Contact-promoting behavior,social development,and relationship with parents in sibling juvenile degus (Octodon Degus)

This study describes infant socialization in captive parent-young units of the caviomorph rodent Octodon degus. Types of parent-young contact (huddling or squatting) and social interaction (body nosing and accompanying behaviors) are described and their ontogenetic trends examined between postnatal Days 1 and 46. Fathers spent less time than mothers in contact with the young. Mother-young contact decreased postnatally, whereas the amounts of mother-young and father-young social interaction, measured in terms of body-nosing exchanges, showed a continuous increase postnatally; sibling interactions also showed a continuous increase. Father-young interactions tended to be dominated by the father. Young reared with the father cohabiting huddled less with their mother, and engaged in less body-nosing, than young reared in the father's absence. Observations suggested that paternal control of the young may curb juvenile interactions. Young observed without their parents in an unfamiliar enclosure did not groom or “play” as in their home cage with parents present, but engaged in relatively more vocalizing, neck-nosing and forepaw-clasping.     

Lymphoid cells in the harderian gland of the rodent Octodon degus

The Harderian gland of the degu (Octodon degus) is composed of tubulo-alveolar secretory units that share most of morphological features found in the Harderian glands of other rodents. However, a peculiar characteristic observed in the glands of female degus is the existence of lymphoid cell clusters within the connective tissue surrounding the secretory adenomeres. Lymphocytes and lymphoblasts are found associated with blood vessels and especially with nerve bundles in the medullary region of the gland. Occasionally, macrophages and plasma cells are also observed. Although the Golgi apparatus appears well developed, the ultrastructural characteristics of most of these lymphoid elements correspond to those of inactive lymphocytes. Unmyelinated fibers containing clear and dense-core vesicles are found closely related to lymphocytes. On some occasions, lymphocytes present extensive areas of apposition with structures resembling intercellular junctions. The analogy of the lymphoid clusters reported in this study with those described in the avian Harderian gland is discussed.© Willey-Liss, Inc.     

Developmental patterns of macronutrient intake in female and male rats from weaning to maturity

Male and female Sprague-Dawley rats had available pure macronutrient diets, protein, carbohydrate and fat, from birth to day 77 of age. Analyses of their intake of these nitrients, as a function of age, demonstrate that, in both sexes, daily protein intake and preference for this nutrient relative to the other macronutrients rise steadily from weaning and peak precisely at the time of puberty (day 37–44 for females and days 42–49 for males), when there is also a peak in body weight gain. This is in contrast to daily carbohydrate intake, which peaks 2 weeks after puberty in males, and also to the female and male rats' preference for carbohydrate, which remains relatively stable from weaning to maturity. These patterns also differ from those observed for daily fat intake and fat preference for females and males, which are relatively high during the first postweaning week and then decline and remain very low until shortly after puberty (day 54), when there occurs a sharp burst in fat intake. Comparisons between the females and males reveal a significantly stronger preference for carbohydrate in the females, exhibited as early as 23 days of age; a stronger preference for protein and fat in the males, evident after day 28; and greater light-period feeding of carbohydrate and fat by females compared to males, apparent after puberty. Correlational analyses demonstrate that body weight and total kcal intake are closely related to daily protein consumption, more strongly in females compared to males; are strongly related to daily fat intake only in males; and are unrelated to intake of carbohydrate, at any age and in either sex.     

Reproductive state and motor activity in female ferrets

The pattern of motor activity in female ferrets (Mustela putorius furo) housed in cages mounted upon rocker platforms was followed under conditions of short-(8 hr) and long-(16 hr) day illumination. A distinct diurnal rhythm was evident that remained unchanged after lesioning of the anterior hypothalamus. The level of activity did not differ between animals kept under short days and long days, between anoestrous and oestrous females, or during the development or waning of oestrus. Ovariectomy did not affect the pattern of activity. These findings are at variance with those of a previous study where wheel-running activity was followed and oestrous females found to be more active than anoestrous ferrets.     

