timing at the transcriptional level; a significant rhythm was found under 12 h L:12 h D. During an exposure of 80 weeks, munia showed two to three cycles of testis maturation and wing primaries moult under all photoperiods, although with a longer period under 12L:12D. Thus, the frequency of light period under 3.5 h L:3.5 h D or LL disrupted circadian clock gene cycles, but did not affect the generation of circannual testis and moult cycles. We conclude that the prevailing light environment and hypothalamic circadian gene cycles do not exert direct control on the timing of the annual reproductive cycle in spotted munia, suggesting independent generation of the circadian and circannual rhythms in seasonally breeding species.