Sleep-related epilepsy in a Long-Evans hooded rat model of depression.

INTRODUCTION: Neonatal treatment with clomipramine (CLI) has been shown to have reliable behavioral and biological changes that mimic major symptomatic and biochemical changes found in depression. This paper further explores a common feature of depression, the comorbidity of seizure activity and depressive behaviors in this mode. METHODS: Rat pups were neonatally treated with 40 mg/kg/day of CLI from postnatal day 8 through 21. In adulthood, they were instrumented with electroencephalographic (EEG) and electromyographic (EMG) electrodes for 24 h of polysomnogram (PSG) recordings. PSG data were analyzed for: (1) sleep-wake cycle; (2) spectral power; and (3) epileptiform activity, including NREM-to-REM transition (NRT) bursts. RESULTS: Neonatal treatment with CLI reliably produces enhanced levels of REM (p < 0.01) and reduced sexual activity (p < 0.05). Theta power was enhanced during NREM sleep in the CLI group (p = 0.02). CLI-treated animals experienced increased frequency at the NRT (p < 0.01), as well as additional epileptiform activity of continuous (CTS; p < 0.05) and petite-continuous (P-CTS; p < 0.01) types, across the sleep-wake cycle. There is a strong temporal correlation with increased REM sleep duration, increased frequency of NRT bursts, and increased theta power during NREM sleep in CLI-treated animals. DISCUSSION: Neonatal CLI-treated animals experienced significantly more epileptiform activity as a whole, in addition to comorbid features of depression in adulthood. Neonatal exposure to CLI will not only produce depressive phenotype but may also enhance risk for epilepsy in some individuals. This warrants further investigation into currently acceptable medicinal use in humans.

Correction: A phenotype of increased sleepiness in a mouse model of pulmonary hypertension and right ventricular hypertrophy.

[This corrects the article DOI: 10.1371/journal.pone.0208540.].

Chronic developmental exposure to phenytoin has long-term behavioral consequences.

Anti-epileptic compounds have been linked to several developmental disorders. Specifically, fetal exposure to phenytoin is linked to fetal hydantoin syndrome in humans. We have developed a rat model of fetal hydantoin syndrome in an effort to explore the relationship between drug exposure, development, and learning and memory. Previous studies of this animal model have used various embryological periods of exposure; however, the human syndrome is reported in the offspring of mothers that maintain drug regimens throughout gestation and nursing. To that end, the present study investigated associative learning in rats exposed to therapeutic levels of phenytoin throughout prenatal development and the postnatal pre-weaning period. We used an instrumental appetitive-to-aversive transfer paradigm, which has hippocampal-dependent components, and an avoidance-conditioning paradigm to test simple associative learning and higher-order learning and memory. Compared to controls, we report increased rates of acquisition and performance by the phenytoin group in both the appetitive and the avoidance learning paradigm, and a substantial impairment in avoidance learning following the transfer from appetitive to aversive conditioning. The positive deficit observed with simple associative learning and the negative transfer effect associated with higher order learning suggests that chronic exposure to phenytoin throughout gestation disrupts hippocampal development, which subsequently leads to impaired function in adulthood.

A phenotype of increased sleepiness in a mouse model of pulmonary hypertension and right ventricular hypertrophy.

The relationship between cardiovascular disease and abnormalities in sleep architecture is complex and bi-directional. Sleep disordered breathing (SDB) often confounds human studies examining sleep in the setting of heart failure, and the independent impact of isolated right or left heart failure on sleep is difficult to assess. We utilized an animal model of right heart failure using pulmonary artery banding (PAB) in mice to examine the causal effect of right heart failure on sleep architecture. Four weeks after PAB or sham (control) surgery, sleep was measured by polysomnography for 48 hours and right ventricular (RV) hypertrophy confirmed prior to sacrifice. PAB resulted in right ventricular hypertrophy based on a 30% increase in the Fulton Index (p < 0.01). After PAB, mice spent significantly more time in NREM sleep compared to the control group over a 24 hour period (53.5 ± 1.5% vs. 46.6 ± 1.4%; p < 0.01) and exhibited an inability to both cycle into REM sleep and decrease delta density across the light/sleep period. Our results support a phenotype of impaired sleep cycling and increased 'sleepiness' in a mouse model of RV dysfunction.

Sex Differences and the Impact of Chronic Stress and Recovery on Instrumental Learning.

We have previously shown that 21-day chronic restraint stress impacts instrumental learning, but overall few studies have examined sex differences on the impact of stress on learning. We further examined sex differences in response to extended 42-day chronic stress on instrumental learning, as well as recovery from chronic stress. Rats were tested in aversive training tasks with or without prior appetitive experience, and daily body weight data was collected as an index of stress. Relative to control animals, reduced body weight was maintained from day 22 through day 42 across the stress period for males, but not for females. Stressed males had increased response speed and lower learning efficiency during appetitive acquisition and aversive learning. Males overall showed slower escape shaping times and more shock exposure. In contrast, stressed females showed slower appetitive response speeds and higher appetitive and aversive efficiency but overall reduced avoidance rates during acquisition and maintenance for transfer animals and during maintenance for aversive-only animals. These tasks reveal important nuances on the effect of stress on goal-directed behavior and further highlight sexually divergent effects on appetitive versus aversive motivation. Furthermore, these data underscore that systems are temporally impacted by chronic stress in a sexually divergent pattern.