Influence of parental deprivation on the behavioral development in Octodon degus: modulation by maternal vocalizations

Repeated separation from the family during very early stages of life is a stressful emotional experience which induces a variety of neuronal and synaptic changes in limbic cortical areas that may be related to behavioral alterations. First, we investigated whether repeated parental separation and handling, without separation from the family, leads to altered spontaneous exploratory behavior in a novel environment (open field test) in 8-day-old Octodon degus. Second, we tested whether the parentally deprived and handled animals display different stimulus-evoked exploratory behaviors in a modified open field version, in which a positive emotional stimulus, the maternal call, was presented. In the open field test a significant influence of previous emotional experience was found for the parameters of running, rearing, and vocalization. Parentally deprived degus displayed increased horizontal (running) and vertical (rearing) motoric activities, but decreased vocalization, compared to normal and handled controls. The presentation of maternal vocalizations significantly modified running, vocalization, and grooming activities, which in the case of running activity was dependent on previous emotional experience. Both deprivation-induced locomotor hyperactivity together with the reduced behavioral response towards a familiar acoustic emotional signal are similar to behavioral disturbances observed in human attachment disorders.     

Suprachiasmatic nucleus and intergeniculate leaflet in the diurnal rodent Octodon degus: retinal projections and immunocytochemical characterization.

The neural connections and neurotransmitter content of the suprachiasmatic nucleus and intergeniculate leaflet have been characterized thoroughly in only a few mammalian species, primarily nocturnal rodents. Few data are available about the neural circadian timing system in diurnal mammals, particularly those for which the formal characteristics of circadian rhythms have been investigated. This paper describes the circadian timing system in the diurnal rodent Octodon degus, a species that manifests robust circadian responses to photic and non-photic (social) zeitgebers. Specifically, this report details: (i) the distribution of six neurotransmitters commonly found in the suprachiasmatic nucleus and intergeniculate leaflet; (ii) the retinohypothalamic tract; (iii) the geniculohypothalamic tract; and (iv) retinogeniculate projections in O. degus. Using immunocytochemistry, neuropeptide Y-immunoreactive, serotonin-immunoreactive and [Met]enkephalin-immunoreactive fibers and terminals were detected in and around the suprachiasmatic nucleus; vasopressin-immunoreactive cell bodies were found in the dorsomedial and ventral suprachiasmatic nucleus; vasoactive intestinal polypeptide-immunoreactive cell bodies were located in the ventral suprachiasmatic nucleus; [Met]enkephalin-immunoreactive cells were located sparsely throughout the suprachiasmatic nucleus; and substance P-immunoreactive fibers and terminals were detected in the rostral suprachiasmatic nucleus and surrounding the nucleus throughout its rostrocaudal dimension. Neuropeptide Y-immunoreactive and [Met]enkephalin-immunoreactive cells were identified in the intergeniculate leaflet and ventral lateral geniculate nucleus, as were neuropeptide Y-immunoreactive, [Met]enkephalin-immunoreactive, serotonin-immunoreactive and substance P-immunoreactive fibers and terminals. The retinohypothalamic tract innervated both suprachiasmatic nuclei equally; in contrast, retinal innervation to the lateral geniculate nucleus, including the intergeniculate leaflet, was almost exclusively contralateral. Bilateral electrolytic lesions that destroyed the intergeniculate leaflet depleted the suprachiasmatic nucleus of virtually all neuropeptide Y- and [Met]enkephalin-stained fibers and terminals, whereas unilateral lesions reduced fiber and terminal staining by approximately half. Thus, [Met]enkephalin-immunoreactive and neuropeptide Y-immunoreactive cells project equally and bilaterally from the intergeniculate leaflet to the suprachiasmatic nucleus via the geniculohypothalamic tract in degus. This is the first report examining the neural circadian system in a diurnal rodent for which formal circadian properties have been described. The data indicate that the neural organization of the circadian timing system in degus resembles that of the most commonly studied nocturnal rodents, golden hamsters and rats. Armed with such data, one can ascertain differences in the functional organization of the circadian system between diurnal and nocturnal mammals.     

