Regional Brain Weights Research Articles

Implementation of a Primary Screen for Developmental Neurotoxicity

A battery of tests to evaluate physical growth/development and neurobehavioral function was conducted with 78 litters of control Sprague-Dawley rats given purified water by intubation. The objectives of this study were to optimize test methods and to document the range and variability of the experimental endpoints. Data are presented for maternal evaluations (body weight gain, food consumption), gestation length, litter size, and postnatal survival. Pup body weight was used to assess postnatal somatic growth rate from birth to 85 days of age, while whole and regional brain weight measurements at 7, 28, and 85 days provided a more specific measure of physical growth relevant to a neurobehavioral study. Physical landmarks of development evaluated were pinna unfolding, incisor eruption, and eye opening while reflex landmarks of development evaluated were the negative geotaxis and pupillary reflexes. The mean percentage of litters acquiring a physical trait or reflex increased sigmoidally with age, and the data suggest that the potential to detect developmental delays would be optimal when ca. 90% of control litters reach the test landmark. Functional evaluations were arranged according to four testing subsets so that each litter was evaluated in each test (1 pup/sex/litter), but repeated testing on pups was minimized. Auditory and tactile startle reflexes, as well as prepulse inhibition, were measured at ages 22 days and 60–64 days and found to increase with age. A passive avoidance paradigm (age 40–43 days) was used to assess exploratory behavior (approach) and memory (avoidance). Swimming performance in a water maze was used to evaluate learning. In this test, escape times and error rates improved to their highest level by five or six trials and showed acceptable degrees of variability. Spontaneous motor activity was monitored for 23 hr at age 54–61 days to evaluate exploratory activity, photoperiod entrainment, and catecholamine-induced locomotion (amphetamine challenge). Finally, landmarks of sexual maturation (balanopreputial separation evident at 45 days of age, vaginal perforation evident at 33 days) and estrous cychcity (4.8 cycles per 21 days) were evaluated as measures of reproductive neuroendocrine function. In sum, the test battery provided an efficient yet comprehensive screen for evaluating effects on physical growth/development and neurobehavioral function which meets practical criteria for preclinical testing of pharmaceutical agents.

Different methods for producing neonatal undernutrition in rats cause different brain changes in the face of equivalent somatic growth parameters.

Similar degrees of undernutrition were induced in neonatal rat pups using a modified Slob technique and a large-litter manipulation. From birth, large litters and Slob litters were comprised of 20 and 10 pups, respectively. On days 2, 4 and 6, half of the pups in the Slob group were cross-fostered to nonlactating foster aunts, while the remaining half of each litter (controls), as well as the large-litter rats were cross-fostered to a lactating dam. On day 10, undernourished Slob and large-litter pups showed similar body weight and body length deficits compared with controls, but differences between the two undernourished groups emerged when regional brain weight and nucleic acids and proteins were examined. The acute intermittent undernutrition of the modified Slob technique had more severe consequences than the large-litter manipulation for brain growth and development. Therefore, two methods of inducing early postnatal undernutrition may yield equivalent somatic effects, but very different brain growth parameters.

Neonatal 6-hydroxydopamine attenuates the neural and behavioral effects of enriched rearing in the rat

Newborn male rats were administered subcutaneous 6-hydroxydopamine (6-OHDA) to deplete forebrain norepinephrine and after weaning were reared in normal or enriched environments. Subsequently the 6-OHDA treated rats and their vehicle controls were trained in a Lashley type III maze and then sacrificed for assay of regional brain weights and brain catecholamines. Whereas for the control rats, enriched rearing was found to: (1) increase hypothalamic and posterior corticol dopamine; (2) increase forebrain and decrease hypothalamic weight; and (3) to enhance maze acquisition, none of these consequences of enriched rearing was found in the 6-OHDA treated rats. We conclude that forebrain norepinephrine plays a permissive role in the neuroanatomical, neurochemical and behavioral alterations induced by the enriched rearing of weanling rats and that it is essential to at least some aspects of the shaping of the brain by experiential factors.

Effects of experimental suppression of active (REM) sleep during early development upon adult brain and behavior in the rat

In order to test the hypothesis that active sleep (AS) is important for the normal development of the central nervous system. 3 different deprivation methods were applied to male Wistar rat pups during the first month of life. Daily injection of clomipramine from 8 to 21 days of age reduced the high level of AS to less than the adult value throughout most of the experimental period. Administration of clonidine from 8 to 21 days of life induced an almost total suppression of AS. Instrumental deprivation, using the ‘pendulum’ method, led to a significant (but less severe) AS reduction during 2–4 weeks of postnatal age. Open-field behavior testing in adulthood revealed a higher than normal level of ambulation in all 3 experimental groups. Masculine sexual responses were deficient, due to a low level of both mounts and ejaculations, in both clomipramine- and clonidine-treated animals. Neither passive avoidance learning nor dark preference tests revealed any differences between the experimental and control rats. Sleep observations showed that there was an abnormally high incidence of large myoclonic jerks during AS in both clomipramine- and clonidine-treated rats. Subsequent measurement of regional brain weights showed a significant reduction in the cerebral cortex and medulla oblongata, as compared with the respective control groups, in both the clomipramine- and the clonidine-treated rats. In addition, DNA and protein determination in the affected brain areas showed a proportional reduction in the cortex and in the medulla. These results demonstrate that interference with normal functioning either of AS per se or of specific monoaminergic transmitter systems during early development can produce long-lasting behavioral as well as brain morphological and biochemical abnormalities in later life.

