Roxanne Sterniczuk

Characterization of the 3xTg-AD mouse model of Alzheimer's disease: Part 2. Behavioral and cognitive changes

Alzheimers disease (AD) is characterized by distinct behavioral and cognitive deficits that differ from those observed in normal aging. Transgenic models of AD are a promising tool in understanding the underlying mechanisms and cause of disease. The triple-transgenic mouse model of AD (3xTg-AD) is the only model to exhibit both Abeta and tau pathology that is characteristic of the human form. The present study characterized the performance of 3xTg-AD mice on several tasks measuring behavioral and cognitive ability. Aged 3xTg-AD females exhibited a higher level of fear and anxiety demonstrated by increased restlessness, startle responses, and freezing behaviors. No differences were observed in muscle strength and visuo-motor coordination. Understanding the behavioral manifestations that occur in this model of AD may aid in the early diagnosis and appropriate treatment of AD symptomology.

Characterization of the 3xTg-AD mouse model of Alzheimer's disease: part 1. Circadian changes.

Circadian disturbances, including a fragmented sleep-wake pattern and sundowning, are commonly reported early in the progression of Alzheimers disease (AD). These changes are distinctly different from those observed in non-pathological aging. Transgenic models of AD are a promising tool in understanding the underlying mechanisms and cause of disease. A novel triple-transgenic model of AD, 3xTg-AD, is the only model to exhibit both Abeta and tau pathology, and mimic human AD. The present study characterized changes pertaining to circadian rhythmicity that occur prior to and post-AD pathology. Both male and female 3xTg-AD mice demonstrated alterations to their circadian pacemaker with decreased nocturnal behavior when compared to controls. Specifically, males showed greater locomotor activity during the day and shorter freerunning periods prior to the onset of AD-pathology, and females had a decrease in activity levels during their typical active phase. Both sexes did not differ in terms of their freerunning periods or photic phase shifting ability. A decrease in vasoactive intestinal polypeptide-containing and vasopressin-containing cells was observed in the suprachiasmatic nucleus of 3xTg-AD mice relative to controls. This study demonstrates that abnormalities in circadian rhythmicity in 3xTg-AD mice precede expected AD pathology. This suggests that human studies may wish to determine if similar circadian dysfunction is predictive of early-onset AD.

Physiological responses of the circadian clock to acute light exposure at night

Circadian rhythms in physiological, endocrine and metabolic functioning are controlled by a neural clock located in the suprachiasmatic nucleus (SCN). This structure is endogenously rhythmic and the phase of this rhythm can be reset by light information from the eye. A key feature of the SCN is that while it is a small structure containing on the order of about 20,000 cells, it is amazingly heterogeneous. It is likely that anatomical heterogeneity reflects an underlying functional heterogeneity. In this review, we examine the physiological responses of cells in the SCN to light stimuli that reset the phase of the circadian clock, highlighting where possible the spatial pattern of such responses. Increases in intracellular calcium are an important signal in response to light, and this increase triggers many biochemical cascades that mediate responses to light. Furthermore, only some cells in the SCN are actually endogenously rhythmic, and these cells likely do not receive strong direct input from the retina. Therefore, this review also considers how light information is conveyed from the retinorecipient cells to the endogenously rhythmic cells that track circadian phase. A number of neuropeptides, including vasoactive intestinal polypeptide, gastrin-releasing peptide and substance P, may be particularly important in relaying such signals, but other neurochemicals such as GABA and nitric oxide may participate as well. A thorough understanding of the intracellular and intercellular responses to light, as well as the spatial arrangements of such responses may help identify important pharmacological targets for therapeutic interventions to treat sleep and circadian disorders.

