The ontogeny of exploratory behaviors in early-protein-malnourished rats exposed to the elevated plus-maze test

Abstract

An elevated plus-maze was used to study the ontogeny of the exploratory behaviors of earlyprotein-malnourished animals in an experimental aversive situation. Rats were malnourished by feeding their dams a 6% protein diet during the lactation period (0-21 days of age); controls received a 16% protein diet. From 21 to 100 days of age, all rats received a balanced lab chow diet. At 21,30, 40, 50, 60, 70, 80, 90, and 100 days of age, independent groups of malnourished and control animals were exposed to the elevated plus-maze and allowed to explore for 5 min. During this period, 12 behavioral categories (number of entries and time spent in the open and enclosed arms, total arms entries, attempts to enter open and closed arms, closed-arm returns, latency of fIrst closed-arm entry, total immobility time, total grooming time, total reatings, total head-dippings, and total stretch attend posture) were recorded. The results showed that anxiety increased with age and that protein malnutrition produced alterations in the ontogeny of exploratory behaviors. It was shown that malnourished rats maintained or increased exploration in the maze with age, in contrast to wellnourished animals, which exhibited a steady decrease in exploration as they matured. The higher number of entries and time spent in the open arms suggest that the protein malnutrition causes a permanent increase in the impulsiveness and/or an increased drive to explore open-arm novelty, leading to a behavior consistent with lower anxiety in malnourished animals, relative to that in wellnourished animals, in this naturalistic animal model of anxiety. Protein malnutrition early in life causes long-lasting structural and neurochemical changes in the central nervous system, as well as behavioral abnormalities (Dob-

The effects of early protein malnutrition and environmental stimulation on behavioral and biochemical parameters in rats.

“…There are several behavioral consequences of malnutrition, and some authors have shown that malnutrition leads to reduced environmental exploration, increased locomotor activity, and low thresholds to aversive stimuli (shocks, intense light, cold water), characterizing an intensified emotional reaction (Almeida et al, 1994; Moreira, de Araujo, de Oliveira, & Almeida, 1997; Rocinholi, Almeida, & de Oliveira, 1997). Increases in the number of entries and in the time spent on the open arms of the elevated plus-maze suggest that the low protein diet causes a permanent increase in impulsiveness and/or a greater tendency to explore the open arm novelty, an indicative of lower anxiety (Almeida et al, 1994).…”

Effects of tactile stimulation and underwater trauma on the behavior of protein-malnourished rats in the elevated plus-maze test.

“…The dams and the pups were housed in transparent plastic cages (40 x 33 x 20 cm) and randomly assigned to a 6% or 16% protein diet ad libitum during the lactation phase (0 – 21 days). The two diets have been described in detail elsewhere (Almeida et al, 1994). Briefly, the protein-deficient diet contained approximately 8% casein (6% protein), a 5% salt mixture, a 1% vitamin mixture, 8% corn oil, 0.2% choline, and 77.8 % cornstarch.…”

“…The videotapes were analyzed by two independent experimenters, and the following behavioral categories were identified and recorded as previously described (Almeida, Garcia, & De Oliveira, 1993; Almeida et al, 1996b; Cole & Rodgers, 1994; Cruz, Frei, & Graeff, 1994; Rodgers & Cole, 1993a; 1993b; Santucci et al, 1994): 1) the percentage of open-arm entries (an arm entry defined as the rat having all four paws inside an arm), 2) the duration of time spent in the open arms, 3) latency to first open-arm entry (latency to enter an open arm timed from the start of the test), 4) head-dipping (scanning over the sides of the maze toward the floor), 5) attempts to enter open arms (entering an open arm with only the forepaws and returning to the central platform or closed arm), 6) rearing (rising on the hind paws). The behavioral categories ‘stretch-attend posture’ and ‘head-dips’ have been previously described as risk-assessment behaviors (Almeida et al, 1994; Rodgers & Cole, 1993a; 1993b). The ‘rearing’ category was included as a classical measure of exploration in a novel environment (Almeida et al, 1994; Almeida et al, 1996b).…”

“…The behavioral categories ‘stretch-attend posture’ and ‘head-dips’ have been previously described as risk-assessment behaviors (Almeida et al, 1994; Rodgers & Cole, 1993a; 1993b). The ‘rearing’ category was included as a classical measure of exploration in a novel environment (Almeida et al, 1994; Almeida et al, 1996b). The other behavioral categories have been behaviorally and pharmacologically validated for rats (Cruz et al, 1994; Pellow, Chopin, File, & Briley, 1985) and mice (Cole & Rodgers, 1994; Lister, 1987 Rodgers & Cole, 1993a; 1993b) as reliable measures of fear/anxiety.…”

“…Furthermore, it is also well known that protein malnutrition during gestation and/or lactation can change the behavior of rats in some animal models of anxiety. Malnourished animals submitted to experimental models of anxiety such as light-dark transition (Brioni & Orsingher, 1988; Santucci, Daud, Almeida, & De Oliveira, 1994), elevated plus-maze (EPM) (Almeida, De Oliveira, & Graeff, 1991; Almeida et al, 1994; Almeira, Tonkiss, & Galler, 1996b; Moreira, De Araújo, De Oliveira, & Almeida, 1997; Riul, Carvalho, Almeida, & De Oliveira, 1998) and elevated T-maze (Almeida, Tonkiss, & Galler, 1996a) presented behavioral changes suggestive of lower anxiety and/or higher impulsiveness.…”