Depression-Like Responses Induced by Daytime Light Deficiency in the Diurnal Grass Rat (Arvicanthis niloticus)

Abstract

Seasonal Affective Disorder (SAD) is one of the most common mood disorders with depressive symptoms recurring in winter when there is less sunlight. The fact that light is the most salient factor entraining circadian rhythms leads to the phase-shifting hypothesis, which suggests that the depressive episodes of SAD are caused by misalignments between the circadian rhythms and the habitual sleep times. However, how changes in environmental lighting conditions lead to the fluctuations in mood is largely unknown. The objective of this study is to develop an animal model for some of the features/symptoms of SAD using the diurnal grass rats Arvichantis niloticus and to explore the neural mechanisms underlying the light associated mood changes. Animals were housed in either a 12∶12 hr bright light∶dark (1000lux, BLD) or dim light∶dark (50lux, DLD) condition. The depression-like behaviors were assessed by sweet-taste Saccharin solution preference (SSP) and forced swimming test (FST). Animals in the DLD group showed higher levels of depression-like behaviors compared to those in BLD. The anxiety-like behaviors were assessed in open field and light/dark box test, however no significant differences were observed between the two groups. The involvement of the circadian system on depression-like behaviors was investigated as well. Analysis of locomotor activity revealed no major differences in daily rhythms that could possibly contribute to the depression-like behaviors. To explore the neural substrates associated with the depression-like behaviors, the brain tissues from these animals were analyzed using immunocytochemistry. Attenuated indices of 5-HT signaling were observed in DLD compared to the BLD group. The results lay the groundwork for establishing a novel animal model and a novel experimental paradigm for SAD. The results also provide insights into the neural mechanisms underlying light-dependent mood changes.

Differential effects of photoperiod length on depression- and anxiety-like behavior in female and male diurnal spiny mice

“…Another study that tested the behavioral effects of short or long photoperiods in hamsters also demonstrated reversed effects on females and males, however the trends were opposite of those we found in the current study: SP female hamsters showed less previous studies in males of other diurnal rodents [31,35,37,40,43]. Yet, female rodents are demonstrated in some studies to be more active than males in the FST [48,49] and moreover, the sensitivity of male and female behavior in the FST to interventions that induce depression-like behavior in males and to antidepressant drugs is different [48,[50][51][52].…”

“…This work demonstrated that several diurnal rodent species, including the fat sand rat (Psammomys obesus), grass Nile rat (Arvicanthis niloticus), Mongolian gerbils (Meriones unguiculatus) and the degu (Octodon degus) indeed change their behavior and show depressive-and anxiety-like phenotypes in response to changes in day length [14][15][16][17][18]. Moreover, the behavioral changes displayed by these diurnal rodents respond to similar treatment used to alleviate symptoms of SAD in humans including antidepressant drugs, bright light exposure and voluntary exercise [19][20][21][22].…”

The first observation of seasonal affective disorder symptoms in Rhesus macaque

“…In accordance with this speculation, several studies have indeed established the model of SAD in diurnal rodents [8][9][10][11][12]. These animals showed depression-related symptoms when exposed to 3 weeks or more of short photoperiod.…”

“…Although a variety of laboratories have shortened the length of photoperiod to model SAD in rodents [8][9][10][11][12][13][14][15], the effects of short photoperiod on depression-like measures in rodents Fig. 4.…”

“…Light therapy is one of the most effective treatments for SAD, further supporting the association between SAD and light [6]. Although the mechanisms through which light affects SAD were not well understood [7], many researchers have observed the depressive-like behaviors in several species by manipulating the photoperiod [8][9][10][11][12][13][14][15]. For instance, it has been found that nocturnal rodents exhibited depressive-like behavior and anhedonia when exposed to short day lengths [13][14][15].…”