Altered photic and non-photic phase shifts in 5-HT1A receptor knockout mice

The mammalian circadian clock located in the suprachiasmatic nucleus (SCN) is thought to be modulated by 5-HT. 5-HT is though to inhibit photic phase shifts by inhibiting the release of glutamate from retinal terminals, as well as by decreasing the responsiveness of retinorecipient cells in the SCN. Furthermore, there is also evidence that 5-HT may underlie, in part, non-photic phase shifts of the circadian system. Understanding the mechanism by which 5-HT accomplishes these goals is complicated by the wide variety of 5-HT receptors found in the SCN, the heterogeneous organization of both the circadian clock and the location of 5-HT receptors, and by a lack of sufficiently selective pharmacological agents for the 5-HT receptors of interest. Genetically modified animals engineered to lack a specific 5-HT receptor present an alternative avenue of investigation to understand how 5-HT regulates the circadian system. Here we examine behavioral and molecular responses to both photic and non-photic stimuli in mice lacking the 5-HT(1A) receptor. When compared with wild-type controls, these mice exhibit larger phase advances to a short late-night light pulse and larger delays to long 12 h light pulses that span the whole subjective night. Fos and mPer1 expression in the retinorecipient SCN is significantly attenuated following late-night light pulses in the 5-HT(1A) knockout animals. Finally, non-photic phase shifts to (+/-)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) are lost in the knockout animals, while attenuation of the phase shift to the long light pulse due to rebound activity following a wheel lock is unaffected. These findings suggest that the 5-HT(1A) receptor plays an inhibitory role in behavioral phase shifts, a facilitatory role in light-induced gene expression, a necessary role in phase shifts to 8-OH-DPAT, and is not necessary for activity-induced phase advances that oppose photic phase shifts to long light pulses.

Enhancement of photic shifts with the 5-HT1A mixed agonist/antagonist NAN-190: Intra-suprachiasmatic nucleus pathway

Chronic desynchronization between the mammalian circadian pacemaker and its external environment, such as that observed from shift work or jet lag, can lead to various long-term health consequences. The circadian clock can be reset by exposure to light, although the magnitude of such adjustments is modest. 5-HT modulates the effects of light, and 5-HT(1A) mixed agonist/antagonists, such as NAN-190, have been found to potentiate the phase resetting ability of light. The mechanism for this potentiation has yet to be uncovered, although it has been proposed that these drugs inhibit raphe output while simultaneously blocking post-synaptic 5-HT(1A) receptors. The current study takes advantage of the heterogeneous network organization of the circadian clock to identify where in the circadian system NAN-190 exerts its influence. Retinorecipient cells in the ventrolateral suprachiasmatic nucleus (SCN) are activated by glutamate and release either gastrin-releasing peptide (GRP) or vasoactive intestinal polypeptide. Application of the glutamate agonist N-methyl-D-aspartic acid (NMDA) or either of these neuropeptides to the SCN mimics the effects of light. We hypothesized that NAN-190 would modify responses to treatments that activate the circadian system upstream, but not downstream, of where NAN-190 is acting. Hamsters were pretreated with NAN-190 or vehicle, followed by one of the neurochemicals 45 min later, during the early- and/or late-subjective night. NAN-190 potentiated NMDA-induced phase advances and delays as well as GRP-induced advances, but attenuated GRP-induced delays. NAN-190 did not potentiate NMDA-induced Fos expression, however greater GRP-induced Fos expression was found within the dorsolateral region of the SCN. These data suggest that NAN-190 acts, in part, by modifying the responsiveness of retinorecipient cells in the circadian clock. An understanding of the neural events that underlie the potentiation of photic phase shifts by NAN-190 could guide the development of novel chronobiotics which could be used to treat a variety of sleep and circadian disorders.

Non‐photic phase shifting of the circadian clock: role of the extracellular signal‐responsive kinases I/II/mitogen‐activated protein kinase pathway

The master circadian clock, located in the suprachiasmatic nucleus (SCN), is synchronized to the external world primarily through exposure to light. A second class of stimuli based on arousal or activity can also reset the hamster circadian clock in a manner distinct from light. The mechanism underlying these non‐photic phase shifts is unknown, although suppression of canonical clock genes and immediate early genes has been implicated. Recently, suppression of one of the mitogen‐activated protein kinases (MAPK), namely extracellular signal‐responsive kinases I/II (ERK), has been implicated in phase shifts to dark pulses, a stimulus with both photic and non‐photic components. We investigated the involvement of the ERK/MAPK pathway in phase shifts in response to 3 h of sleep deprivation initiated at mid‐day. About three‐quarters of animals subjected to this procedure demonstrated large phase advances of about 3 h. Those that shifted exhibited a significant decrease in phosphorylated ERK (p‐ERK) in the SCN. Those animals that were perfused during the sleep deprivation also exhibited immunoreactivity for p‐ERK in a distinct portion of the ventrolateral SCN. Finally, injections of U0126 to the SCN to prevent phosphorylation of ERK significantly decreased levels of p‐ERK but did not produce phase shifts. These data demonstrate that a purely non‐photic manipulation is able to alter the activity of the MAPK pathway in the SCN, with downregulation in the SCN shell and activation in a portion of the SCN core.

