Regional difference in sulcal infolding progression correlated with cerebral cortical expansion in cynomolgus monkey fetuses.

The present study aimed to specify the cerebral sulci developed by cortical expansion in cynomolgus monkey fetuses. The degree of sulcal infolding was evaluated by the gyrification index (GI), which was quantified using ex vivo magnetic resonance imaging. The correlation of cortical volume with the sulcal GI was most frequent during embryonic days (EDs) 100 to 120. Interestingly, the high correlation was marked during EDs 140 to 150 in restricted primary sulci in prefrontal, parietotemporal and medial temporal regions. The present results suggest that cortical expansion is involved in gyral demarcation by sulcal infolding, followed by the sulcal infolding progression in phylogenetically-newer cortices.

Postnatal change in sulcal length asymmetry in cerebrum of cynomolgus monkeys (Macaca fascicularis).

The purpose of this study was to determine the timing of the onset of adult-type sulcal length asymmetry during postnatal development of the male cynomolgus monkey cerebrum. The monkey brain has already reached adult size by 3 months of age, although the body weight only represents 1/8 of the adult body weight by that time. The fronto-occipital length and the cerebral width also reached adult levels by that postnatal age with no left/right bias. Consistently, lengths of the major primary sulci reached adult levels by 3 months of age, and then decreased slightly in sexually mature monkeys (4-6.5 years of age). Asymmetry quotient analysis showed that sulcal length asymmetry patterns gradually changed during postnatal development. The male adult pattern of sulcal length asymmetry was acquired after 24 months of age. In particular, age-dependent rightward lateralization of the arcuate sulcal length was revealed during cerebral maturation by three-way ANOVA. The results suggest that the regional difference in cerebral maturation from adolescence to young adulthood modifies the sulcal morphology with characteristic asymmetric patterns in male cynomolgus monkeys.

Fetal gyrification in cynomolgus monkeys: a concept of developmental stages of gyrification.

Our article summarizes a series of studies about fetal gyrification and its relation to cerebral growth in cynomolgus monkeys. Based on the cerebral growth (i.e., brain weight, cerebral volume, and frontooccipital length of the cerebral hemisphere) and the developmental pattern of gyrification in each sulcus of cynomolgus monkeys, we divided the gyrification process into four stages: Stage 1. Demarcation of cerebral lobes and limbic gyri; Stage 2. Demarcation of neocortical gyri; Stage 3. Emergence of secondary and tertiary sulci; and Stage 4. Growth of sulcal length and depth. Each stage of those gyrification processes was influenced by different developmental events, such as the emergence of corticocortical long-associative fiber tracts, cortical maturations, and subcortical white-matter development. This is the first report to systematically propose gyrification processes closely related to the order of phyologenetical development of the cerebral cortex in primates.

Neuroanatomic and magnetic resonance imaging references for normal development of cerebral sulci of laboratory primate, cynomolgus monkeys (Macaca fascicularis).

Cynomolgus monkey (Macaca fascicularis) is a popular laboratory primate belonging to Old World monkeys, which are the group most closely related to humans except for the apes. This paper summarizes a series of our studies regarding the development of cerebral sulci and gyri in this primate, and the stated possibility of evaluation of the sulcal development for assessing the developmental toxicity testing. The cerebrum of cynomolgus monkeys experienced a regular sequence of emergence of sulci and gyri on gross observation while such timetables corresponded to those obtained by magnetic resonance imaging (MRI) with a lag time of 10-30 days. When the timetables for the emergence of anatomically identical primary sulci and gyri were compared between cynomolgus monkeys and humans, their chronological sequences were comparable, while some sulci and gyri located on the phylogenetically newer cortical region in humans emerged earlier in monkeys. The present paper further indicates brief procedures for evaluating cerebral abnormalities and/or maturity using brain specimens without MRI measurements. The primary sulcal lengths measured by the 'cotton thread' method were a brief index of the degree of regional gyrification. As the development of a calcarine sulcus was closely correlated with morphological maturation of the lateral ventricle, which changed drastically during embryonic days (EDs) 90-100, the cerebral maturity on ED 100 could be evaluated by the infolding of that sulcus. Thus, the present paper provides gross anatomical and MRI references and brief procedures for investigating the normality of the development of cerebral sulci and gyri of laboratory primates, cynomolgus monkeys.

Correlation between formation of the calcarine sulcus and morphological maturation of the lateral ventricle in cynomolgus monkey fetuses.

In the present study developmental changes in the cerebral sulci and volumes of subcortical and archicortical structures of the cerebrum in cynomolgus monkey fetuses were examined with T(1)-weighted magnetic resonance (MR) images in 3D. On the embryonic day (ED) 90, the lateral ventricle had still an immature vesicular shape in the occipital region of the cerebrum, and it dramatically closed its lumen by ED 100. In that period the calcarine sulcus progressively infolded from the medial surface of the cerebral hemisphere narrowing the lumen of the lateral ventricle in the occipital region. Volume of the lateral ventricle decreased in the period ED 90-100, increasing afterwards in spite of increasing volumes of subcortical and archicortical structures such as the caudate nucleus, putamen, globus pallidus, amygdala and hippocampal formation. During the same time, the volume of the germinal matrix around lateral ventricles decreased to disappear completely by ED 120. These results suggest that the morphological maturation of lateral ventricle is linked to the development of calcarine sulcus in cynomolgus monkey fetuses. The degree of infolding of calcarine sulcus on ED 100 would be useful as a gross anatomical landmark for evaluating the cerebral maturation in cynomolgus monkey fetuses.

