Group-housed Rats Research Articles

Rapid effects of environmental disturbance on rat plasma unesterified fatty acid and tryptophan concentrations and their prevention by antilopolytic drugs.

1 Changes of plasma unesterified fatty acid (UFA) and tryptophan concentration in group-housed rats following removal of their cage-mates and the effects of antilipolytic drugs on these changes were investigated. 2 Removal of group-housed 24 h fasted rats but not fed rats from cages resulted in increased plasma UFA concentration in the remaining rats which was associated with significant increases of the proportion of free tryptophan but significant falls of total tryptophan concentration. These rapid changes were not associated with brain tryptophan changes. Plasma tyrosine concentration was unaffected. 3 The fall of plasma tryptophan did not appear to be due to passage into red cells as erythrocyte tryptophan concentration remained unchanged. 4 Plasma UFA concentrations correlated positively and significantly with corticosterone concentrations which were also increased following removal of cage-mates. 5 Plasma UFA increases and tryptophan changes in the fasting rats were both prevented by nicotinic acid or propranolol. Corticosterone concentration was increased by nicotinic acid but unaffected by propranolol. 6 The possible importance of these rapid changes of plasma tryptophan and of their prevention by antilipolytic drugs is discussed.

Supersensitivity to isoprenaline induced in rats by prolonged isolation.

1 The effect of isoprenaline on diastolic blood pressure and heart rate was determined in anaesthetized male rats which had been housed individually for 6-8 weeks after weaning, and compared with its effect in group-housed litter-mate controls.2 Isoprenaline caused a significantly greater fall in diastolic pressure in isolated rats and a greater increase in heart rate.3 Low doses of noradrenaline (5-10 ng) caused vasodepressor responses in isolated, but not in group-housed rats.4 The pressor response to noradrenaline, which was smaller in isolated rats, was increased to the level of group-housed controls by (+/-)-propranolol.5 Prolonged isolation of rats may bring about an increase in sensitivity of beta-adrenoceptors to isoprenaline and noradrenaline.

The effect of dl-propranolol, d-propranolol and practolol on the hyperactivity induced in rats by prolonged isolation.

Exploratory behaviour in an open field situation was found to be greatly increased in rats, isolated for 6–8 weeks, when compared with grouphoused controls. Propanolol, dl- and d- and practolol, 0.2–0.5 mg/kg reduced hypermotility, sniffing and rearing in isolated rats without affecting behaviour of group-housed rats. 20 mg/kg dl-propanolol was needed to reduce exploratory behaviour of group housed rats. Chlorpromazine reduced activity of isolated rats at a dose of 0.1 mg/kg, and group housed rats at 0.5–1 mg/kg. The action of propranolol does not appear to result from central receptor blockade because of the almost equal activity of d- and dl-propranolol. Since practolol was also active in this test, the effect of these drugs also does not appear to result from general C.N.S. depression. It is suggested that these compounds may reduce hyperactivity by diminishing an excessive release of central catecholamines.

Effects of lithium chloride on the activity of rats tested alone or in pairs.

Group-housed rats, injected with an acute dosage of 3 meq/kg lithium chloride, were tested on an activity platform either alone or in pairs 20 min or 3 h after drug administration. Contrary to previous findings, rats administered lithium were less active than those treated with saline after both post-injection periods. However the activity of the saline control animals tested alone after 3 h was considerably less than that exhibited by the same group after 20 min. This activity difference, which could be interpreted as a lithium-social or lithium-time interaction, is more simply explained in terms of the effects of the social isolation occuring between drug administration and testing.