Effects of prenatal exposure to a mild chronic variable stress on body weight, preweaning mortality and rat behavior

Transcription

1 Brazilian Journal of Medical and Biological Research (1999) 32: Prenatal chronic stress and behavior ISSN 1-879X 1229 Effects of prenatal exposure to a mild chronic variable stress on body weight, preweaning mortality and rat behavior R.J. Cabrera, E.L. Rodríguez-Echandía, A.S.G. Jatuff and M. Fóscolo Laboratorio de Investigaciones Cerebrales and Cátedra de Farmacología, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, Mendoza, Argentina Correspondence E.L. Rodríguez-Echandía Casilla Correo Mendoza Argentina Fax: sacchio@raiz.uncu.edu.ar Research supported by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, No. PID ). Received November 4, 1998 Accepted July 26, 1999 Abstract c Key words Prenatal stress Chronic stress Body weight Behavior Mortality Rat

2 123 R.J. Cabrera et al. Introduction Material and Methods Treatment during pregnancy

3 Prenatal chronic stress and behavior 1231 Treatment of newborn pups and housing conditions Procedures Table 1 - Chronic aleatory stress treatment. Day Treatment Procedure 1 Noise stress Cage blows, 3 exposures to 3 blows within 3 min 2 Cold stress Home cage placed in a freezer (-2 o C) for 2 min 3 Tail pinch stress One trial with the proximal third of the tail pinched with a plastic clothespin, 1 min 4 White noise stress 95 db, 3 exposures of 3 s within 5 min 5 Free Undisturbed 6 Shaking stress Horizontal high-speed shakes in the empty water bath box of a Dubnoff metabolic shaking incubator for 2 min 7 Water deprivation stress Housing group without water for 24 h (food pellets ad libitum) 8 Water deprivation stress Housing group without enough water for 12 h (food pellets ad libitum) 9 Crowding stress 8 rats/home cage for 24 h 1 Restraint stress Animals placed in a transparent acrylic cylinder (5 x 18 cm) with five holes measuring 5 mm each at the head end and a removable top at the back end, 15 min 11 Forced swim stress Individual swimming inside a cylinder (44 x 16 cm in diameter) with water (23 o C) up to a level of 2 cm for 2 min 12 Free Undisturbed 13 Foot shock stress Inescapable electric shocks in a Plexiglas box (4 x 27 x 2 cm) with a floor grid consisting of 1-cm stainless steel bars spaced 5 mm apart. Shocks average 1 ma, 1-s duration, 3 shocks/min, 3 min 14 Lighting stress 3 individual exposures (1 min each) to darkness followed by overlighting (1-W lamp, 5 cm above) 15 Noise stress 3 exposures to 3 blows within 3 min 16 Rat blood odor Exposure to fresh blood diluted in distilled water (on a Petri dish) for 3 min 17 Restraint stress Identical to 1 18 Free Undisturbed 19 Cold stress Identical to 2 2 Isolation stress Individual housing, 24 h 21 Birth stress Parturition

4 1232 R.J. Cabrera et al.

5 Prenatal chronic stress and behavior 1233 Statistical analysis c Results Effects of PS on preweaning mortality c Effects of PS on body weight Effects of PS on spontaneous motor activity Effects of PS on enriched environment test responses Grams/pup Day 2 Day 28 Day Figure 1 - Body weight (g/pup) at days 2, 28 and 6 of age (N = 12 for each group). The PS group showed lower weight than controls at all ages. C: Controls; CF: control-fostering; PS: prenatal stress; PSF: prenatal stressfostering (means ± SEM). P<.5 compared to controls (Duncan s test) C PS C CF PS PSF C CF PS PSF

6 1234 R.J. Cabrera et al. Total activity (counts/5 min) Total activity (counts/5 min) Day 28 Day 37 2 Day 42 Day 42 2 Figure 2 - Day 28: Total motor activity (counts/5 min) (N = 12 for each group). All experimental groups displayed less motor activity than controls. Day 37: Enriched environment test showing the scores of total time spent exploring the novel object (s/5 min; N = 12 for each group). All experimental groups showed lower exploration time than controls. C: Controls; CF: control-fostering; PS: prenatal stress; PSF: prenatal stress-fostering (means ± SEM). P<.5 and P<.1 compared to controls (Duncan s test). Total time (s/5 min) 15 1 C CF PS PSF C CF PS PSF Figure 3 - Social behavior test performed after 24 h of social isolation at day 42 of age showing total motor activity (counts/5 min) and total time spent (s/5 min) in active social interactions by pairs of controls (C), control-fostering (CF), prenatally stressed (PS) and prenatally stressed-fostered rats (PSF). Only the PS group displayed lower motor activity and lower time spent in social behavior than controls. Means ± SEM. P<.5 compared to controls (Duncan s test). Total time (s/5 min) 15 1 C CF PS PSF C CF PS PSF 5 5 Effects of PS on social behavior Discussion

7 Prenatal chronic stress and behavior 1235

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