Resynchronization of hormonal rhythms after an eastbound flight in humans: effects of slow-release caffeine and melatonin

The aim of this work was to investigate the potential chronobiotic properties of slow-release caffeine, in comparison with melatonin, on resynchronization of endogenous melatonin and cortisol secretions after an eastbound flight by jet incurring a time loss of 7 h. A group of 27 reservists of the US Air Force received either slow-release caffeine (300 mg), melatonin (5 mg) or placebo before, during and/or after the transmeridian flight. Saliva and urine were sampled before the flight in the United States (from day –2 to day 0) and after the flight in France (from day 1 to day 10). Saliva was collected once a day on waking to determine saliva melatonin and cortisol concentrations. In addition, concentrations of caffeine in saliva were determined three times a day and of 6-sulphatoxymelatonin in urine collected overnight to check that the treatment regimes had been complied with. From day 3 to day 5, post-flight saliva melatonin concentrations were significantly different from control values in the placebo group only. During treatment with melatonin, the mean urinary 6-sulphatoxymelatonin concentration in the melatonin group was more than twice as high as in the two other groups. In the slow-release caffeine group and the melatonin group, mean saliva cortisol concentrations were significantly lower than control from day 2 to day 5, whereas the placebo group had a mean saliva cortisol concentration significantly lower than the control value from day 2 to day 9. In conclusion, these results indicate that administration of slow-release caffeine, as well as of melatonin, allows a faster resynchronization of hormone rhythms during the 4 days following an eastbound flight incurring the loss of 7 h. Electronic Publication     

Anxiety-like behavior in weanling and young adult male and female malnourished rats

The present study determined whether protein-calorie malnutrition alters anxiety-like behavior in weanling and young adult, male and female malnourished rats. On the day of birth, litters of Wistar rats were divided into Control (C) and Malnutrition (M) groups. In the C group, litters were fed by dams receiving ad libitum lab chow, whereas in the M group, litters were fed by dams receiving 40% of the total amount of the diet offered to dams in the C group. After weaning (PND21) until PND50, animals received the same food as theirs mothers (i.e., ad libitum access in the C group and 40% of the C group food in the M group). On PND21 and PND50, independent C (male [CM] and female [CF]) and M (male [MM] and female [MF]) groups were exposed to the elevated T-maze. The time taken to withdraw four paws from this arm was recorded (baseline latency [BL]). The same measurement was repeated twice at 30 s intervals (avoidance trial 1 [AT1] and avoidance 2 [AT2]). The cutoff time in each trial was 300 s. ANOVA indicated a four-way age × diet × sex × trials interaction. Post hoc comparisons revealed that PND50 rats had a lower BL and AT1 latency compared with PND21 rats. Training increased both AT1 and AT2 latencies compared with BL in both the CM and CF groups. Weanling malnourished rats exhibited reduced anxiety-like behavior and young adult male rats presented less anxiety-like behavior than young adult female rats in this experimental model.     

Brief periods of positive peer interactions mitigate the effects of total social isolation in young Octodon degus

We investigated whether positive daily peer‐interactions counteract the effects of isolation in Octodon degus. Twenty‐five‐day‐old degus were either isolated (ISO), socially housed (SOCIAL), or isolated and allowed 1‐hr daily peer interaction (PARTIAL‐ISO). The animals were observed over 4 weeks. Just prior to isolation and after 2 weeks of individual housing, the subjects were assessed for response to pleasant stimuli via a sucrose preference test and to fearful situations in open field and startle tests. Two weeks after the previous tests, the subjects were retested as above and observed in novelty and sociability tests. Only the ISO group showed significant alterations in sensitivity to reward and increased risk‐taking behavior in fearful situations. The ISO group consumed more sucrose, spent less time freezing in the startle test and exhibited increased exploration in open field and novelty tests compared to PARTIAL‐ISO and SOCIAL groups. In the sociability test, the SOCIAL group vocalized more than the other two groups during encounters with an unfamiliar degus. Our findings suggest that (i) chronic isolation induces alteration of hedonic, emotional and social profiles, with a maturational delay in fear‐related responses; (ii) friendly interaction attenuates most behavioral changes induced by total social isolation. However, the positive effects of daily social interactions did not fully counteract deficits in social vocalizations. Our study represents one of the few available studies focused not only on the consequences of negative life events in this species, but also the protective role of relatively short periods of positive social activity on subsequent emotional development. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 53:280–290, 2011.     

