Effects of interference with cerebellar maturation on the development of locomotion. An experimental model of neurobehavioral retardation

Cerebral morphology and functional sparing after prenatal frontal cortex lesions in rats

Rats were given suction lesions of the presumptive frontal cortex on embryonic day 18 (E18) and subsequently tested, as adults, on tests of spatial navigation (Morris water task, radial arm maze), motor tasks (Whishaw reaching task, beam walking), and locomotor activity. Frontal cortical lesions at E18 affected cerebral morphogenesis, producing unusual morphological structures including abnormal patches of neurons in the cortex and white matter as well as neuronal bridges between the hemispheres. A small sample of E18 operates also had hydrocephaly. The animals with E18 lesions without hydrocephalus were behaviorally indistinguishable from littermate controls. The results demonstrate that animals with focal lesions of the presumptive frontal cortex have gross abnormalities in cerebral morphology but the lesions leave the functions normally subserved by the frontal cortex in adult rats unaffected. The results are discussed in the context of a hypothesis regarding the optimal times for functional recovery from cortical injury.

Alterations in hippocampal hemicholinium-3 binding and related behavioural and biochemical changes after prenatal phenobarbitone exposure

Previous studies demonstrated postsynaptic septohippocampal cholinergic alterations after early exposure to phenobarbital. The present study was designed to ascertain possible corresponding presynaptic alterations while confirming the known behavioral deficits and extending previous findings on postsynaptic cholinergic alterations. Pregnant heterogeneous mice received milled mouse food containing 3 g/kg phenobarbital on gestation days 9-18. At age 50 days, [3H]hemicholinium-3 binding, which labels the presynaptic transporter for high affinity choline uptake, was increased in treated mice by 100% (P < 0.001). This change was not accompanied by a change in the affinity of the transporter to the ligand. Another group of offspring was tested for hippocampus-related behaviors. Consistent with our previous studies in the Morris maze, treated animals took longer to reach the platform in the place test as compared to control, and swam fewer times over the missing platform location in the spatial probe test. In the eight-arm maze, the treated offspring needed more entries than control to visit all the arms. In the spontaneous alternation test, the treated mice showed fewer alternations than controls. Biochemically, as in our previous results, prenatal phenobarbital exposure resulted in an increase in the degree of stimulation of inositol phosphate formation by carbachol (P < 0.05), an action presumed to occur at postsynaptic muscarinic receptors. While the present results show that the effect of a combination of raised K+ in the presence of physostigmine and carbachol was significantly greater in barbiturate-treated mice (P < 0.05), the action of K+ in the presence of physostigmine, but without carbachol, was not affected by the phenobarbital treatment. The results point to the uniqueness of outcome of early insults where alterations along nerve conduction cascades do not necessarily follow the common rules in that upregulation could simultaneously occur both pre- and post synaptically.

Alterations in gait following ethanol exposure during the brain growth spurt in rats

Walking patterns were assessed in rats that had been exposed to alcohol neonatally during a period encompassing the brain growth spurt. Rat pups were exposed via an artificial rearing technique to either a 2.50% (w/v) or 2.15% (w/v) EtOH-milk formula on Days 26-32 postconception. An artificially reared control group and a suckle-control group were also included in the experiment. Gait patterns were assessed in animals from each of the neonatal treatment groups at 43, 67, and 87 days postconception. No differences in gait patterns were evident on Day 43 postconception; however, on Days 67 and 87 animals exposed to alcohol during the neonatal period displayed an abnormal gait. These animals had a shortened stride length and an increased angle of placement of the hindfeet relative to artificially reared and suckle-control animals. The altered gait pattern may be the result of alcohol-induced hippocampal and cerebellar damage during the brain growth spurt.

Studies concerning the effects of low level prenatal X-irradiation on postnatal growth and adult behaviour in the Wistar rat

Fifty-nine pregnant Wistar strain rats were sham irradiated or subjected to a 0.1 or 0.2 Gy exposure of X-radiation on the 9th or 17th day of gestation. Twenty-seven of the females were killed at term for teratologic analysis. The remaining mothers raised their young. At 60 days of age the 252 offsprings were randomly assigned three of six tests: open field, swimming, hanging, activity wheel, water T-maze, or conditioned avoidance response. Male offspring exposed at the 0.2 Gy level exhibited retarded growth only during the first few weeks of postnatal life. Female offspring exposed on the 17th day to 0.2 Gy X-radiation were growth retarded throughout the test period. Postnatal growth rates, however, were not significantly different between the irradiated and control groups. There were no significant alterations in adult behaviour due to prenatal X-irradiation. There were sex differences in activity wheel and forelimb hanging performance, unrelated to radiation exposure. These results indicate that prenatal low level X-irradiation on the 9th or 17th day of gestation does not result in significant alterations in adult behavioural performance in the rat, but prenatal growth retardation persists postnatally. Growth may be a more sensitive indicator of the effects of prenatal exposure to X-radiation than postnatal behaviour.

