A critical period for reduced brain vulnerability to developmental injury. II. Volumetric study of the neocortex and thalamus in cats

Ontogenesis of morphine-induced behavior in the cat

We analyzed the behavioral responses to a single dose of morphine in kittens at postnatal (P) ages 7, 15, 30, 60, 90, and 120 days. Each kitten received 0.5 or 3.0 mg/kg i.p. of morphine sulphate or saline vehicle. An average of 6.5 kittens were studied at each dose and age. An ethogram was constructed, based on morphine effects in adult cats, to score appropriate behaviors from direct observation and video sampling. After injection behaviors were sampled for periods of 2 min every 15-30 min for a total of 4 h. The frequency of each selected behavior was scored at 2 s intervals during each of the 2 min periods and it was expressed as a percent of all time samples scored for the 4 h period. Statistical comparisons were made with control (saline) littermates. At P7-15 the drug's main effect was behavioral depression; i.e., kittens, away from the litter, laid sprawled as if with no muscle tonus; Nursing was suppressed and Vocalization was distressed. Mainly with the higher dose, at P30, morphine-specific behaviors appeared for the first time. With the kitten in a Sitting position, these included stereotypical Head and Paw Movements and body Torsion. At P60 other drug-elicited behaviors emerged, including Spinning, Retching, and Vomiting. By P90-120 the frequency of Head (16.0%) and Paw (16.9%) Movements doubled relative to P30-60. Morphine significantly changed frequencies of newly matured behaviors (in control kittens) including Sniffing and Licking (increased), and Grooming (decreased/blocked). Retching and Vomiting increased to adult levels. Morphine-induced hyperthermia was first detected at P60 and peaked by P90-P120. The early behavioral depression shifted to a pattern of increasing activity starting at P30 and peaking at P90-120, at which time Sleep was absent and Laying was reduced, while Walking and Sitting were increased. We concluded that the maturation of the stereotypical behavioral responses to morphine in cats begins at about P30 and is completed between P90 and 120. Results are discussed in terms of developmental parameters and putative brain sites of morphine's actions.

Metabolic maturation of the brain: A study of local cerebral protein synthesis in the developing cat

We used quantitative L-[1-(14)C]leucine autoradiography to study the maturation of cerebral protein synthesis metabolism in kittens, starting at birth and through postnatal age (P) 180 days as well as in adult cats. We found that at birth most brain structures show protein synthesis (nmol/min/g; lCPS(leu)) rates already within the range of adult values (with some exceptions; e.g., the hippocampus and putamen). Likewise, most structures show a transient developmental peak during which the rates climb to levels higher than in adulthood. This peak often occurred at P60, but in some regions lasted from P30 to P90. Therefore, there is some regional heterogeneity in the maturation of brain protein synthesis. These results are compared with our previous findings on the maturation of cerebral glucose utilization and oxidative metabolism. We discuss the meaning of these maturational profiles in terms of time course of morphological development and of maturation of behavior in the cat. Correlations with findings in other mammalian species are also discussed.

Disparity of Verbal and Performance IQ Following Early Bilateral Brain Damage

OBJECTIVE

To examine the effects of early bilateral brain damage on Full Scale IQ (FSIQ), Verbal IQ (VIQ) and Performance IQ (PIQ).

BACKGROUND

Early unilateral brain damage typically results in relatively spared intellectual function, with IQ in the normal range and no significant differences between VIQ and PIQ, regardless of the side of the lesion. However, little is known about intellectual function in children after bilateral damage.

METHOD

FSIQ, VIQ, and PIQ scores of 10 children, ages 6-12 years, with early-onset bilateral focal lesions (BFL), were compared with those of age- and sex-matched controls.

RESULTS

FSIQ was in the average range for BFL and control children. A bimodal distribution of VIQ was identified, resulting in 2 distinct groups, one performing above the average range and the other below. The unimpaired group displayed a significant discrepancy between VIQ and PIQ, with VIQ in the superior range and PIQ in the low average range. The impaired group did not demonstrate disparate VIQ and PIQ: both were in the borderline range. The 2 groups were differentiated by greater degree of cortical brain damage in the impaired than in the unimpaired group.

CONCLUSIONS

The striking difference between the outcome of the unimpaired and impaired groups may reflect different processes of reorganization that are associated with the extent of cortical involvement.

