Stephany M. Biello

Neuropeptide y and behaviorally induced phase shifts

Neuropeptide Y-containing fibers project from the intergeniculate leaflet of the lateral geniculate nucleus to the suprachiasmatic nucleus. Previous studies have indicated that this pathway may be involved in non-photic resetting of the circadian clock. Therefore, we investigated the possibility that neuropeptide Y mediates phase shifts induced by a particular non-photic stimulus, a pulse of running in a novel wheel. Confining hamsters to a small nest box failed to block phase shifts induced by neuropeptide Y given at zeitgeber time 4; this indicates that increased locomotor activity is not necessary for the observed shifts. Antiserum raised against neuropeptide Y or normal serum was administered at circadian time 5 through a cannula aimed at the suprachiasmatic nucleus. The hamsters were then removed from their cages and placed in a novel wheel for 3 h. Hamsters that received normal serum and ran > 5000 revolutions in the novel wheel advanced their rhythms (mean shift 2.55 h +/- 0.22 S.E.M.) by amounts similar to those of unoperated hamsters. Administration of neuropeptide Y antiserum attenuated the shift normally associated with running in a novel wheel (mean shift 0.21 h +/- 0.14 S.E.M.). These studies indicate that the neuropeptide Y input from the lateral geniculate nucleus to the biological clock is involved in the phase shifts seen in response to novelty-induced wheel running. It also provides another example of the ability of antisera to alter behavior. This may be a useful approach in manipulations of neurochemical activity when antagonists are not yet available or poorly defined.

Genetic knockout and pharmacological blockade studies of the 5-HT7 receptor suggest therapeutic potential in depression

The affinity of several antidepressant and antipsychotic drugs for the 5-HT7 receptor and its CNS distribution suggest potential in the treatment of psychiatric diseases. However, there is little direct evidence of receptor function in vivo to support this. We therefore evaluated 5-HT7 receptors as a potential drug target by generating and assessing a 5-HT7 receptor knockout mouse. No difference in assays sensitive to potential psychotic or anxiety states was observed between the 5-HT7 receptor knockout mice and wild type controls. However, in the Porsolt swim test, 5-HT7 receptor knockout mice showed a significant decrease in immobility compared to controls, a phenotype similar to antidepressant treated mice. Intriguingly, treatment of wild types with SB-258719, a selective 5-HT7 receptor antagonist, did not produce a significant decrease in immobility unless animals were tested in the dark (or active) cycle, rather than the light, adding to the body of evidence suggesting a circadian influence on receptor function. Extracellular recordings from hypothalamic slices showed that circadian rhythm phase shifts to 8-OH-DPAT are attenuated in the 5-HT7 receptor KO mice also indicating a role for the receptor in the regulation of circadian rhythms. These pharmacological and genetic knockout studies provide the first direct evidence that 5-HT7 receptor antagonists should be investigated for efficacy in the treatment of depression.

Neuropeptide Y phase shifts the circadian clock in vitro via a Y2 receptor

The suprachiasmatic nuclei (SCN) contain a circadian clock whose activity can be recorded in vitro for several days. This clock can be reset by the application of neuropeptide Y. In this study, we focused on determination of the receptor responsible for neuropeptide Y phase shifts of the hamster circadian clock in vitro. Coronal hypothalamic slices containing the SCN were prepared from Syrian hamsters housed under a 14 h:10 h light:dark cycle. Tissue was bathed in artificial cerebrospinal fluid (ACSF), and the firing rates of individual cells were sampled throughout a 12 h period. Control slices received either no application or application of 200 nl ACSF to the SCN at zeitgeber time 6 (ZT6; ZT12 was defined as the time of lights off). Application of 200 ng/200 nl of neuropeptide Y at ZT6 resulted in a phase advance of 3.4 h. Application of the Y2 receptor agonist, neuropeptide Y (3-36), induced a similar phase advance in the rhythm, while the Y1 receptor agonist, [Leu31, Pro34]-neuropeptide Y had no effect. Pancreatic polypeptide (rat or avian) also had no measurable phase-shifting effect. Neuropeptide Y applied at ZT20 or 22 had no detectable phase-shifting effect. These results suggest that the phase-shifting effects of neuropeptide Y are mediated through a Y2 receptor, similar to results found in vivo.