Sexual dimorphism of sulcal length asymmetry in the cerebrum of adult cynomolgus monkeys (Macaca fascicularis).

The present study aimed to quantitatively clarify the gross anatomical asymmetry and sexual dimorphism of the cerebral hemispheres of cynomolgus monkeys. While the fronto-occipital length of the right and left cerebral hemispheres was not different between sexes, a statistically significant rightward asymmetry was detected in the cerebral width at the perisylvian region in females, but not in males (narrower width of the left side in the females). An asymmetry quotient of the sulcal lengths revealed a rightward asymmetry in the inferior occipital sulcus and a leftward asymmetry in the central and intraparietal sulci in both sexes. However, the laterality of the lengths of other sulci was different for males and females. The arcuate sulcus was directed rightward in males but there was no rightward bias in females. Interestingly, the principle sulcus and lateral fissure were left-lateralized in the males, but right-lateralized in the females. The results suggest that lateralization patterns are regionally and sexually different in the cerebrum of cynomolgus monkeys. The present results provide a reference for quantitatively evaluating the normality of the cerebral cortical morphology in cynomolgus monkeys.

Developmental toxicity of dibutyltin dichloride given on three consecutive days during organogenesis in cynomolgus monkeys.

We previously reported that the administration of dibutyltin dichloride (DBTCl) by nasogastric intubation during the entire period of organogenesis, days 20-50 of pregnancy, was embryolethal, but not teratogenic, in cynomolgus monkeys. The present study was conducted to further evaluate the developmental toxicity of DBTCl given to pregnant monkeys on 3 consecutive days during organogenesis. Cynomolgus monkeys were given DBTCl at 7.5 mg/kg body weight/day by nasogastric intubation on days 19-21, 21-23, 24-26, 26-28, 29-31, 31-33, or 34-36 of pregnancy, and the pregnancy outcome was determined on day 100 of pregnancy. Embryonic/fetal loss was observed in 1 female given DBTCl on days 19-21, 2 females given DBTCl on days 24-26, and 1 female given DBTCl on days 34-36. There were no effects of DBTCl on developmental parameters in surviving fetuses, including fetal body weight, crown-rump length, tail length, or placental weight. No external, internal, or skeletal malformations were detected in fetuses in any group. DBTCl did not affect the incidence of fetuses with skeletal variation or skeletal ossification of fetuses. These data confirm our previous findings that DBTCl was embryolethal, but not teratogenic, in cynomolgus monkeys.

Developments of sulcal pattern and subcortical structures of the forebrain in cynomolgus monkey fetuses: 7-tesla magnetic resonance imaging provides high reproducibility of gross structural changes.

The aim of this study was to spatio-temporally clarify gross structural changes in the forebrain of cynomolgus monkey fetuses using 7-tesla magnetic resonance imaging (MRI). T(1)-weighted coronal, horizontal, and sagittal MR slices of fixed left cerebral hemispheres were obtained from one male fetus at embryonic days (EDs) 70-150. The timetable for fetal sulcation by MRI was in good agreement with that by gross observations, with a lag time of 10-30 days. A difference in detectability of some sulci seemed to be associated with the length, depth, width, and location of the sulci. Furthermore, MRI clarified the embryonic days of the emergence of the callosal (ED 70) and circular (ED 90) sulci, which remained unpredictable under gross observations. Also made visible by the present MRI were subcortical structures of the forebrain such as the caudate nucleus, globus pallidus, putamen, major subdivisions of the thalamus, and hippocampal formation. Their adult-like features were formed by ED 100, corresponding to the onset of a signal enhancement in the gray matter, which reflects neuronal maturation. The results reveal a highly reproducible level of gross structural changes in the forebrain using a high spatial 7-tesla MRI. The present MRI study clarified some changes that are difficult to demonstrate nondestructively using only gross observations, for example, the development of cerebral sulci located on the deep portions of the cortex, as well as cortical and subcortical neuronal maturation.

Repeated-dose and reproductive toxicity of the ultraviolet absorber 2-(3',5'-di- tert-butyl-2'-hydroxyphenyl)-5-chlorobenzotriazole in rats.

