NR2F1 regulates regional progenitor dynamics in the mouse neocortex and cortical gyrification in BBSOAS patients.

The relationships between impaired cortical development and consequent malformations in neurodevelopmental disorders, as well as the genes implicated in these processes, are not fully elucidated to date. In this study, we report six novel cases of patients affected by BBSOAS (Boonstra-Bosch-Schaff optic atrophy syndrome), a newly emerging rare neurodevelopmental disorder, caused by loss-of-function mutations of the transcriptional regulator NR2F1. Young patients with NR2F1 haploinsufficiency display mild to moderate intellectual disability and show reproducible polymicrogyria-like brain malformations in the parietal and occipital cortex. Using a recently established BBSOAS mouse model, we found that Nr2f1 regionally controls long-term self-renewal of neural progenitor cells via modulation of cell cycle genes and key cortical development master genes, such as Pax6. In the human fetal cortex, distinct NR2F1 expression levels encompass gyri and sulci and correlate with local degrees of neurogenic activity. In addition, reduced NR2F1 levels in cerebral organoids affect neurogenesis and PAX6 expression. We propose NR2F1 as an area-specific regulator of mouse and human brain morphology and a novel causative gene of abnormal gyrification.

T2* relaxometry of fetal brain at 1.5 Tesla using a motion tolerant method.

PURPOSE: The aim of this study was to determine T2* values for the fetal brain in utero and to compare them with previously reported values in preterm and term neonates. Knowledge of T2* may be useful for assessing brain development, brain abnormalities, and for optimizing functional imaging studies. METHODS: Maternal respiration and unpredictable fetal motion mean that conventional multishot acquisition techniques used in adult T2* relaxometry studies are not practical. Single shot multiecho echo planar imaging was used as a rapid method for measuring fetal T2* by effectively freezing intra-slice motion. RESULTS: T2* determined from a sample of 24 subjects correlated negatively with gestational age with mean values of 220 ms (±45) for frontal white matter, 159 ms (±32) for thalamic gray matter, and 236 ms (±45) for occipital white matter. CONCLUSION: Fetal T2* values are higher than those previously reported for preterm neonates and decline with a consistent trend across gestational age. The data suggest that longer than usual echo times or direct T2* measurement should be considered when performing fetal fMRI to reach optimal BOLD sensitivity.

Sequential analysis of the normal fetal fissures with three-dimensional ultrasound: a longitudinal study.

OBJECTIVE: To perform a sequential analysis of the main cortical fissures in normal fetuses using 3D ultrasound. METHODS: A cohort of patients with uncomplicated singleton pregnancies underwent three consecutive transabdominal scans at 19-21, 26-28 and 30-34 weeks. Volumes of the fetal head were acquired and searched in the multiplanar mode for the following cortical fissures: sylvian, parieto-occipital, calcarine, hippocampus and cingulate. A qualitative analysis of these sulci was performed in each volume by an experienced operator (A) and a trainee (B). By placing the dot on the sulcus in one plane, it was evaluated whether it was visible also in other planes. RESULTS: Fifty patients were included in the study. At 19-21 weeks, the sylvian and parieto-occipital sulci were visualized on at least one plane by both operators in all cases. At 26-28 weeks, all fissures were visualized by both operators on at least one plane, with no significant difference between the performances of the two operators. At 30-34 weeks, a mild overall decline in the accuracy of identification of all the cerebral fissures was observed. CONCLUSIONS: 3D multiplanar mode allows a systematic evaluation of the cortical fissures in normal fetuses since midtrimester.

Usability of virtual-reality simulation training in obstetric ultrasonography: a prospective cohort study.

OBJECTIVE: To assess the usability of virtual-reality (VR) simulation for obstetric ultrasound trainees. METHODS: Twenty-six participants were recruited: 18 obstetric ultrasound trainees (with little formal ultrasonography training) and eight certified experts. All performed five sequential VR-simulated crown-rump length (CRL) scans in a single session and three repetitions of biparietal diameter (BPD), occipitofrontal diameter (OFD) and femur length (FL) measurements. Outcome measures included mean percentage deviation from target for all measurements. Time taken to perform each type of scan was recorded. RESULTS: The mean percentage difference for the first scan was significantly greater for the trainee group than for the expert group for BPD (P = 0.035), OFD (P = 0.010) and FL (P = 0.008) and for time taken for the first CRL (P < 0.001) and fetal biometry (including BPD, OFD and FL measurements) scan (P < 0.001), demonstrating that trainees were initially significantly less accurate and less efficient. Over subsequent scans, the trainees became more accurate for all measurements with a significant improvement shown for OFD and FL (P < 0.05). The time taken for trainees to complete CRL and fetal biometry scans decreased significantly (all P < 0.05) with repetition, to near-expert efficiency. CONCLUSIONS: All participants were able to use the simulator and produce clinically meaningful biometry results. With repetition, beginners quickly approached near-expert levels of accuracy and speed. These data demonstrate that obstetricians with minimal experience can improve their ultrasonographic skills with short-phase VR-simulation training. The speed of improvement suggests that VR simulation might be useful as a warm-up exercise before clinical training sessions in order to reduce their impact on clinical service.