Diurnal variation of the startle reflex in relation to HPA-axis activity in humans

Diurnal variation of baseline startle amplitude was examined in 14 normal inpatients on a research unit where behavioral activity and environmental stimuli were highly controlled. We tested a hypothesized association between diurnal variations of salivary cortisol and reflex amplitude by recording acoustic startle eyeblinks shortly before bedtime, when cortisol was near its lowest daily level, and just after awakening, when cortisol was at its peak. Results showed that startle eyeblinks were greater during evening than morning sessions, whereas the opposite was true for cortisol levels. Skin conductance levels and reaction time performance also increased from morning to evening. These findings are consistent with accumulating evidence suggesting a possible link between startle reactivity and hypothalamic-pituitary-adrenal axis activity, and an association between diurnal variations in endogenous arousal and startle amplitude.     

Analysis of the disruption of maternal social bonds in Octodon degus: separation distress in restricted reunion tests

Octodon degus is a social caviomorph species that exhibits strong social bonds and robust distress responses to maternal separation. To understand the impact of early social isolation on social motivation, we investigated how social isolation during infancy, associated with repeated restricted interactions with mother and siblings, altered social motivation in young degus. In Experiment 1, three treatments were compared: complete isolation (ISOLATED group), nearly complete isolation, with daily half hour partition-restricted reunions with the mother and siblings (RESTRICTED group), and social-housing with the mother and siblings (FAMILY group). After 10 days of treatment, all subjects underwent a 5-day choice test between mothers and unfamiliar females. During the treatment period, the RESTRICTED animals emitted more isolation calls and spent more time close to the partition that separated them from mothers than ISOLATED animals. During the first social-choice day, FAMILY reared animals showed a preference for the mother for a few minutes, while the RESTRICTED animals preferred the mother for the whole session. Totally ISOLATED pups exhibited no social preferences. Since during successive testing periods the isolation calls decreased over the days, in Experiment 2 we investigated whether this decline was related to age or habituation to testing procedures. Animals were observed during a single exposure to isolation (ISOLATED) or restricted-reunion (RESTRICTED) at PND 21 and 31. The decrease of vocalizations was due to an age-effect. The findings clarify the nature of social bonds in degus.     

Recognition of Mother's voice evokes metabolic activation in the medial prefrontal cortex and lateral thalamus of Octodon degus pups

In a variety of animal species, including primates, vocal communication is an essential part to establish and maintain social interactions, including the emotional bond between the newborn, its parents and siblings. The aim of this study in pups of the trumpet-tailed rat, Octodon degus, was to identify cortical and subcortical brain regions, which are involved in the perception of vocalizations uttered by the mother. In this species, which is characterized by an elaborated vocal repertoire, the (14C)-2-fluoro-deoxyglucose autoradiography was applied to measure region-specific metabolic activation in response to the presentation of a learned emotionally relevant acoustic stimulus, the maternal calls. Already at the age of eight days the precentral medial cortex, anterior cingulate cortex and the lateral thalamus could be identified by their enhanced metabolic activation in response to the presentation of the emotionally relevant maternal nursing calls, whereas other brain areas, such as the hippocampus and amygdala did not show stimulus-induced activation.Since in humans changes of activity patterns in relation to the emotional content of spoken language have been observed in similar brain regions, e.g. in the anterior cingulate cortex, Octodon degus may provide a suitable animal model to study the cellular and synaptic mechanisms underlying perception, production and processing of conspecific vocalizations.     

