Interacting Influences of Sleep, Pain, and Analgesic Medications on Sleep Studies in Rodents

A common neuronal ensemble in nucleus accumbens regulates pain-like behaviour and sleep

A comorbidity of chronic pain is sleep disturbance. Here, we identify a dual-functional ensemble that regulates both pain-like behaviour induced by chronic constrictive injury or complete Freund's adjuvant, and sleep wakefulness, in the nucleus accumbens (NAc) in mice. Specifically, a select population of NAc neurons exhibits increased activity either upon nociceptive stimulation or during wakefulness. Experimental activation of the ensemble neurons exacerbates pain-like (nociceptive) responses and reduces NREM sleep, while inactivation of these neurons produces the opposite effects. Furthermore, NAc ensemble primarily consists of D1 neurons and projects divergently to the ventral tegmental area (VTA) and preoptic area (POA). Silencing an ensemble innervating VTA neurons selectively increases nociceptive responses without affecting sleep, whereas inhibiting ensemble-innervating POA neurons decreases NREM sleep without affecting nociception. These results suggest a common NAc ensemble that encodes chronic pain and controls sleep, and achieves the modality specificity through its divergent downstream circuit targets.

Longitudinal, bidirectional relationships of insomnia symptoms and musculoskeletal pain across adolescence: the mediating role of mood

ABSTRACT

Previous studies have established a bidirectional relationship between sleep and pain, and mood has been proposed as a mediator of this relationship. There are only a limited number of longitudinal studies examining the mediational role of mood, and the directionality of effects between sleep, pain, and mood is uncertain. In addition, despite the high prevalence of pain and sleep problems during adolescence, these relationships have rarely been examined in a longitudinal sample of adolescents. Here, longitudinal survey data with 5 yearly measurements were used to examine the bidirectional relationship between insomnia symptoms and pain across adolescence (Mbaseline age = 13.65 years, Nbaseline = 2767). We also explored if depressed mood, positive affect, and anxious mood are mediators in both directions of the sleep-pain relationship. Using latent variables for insomnia, pain, and mood at multiple time points, the data were analyzed with cross-lagged panel models for longitudinal data with structural equation modeling. Current results confirmed a bidirectional relationship between insomnia symptoms and pain, where the effect of insomnia symptoms on pain was stronger than vice versa. Depressed mood and anxious mood mediated the effect of insomnia symptoms on pain, but not the reverse effect of pain on insomnia symptoms. Positive affect did not serve as a mediator in either direction. These findings add novel insights into the temporal directionality of sleep, pain, and mood during adolescence, suggesting a temporal path from sleep to pain, through mood, rather than a reciprocal relationship between the constructs.

A functional linear modeling approach to sleep-wake cycles in dogs

The study of companion (pet) dogs is an area of great translational potential, as they share a risk for many conditions that afflict humans. Among these are conditions that affect sleep, including chronic pain and cognitive dysfunction. Significant advancements have occurred in the ability to study sleep in dogs, including development of non-invasive polysomnography; however, basic understanding of dog sleep patterns remains poorly characterized. The purpose of this study was to establish baseline sleep-wake cycle and activity patterns using actigraphy and functional linear modeling (FLM), for healthy, adult companion dogs. Forty-two dogs were enrolled and wore activity monitors for 14 days. FLM demonstrated a bimodal pattern of activity with significant effects of sex, body mass, and age; the effect of age was particularly evident during the times of peak activity. This study demonstrated that FLM can be used to describe normal sleep-wake cycles of healthy adult dogs and the effects of physiologic traits on these patterns of activity. This foundation makes it possible to characterize deviations from normal patterns, including those associated with chronic pain and cognitive dysfunction syndrome. This can improve detection of these conditions in dogs, benefitting them and their potential as models for human disease.