Reference ranges for fetal brain fissure development on 3-dimensional sonography in the multiplanar mode.

OBJECTIVES: To determine reference ranges for measurements of fetal cerebral fissures by 3-dimensional (3D) sonography in the multiplanar mode and to evaluate the reliability and concordance of these measurements. METHODS: A cross-sectional study was conducted on 393 women with normal pregnancies at 22 weeks to 33 weeks 6 days. The distances between the internal bone plate of the fetal calvaria and the sylvian, parieto-occipital, hippocampal, and calcarine fissures were assessed. To obtain the distances for the first 3 fissures, a 3D sweep was made in the axial plane, at the level of the lateral ventricles. To obtain the distance for the calcarine fissure, a coronal sweep was used, at the level of the occipital lobes. To evaluate the correlation between the fissures and gestational age, polynomial regression was performed with adjustments using the coefficient of determination (R(2)). Reliability was determined with intraclass correlation coefficients and concordance with concordance limits. RESULTS: The mean distances ± SD to the sylvian, parieto-occipital, hippocampal, and calcarine fissures were 10.42 ± 2.28, 22.38 ± 3.23, 24.88 ± 4.67, and 21.19 ± 2.73 mm, respectively. These distances correlated with gestational age such that the best fit with the linear equation produced R(2) values of 0.582, 0.627, 0.860, and 0.458 for the sylvian, parieto-occipital, hippocampal, and calcarine fissures. Reliability analyses showed intraobserver and interobserver intraclass correlation coefficients of 0.90 to 0.95 and 0.85 to 0.97. The concordance limits were-1.33 to 1.30 and -2.38 to 2.28 mm for the intraobserver evaluation and -1.60 to 2.57 and -3.51 to 2.73 mm for the interobserver evaluation. CONCLUSIONS: Cerebral fissures can be measured by 3D sonography at 22 to 33 weeks of pregnancy with acceptable reliability and concordance. Reference ranges for this gestational period have thus been described.

Subcortical and cortical structural central nervous system changes and attention processing deficits in preschool-aged children with prenatal methamphetamine and tobacco exposure.

OBJECTIVE: To examine the independent contributions of prenatal methamphetamine exposure (PME) and prenatal tobacco exposure (PTE) on brain morphology among a sample of nonalcohol-exposed 3- to 5-year-old children followed prospectively since birth. STUDY DESIGN: The sample included 20 children with PME (19 with PTE) and 15 comparison children (7 with PTE), matched on race, birth weight, maternal education and type of insurance. Subcortical and cortical volumes and cortical thickness measures were derived through an automated segmentation procedure from T1-weighted structural magnetic resonance images obtained on unsedated children. Attention was assessed using the computerized Conners' Kiddie Continuous Performance Test Version 5 (K-CPT™ V.5). PME effects on subcortical and cortical brain volumes and cortical thickness were tested by general linear model with type III sum of squares, adjusting for PTE, prenatal marijuana exposure, age at time of scan, gender, handedness, pulse sequence and total intracranial volume (for volumetric outcomes). A similar analysis was done for PTE effects on subcortical and cortical brain volumes and thickness, adjusting for PME and the above covariates. RESULTS: Children with PME had significantly reduced caudate nucleus volumes and cortical thickness increases in perisylvian and orbital-frontal cortices. In contrast, children with PTE showed cortical thinning in perisylvian and lateral occipital cortices and volumetric increases in frontal regions and decreases in anterior cingulate. PME was positively related and caudate volume was inversely related to K-CPT reaction time by inter-stimulus interval, a measure of the ability to adjust to changing task demands, suggesting that children with PME may have subtle attentional deficits mediated by caudate volume reductions. CONCLUSIONS: Our results suggest that PME and PTE may have distinct differential cortical effects on the developing central nervous system. Additionally, PME may be associated with subtle deficits in attention mediated by caudate volume reductions.