Developing experimental models to address traumatic brain injury in children

Traumatic brain injury (TBI) is the leading cause of injury-related death and disability among children under the age of 15 years in the United States. Epidemiological studies have revealed that even within the pediatric population there are differences in incidence, gender differences, causes, types of injuries sustained, and mortality within age subdivisions. This heterogeneity must be taken into account when developing appropriate models to address TBI in children. This review explores the current developmental TBI models, including fluid percussion, weight drop, and controlled cortical impact. It also addresses unique considerations to modeling pediatric brain injury that require special attention when modeling and designing studies: age appropriateness, injury severity, evaluation of recovery, plasticity, and anesthesia.

The lesion methodology: contrasting views from adult and child studies

A traditional approach for examining brain-behavior relations has been the lesion method. This method assumes a direct correspondence between the cognitive process compromised and the site of lesion. Historically, studies with adults have used this framework to map brain functions. In contrast, studies of children with early injury have addressed quite different issues. Developmental animal lesion studies and pediatric neuropsychology studies have focused on the level of plasticity exhibited following early injury. Resilency in behavioral development has suggested change in the underlying neural substrate. A new set of studies has applied converging, MRI-based methods to examine anatomical and functional development in intact brain regions following early injury and compared these data with behavioral outcomes on the same children. The findings reveal an interaction between early injury and normal mechanisms of development, which manifest as atypical behavioral, structural, and functional development.

A critical maturational period of reduced brain vulnerability to injury. A study of cerebral glucose metabolism in cats

We have developed a feline cerebral hemispherectomy model as an analog to the surgical procedure used in pediatric intractable epilepsy. Previous work with this model has shown a remarkable plasticity associated with an early period of brain development, which we have defined using morphological, cerebral metabolic and behavioral methods. However, the important functional-metabolic bracketing of this period has not yet been performed. We have conducted the present study to answer questions raised by our previous findings using [14C] 2-deoxy-D-glucose autoradiography but only including animals lesioned at day 10 postnatally (P10) or in adulthood. The questions were; (a) is there any age better than P10 for an optimal metabolic outcome?, and (b) can we determine a cutoff point for the beneficial effects of the young age-at-lesion? Twenty-one adult cats were studied. Seven cats served as intact controls, five received a left hemineodecortication at P30, three at P60, three at P90 and three at P120, respectively. Histological analysis indicated that the extent of the lesion was similar between the age groups. Local glucose metabolic rates (LCMR(glc)) were measured in 50 structures bilaterally and used to calculate overall LCMR(glc) for seven grouped sites within the cerebral cortex, thalamus, basal ganglia, mesencephalic tegmentum (and tectum), limbic system and cerebellum. Results indicated a widespread bilateral depression of LCMR(glc) in all age-at-lesion groups. The depression in overall LCMR(glc) across all structures measured in each hemisphere was significant (P<0.05) for the P120 group relative to intacts for both ipsilateral (left) and contralateral (right) sides of the brain. The ipsilateral thalamus was the region most effected by the injury, with significant losses for all age-at-lesion groups. In addition, while there were widespread depressions for all lesion groups, these losses were significant for the P120 group in five groups of structures ipsilaterally (thalamus, basal ganglia, tectum, limbic system, cerebellum) and in three contralaterally (thalamus, tectum, cerebellum). In contrast, significant depressions for the earlier age-at-lesion groups (P30, P60, P90) were found only in the ipsilateral thalamus and bilaterally in the tectum. These results, together with our previous results for the P10 group, indicate a relative sparing of LCMR(glc) after hemineodecortication during the first 60 days of life, with gradually decreasing plasticity thereafter, such that there is some residual sparing at 90 days of age, and afterwards an almost complete loss of metabolic plasticity, with lesions at P120 producing a dismal outcome. These results complement earlier morphological and behavioral studies and support the concept of a 'Critical Maturational Period' of reduced vulnerability to developmental injury.

The growth of the feline brain from late fetal into adult life. I. A morphometric study of the neocortex and white matter

