Repeated predictable or unpredictable stress: effects on cocaine-induced locomotion and cyclic AMP-dependent protein kinase activity

Stressful experiences appear to have a strong influence on susceptibility to drug taking behavior. Cross-sensitization between stress and drug-induced locomotor response has been found. Locomotor response to novelty or cocaine (10 mg/kg, i.p.), cyclic AMP-dependent protein kinase (PKA) activity in the nucleus accumbens and basal corticosterone levels were evaluated in male adult rats exposed to acute and chronic predictable or unpredictable stress. Rats exposed to a 14-day predictable stress showed increased locomotor response to novelty and to cocaine, whereas rats exposed to chronic unpredictable stress demonstrated increased cyclic AMP-dependent PKA activity in the nucleus accumbens. Both predictable and unpredictable stress increased basal corticosterone plasma levels. These experiments demonstrated that stress-induced early cocaine sensitization depends on the stress regime and is apparently dissociated from stress-induced changes in cyclic AMP-dependent PKA activity and corticosterone levels. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Exposure to acute restraint stress reinstates nicotine-induced place preference in rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The influence of chronic stress imposed on pregnant rats on the induced bone loss in their adult offspring

Background and objective: Stress during pregnancy may alter offspring susceptibility to diseases during adulthood. In the present study, female Lewis rats were subjected to chronic stress during the gestational period, and the effect of this stress was evaluated histometrically on the progression of ligature-induced bone loss in their adult offspring.Material and methods: After confirming pregnancy, half of the pregnant rats were randomly designated as control animals (no stress regimen was imposed), and the other half was submitted to a chronic stress model (immobilization at cold temperature) between the 7th and the 18th gestational day. After birth, 12 male rats delivered by stressed mothers - Group 1 (G1) - and 12 male rats delivered by non-stressed mothers - Group 2 (G2) - were selected. When birthed rats reached 250 g of body weight, a silk ligature was placed around their maxillary right second molar in order to induce bone loss. The non-ligated left side served as a control. Sixty days later, these animals were sacrificed by anaesthetic overdose. After routine laboratorial processing, images of the histological sections were digitized and submitted for histometric measurement using two parameters: histological attachment loss and bone loss.Results: on the ligated side, G1 presented with greater histological attachment and bone loss than G2 (p < 0.05). on the non-ligated control side, neither of the groups presented with alterations in these parameters (p > 0.05).Conclusion: The chronic stress regimen imposed on pregnant rats produced a greater progression of ligature-induced bone loss in their adult offspring. (C) 0 2011 Elsevier Ltd. All rights reserved.

Caution for using ventilatory frequency as an indicator of stress in fish

This study tested the use of ventilatory frequency (VF) as an indicator of stress in the Nile tilapia, Oreochromis niloticus (L.). Firstly, we tested the relationship between VF and plasma cortisol after confinement. Confined fish showed higher VF and plasma cortisol levels, but the latter continued to increase significantly for longer time than VF. Secondly, we conducted another experiment to test the use of VF as indicator of fish stress. In four out of six treatment, we confined the fish for different intervals (30 s, 5, 15 or 30 min). The others were used as control. In one, no handling was imposed. The other control consisted of introducing the partition (the same used to perform the confinement) into the aquarium for less than 4 s, without confinement and immediately removing the partition (partition control). Ventilatory frequency was increased for the partition control as much as for the longer duration of confinement. This clearly indicates that VF is a very sensitivity response to disturbance, but of limited use because this parameter does not reflect the severity of the stimulus. Thus, although VF is a non-invasive technique that does not require sophisticated recording equipment, its usefulness is limited. (C) 2004 Elsevier B.V. All rights reserved.

Ventilation rates indicate stress-coping styles in Nile tilapia

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of electrolytic and neurotoxic lesions of the median raphe nucleus on anxiety and stress

To study the role played by 5-HT mechanisms of the MRN, behavioural and physiological parameters were presently measured in rats having either electrolytic or 5,7-dihydroxytryptamine (5,7-DHT) lesion of the MRN made 7 days before testing. Half the animals were submitted to 2-h restraint 24 h before the test. In the elevated plus-maze, the electrolytic lesion increased the percentage of open-arm entries and of time spent on open arms - an anxiolytic effect - in both restrained and nonrestrained rats. The neurotoxic lesion had a similar effect, but only on restrained rats. Restraint had anxiogenic effect. The electrolytic lesion increased transitions between the light and dark compartments and the time spent in the bright compartment of the light-dark box in both restrained and nonrestrained rats. The neurotoxic lesion only increased bright time in restrained rats. The incidence, number and size of gastric ulcers were increased by either the electrolytic or the neurotoxic lesion in both restrained and nonrestrained animals. Both types of lesion depleted 5-HT in the hippocampus in restrained and nonrestrained rats. Restraint increased 5-HT levels. These results implicate 5-HT mechanisms of the median raphe nucleus in the regulation of anxiety and in the genesis of gastric stress ulcers. (C) 2001 Elsevier B.V. All rights reserved.

Unpredictable chronic mild stress exerts anxiogenic-like effects and activates neurons in the dorsal and caudal region and in the lateral wings of the dorsal raphe nucleus

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)