Fetal brain asymmetry: in utero sonographic study of normal fetuses.

OBJECTIVE: The objective of the study was to evaluate the magnitude of normal fetal brain asymmetry. STUDY DESIGN: This was a prospective study. Normal fetuses between 19-28 weeks of gestation were studied. The cerebral atria, occipital cortex, and hemispheres in both sides were measured. The difference between each side was evaluated and was correlated with sex, head biometry, and estimated weight. RESULTS: Four hundred six fetuses were studied. Mean atrial width was larger in the males and on the left side (5.2% and 6.5%, respectively). Mean cortical width was 2.6% larger in males but 5.5% thinner on the left side. Mean hemisphere width was larger in males and on the left side (2.3% and 1.5%, respectively). The atria and the cortex presented an inverse relationship regarding fetal growth parameters. CONCLUSION: Brain asymmetry represents normal fetal brain developmental phenomena. It is sex dependent and lateralized in most cases to the left. Lateralization was more accentuated in males.

Regulation of area identity in the mammalian neocortex by Emx2 and Pax6.

The contribution of extrinsic and genetic mechanisms in determining areas of the mammalian neocortex has been a contested issue. This study analyzes the roles of the regulatory genes Emx2 and Pax6, which are expressed in opposing gradients in the neocortical ventricular zone, in specifying areas. Changes in the patterning of molecular markers and area-specific connections between the cortex and thalamus suggest that arealization of the neocortex is disproportionately altered in Emx2 and Pax6 mutant mice in opposing manners predicted from their countergradients of expression: rostral areas expand and caudal areas contract in Emx2 mutants, whereas the opposite effect is seen in Pax6 mutants. These findings suggest that Emx2 and Pax6 cooperate to regulate arealization of the neocortex and to confer area identity to cortical cells.

Morphologic Evolution and Coordinated Development of the Fetal Lateral Ventricles in the Second and Third Trimesters.

BACKGROUND AND PURPOSE: Few investigators have studied the lateral ventricle formation related to the development of the calcarine sulcus. Our purpose was to establish the relationship between the lateral ventricles and the calcarine sulcus in the second and third trimesters. MATERIALS AND METHODS: Fetal brain MR imaging (3T and 7T) was performed in 84 fetuses at 14-35 gestational weeks. The lateral ventricles and calcarine sulcus were 3D-reconstructed, and quantitative measurements were obtained. RESULTS: The lateral ventricle volume decreases slowly at 14-23 gestational weeks and then increases rapidly at 24-35 gestational weeks. The depth and length of the calcarine sulcus develop with the increase in gestational weeks, leading to be squeezed in the lateral ventricle posterior horn. A linear correlation occurs between the calcarine sulcus length and posterior horn length: Right-length = 2.4204 (LPH) - 27.5706, Left-length = 2.0939 (LPH) - 23.4099. CONCLUSIONS: The variation of lateral ventricle volume evolved from a slow to rapid increase at 14-35 gestational weeks. The shrinkage in the lateral ventricle posterior horn is accompanied by the development of the calcarine sulcus, resulting in a better linear correlation between the calcarine sulcus length and the posterior horn length. The present results are valuable in elucidating the evolution of lateral ventricle development and provide clues for the diagnosis of lateral ventricle abnormalities in the prenatal examination.

Heterotopic, not homotopic, fetal occipital allografts in adult hosts project to visual-related extracortical targets.

PURPOSE: Fetal occipital allografts implanted into the posterior cortex of adult mice project massively throughout the ipsilateral pallium of the host, but rarely outside this domain (Gaillard et al., 2004). The present study was undertaken to examine in detail whether this pattern is specific to graft location. METHODS: Cortical fragments corresponding to presumptive occipital areas were harvested from E15 mice fetuses expressing ubiquitously the eGFP protein, and implanted in correct (homotopic) and incorrect (heterotopic) cortical loci in wild-type adults. Two months later, efferents were detected by immunohistochemistry and quantified on selected DAB-treated sections. RESULTS: The present findings show (i) that robust projections are present in the ipsilateral host cortex regardless of the graft location; (ii) that 55% the grafts located in parietal and frontal cortices have obvious but sparse callosal and subcortical projections; and (iii) that grafts placed in occipital areas never contact ipsilateral subcortical targets, likely because graft-related axons are unable to cross obliquely the thalamocortical fascicles in the underlying white matter. CONCLUSIONS: These puzzling results question the use of transplantation strategies for repairing damaged networks in adults where rewiring involves complex white matter trajectories.