Maternal separation and social isolation modulate the postnatal development of synaptic composition in the infralimbic cortex of Octodon degus

We analysed the influence of preweaning periodic maternal separation followed by postweaning chronic social isolation on the development of synaptic composition in the infralimbic cortex of Octodon degus, a South American species formerly classified as a caviomorph rodent but now considered to belong to Lagomorpha (rabbits). Three groups of animals were analysed: (1) control pups which remained undisturbed with their families; (2) pups which were exposed to individual periodic maternal deprivation [postnatal day 1 (P1) until P21], followed by social isolation (P22 until P45); and (3) pups which were handled daily without being removed from the families (P1 until P21) and thereafter remained undisturbed with the family (P22 until P45). The mean synaptic density and mean projected height of synapses were quantified using the "dissector" method. In the deprived group, significantly higher (up to 137.8%) mean synaptic densities were found in layer II of the infralimbic cortex compared to normal control animals. In handled pups, asymmetric shaft synapses were significantly decreased (down to 54%) compared to the control group.These results indicate that early postnatal changes in the socio-emotional environment change the number of synaptic connections in the infralimbic cortex. Since this subregion of the medial prefrontal cortex is involved in a variety of emotional behaviors and plays a role in associative learning tasks, these environmentally induced synaptic changes may be indicative, and perhaps the cause, of alterations of behavioral and cognitive capacities.     

Splitting of wheelrunning rhythms by castrated or steroid treated male and female hamsters

Male and female hamsters, with or without gonadal hormones, were housed in constant light (LL) while wheel running rhythms were recorded. Estradiol benzoate (EB) in Silastic capsules reduced rhythm desynchronies, such as splitting, in ovariectomized animals compared to blank implanted controls. In males, there were no significant effects of testosterone or EB in Silastic implants, castration or sham operation on incidence of rhythm desynchronies. Males generated split rhythms which differed from females in clarity and the angle at which the limbs of the splitting rhythms diverged. Other differences were (a) greater activity onset variability for castrated females with relatively little onset variability for other groups and (b) more running time by EB treated males than any other group. Splitting for all animals occurred with an average latency in LL of 55±3 days; the period stabilized in 12±1 days and was 0.2 hr shorter in length. The two limbs of the split rhythm were a mean 181±5° apart. Induction of splitting by LL is critically discussed with special reference to the two oscillator model of hamster activity and existing evidence for more than two oscillations in wheelrunning activity.     

The structured interview and questionnaire methods of assessing coronary-prone behavior in male and female college students

Several self-report measures of type A behavior were compared with the Rosenman and Friedman structured interview method of assessment in male and female college students. The student version of the Jenkins Activity Survey was found to correlate relatively weakly with the interview for both males and females, while scales derived from the Gough and Thurstone inventories showed moderate correlations with interview typing for both sexes. A brief scale derived from a recent reanalysis of the Framingham study correlated with the interview appreciably greater for females than for males. In all, these data suggest the need for caution in using only paper-and-pencil tests to assess type A behavior.     

Age Progression of Neuropathological Markers in the Brain of the Chilean Rodent Octodon degus,a Natural Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder and the leading cause of age‐related dementia worldwide. Several models for AD have been developed to provide information regarding the initial changes that lead to degeneration. Transgenic mouse models recapitulate many, but not all, of the features of AD, most likely because of the high complexity of the pathology. In this context, the validation of a wild‐type animal model of AD that mimics the neuropathological and behavioral abnormalities is necessary. In previous studies, we have reported that the Chilean rodent Octodon degus could represent a natural model for AD. In the present work, we further describe the age‐related neurodegeneration observed in the O. degus brain. We report some histopathological markers associated with the onset progression of AD, such as glial activation, increase in oxidative stress markers, neuronal apoptosis and the expression of the peroxisome proliferative‐activated receptor γ coactivator‐1α (PGC‐1α). With these results, we suggest that the O. degus could represent a new model for AD research and a powerful tool in the search for therapeutic strategies against AD.     

