Adriana Garau

Perinatal hypothyroidism effects on neuromotor competence, novelty-directed exploratory and anxiety-related behaviour and learning in rats

Thyroid hormone is essential for proper development of the mammalian CNS. Previous studies have documented a decrease in the ability of neonatal hypothyroid animals to learn and to habituate to maze tests and an increase in spontaneous activity. However, there is little information about the effects of perinatal (i.e. perinatal and postnatal) hypothyroidism on behaviour. The aim of the present work was to investigate the longitudinal effects of perinatal hypothyroidism on certain aspects of the behaviour in rats. Neuromotor competence was tested at 21, 40 and 60 days, novelty-directed exploratory behaviour and anxiety-related behaviour were evaluated at 40 and 60 days by means of the Boissier tests and associative learning ability was tested at 80 days by means of a step-through passive avoidance task. The persistence of the effects of perinatal hypothyroidism on psychomotor performance was highly dependent on the task examined. Perinatal hypothyroidism caused an increase of locomotor activity as revealed by the total distance travelled in the Boissier test and this increase also comprised a component of decreased anxiety-related behaviour. Methimazole-treated subjects also had higher head-dip scores than controls at 40 days while no differences were observed at 60 days. Finally, our results showed that methimazole-treated rats performed poorly in a passive avoidance learning task.

Effects of adult dysthyroidism on the morphology of hippocampal neurons.

This study investigates the effect of thyroid hormones on the morphology of hippocampal neurons in adult rats. Hypo- and hyperthyroidism were induced by adding 0.02% methimazole and 1% l-thyroxine, in drinking water from 40 days of age, respectively. When the rats were 89 days old their brains were removed and stained by a modified Golgi method and blood samples were collected in order to measure T4 serum levels. Neurons were selected and drawn using a camera lucida. Our results show that methimazole administration reduces the dendritic branching of the apical shafts of CA3 and CA1 pyramidal neurons mainly by increasing the distance to the first branch point in both types of neurons, and reducing branch points in the radius of 50 microm from the soma in CA1 neurons. Nevertheless, it was observed an increase of apical spine density in CA3 neurons from this group. Thyroxine reduces apical and basal tree of CA3 pyramidal neurons increasing the distance to the first branch point, reducing branch points in the radius of 50 microm from the soma and increases their apical and basal spine density. In CA1 field, thyroxine reduces the number of basal branch points. Both treatments seems to provoke alterations in the same direction reducing the dendritic branching and increasing spine density, although no significances appeared in some of the parameters analyzed. The effects are more evident in thyroxine than methimazole group; and in CA3 neurons than in CA1 neurons. In discussion it is pointed that the increase of spine density could be a mechanism to compensate the functionality reduction that can be provoke by the treatment effect on dendritic branching.

Effects of dysthyroidism in plus maze and social interaction tests

The aim of the present study was to determine the influence of thyroid hormones on the anxiety of male Wistar rats. Dysthyroidism was induced by adding 20 mg of methimazole (100 ml) to their drinking water or by adding 0.3 mg of L-thyroxine (100 ml) to their drinking water from the ninth day of gestation. After weaning, the drugs were administered to young rats until the end of the experiment. Anxious behavior was measured using the elevated plus maze and social interaction tests when the animals were 85 days old. Chronic methimazole administration produced a significant anxiolytic pattern in both tests. In the plus maze test, the methimazole-treated animals entered and remained more time in the open arms than the control animals. In the social interaction test, they spent more time in bodily contact, and did this more frequently than those in the control group did. Results from this experiment suggest that chronic thyroid deficiency produces an anxiolytic-like effect in both tests.

Perinatal alterations of thyroid hormones and behaviour in adult rats

Several studies have shown the relevance of the neuroendocrinological system in the development and function of the nervous system. In order to observe the influence of thyroid hormones during development on the behaviour of adult rats we induced dysthyroid states during the perinatal period. Results indicate that some behaviours are more susceptible to the action of thyroid hormones than others. We observed that the thyroid hormone deficiency causes an increase of activity in animals in spite of a large period of rehabilitation. Thyroxine-treated rats showed an anxiogenic behavioural pattern in the elevated plus-maze, while animals rehabilitated from perinatal deficit of thyroid hormones showed an anxiolitic pattern. These findings suggest that an excess of thyroid hormones has less effect on behaviour than a deficiency of these hormones.

Age effects on the social interaction test in early adulthood male rats

The effects of age on active and passive social interaction were studied in Wistar rats using the social interaction test (S.I.T.). Individual behaviors such as ambulation, rearing, and defecation were also studied. Despite the widespread use of the S.I.T. in anxiety research, the effects of age on the S.I.T have not been studied thoroughly. Male Wistar rats of 75, 135, and 180 days old were used. Our results showed age effects on active social contact, passive social contact, ambulation, rearing, and defecation. At 135 days old, animals presented the lowest scores on active social behavior and the highest scores on defecation. Moreover, exploratory behavior measured by ambulation and rearing decreased with age. These results suggest that age could be a relevant variable in the social interaction test. Depression and Anxiety 12:226–231, 2000.

Perinatal hypothyroidism effects on step-through passive avoidance task in rats

Previous studies have documented a decrease in the ability of neonatal hypothyroid animals to learn and habituate to maze tests, and an increase in spontaneous activity. However, there is little information about the effects of perinatal (i.e., prenatal and postnatal) hypothyroidism on behaviour. The present study was designed to assess whether perinatal hypothyroidism in rats induces alteration on acquisition and/or short- and long-term retention of a learned response in male Wistar rats. Perinatal hypothyroidism was induced by prolonged (E9-P21) exposure of pregnant and lactating dams to methimazole (administered orally in drinking water, 0.2 mg/ml). Cognitive function was tested at 50 days by means of a step-through passive avoidance task. The effects of perinatal hypothyroidism on the retention of the passive avoidance response are long lasting being, however, highly dependent on the retention after the original training. Our results showed that methimazole-treated rats performed more poorly when retention was tested at long-term (24 h and 7 days) retention interval. Instead, methimazole-treated rats showed longer retrieval latencies than the control ones did when retention was tested at short term (1 h).

Is prolactin related to activity and emotional reactivity in rats

Recent studies have shown different relationships between hormones and personality in humans, including a relationship between prolactin levels and impulsivity. The aim of the present work was to study the relationships between basal levels of prolactin and some measures of activity and emotional reactivity in rats. One of the most consistent results showed a negative correlation between basal prolactin levels and activity. This finding is in line with the serotonergic theories of impulsive behavior and with the effects of dopamine upon activity.

Personality in rats and pain measures

Abstract The pain threshold of rats previously selected according to ambulation and defecation scores was assessed. S s were 89 Sprague-Dawley rats aged 90 days. They were submitted to a low-frightening open-field (LFOF) test and 40 rats were selected on the grounds of extreme ambulation and defecation scores. The pain threshold was then assessed in 10 daily tests during 2 consecutive days. The mean of the 20 tests was used as the measure of the threshold and the mean of the two most extreme values was used as the measure for pain tolerance. The results obtained show that the pain thresholds of high-defecatory rats are significantly lower than those of low-defecatory rats. A similar relationship is found between low- and high-ambulatory rats, but the differences do not reach statistical significance. When the results of all 4 groups are compared the low-ambulatory and high-defecatory rats (introvert-neurotic) show the lowest threshold value, and the high-ambulatory and low-defecatory rats (extravert-stable) show the highest one which is significantly different from any other group. The results obtained with respect to the tolerance threshold, in spite of the lack of statistical significance, follow the same direction as those shown by the pain threshold.