[Sonographic cerebral sulcal pattern in normal fetuses]. / Repères échographiques de gyration cérébrale foetale normale.

PURPOSE: Define normal sulcation patterns and their chronological order of appearance on transabdominal ultrasound by comparing them with brain maturation references available in fetopathological studies and MRI findings. PATIENTS AND METHODS: By means of a prospective study, 158 normal fetal brains aged 21 to 34 gestational weeks have been analyzed with standardized data by transabdominal ultrasound in eleven different views using axial, coronal and sagittal orientation. RESULTS: The sequential development of cerebral sulci has been described according to the gestational age. This chronology was consistent with anatomo-pathologic references presenting a mean late period of one week and with MRI but without any late period. This study is available on the following website: CONCLUSION: This ultrasound study provides accurate landmarks and imaging features of normal fetal brain sulcation. The analysis and the knowledge of this sulcation provide better understanding of the brain cortex maturation and may be helpful in diagnosing brain diseases.

Telencephalic Flexure and Malformations of the Lateral Cerebral (Sylvian) Fissure.

After sagittal division of the prosencephalon at 4.5 weeks of gestation, the early fetal cerebral hemisphere bends or rotates posteroventrally from seven weeks of gestation. The posterior pole of the telencephalon thus becomes not the occipital but the temporal lobe as the telencephalic flexure forms the operculum and finally the lateral cerebral or Sylvian fissure. The ventral part is infolded to become the insula. The frontal and temporal lips of the Sylvian fissure, as well as the insula, all derive from the ventral margin of the primitive telencephalon, hence may be influenced by genetic mutations with a ventrodorsal gradient of expression. The telencephalic flexure also contributes to a shift of the hippocampus from a dorsal to a ventral position, the early rostral pole of the hippocampus becoming caudal and dorsal becoming ventral. The occipital horn is the most recent recess of the lateral ventricle, hence most vulnerable to anatomic variations that affect the calcarine fissure. Many major malformations include lack of telencephalic flexure (holoprosencephaly, extreme micrencephaly) or dysplastic Sylvian fissure (lissencephalies, hemimegalencephaly, schizencephaly). Although fissures and sulci are genetically programmed, mechanical forces of growth and volume expansion are proposed to be mainly extrinsic (including ventricles) for fissures and intrinsic for sulci. In fetal hydrocephalus, the telencephalic flexure is less affected because ventricular dilatation occurs later in gestation. Flexures can be detected prenatally by ultrasound and fetal magnetic resonance imaging and should be described neuropathologically in cerebral malformations.

Regional differences in neurotrophin availability regulate selective expression of VGF in the developing limbic cortex.

Gene and protein expression patterns in the cerebral cortex are complex and often change spatially and temporally through development. The signals that regulate these patterns are primarily unknown. In the present study, we focus on the regulation of VGF expression, which is limited to limbic cortical areas early in development but later expands into sensory and motor areas. We isolated neurons from embryonic day 17 rat cortex and demonstrate that the profile of VGF expression in perirhinal (expressing) and occipital (nonexpressing) populations in vitro is similar to that in the perinatal cortex in vivo. The addition of neutralizing neurotrophin antibodies indicates that endogenous brain-derived neurotrophic factor (BDNF) is necessary for the normal complement of VGF-expressing neurons in the perirhinal cortex, although endogenous neurotrophin-3 (NT-3) regulates the expression of VGF in a subpopulation of cells. ELISA analysis demonstrates that there is significantly more BDNF present in the perirhinal cortex compared with the occipital cortex in the perinatal period. However, the total amount of NT-3 is similar between the two regions and, moreover, there is considerably more NT-3 than BDNF in both areas, a finding seemingly in conflict with regional VGF expression. Quantification of the extracellular levels of neurotrophins in perirhinal and occipital cultures using ELISA in situ analysis indicates that perirhinal neurons release significantly more BDNF than the occipital population. Furthermore, the amount of NT-3 released by the perirhinal neurons is significantly less than the amount of BDNF. Local injection of BDNF in vivo into a normally negative VGF region results in robust ectopic expression of VGF. These data suggest that the local availability of specific neurotrophins for receptor occupation, rather than the total amount of neurotrophin, is a critical parameter in determining the selective expression of VGF in the developing limbic cortex.

