Neonatal tactile stimulation reverses the effect of neonatal isolation on open-field and anxiety-like behavior, and pain sensitivity in male and female adult Sprague-Dawley rats.
ABSTRACT It is well known that early life events induce long-lasting psychophysiological and psychobiological influences in later life. In rodent studies, environmental enrichment after weaning prevents the adulthood behavioral and emotional disturbances in response to early adversities. We compared the behavioral effect of neonatal isolation (NI) with the effect of NI accompanied by tactile stimulation (NTS) to determine whether NTS could reverse or prevent the effects of NI on the adulthood behavioral and emotional responses to environmental stimuli. In addition, we also examined the sex difference of the NTS effect. Measurements of body weights, an open-field locomotor test, an elevated plus maze test, a hot-plate test, and a contextual fear-conditioning test were performed on postnatal day 60. As compared with rats subjected to NI, rats subjected to NTS showed significantly higher activity and exploration in the open-field locomotor test, lower anxiety-like behavior in the elevated plus maze test, and significantly prolonged latencies in the hot-plate test, and this effect was equal among males and females. In the contextual fear-conditioning test, whereas NTS significantly reduced the enhanced freezing time due to NI in females, no significant difference in the freezing time between NI and NTS was found in males. These findings indicate that adequate tactile stimulation in early life plays an important role in the prevention of disturbances in the behavioral and emotional responses to environmental stimuli in adulthood induced by early adverse experiences.
- SourceAvailable from: Gabriela Díaz-Véliz[show abstract] [hide abstract]
ABSTRACT: The influence of the estrous cycle and the effects of exogenous administration of estradiol and progesterone on level of anxiety were studied in intact and ovariectomized rats. Intact Sprague-Dawley female rats were classified according to the stages of estrous cycle. Another group of rats was ovariectomized bilaterally and, 14 days after surgery, they received estradiol benzoate (10 μg/kg, SC) and/or progesterone (25 mg/kg, SC) or corn oil (1 ml/kg). The behavioral tests began 3 h after estradiol or 6 h after progesterone and consisted of: (1) exploration of an elevated plus-maze; and (2) retention of a passive avoidance response. Open-arm exploration of the plus-maze varied according to light intensity and the stages of the estrous cycle. There was a slight increase in open-arm exploration by rats in metestrus, under high light intensity. Low light intensity increased the exploration of the open arms by rats in proestrus and estrus, compared to the other phases of the cycle. Retention of the passive avoidance response was inhibited during proestrus and estrus. Progesterone increased open-arm exploration of the plus-maze under high light conditions, whereas estradiol antagonized this effect. Retention of passive avoidance was inhibited after estradiol or progesterone injection. These results suggest that the behavioral indices of anxiety can vary across the estrous cycle, that low light intensities have anxiolytic-like effects, and that the sensitivity to this effect is higher during proestrus and estrus. This could be explained through modulatory effects of ovarian hormones upon behavioral indices of anxiety.Psychoneuroendocrinology 11/1996; · 5.14 Impact Factor
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ABSTRACT: The endocrine response to stress is an important homoeostatic mechanism, and the secretion of glucocorticoids from the adrenal cortex is a central feature of this response. During early postnatal development, the neonatal rat displays a reduced hypothalamic-pituitary-adrenal (HPA) response to stress. This early period has been termed the 'stress hyporesponsive period' (SHRP). Maternal separation (Sep) of neonates from their mothers during early postnatal development alters the HPA response to stress. In this study, we report the effects of Sep during the SHRP. Female rats were time mated and randomly divided into control or Sep groups before birth. The Sep litters were removed from the mothers during the dark cycle for 6 h per day from postnatal day (PND) 2 to 10. On PND 28, the pups from both groups were weighed, the anogenital distance (AGD) was measured and the animals weaned. At 40 days of age, male and female animals from both groups were tested for open-field activity. As the animals matured, vaginal opening and estrous cycles were measured in females, and males were tested for male sexual behavior at adulthood. Basal, stress, and stress recovery serum corticosterone levels were measured from control and Sep male and female animals. Open-field activity was not significantly different between control or Sep male or female animals. Sep did not affect either vaginal opening or estrous cycles in female animals. Corticosterone secretion in response to stress was similar in control and Sep males and females; however, the recovery levels were significantly higher in Sep females than in Sep males or female control values. In male sexual behavior tests, Sep males had significantly longer mount latencies (time to the first mount), longer intromission latencies (time to the first intromission) and a significant reduction in the percent of animals ejaculating versus control values (controls 84 and Sep 50%). Therefore, Sep males as adults displayed altered reproductive behavior, whereas their stress recovery levels of corticosterone returned to near basal levels in a similar fashion to that observed for control non-handled males. In contrast, females displayed normal reproductive physiology, while their recovery levels of corticosterone remained high, unlike that observed with control females. Thus, significant gender differences in response to Sep (during the dark phase of the circadian cycle) were observed in the paradigm used in the present study.Behavioural Brain Research 09/2001; 123(1):1-10. · 3.33 Impact Factor
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ABSTRACT: Rats which received either handling from Days 1–14 (EH) or 22–35 (LH) of life or no handling (NH) were tested in the shock-induced fighting situation in adulthood. Ten males and 10 females from each group were either paired for fighting (F), shocked singly (S), or received no shock (N) in the test chamber for 4.5 min in 3 sessions given 48 hr apart. Immediately after the third test session, trunk blood was obtained for determination of plasma ACTH concentrations. Males and females did not differ with respect to fighting frequency in response to shock, but males displayed the fighting posture substantially more than did females. Rats handled either preweaning (EH) or postweaning (LH) fought more often at the two lower shock intensities (0.5 and 1.3 mA) than did nonhandled controls (NH). The incidence of fighting positions did not differ as a function of prior handling. In all groups but one, the pattern of ACTH response to the different test conditions coincided with previous reports: higher levels of ACTH were found in response to shock alone than in response to fighting plus shock, and the lowest levels were found in the nonshocked controls. In the exceptional group, the NH males (but not females), there was a nondiscriminatory ACTH response to the S and F test conditions. The effects of prior handling are discussed in terms of an enhanced coping ability. The results point to the importance of comparing both pre- and postweaning groups when studying the handling phenomenon.Physiology & Behavior 05/1975; · 3.16 Impact Factor