Temperature-robust rapid eye movement and slow wave sleep in the lizard Laudakia vulgaris

Local sleep in songbirds: different simultaneous sleep states across the avian pallium

Wakefulness and sleep have often been treated as distinct and global brain states. However, an emerging body of evidence on the local regulation of sleep stages challenges this conventional view. Apart from unihemispheric sleep, the current data that support local variations of neural oscillations during sleep are focused on the homeostatic regulation of local sleep, i.e., the role preceding awake activity. Here, to examine local differences in brain activity during natural sleep, we recorded the electroencephalogram and the local field potential across multiple sites within the avian pallium of zebra finches without perturbing the previous awake state. We scored the sleep stages independently in each pallial site and found that the sleep stages are not pallium-wide phenomena but rather deviate widely across electrode sites. Importantly, deeper electrode sites had a dominant role in defining the temporal aspects of sleep state congruence. Altogether, these findings show that local regulation of sleep oscillations also occurs in the avian brain without prior awake recruitment of specific pallial circuits and in the absence of mammalian cortical neural architecture.

Sleep homeostasis in lizards and the role of the cortex

Slow-wave sleep (SWS) and rapid eye movement sleep are the two primary components of electrophysiological sleep (e-sleep) in mammals and birds. Slow waves in the cortex not only characterize SWS but are also used as biological markers for sleep homeostasis, given their rebound after sleep deprivation (SD). Recently, it has been reported that the Australian dragon Pogona vitticeps exhibits a two-stage sleep pattern in the dorsal ventricular ridge (DVR), which includes a homologue of the mammalian claustrum (CLA). It remains unclear whether reptilian e-sleep, which has been characterized by activity outside the cortex, compensates for sleep loss, as observed in mammals. We here report a significant rebound in the local field potential (LFP) after 7 h of SD. Meanwhile, the mean bout length of each sleep state remained unaffected. We further investigated a possible role of the cortex in e-sleep regulation and homeostasis in Pogona and found that although a corticotomy had no obvious effect on the LFP features of baseline sleep, it abolished LFP power rebound in the CLA/DVR after SD. These findings suggest that e-sleep homeostasis is a common feature in amniotes and that the cortex is involved in regulating activity rebounds in reptiles and mammals.

Monoaminergic signaling during mammalian NREM sleep - Recent insights and next-level questions

Subcortical neuromodulatory activity in the mammalian brain enables flexible wake behaviors, which are essential for survival in an ever-changing external environment. With the suppression of such behaviors in sleep, this activity is, on average, much reduced. Recent discoveries, enabled by unprecedented technical advancements, challenge the long-standing view that monoaminergic systems-noradrenaline (NA), dopamine (DA), and serotonin (5-HT)-remain largely inactive during sleep. This review highlights recent technological and scientific progress in this field, summarizing evidence that monoaminergic signaling in the brain supplements sleep with essential wake-related functions. Stress and/or neuropsychiatric conditions negatively impact on monoaminergic signaling, which can lead to sleep disruptions. Furthermore, subcortical neuromodulatory systems are vulnerable to neurodegenerative pathologies, which implies them in sleep disruptions at early stages of disease. We propose that future research will be well-invested in elucidating the spatiotemporal organization, cellular mechanisms, and functional relevance of neuromodulatory dynamics across species, and in identifying the molecular and physiological processes that sustain their integrity throughout the lifespan.

ReptiLearn: An automated home cage system for behavioral experiments in reptiles without human intervention

Understanding behavior and its evolutionary underpinnings is crucial for unraveling the complexities of brain function. Traditional approaches strive to reduce behavioral complexity by designing short-term, highly constrained behavioral tasks with dichotomous choices in which animals respond to defined external perturbation. In contrast, natural behaviors evolve over multiple time scales during which actions are selected through bidirectional interactions with the environment and without human intervention. Recent technological advancements have opened up new possibilities for experimental designs that more closely mirror natural behaviors by replacing stringent experimental control with accurate multidimensional behavioral analysis. However, these approaches have been tailored to fit only a small number of species. This specificity limits the experimental opportunities offered by species diversity. Further, it hampers comparative analyses that are essential for extracting overarching behavioral principles and for examining behavior from an evolutionary perspective. To address this limitation, we developed ReptiLearn-a versatile, low-cost, Python-based solution, optimized for conducting automated long-term experiments in the home cage of reptiles, without human intervention. In addition, this system offers unique features such as precise temperature measurement and control, live prey reward dispensers, engagement with touch screens, and remote control through a user-friendly web interface. Finally, ReptiLearn incorporates low-latency closed-loop feedback allowing bidirectional interactions between animals and their environments. Thus, ReptiLearn provides a comprehensive solution for researchers studying behavior in ectotherms and beyond, bridging the gap between constrained laboratory settings and natural behavior in nonconventional model systems. We demonstrate the capabilities of ReptiLearn by automatically training the lizard Pogona vitticeps on a complex spatial learning task requiring association learning, displaced reward learning, and reversal learning.

Circadian control of sleep-related neuronal activity in lizards

Although diurnal animals displaying monophasic sleep patterns exhibit periodic cycles of alternating slow-wave sleep (SWS) and rapid eye movement sleep (REMS), the regulatory mechanisms underlying these regular sleep cycles remain unclear. Here, we report that in the Australian dragon Pogona vitticeps exposed to constant darkness (DD), sleep behavior and sleep-related neuronal activity emerged over a 24-h cycle. However, the regularity of the REMS/SWS alternation was disrupted under these conditions. Notably, when the lizards were then exposed to 12 h of light after DD, the regularity of the sleep stages was restored. These results suggest that sleep-related neuronal activity in lizards is regulated by circadian rhythms and that the regularity of REMS and SWS cycling is influenced by daytime light exposure.

A flexible implant for acute intrapancreatic electrophysiology

Microelectrode arrays (MEAs) have proven to be a powerful tool to study electrophysiological processes over the last decades with most technology developed for investigation of the heart or brain. Other targets in the field of bioelectronic medicine are the peripheral nervous system and its innervation of various organs. Beyond the heart and nervous systems, the beta cells of the pancreatic islets of Langerhans generate action potentials during the production of insulin. In vitro experiments have demonstrated that their activity is a biomarker for blood glucose levels, suggesting that recording their activity in vivo could support patients suffering from diabetes mellitus with long-term automated read-out of blood glucose concentrations. Here, we present a flexible polymer-based implant having 64 low impedance microelectrodes designed to be implanted to a depth of 10 mm into the pancreas. As a first step, the implant will be used in acute experiments in pigs to explore the electrophysiological processes of the pancreas in vivo. Beyond use in the pancreas, our flexible implant and simple implantation method may also be used in other organs such as the brain.

Sleep: Hemispheres fight for dominance

A new study shows that bearded dragons have a peculiar way to coordinate sleep state changes between brain hemispheres. The hemisphere that acts first imposes its activity on the other during their REM sleep-like state.