Development of fetal retina, tectum, and cortex transplanted to the superior colliculus of adult rats.

Earlier studies showed that embryonic retina, cortex, or tectum transplanted adjacent to the superior colliculus of newborn host rats differentiated many of the histological features appropriate for the donor region and developed interconnections with the host nervous system. In the study presented here, the same regions were transplanted to the brain of adult host rats and the development of these transplants was compared to those into newborn hosts. Retina, rostral tectum, or occipital cortex was dissected from donor rat embryos on gestational day 14 or 15. A portion of cortex was aspirated in 2-month-old host rats to expose the right superior colliculus, and one of the donor tissues was placed adjacent to the colliculus in each host. Two to 4 months after transplantation, transplant histology and neuronal interconnections between the transplant and host nervous system were studied by using Nissl and neurofibrillar stains and 3H-proline and HRP tract tracing techniques. Four main points can be drawn from these results. First, 80% of the transplants survived in adult hosts - a percentage comparable to that found in newborn hosts. Second, each of the types of tissues transplanted differentiated histological characteristics appropriate for its site or origin, although the degree of differentiation was always much less than in transplants to newborns. Third, the transplants developed only relatively local projections into the host cortex and superior colliculus. This contrasts with the extensive projections found from the transplants into the brain of newborn hosts. Fourth, no definitive projections from the host retina or brain were identified to any of the transplants into adults, whereas both cortical and tectal transplants into newborns received projections from the host.

Autoradiographic tracing of developing subcortical projections of the occipital region in fetal rabbits.

Thirty rabbit embryos and two neonates (E18-P1) received micropipette injections of 3H-Leucine into the occipital region of one hemisphere and were killed after 0.5--5 hours. Incorporated tracer was demonstrated by autoradiography of serial sections of the brains. The first axons were seen in the intermediate zone of the developing cerebral cortex, on day E20, and by day E22 they reached the internal capsule. The entire cortico-peduncular bundle and a short branch of the superficial (thalamic) bundle were labeled on day E24. On day E25, additional branches directed to claustrum, thalamus (deep bundle), and cerebellum were distinguished. By day E28 the first indications of terminal field development were observed. One day before birth (E30), the neonate pattern of subcortical pathways was fully established and silver grain condensations were present over most of the subcortical target areas. Subcortically, the axons followed preferentially preexisting fiber tracts. There was a period of at least 2--3 days between the arrival of the supplying bundles at the target sites and the onset of terminal field formation: The axon bundles grew first towards more distal targets, and even beyond, before terminal fields developed proximally. Transient axon bundles reaching the cerebellar paraflocculus and traveling along the pyramidal tract and the external and extreme capsules failed to form terminal fields and disappeared around birth. The data suggest that growth of long axonal tracts and the development of terminal fields are separate phenomena possibly regulated by different mechanisms.

Transplantation of embryonic occipital cortex to the tectal region of newborn rats: a light microscopic study of organization and connectivity of the transplants.

Occipital cortex was taken from fetal rats and transplanted to the tectal region of newborn rats, where it developed a specific structural identity reflecting in part its cortical origin. The implants showed locally distributing intratransplant connections, and the majority formed connections with defined regions of te host cerebral cortex and the brainstem. A sparse afferent projection from the host had its origin in visual, somatosensory, and cingulate areas of te cortex, pretectum, superior colliculus, central gray, hypothalamus, pontine reticular formation, raphe nuclei, and the locus coeruleus. No input was identified from either the retina or the dorsal thalamus. Efferent fibers were observed in normal fiber preparations as compact bundles running through the host brainstem along two main routes, one group of bundles in a dorsal position and a second group more ventral. Efferent fibers traveling rostrally along the first pathway distributed in the lower part of the stratum griseum superficiale and in the intermediate laminae of the superior colliculus, and in some cases they reached the pretectum and the lateral posterior thalamic nucleus. Deep efferent fibers ran rostrally and caudally in the central gray, and in some cases laterally directed fibers were seen to distribute in the midbrain tegmentum and reticular formation, in one case reaching the pontine gray. The finding that most afferent and many efferent connections of cortical transplants are uncharacteristic of normal cortex stands in marked contrast to retina and tectum, which, when transplanted to the same region, make relatively normal connections.

Prenatal and postnatal development of GABA-accumulating cells in the occipital neocortex of rat.