An inverse relationship between typical alcohol consumption and facial symmetry detection ability in young women.

The relationship between monthly alcohol consumption over the past 6 months and facial symmetry perception ability was examined in young sober women with typical college-age drinking patterns. Facial symmetry detection performance was inversely related to typical monthly alcohol consumption, r (41) = —0.57, p < 0.001. Other variables that were predictive of facial symmetry detection included alcohol-related hangover and blackout frequency over the past 6 months, number of alcoholic drinks over the past week, early adolescent alcohol consumption and frequency of drug use. The relationship between alcohol use and symmetry detection could not be explained by individual differences in personality, family alcoholism history or other drug use. These findings suggest the possibility of a neurotoxic effect of alcohol on facial symmetry perception ability in female undergraduate students. As similar results did not emerge for a test of dot symmetry detection, the findings appear specific to facial symmetry. No previous studies have examined the effect of alcohol history on symmetry detection. The findings add to a growing literature indicating negative visuospatial effects of early alcohol use, and suggest the importance of further research examining alcohol and drug effects on sober facial perception in non-alcoholic populations.

Non-photic modulation of phase shifts to long light pulses.

Circadian rhythms can be reset by both photic and non-photic stimuli. Recent studies have used long light exposure to produce photic phase shifts or to enhance non-photic phase shifts. The presence or absence of light can also influence the expression of locomotor rhythms through masking; light during the night attenuates locomotor activity, while darkness during the day induces locomotor activity in nocturnal animals. Given this dual role of light, the current study was designed to examine the relative contributions of photic and non-photic components present in a long light pulse paradigm. Mice entrained to a light/dark cycle were exposed to light pulses of various durations (0, 3, 6, 9, or 12 h) starting at the time of lights-off. After the light exposure, animals were placed in DD and were either left undisturbed in their home cages or had their wheels locked for the remainder of the subjective night and subsequent subjective day. Light treatments of 6, 9, and 12 h produced large phase delays. These treatments were associated with decreased activity during the nocturnal light and increased activity during the initial hours of darkness following light exposure. When the wheels were locked to prevent high-amplitude activity, the resulting phase delays to the light were significantly attenuated, suggesting that the activity following the light exposure may have contributed to the overall phase shift. In a second experiment, telemetry probes were used to assess what effect permanently locking the wheels had on the phase shift to the long light pulses. These animals had phase shifts fully as large as animals without any form of wheel lock, suggesting that while non-photic events can modulate photic phase shifts, they do not play a role in the full phase-shift response observed in animals exposed to long light pulses. This paradigm will facilitate investigations into non-photic responses of the mouse circadian system.

Investigating the role of substance P in photic responses of the circadian system: individual and combined actions with gastrin-releasing peptide.

The suprachiasmatic nucleus (SCN) contains the master mammalian circadian pacemaker. It is comprised of several phenotypically distinct cell groups, some of which are situated in the weakly rhythmic retinoresponsive ventrolateral region while others are found in the rhythmic, non-retinoresponsive dorsomedial region. The mechanism by which retinorecipient cells convey photic information to the dorsomedial clock cells is unclear. The ventrolateral SCN core contains a variety of cell phenotypes. Two neuropeptides, namely substance P (SP) and gastrin-releasing peptide (GRP) extensively colocalize with calbindin D28K, a marker for SCN cells that are strongly light-responsive. Previous studies have implicated these neuropeptides in photic phase shifting of the circadian system. The present study examines how these peptides interact to regulate photic responses of the circadian system. It was observed that 55.5 +/- 9.1% of SP cells colocalized GRP. SP did not enhance GRP-induced phase shifts in the early-subjective night, while it significantly attenuated GRP-induced phase shifts during the late-subjective night. SP induced significant phase shifts that did not resemble light in the early-subjective night, but was not necessary for light-induced phase shifts and Fos expression at this time. SP induced significant Fos expression only in the late subjective night. SP may not be a necessary component in the pathway(s) involved in photic phase shifting during the early-subjective night, but may modulate phase shifts during the late-subjective night. Distinct biochemical mechanisms that underlie behavioral phase shifts may account for the differences observed in the early- vs. late-subjective night.