Effects of a program of human interaction and alterations in diet composition on activity of the hypothalamic-pituitary-adrenal axis in dogs housed in a public animal shelter.

OBJECTIVE: To determine whether a program of human interaction or alterations in diet composition would alter activity of the hypothalamic-pituitary-adrenal (HPA) axis in dogs housed in an animal shelter. DESIGN: Prospective study. ANIMALS: 40 dogs. PROCEDURE: Dogs were (n = 20) or were not (20) enrolled in a program of regular supplemental human interaction (20 min/d, 5 d/wk, for 8 weeks) involving stroking, massaging, and behavioral training. In addition, half the dogs in each group were fed a typical maintenance-type diet, and the other half were fed a premium diet. Plasma cortisol and ACTH concentrations were measured during weeks 0, 2, 4, and 8 and before and after exposure to a battery of novel situations during weeks 0 and 8. RESULTS: Plasma cortisol concentration was significantly decreased by week 2, but plasma ACTH concentration was not significantly decreased until week 8 and then only in dogs fed the premium diet. Following exposure to novel situations, plasma cortisol and ACTH concentrations were significantly increased. However, during week 8, dogs enrolled in the program of human interaction had significantly lower increases in cortisol concentration than did dogs not enrolled in the program. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that both a program of human interaction and alterations in diet composition have moderating effects on activity of the HPA axis in dogs housed in an animal shelter and that activity of the HPA axis may be increased for a longer period during shelter housing than measurement of plasma cortisol concentration alone would suggest.

Exploring human interaction and diet effects on the behavior of dogs in a public animal shelter.

This study examined the effects of 2 manipulations--a brief, regular period of human contact and diet--on the behavior of dogs confined in a public animal shelter. A behavioral battery designed to assess reactions to novel situations, and a test of responsiveness to an unfamiliar human were administered both prior to (pretest) and immediately following (posttest) the 8-week intervention period. Overall, the regular periods of increased human contact together with a diet that contained augmented levels of digestible protein, fat, calories, and animal-derived ingredients reduced signs of behavioral reactivity from pretest to posttest. In some cases, the comparison diet appeared more effective, but only for dogs receiving minimal human interaction. The results indicate that a combination of human interaction and high quality diet may positively affect the behavior of dogs in animal shelters.

The Effects of Sex and Chronic Restraint on Instrumental Learning in Rats.

Chronic stress has been shown to impact learning, but studies have been sparse or nonexistent examining sex or task differences. We examined the effects of sex and chronic stress on instrumental learning in adult rats. Rats were tested in an aversive paradigm with or without prior appetitive experience, and daily body weight data was collected as an index of stress. Relative to control animals, reduced body weight was maintained across the stress period for males (-7%, P ≤ .05) and females (-5%, P ≤ .05). For males, there were within-subject day-by-day differences after asymptotic transition, and all restrained males were delayed in reaching asymptotic performance. In contrast, stressed females were facilitated in appetitive and aversive-only instrumental learning but impaired during acquisition of the aversive transfer task. Males were faster than females in reaching the appetitive shaping criterion, but females were more efficient in reaching the appetitive tone-signaled criterion. Finally, an effect of task showed that while females reached aversive shaping criterion at a faster rate when they had prior appetitive learning, they were impaired in tone-signaled avoidance learning only when they had prior appetitive learning. These tasks reveal important nuances on the effect of stress and sex differences on goal-directed behavior.

Mild Transient Hypercapnia as a Novel Fear Conditioning Stimulus Allowing Re-Exposure during Sleep.

INTRODUCTION: Studies suggest that sleep plays a role in traumatic memories and that treatment of sleep disorders may help alleviate symptoms of posttraumatic stress disorder. Fear-conditioning paradigms in rodents are used to investigate causal mechanisms of fear acquisition and the relationship between sleep and posttraumatic behaviors. We developed a novel conditioning stimulus (CS) that evoked fear and was subsequently used to study re-exposure to the CS during sleep. METHODS: Experiment 1 assessed physiological responses to a conditioned stimulus (mild transient hypercapnia, mtHC; 3.0% CO2; n = 17)+footshock for the purpose of establishing a novel CS in male FVB/J mice. Responses to the novel CS were compared to tone+footshock (n = 18) and control groups of tone alone (n = 17) and mild transient hypercapnia alone (n = 10). A second proof of principle experiment re-exposed animals during sleep to mild transient hypercapnia or air (control) to study sleep processes related to the CS. RESULTS: Footshock elicited a response of acute tachycardia (30-40 bpm) and increased plasma epinephrine. When tone predicted footshock it elicited mild hypertension (1-2 mmHg) and a three-fold increase in plasma epinephrine. When mtHC predicted footshock it also induced mild hypertension, but additionally elicited a conditioned bradycardia and a smaller increase in plasma epinephrine. The overall mean 24 hour sleep-wake profile was unaffected immediately after fear conditioning. DISCUSSION: Our study demonstrates the efficacy of mtHC as a conditioning stimulus that is perceptible but innocuous (relative to tone) and applicable during sleep. This novel model will allow future studies to explore sleep-dependent mechanisms underlying maladaptive fear responses, as well as elucidate the moderators of the relationship between fear responses and sleep.