We measured the growth of the neocortex (NCx) and telencephalic white matter (WM) in the brain of 64 cats allocated to the following 11 age-groups: fetal (E) 59 days (birth is at E63-65), postnatal (P) days 1, 7, 15, 30, 45, 60, 90, 120, 180, and adult. There were six subjects per group (except for E59, n=4). Using a projection microscope and cytochrome oxidase-stained coronal sections, a total of 4300 and 4325 sections at left and of 4282 and 4264 sections at right were drawn for the NCx and for the WM, respectively. With computer assistance, the drawings were digitized to calculate mean cross-sectional area and then the mean volume of each structure per age-group. The two structures grew heterochronously. In terms of percentage of the adult volume, for the left side (both side grew at a similar rate), the size of the NCx grew very fast from a 15.7% at E59 to an adult-range value of 93.7% at P30. In contrast, the WM grew slowly. Starting at a larger volume of 55%, the WM was only 72. 5% of the adult size at P30 reaching an adult-range value only by P180 (94.7%). After P30, both structures showed a small, albeit consistent, left versus right asymmetry with the right size been larger at all (but fetal) ages by a margin ranging between 0.4 and 4. 1%. In addition, after P30 the NCx tended to overgrow with all groups showing higher values relative to adult cats, and reaching significance at P60 (volume higher by 19.2%, P<0.01) and at P180 (higher by 14.5%, P<0.05). For the NCx there were no within group correlations between volume of the structures and the subjects' body weight, while a positive correlation was present for four of the WM postnatal groups. There were no correlations between the size of the structures and the sex of the cats. The data is discussed in the context of the extant human and animal literature and, in the ensuing paper, also within the context of growth of subcortical structures.

The growth of the feline brain from fetal into adult life. II. A morphometric study of subcortical nuclei

As a continuation of the morphometric studies on the preceding paper, here we report on the rate of growth of the caudate nucleus (n.), thalamus, red n., and the substantia (s.) nigra using, with few exceptions, the same cohort of cats. The same previously used brains (n=64 cats) were allocated to the following age groups: fetal (E) 59 days, postnatal (P) days 1, 7, 15, 30, 45, 60, 90, 120, and 180. Sixteen additional cats, interspersed within the groups, were substituted for the red n. and s. nigra studies. There were six subjects per group (except for E59, n=4). Using a projection microscope and cytochrome oxidase-stained coronal sections, a combined (left plus right sides) total of 4693, 3822, 1636, and 1180 sections were drawn for the caudate, thalamus, s. nigra, and red n., respectively. With computer assistance, the drawings were digitized to calculate mean cross-sectional areas and then the mean volume of each structure per group. The growth time tables for the caudate n., thalamus and s. nigra were fairly synchronous. In terms of percentage of the adult volume, for the left side (both sides grew at a similar rate), the three structures grew at a fast pace between E59 and P30. Thus, at E59 their respective percentages relative to adult volume were 23.7, 29.8 and 22.6% and by P30 the percentages were within adult range (85.2, 115.1 and 87.5%, respectively). Starting at P30, for the thalamus and at P45 for the caudate n., there was a consistent tendency to an overgrow which ranged between 4.3 and 30.9% (at P180, P<0.5) for the caudate and between 0.3 and 15.1% for the thalamus. In addition, starting at P30, the right thalamus tended to be consistently larger than the left by a margin ranging between 0.5 and 11.2% (P120, P<0.05). The red n. grew at a different, slower pace. Starting from a fetal volume equivalent to an 18.6% of adult size, its volume was only a 61.0% of the adult value at P30 and came within range of adulthood size only by P60 (81. 3%). Neither the s. nigra nor the red n. showed any consistent tendency to overgrow or to asymmetry. These findings are discussed in the context of the literature. Furthermore, we discuss general conclusions and considerations pertaining to both papers as well as draw comparisons with the maturational time tables of other developmental landmarks in cats. Finally, in a comparison with growth of human brain structures, we point at the limitations and complexities involved in studying human material and, noting interspecies similarities, we propose that the present data from an advanced gyrencephalic mammal may form the bases for a model of structures maturation in humans.

Developmental neuroplasticity in a model of cerebral hemispherectomy and stroke

Cerebral hemispherectomy, a last resort treatment for childhood epilepsy, is a standard procedure which dramatically illustrates the resilience of the brain to extensive damage. If this operation, also mimicking long-term, extensive unilateral capsular stroke, is performed in postnatal cats of up to 60 days of age, there is a remarkable recovery/sparing of neurological functions that is not seen when the lesion occurs during late fetal life or in adulthood. A long-term effect at all ages is loss of neurons in bilateral brain areas remote from the resection site. This is pronounced in adult cats and shows intriguing, paradoxical features in fetal animals, but is substantially attenuated in neonatal cats. Similarly, large-scale reinnervation of subcortical sites (sprouting) by neurons of the remaining, intact hemisphere is prominent in young cats, but not in fetal or adult animals. These and other restorative processes (described herein) in young postnatal animals are matched by relatively higher rates of local cerebral glucose utilization, supporting the notion that they underlie the improved behavioral outcome. Thus, during a critical, defined stage of maturation, presumably common to higher mammals including humans, the brain entirely remodels itself in response to extensive but focal injury. Perhaps the molecular environment allowing for rescue of neurons and enhanced reinnervation at a specific developmental stage could be recreated in subjects with brain lesions at less favorable ages, thereby helping to restore circuitry and spare neurons. However, replacement via transplantation of neurons eliminated by the damage appears to be crucial in attempts to further preserve cells located remotely but yet destined to die or decrease in size. This article presents abundant evidence to show that there is a surprisingly comprehensive long-term morphological remodeling of the entire brain after extensive unilateral damage and that this occurs preferentially during a discrete period of early life. Additional evidence strongly suggests that the remodeling underlies the outstanding behavioral and functional recovery/sparing following early cerebral hemispherectomy. We argue that this period of reduced brain vulnerability to injury also exists in other higher mammals, including man, and suggest ways to enhance restorative processes after stroke/hemispherectomy occurring at other ages.

