Beyond Emotional and Spatial Processes: Cognitive Dysfunction in a Depressive Phenotype Produced by Long Photoperiod Exposure

Abstract

Cognitive dysfunction in depression has recently been given more attention and legitimacy as a core symptom of the disorder. However, animal investigations of depression-related cognitive deficits have generally focused on emotional or spatial memory processing. Additionally, the relationship between the cognitive and affective disturbances that are present in depression remains obscure. Interestingly, sleep disruption is one aspect of depression that can be related both to cognition and affect, and may serve as a link between the two. Previous studies have correlated sleep disruption with negative mood and impaired cognition. The present study investigated whether a long photoperiod-induced depressive phenotype showed cognitive deficits, as measured by novel object recognition, and displayed a cognitive vulnerability to an acute period of total sleep deprivation. Adult male Wistar rats were subjected to a long photoperiod (21L:3D) or a normal photoperiod (12L:12D) condition. Our results indicate that our long photoperiod exposed animals showed behaviors in the forced swim test consistent with a depressive phenotype, and showed significant deficits in novel object recognition. Three hours of total sleep deprivation, however, did not significantly change novel object recognition in either group, but the trends suggest that the long photoperiod and normal photoperiod groups had different cognitive responses to total sleep deprivation. Collectively, these results underline the extent of cognitive dysfunction present in depression, and suggest that altered sleep plays a role in generating both the affective and cognitive symptoms of depression.

RETRACTED: BNDF heterozygosity is associated with memory deficits and alterations in cortical and hippocampal EEG power

“…The NOR procedure was performed as previously described [41]. Briefly, the NOR procedure consisted of two habituation days, a sample phase day, and a test phase.…”

“…Only the first two minutes of each video were scored, since this is the time period when animals are most sensitive to novelty and discrimination is detectable, as previously described [41–43]. All videos were scored using EthoVision XT software (Noldus Information Technology, Wageningen, The Netherlands), which automatically tracks the animal’s nose-point and calculates exploration times as the amount of time the nose-point is < 2 cm from each object.…”

Photoperiod-Induced Neuroplasticity in the Circadian System

“…Changing dopamine and somatostatin transmission resulted in altered anxiety and depression-like behaviors. In line with this work, another study found that rats exposed to long photoperiod exhibit depressive phenotypes in the forced swimming test and cognitive deficits in the novel object recognition task [ 107 ].…”

Protection of Episodic Memory by Neuroprotective Peptide Treatments in Sprague-Dawley Rats Subjected to Hypoxic Exposure

“…Rats were subjected to NOR testing following the procedure described by Barnes et al [24] at Days 27 and 28 after the daily…”