Who is pre-occupied with sleep? A comparison of attention bias in people with psychophysiological insomnia, delayed sleep phase syndrome and good sleepers using the induced change blindness paradigm

Cognitive models of insomnia suggest that selective attention may be involved in maintaining the disorder. However, direct assessment of selective attention is limited. Using the inducing change blindness (ICB) paradigm we aimed to determine whether there is attentional preference for sleep‐related stimuli in psychophysiological insomnia (PI) relative to delayed sleep phase syndrome (DSPS) and good sleepers (GS). In the ICB task, a visual scene, comprising both sleep‐related and neutral stimuli, ‘flickers’ back and forth with one element (sleep or neutral) of the scene changing between presentations. Therefore, a 2 × 3 totally between‐participants design was employed. The dependent variable was the number of flickers it took for the participant to identify the change. Ninety individuals (30 per group) were classified using ICSD‐R criteria, self‐report diaries and wrist actigraphy. As predicted, PI detected a sleep‐related change significantly quicker than DSPS and GS, and significantly quicker than a sleep‐neutral change. Unexpectedly, DSPS detected a sleep‐related change significantly quicker than GS. No other differences were observed between the two controls. These results support the notion that there is an attention bias to sleep stimuli in PI, suggesting that selective attention tasks such as the ICB may be a useful objective index of cognitive arousal in insomnia. The results also suggest that there may be an element of sleep preoccupation associated with DSPS. Results are discussed with reference to other experiments on attentional processing in insomnia.

Blocking the Phase-Shifting Effect of Neuropeptide Y with Light

Previous studies have indicated that the neuropeptide Y input from the intergeniculate leaflet of the lateral geniculate nucleus to the suprachiasmatic nucleus is the final part of a non-photic phase shifting pathway to pacemakers in hamsters, or that neuropeptide Y is necessary for other pathways to be effective. Experiments in which two stimuli are presented during the same circadian cycle have shown that phase shifts in response to at least two non-photic stimuli are attenuated by a subsequent light pulse during the subjective day. This study was conducted to investigate the neural site of the blocking effect of light on non-photic stimuli. Experiment 1 showed that phase shifts in response to induced wheel-running during the subjective day are greatly attenuated by a subsequent light pulse. Experiment 2 showed that phase shifts in response to injections of neuropeptide Y in the middle of the subjective day were also greatly reduced by a subsequent light pulse. These results provide some insight about the site of the blocking action of light on non-photic phase shifts. Because there is evidence indicating that neuropeptide Y may mediate phase shifts in response to induced activity, and because light was able to block phase shifts produced by neuropeptide Y, we conclude that, in blocking activity-induced shifts, light must act downstream from the release of neuropeptide Y into the suprachiasmatic nucleus.

Enhanced photic phase shifting after treatment with antiserum to neuropeptide Y.

Previous work has shown that antiserum to neuropeptide Y blocks phase shifts to certain non-photic stimuli at circadian time 4. To examine the role of NPY in photic phase shifts, antiserum to neuropeptide Y was administered just prior to a light pulse at circadian time 18. Hamsters were implanted with guide cannulae aimed at the suprachiasmatic nucleus, and housed in constant darkness. Animals were injected at circadian time 18 under a dim red safe light with 200 nl of either antiserum to neuropeptide Y or normal serum. They were then either exposed to light (approximately 100 lux) for 15 min or returned to constant darkness. Hamsters shifted more to the light pulse when pretreated with antiserum to neuropeptide Y (mean normal serum + light = 1.18 h: mean antiserum to neuropeptide Y + light = 1.92 h; P < 0.01 on a two-tailed paired t-test). Therefore, antiserum to neuropeptide Y enhanced photic advances at circadian time 18.

Disrupted seasonal biology impacts health, food security and ecosystems

The rhythm of life on earth is shaped by seasonal changes in the environment. Plants and animals show profound annual cycles in physiology, health, morphology, behaviour and demography in response to environmental cues. Seasonal biology impacts ecosystems and agriculture, with consequences for humans and biodiversity. Human populations show robust annual rhythms in health and well-being, and the birth month can have lasting effects that persist throughout life. This review emphasizes the need for a better understanding of seasonal biology against the backdrop of its rapidly progressing disruption through climate change, human lifestyles and other anthropogenic impact. Climate change is modifying annual rhythms to which numerous organisms have adapted, with potential consequences for industries relating to health, ecosystems and food security. Disconcertingly, human lifestyles under artificial conditions of eternal summer provide the most extreme example for disconnect from natural seasons, making humans vulnerable to increased morbidity and mortality. In this review, we introduce scenarios of seasonal disruption, highlight key aspects of seasonal biology and summarize from biomedical, anthropological, veterinary, agricultural and environmental perspectives the recent evidence for seasonal desynchronization between environmental factors and internal rhythms. Because annual rhythms are pervasive across biological systems, they provide a common framework for trans-disciplinary research.