The development of the 3H-GABA-accumulating cells in the neocortex has been followed by light microscopical autoradiography, and after resectioning of the original autoradiograms, by electron microscopy. The validity of the methods used are discussed. The study has been limited to the primary visual cortex and its precursors of rat, from embryonic day (E) 15 to adult. GABA-accumulating cells were found from E 16 onwards in the occipital cortex, which is one to two days after cells arrive in the pallial anlage and one day before the first synapses have been found. Until E 18, the prevalent positions of labeled cells were in lamina I and below the cortical plate. Later, labeled cells also occurred as strands within the cortical plate. During the perinatal period, more and more GABA-accumulating neurons and glial cells began to differentiate and show a characteristic distribution at the periphery of unlabeled cell clusters. From postnatal day 11, no apparent change in density or position of labeled neurons took place. At prenatal stages, two main types of labeled cells were found: 1) Comparatively large cells with rounded nuclei and rough endoplasmic reticulum consisting of narrow, electron-lucent cisterns. These cells were tentatively identified as preneurons. 2) Smaller, polymorphous cells with irregular nuclei and rough endoplasmic reticulum with wide cisterns filled with a dense matrix. These cells are probably precursors of glial cells. Both labeled neurons and glial cells were identified at postnatal stages. In young and adult rats, only neurons to be characterized as nonpyramidal neurons were labeled. Synapses were not found on the perikarya of labeled cells until E 21. Also, in postnatal preparations, labeled neurons showed few axo-somatic synapses. These data were correlated with other events of the structural and functional development of the neocortex. The delay between the appearance of GABA accumulating cells and synaptogenesis indicates that apart from being an inhibitory neurotransmitter, GABA might play a specific morphogenetic role in synaptogenesis. This could even be its primary function during early developmental stages.

Neurotransmitter receptors in the proliferative zones of the developing primate occipital lobe.

Film autoradiography was used to investigate the expression of several neurotransmitter receptor subtypes in the transient ventricular and subventricular proliferative zones of the developing occipital lobe in two groups of macaque monkey fetuses. The first group of fetuses were between 60 and 93 days after conception (E60-E93), when the ventricular and subventricular zones of the monkey occipital lobe produce neurons destined for the visual cortex. In the second group, fetuses were between E107 and E128, after generation of cortical neurons has ceased. In the E60-E93 group of fetuses, ventricular and subventricular zones displayed high densities of 5-HT1-serotonergic, D1-dopaminergic, alpha 1- and alpha 2-adrenergic and high affinity kainate receptors. The activation of these receptors has previously been shown to stimulate cell proliferation in other cell systems. The possible involvement of these receptors in regulation of neuronal production is also supported by their absence in the deep laminae of the embryonic cerebral wall after E107, after cortical neurogenesis has been completed. The only exception is a high density of alpha 2-adrenergic receptors maintained near the ventricular surface long after all cortical neurons have been generated. We also found that during neurogenesis, proliferative zones in E66-E90 fetuses displayed virtually no 5-HT2-serotonergic, D2-dopaminergic, beta-adrenergic, M1-muscarinic cholinergic, gamma aminobutyric acid (GABA)A, N-methyl-D-aspartate (NMDA), or alpha-amino-3-hydroxy-5-menthy-4-isoxazole proprionate (AMPA) sites; most of these receptor subtypes have been reported to mediate the suppression of cell proliferation. The present findings suggest that dividing and/or newly generated cortical neurons are capable of receiving specific signals from multiple neurotransmitters present in their environment.

Development of vasoactive-intestinal-polypeptide-immunoreactive neurons in the rat occipital cortex: a combined immunohistochemical-autoradiographic study.

The postnatal development of vasoactive intestinal polypeptide (VIP)-immunoreactive neurons, previously labeled with [3H]thymidine on embryonic days E14-E22, has been studied in the rat occipital cortex. Immuno-histochemistry combined with autoradiography showed very little evidence of an "inside-out" pattern of maturation. Most VIP neurons are generated between E17 and E21 and are found in layers II-IV of the cortex, but their position within these layers is not dictated by their date of birth. There is evidence of a temporal maturation since E17 VIP neurons were seen first (at day 7) and E21 last. Peak numbers of VIP neurons were generated on E19. The numbers of VIP-immunoreactive neuronal somata detected in the cortex increased from the first week after birth to the third week and declined thereafter. However VIP-immunoreactive dendrites were still visible, suggesting that VIP levels in the cell bodies were very low, and not that there was a loss of neurons.