Pharmacological suppression of REM sleep prior to weaning counteracts the effectiveness of subsequent environmental enrichment on cortical growth in rats

Male Wistar rat pups were deprived of REM sleep by means of daily injections of clonidine between 8 and 21 days after birth. From day 28 they were reared under either 'enriched' or 'standard' environmental conditions. At 75 days of age the animals were sacrificed, and the regional brain weights were compared with two (differentially reared) control groups. Whereas cortical weight was greater in the enriched than in the standard control rats, no differences were found between the corresponding REM sleep-deprived (i.e. clonidine-treated) groups. These results suggest that REM sleep deprivation and/or disturbances of central noradrenergic function during early development can counteract growth responses of the brain to environmental stimulation later in life.

Castration decreases olfactory bulb norepinephrine in male rats but not hamsters

Norepinephrine (NE) concentrations were measured in the olfactory bulbs and olfactory cortex of male albino rats and golden hamsters sacrificed 13-16 days after castration or sham surgery. Castration significantly decreased NE concentrations in the olfactory bulbs of rats but not hamsters. Castration had no significant influence on NE levels in the olfactory cortex of either species. Regional brain weights were not influenced by surgery, and previous olfactory exposure had no significant effect on any variable measured. The decrease in rat olfactory bulb NE levels may be involved in castration-induced changes in preferences for conspecific odors.

Behaviour, brain and body growth of guinea-pigs after prenatal growth restriction.

1. Guinea-pigs were growth-retarded in early life by feeding their mothers a restricted quantity of food during the second half of pregnancy. After birth, all animals were fed ad lib. Body-weights were recorded weekly and behavioural tests were made on adult males. The animals were then killed and their brains dissected into forebrain, cerebellum and brain stem. These regions were weighed and DNA-phorphorus content measured.2. At 14 weeks each male was paired with another male for 10 min on four consecutive days and their social behaviour scored. Tests 1 and 2 were on like-treatment pairs and tests 3 and 4 on unlike-treatment pairs. At 25 weeks the same animals were subjected to six graded series of brief, unavoidable shocks and their responses recorded. After 3 d, thresholds of aversion to electric shock were measured by recording the period of time spent on the ‘safe’ side of a rectangular box at five shock levels.3. Undernourished guinea-pigs were significantly lighter than controls at birth but not at adulthood. Regional brain weights and DNA-P content of previously-undernourished guinea-pigs were significantly lower than those of controls, with the greatest deficit in brain stem.4. Pairs of previously-undernourished guinea-pigs began to interact more quickly and threatened and nosed each other more often than pairs of controls. In mixed pairs previously-undernourished animals chased controls more than their control partners chased them. There were no differences between groups in responsiveness to unavoidable shock or in aversion thresholds.

GROWTH AND DEVELOPMENT OF THE BRAIN IN NORMAL AND HEAT‐RETARDED GUINEA‐PIGS

Guinea‐pigs were exposed to a temperature of 41.5–42.5°C for 1h daily on days 20–23 of gestation. Fetuses from control and from heated mothers were studied at 30, 35, 41, 48, 55 and 62 days gestation and post‐natal offspring at 69, 76, 83, 90, 104, 118, 132, 146 and 160 days after conception. Body weights, whole and regional brain weights, and the dry matter, DNA (an index of cellularity) and cholesterol (an index of myelination) contents of these brain regions were measured. There was frequently a small but variable deficit in the body weight of heated offspring. A significant reduction of whole brain weight was found in the heated groups. The deficit in brain weight was detected 7 days after the heat‐stress and remained at about the same relative level until maturity. The DNA and cholesterol concentrations were the same in control and heated brains, but the absolute amounts were less in the latter which resembled proportional, normally shaped miniatures of the control brains. Hyperthermia is known to disrupt cellular proliferations, and since it was given during neurogenesis it is concluded that the size which might be attained by the brain is largely determined by the extent of early neuronal proliferation.

Motor co-ordination and cerebellar size in adult rats undernourished in early life

The male progeny of mother rats which had been undernourished during most of gestation and all of lactation were divided into two groups when weaned at 25 days. One group was nutritionally rehabilitated (G −L −) while the other was underfed for a further 9 weeks (G −L −W −) before nutritional rehabilitation. Despite this further undernutrition the G −L −W − rats eventually caught up in both body and brain weight with the G −L − group. Compared with control rats of the same age that had been well fed throughout life, the G −L − and G −L −W − animals had permanent deficits in body and regional brain weights. At 36 weeks rats were given two tests of motor co-ordination. They were required (a) to run backwards on a revolving drum and (b) to cross a chasm bridged by a ladder or parallel rods for a food reward. Both previously undernourished groups did consistently worse than controls of the same age or of similar body weight on two measures of co-ordination: falls from the revolving drum and stumbles on the bridge-crossing test. It is postulated that these differences indicate impaired cerebellar function in the previously undernourished rats.