2-(3',5'-Di-tert-butyl-2'-hydroxyphenyl)-5-chlorobenzotriazole (DBHCB) is widely used as an ultraviolet (UV) absorber. In this study, the repeated dose and reproductive toxicity of DBHCB was evaluated in rats. Crj:CD(SD)IGS rats were given DBHCB by gavage at 0, 2.5, 25, or 250 mg/kg/d. Male and female rats were dosed beginning 28 d before mating, and each female rat was mated with a male rat of the same dosage group. Males were dosed for a total of 56-57 d, and females were dosed for a total of 55-69 d up to Day 3 of lactation throughout the mating and pregnancy periods. Ten males from each group were killed on the next day of the last administration, and 10 females were killed on Days 4-6 after parturition. Five rats/sex treated at 0 and 250 mg/kg/d for 56 d were then kept without treatment for 14 d (recovery period). No deaths were found in any group. No effects of DBHCB on general condition, body weight, food consumption, or reproductive/developmental parameters were observed. Significant increases in serum albumin and an albumin/globulin ratio at 25 mg/kg/d and higher and alkaline phosphatase levels at 250 mg/kg/d were noted in males. The absolute and relative weights of the liver were significantly increased in males at 25 mg/kg/d and higher. Significantly increased serum albumin and absolute and relative liver weight were also found in males at 250 mg/kg/d after the recovery period. No changes in these parameters were observed in females of any DBHCB-treated groups. No significant changes in organ histopathology were found in males or females. These findings indicated a sex difference in the toxicity of DBHCB in rats.

Development of cerebral sulci and gyri in fetuses of cynomolgus monkeys (Macaca fascicularis). II. Gross observation of the medial surface.

This study aimed to clarify chronological sequences of the appearances of sulci and gyri on the medial cerebral surface and its relation to the regional development of the cerebrum in cynomolgus monkeys. The lengths of cingulate and calcarine sulci were measured, and the ratios of these lengths to fronto-occipital length were estimated as indices of the size of the "frontoparietal" and "occipital" regions, respectively. The relative length of cingulate sulcus showed a biphasic increase: a slow phase from EDs 100 to 110, and a rapid phase from EDs 110 to 130. The gyri in the "frontoparietal region" were convoluted in the limbic cortex during the initial slow phase and in the neocortical region during the rapid phase. The relative length of calcarine sulcus lineally increased between EDs 90 and 130, and the gyri in the "occipital region" generated in a dorso-ventral manner: the gyrus convolutions occurred first in the "phylogenetically older" striate and dorsal extrastriate cortices, and then in the "phylogenetically newer" ventral extrastriate cortex. The results suggest that the chronological order of appearance of sulci and gyri is closely associated with the order of phylogenetical development of the cerebral cortex. The present study provides a standard reference for the development of cerebral sulci and gyri of cynomolgus monkeys together with our previous study (Fukunishi et al. Anat Embryol 211:757-764, 2006).

Developmental toxicity of dibutyltin dichloride in cynomolgus monkeys.

Dibutyltin dichloride (DBTCl) has been shown to be teratogenic in rats. The present study was conducted to determine the teratogenic potential of DBTCl given to pregnant monkeys during the entire period of organogenesis. Cynomolgus monkeys were dosed once daily by nasogastric intubation with DBTCl at 0, 2.5 or 3.8 mg/kg on days 20-50 of pregnancy, the whole period of organogenesis. The pregnancy outcome was determined on day 100 of pregnancy. In both DBTCl-treated groups, a significant increase in the incidence of pregnant females with soft stool and/or diarrhea, and with yellowish stool was observed. Maternal body weight gain at 3.8 mg/kg and food consumption at 2.5 and 3.8 mg/kg were decreased during the administration period. The survival rate of fetuses at terminal cesarean sectioning was decreased in the DBTCl-treated groups and significantly decreased at 2.5 mg/kg. There were no changes in the developmental parameters of surviving fetuses, including fetal body weight, crown-rump length, tail length, sex ratio, anogenital distance and placental weight, in the DBTCl-treated groups. No external, internal or skeletal malformations were found in the fetuses in any group. Although internal and skeletal variations were found, no difference in the incidence of fetal variation was noted between the control and DBTCl-treated groups. No effect on skeletal ossification was observed in fetuses in the DBTCl-treated groups. The data demonstrate that DBTCl is embryolethal but not teratogenic in cynomolgus monkeys.

Evaluation of developmental toxicity of ultraviolet absorber 2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)-5-chlorobenzotriazole in rats.

2-(3',5'-Di-tert-butyl-2'-hydroxyphenyl)-5-chlorobenzotriazole (DBHCB) is widely used as a UV absorber. In this study, the developmental toxicity of DBHCB was evaluated in rats. Pregnant rats were given DBHCB at 0, 62.5, 250, or 1000 mg kg(-1) day(-1) by gavage on days 5-19 of pregnancy. No deaths were observed in the pregnant rats of any group. No effect of DBHCB on the general conditions, body weight gain, or feed consumption was observed in the pregnant rats. There were no changes in the ovarian weight, gravid uterine weight, or necropsy findings in the maternal rats of the DBHCB-treated groups. No significant effects of DBHCB were found in the number of corpora lutea, implantations, live fetuses, resorptions or dead fetuses, incidence of pre- or postimplantation embryonic loss, viability of fetuses, fetal weight, or sex ratio of live fetuses. No significant difference in the incidence of fetuses with malformations or variations or degree of ossification was detected between the DBHCB-treated and control groups.