Postnatal locomotion development in a neurological mutant of rolling mouse Nagoya

Postural control skills and quadrupedal locomotor pattern in infant rolling mice, a neurological mutant, were observed in the following situations: hindlimb support when suspended, rope descent, narrow path traverse, quadrupedal locomotion on an inclined corridor, and swimming behavior when entirely submerged. Until the second week of age, rolling mice developed primitive responses similar to, or somewhat slower than, their unaffected littermates, but failed to show mature adaptive and coordinated movements from Days 16-18 onward in hinblimb support and rope descent tests. The gait was broadbased and they frequently lurched, rolled over on the side in the narrow-path and incline situations. Also, swimming behavior was extremely clumsy with varying degrees of disturbed rhythm and inconsistent movement of hindlimb paddling. These findings might result from an immature development of hindlimb muscle tonus control system and distortion of smooth and orderly sequence of hindlimb muscular contractions which characterize skillful quadrupedal locomotion.

Degranulation of rat cerebellum induces selective variations in gene expression

Selective variations in the composition of poly(A)-containing mRNA were found to be induced in the rat cerebellum by X-irradiation. mRNA populations prepared from normal and X-irradiated rat cerebella at different stages of their development displayed equal efficiencies when translated in vitro in reticulocyte lysates. Specific differences were revealed, however, when the labeled translation products of both mRNA preparations were subjected to two-dimensional gel electrophoresis followed by fluorography of the dried gels. Of more than 100 polypeptide products, several showed marked intensity differences, indicating changes in the abundance of their directing mRNA species. These differences appear both in developing and in mature cerebellar mRNA, and the extent of modification in mRNA is much higher than the consequent changes in the composition of proteins in the irradiated cerebellum. The degranulation-induced modifications in levels of specific cerebellar mRNA species can be used to identify proteins whose biosynthesis depends on the presence of interneurons.

Development of motor activity in kittens

Developmental alterations in motor activity were quantified for the 1st 7 postnatal months in the kitten. Motor activity measured with a stabilimeter was low and constant for the 1st 9 postnatal days, increased markedly until Day 14, and remained stable until Day 21. Locomotor activity measured in an open field decreased slightly during the 1st 3 weeks, increased markedly during the next 2 weeks, and then remained relatively constant until the 9th week. Activity increased again during the 3rd and 4th month and then declined until 7 months of age. We suggest that the marked increase in motor activity during the 2nd week reflects development of visual and auditory systems whereas the increase in locomotor activity during the 4th and 5th weeks represents maturation of neural systems concerned with motor control. The underlying causes of the final activity changes probably represent the maturation of many neural systems and concomitant development of adult behavior in the cat.

Restitution of bromodeoxyuridine-induced changes in cerebellar development

Previously, it was shown that bromodeoxyuridine (BrdU) in 2-day-old rats caused hypoplasia of the external cerebellar granular layer. Significant restitution was achieved after removal of BrdU by an increase in the rate and duration of proliferative activity of the EGL cells, but abnormal cerebellar cytoarchitecture remained detectable at 35 days of age due mainly to polarity changes in the regenerated cells. The present report concerns repair of the EGL after giving BrdU to 7-day-old rats i.p. (15 mg/100 g body weight) twice daily for 3 days and killed at 15 days-of-age. Now, the regenerative capacity of the EGL was severely curtailed. The proliferative activity of the EGL of the treated animals was similar to normal controls and there was no change in the orientation of either the EGL cells or the parallel fibers. The only noticeable differences were a decrease in the width of the molecular layer and the presence of unusually elongated primary dendrites in many Purkinje cells of the BrdU treated rats. It was concluded that lengthening of the cell cycle time had slowed down the removal of BrdU and thus reduced the regenerative potential of the EGL at this age.