Obesity accentuates circadian variability in breathing during sleep in mice but does not predispose to apnea.

Obesity is a primary risk factor for the development of obstructive sleep apnea in humans, but the impact of obesity on central sleep apnea is less clear. Given the comorbidities associated with obesity in humans, we developed techniques for long-term recording of diaphragmatic EMG activity and polysomnography in obese mice to assess breathing patterns during sleep and to determine the effect of obesity on apnea generation. We hypothesized that genetically obese ob/ob mice would exhibit less variability in breathing across the 24-h circadian cycle, be more prone to central apneas, and be more likely to exhibit patterns of increased diaphragm muscle activity consistent with obstructive apneas compared with lean mice. Unexpectedly, we found that obese mice exhibited a greater circadian impact on respiratory rate and diaphragmatic burst amplitude than lean mice, particularly during rapid eye movement (REM) sleep. Central apneas were more common in REM sleep (42 ± 17 h(-1)) than non-REM (NREM) sleep (14 ± 5 h(-1)) in obese mice (P < 0.05), but rates were not different between lean and obese mice in either sleep state. Even after experimentally enhancing central apnea generation by acute withdrawal of hypoxic chemoreceptor activation during sleep, central apnea rates remained comparable between lean and obese mice. Last, we were unable to detect patterns of diaphragmatic burst activity suggestive of obstructive apnea events in obese mice. In summary, obesity does not predispose mice to increased occurrence of central or obstructive apneas during sleep, but does lead to a more pronounced circadian variability in respiration.

Effects of restricted spectral rearing on the development of zebrafish retinal physiology.

Research has shown that rearing in abnormal lighting environments affects both visual behavior and retinal physiology in zebrafish larvae. These studies, however, used only constant dark and constant white light as the experimental rearing conditions. This study assessed the effects of rearing larvae in restricted spectral lighting environments on zebrafish retinal physiology. Larvae were reared in one of seven different lighting environments: cyclic white light (control group), constant blue light, constant green light, constant orange light, cyclic blue light, cyclic green light, and cyclic orange light. Assessment of retinal physiology was done using the electroretinogram (ERG). Results showed that rearing larvae in constant light conditions caused deficits in sensitivity to ultraviolet- and short-wavelength stimuli, but had little effect on sensitivity to middle- and long-wavelength stimuli. Rearing larvae in cyclic light did not cause differences in sensitivity to middle- and long-wavelength stimuli, but did cause extreme deficits in sensitivity to ultraviolet- and short-wavelength stimuli in the cyclic green and orange light-rearing conditions. Sensitivity of the cyclic blue light-rearing group was similar to the control group to stimuli of all wavelengths. The results support the notion that the light-rearing environment impacts the development of the ultraviolet- and short-wavelength cone mechanisms but has little impact on the development of the middle- and long-wavelength cone mechanisms; these effects coincide with the development of the various cone types. This study supports the notion that the zebrafish is a viable model for studying the effects of the lighting environment on visual development.

Visual processing of the zebrafish optic tectum before and after optic nerve damage.

Although the zebrafish has become an important model in visual neuroscience, little has been done to examine the processing of its higher visual centers. The purpose of this work was twofold. The first purpose was to examine the physiology of the zebrafish retinotectal system and its relationship to retinal physiology. Spectral sensitivity functions were derived from visually evoked tectal responses and these functions were compared to the functions of electroretinogram (ERG) responses obtained using the same stimulus conditions. The second purpose was to examine the recovery of visual functioning of the tectum following optic nerve damage. The optic nerves of adult zebrafish were damaged (crushed), and tectal visual processing was assessed following damage. The results showed that the spectral sensitivity functions based on the On-responses of the tectum and ERG were qualitatively similar. The functions based on each response type received similar cone contributions including both nonopponent and opponent contributions. However, the spectral sensitivity functions based on the Off-responses of the tectum and ERG differed. The results also showed that the zebrafish visual system is capable of neural regeneration. By 90 days following an optic nerve crush, the spectral sensitivity function based on the tectal On-response was similar to functions obtained from normal zebrafish. Although the tectal Off-response did recover, the spectral sensitivity based on the Off-response was not the same as the function of normal zebrafish. These results support the notion that different levels of the visual system process information differently and that the zebrafish visual system, like those of other lower vertebrates, is capable of functional regeneration.