Circadian rhythms in the rat: Constant darkness,entrainment to T cycles and to skeleton photoperiods

Free running activity and drinking rhythms of male Sprague-Dawley rats were observed in constant darkness (DD) for up to 44 days. The average period of the rhythms ($\text{τ}{}_{\mathrm{<mtext>dd</mtext>}}$) was 24.2 hr (±0.12 hr) and the activity time was near one half of the circadian cycle. In the second experiment, rats were entrained to T cycles (T=period) with 2 hr of light per cycle. At T=23 and T=26 about one half of the rats entrained indicating that these periods are near the limits of entrainment. T=23 induced a lasting aftereffect on $\text{τ}{}_{\mathrm{<mtext>dd</mtext>}}$ while T=26 affected $\text{τ}{}_{\mathrm{<mtext>dd</mtext>}}$ only briefly. In contrast to some other nocturnal rodents, activity time was not compressed as T neared the limits of entrainment. In the third experiment, rats and hamsters were entrained to 24 hr skeleton photoperiods (two 1 hr light pulses/cycle). Rats phase jumped to the longer subjective night when the interval between the light pulses was reduced to 6 or 5 hr, while most hamsters phase jumped at 3.5 hr. Furthermore, all rats phase jumped by means of delaying transients while most hamsters showed advancing transients. Finally, while skeleton photoperiods compressed activity time in hamsters to 6 hr or less, activity time remained fairly constant in rats. These results demonstrate considerable differences in the organization of the circadian system among commonly studied nocturnal rodents.     

Quantitative changes in reduced nicotinamide adenine dinucleotide phosphate-diaphorase-reactive neurons in the brain of Octodon degus after periodic maternal separation and early social isolation

The influence of preweaning maternal separation and postweaning social isolation on the development of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reactive neurons in prefrontal cortical areas, in subdivisions of the nucleus accumbens and in the corpus callosum was quantitatively investigated in the precocious rodent Octodon degus. Forty-five-day-old degus from three animal groups were compared: (i) degus that were reared under normal undisturbed social conditions; (ii) degus that were repeatedly separated from their mothers during the first three postnatal weeks and thereafter reared with their family; and (iii) degus that remained undisturbed with the family until weaning (postnatal day 21) and thereafter were reared in social isolation. Preweaning maternal separation led to a significant decrease in NADPH-diaphorase-containing neurons in the corpus callosum in both genders (down to 33%) compared with the social control group. No significant changes were found in the subregions of the medial prefrontal cortex and nucleus accumbens. Postweaning social isolation led to a reduced density of NADPH-diaphorase-containing neurons in the corpus callosum in both genders (down to 52%) compared with the social control group. Furthermore, in the precentral medial cortex of female pups, a significant reduction in NADPH-diaphorase-reactive neurons (down to 72%) was detectable. All other regions of the medial prefrontal cortex and the nucleus accumbens remained unchanged. The observed deprivation-induced changes may reflect either an excessive reduction in NADPH-diaphorase-positive neurons or a down-regulation of the enzyme in neurons that normally express it.Our results indicate a link between early adverse socio-emotional experience and the maturation of NADPH-reactive neurons. Further studies are required to analyse the functional implications of this experience-induced brain pathology.     

Food and light as entrainers of circadian running activity in the rat

The purpose of this experiment was to determine the extent to which circadian running activity could be controlled by two different environmental cues: periodic access to food and ambient light cycles. Seven male rats were successively exposed to the following four conditions: (1) With light cycles (LD 12:12) and continuous access to food, the animals displayed a basically nocturnal pattern of running. (2) With access to food for two hours during the illuminated portion of the LD cycle, all of the animals showed a burst of running preceding food presentation. Three of these seven animals concurrently showed diminished running associated with the light cycle. (3) The animals continued to run before the periodic presentation of food when constant light replaced the LD cycle. (4) When allowed continuous access to food, and still exposed to constant light, the animals continued to show bursts of running around the time that food had been delivered. Rats' circadian activity cycles were therefore influenced by periodic access to food. Moreover, when periodic food was offered during the illuminated portion of the LD cycle (when rats are normally inactive) food presentation was a more potent entrainer than photic cues in controlling running activity.