Attenuation of circadian light induced phase advances and delays by neuropeptide Y and a neuropeptide Y Y1/Y5 receptor agonist

Circadian rhythms can be synchronised to photic and non-photic stimuli. The circadian clock, anatomically defined as the suprachiasmatic nucleus in mammals, can be phase shifted by light during the night. Non-photic stimuli reset the circadian rhythm during the day. Photic and non-photic stimuli have been shown to interact during the day and night. Precise mechanisms for these complex interactions are unknown. A possible pathway for non-photic resetting of the clock is thought to generate from the intergeniculate leaflet, which conveys information to the suprachiasmatic nucleus (SCN) through the geniculohypothalamic tract and utilises neuropeptide Y (NPY) as its primary neurotransmitter. Interactions between light and NPY were investigated during the early (2 h after activity onset) and late (6 h after activity onset) night in male Syrian hamsters. NPY microinjections into the region of the SCN significantly attenuated light-induced phase delay, during the early subjective night. Phase advances to light were completely inhibited by the administration of NPY during the late night. The precise mechanism by which NPY attenuates or blocks photic phase shifts is unclear, but the NPY Y5 receptor has been implicated in the mediation of this inhibitory effect. The NPY Y1/Y5 receptor agonist, [Leu(31),Pro(34)]NPY, was administered via cannula microinjections following light exposure during the early and late night. [Leu(31),Pro(34)]NPY significantly attenuated phase delays to light during the early night and blocked phase advances during the late night, in a manner similar to NPY. These results show the ability of NPY to attenuate phase shifts to light during the early night and block light-induced phase advances during the late night. Furthermore, this is the first in vivo study implicating the involvement of the NPY Y1/Y5 receptors in the complex interaction of photic and non-photic stimuli during the night. The alteration of photic phase shifts by NPY may influence photic entrainment within the circadian system.

Psychophysiological reactivity to sleep-related emotional stimuli in primary insomnia.

The present study examined psychophysiological reactivity to emotional stimuli related and non-related to sleep in people with primary insomnia (PPI) and in good sleepers (GS). Twenty-one PPI and 18 GS were presented with five blocks of neutral, negative, positive, sleep-related negative and sleep-related positive pictures. During the presentation of the pictures, facial electromyography (EMG) of the corrugator and the zygomatic muscles, heart rate (HR) and cardiac vagal tone (CVT) were recorded. Subjective ratings of the stimuli were also collected. We found that only PPI exhibited greater inhibition of the corrugator activity in response to sleep-related positive stimuli compared to the other blocks of stimuli. Furthermore, PPI rated the sleep-related negative stimuli as more unpleasant and arousing and showed higher CVT in response to all stimuli as compared to GS. Results were interpreted as indicating that PPI exhibit craving for sleep-related positive stimuli, and also hyper-arousability in response to sleep-related negative stimuli, as compared to GS. Our results suggest that psychological treatment of insomnia could benefit by the inclusion of strategies dealing with emotional processes linked with sleep processes.

Phase Response Curves to Neuropeptide Y in Wildtype and Tau Mutant Hamsters

Neuropeptide Y (NPY)-containing fibers project from the intergeniculate leaflet to the suprachiasmatic nucleus. NPY has been shown to phase shift the circadian locomotor activity rhythm of wildtype hamsters, producing large phase advances in the subjective day and small delays in the subjective night. Previous studies have implicated this pathway in the mediation of activity-induced resetting of the circadian clock. Homozygous tau mutant and wildtype hamsters respond very differently to pulses of activity Not only is the amplitude of the phase response curve exaggerated in the mutants with shifts of up to 7 h, but the stimuli are effective at different times during the cycle. Homozygous tau mutant hamsters and wildtype controls were implanted with guide cannulas aimed at the suprachiasmatic nucleus and injected with NPY at various times during the circadian cycle. The responses of homozygous tau mutant hamsters to NPY resembled their responses to nonphotic stimuli in both timing and direction of phase shift. This finding provides correlational evidence that NPY is involved in the effects of nonphotic behavioral events on the circadian system.