Effects of a restricted unilateral neocortical lesion upon cerebral glucose and oxidative metabolisms in fetal and neonatal cats

The present study was designed to measure cerebral glucose and oxidative metabolisms and to assess relationships with previously identified morphological changes in adult cats with a unilateral, restricted neocortical lesion sustained either during fetal life or neonatally. Local cerebral metabolic rates for glucose (LCMR(glc)) were measured using the [14C]2-deoxy-D-glucose (2 DG) autoradiography method and oxidative capacity was determined using cytochrome oxidase histochemistry (C.O.). Only glucose metabolism in the fetal-lesioned cats was affected substantially. There was a global decrease (31.0% relative to controls) of the LCMR(glc) for both cerebral hemispheres while focal decreases were seen mainly in thalamic and neostriatal nuclei (and reaching declines of over 50%). Cats with a neonatal lesion showed only a tendency to such declines (19.5% and 22.0% for the right and left hemispheres, respectively). C.O. values were not affected significantly either globally or locally in any of the age-at-lesion groups. In previous work using fetal animals with similar lesions, morphological evidence of subcortical neuropile degeneration was not observed; instead, a marked decrease in size of the ipsilateral remaining neocortex and a pronounced distortion of gyri and sulci patterns bilaterally were found. In this context, we propose that in the fetal-lesioned cats, there was a widespread lesion-induced decrease in corticofugal (and transcortical) synaptic inputs which was responsible for a decline in functional (synaptic) activities, and that this, in turn, caused a downturn in glucose utilization. In the neonatal cats minor degeneration, coupled with lack of reinnervation, would account for the tendency to 2 DG declines. These results indicate that the long-term metabolic response of the fetal brain to injury is also less adaptive than that of the neonatal brain. Since standard methods are available to measure cerebral metabolism in humans, our studies in animal models may help understanding the long term physiological consequences of developmental focal brain damage in patients as well as to predict the relationships between cerebral metabolism and the underlying long-term morphological effects of such lesions.

A critical maturational period of reduced brain vulnerability to developmental injury. I. Behavioral studies in cats

Groups of cats with resection of the neocortex of the left cerebral hemisphere at postnatal (P) ages (in days) 5-15 (P10), 30 (P30), 60 (P60), 90 (P90), 120 (P120), and in adulthood, were compared using a comprehensive battery of 16 neurobehavioral tests administered when they were at least 6 months post-lesion. For all behaviors, except 3 (including the paw contact placing reaction which never recovered), the performance was significantly better for the cats lesioned between P10 and P30 compared to cats lesioned at older ages. For 10 of the behaviors, the transition from age-at-lesion P30 to P60 was rather abrupt and characterized by a significant increment in impairments. However, cats with the resection at ages P90 and P120 still showed some behavioral advantage over the adult-lesioned animals. Overall, for most of the behaviors tested, there was a significant linear trend for an increase in the magnitude of impairments across the entire age-at-lesion range. We previously reported that cats with a unilateral frontal cortical lesion sustained during the late fetal life showed substantial behavioral impairments, while animals with a similar resection sustained early postnatally exhibited minimal abnormalities. These findings, together with the present results, indicate that the long-term behavioral outcome of neocortical injury is best when the lesion is sustained during a discrete period of the life of the cat. This period extends from about fetal age 55 days (the oldest lesion age in our fetal studies) to about P60, as shown in the present paper. For these reasons, we propose that there is a Critical Maturational Period (CMP) for optimal post injury brain and behavioral restoration. We hypothesize that this span of reduced vulnerability is linked to specific developmental morphological events which occur during the same time period. Since, as discussed, such ontogenetic events also occur in other mammal species (albeit at different chronological ages), we further propose that the timing of the CMP as delineated in cats, can be extrapolated to other higher mammals species including humans.