Effect of temperature, age and the pons on respiratory rhythm in the rat brainstem-spinal cord.

Neonatal animals are extremely tolerant of hypothermia. However, cooling will ultimately lead to ventilatory arrest, or cessation of respiratory movements. Upon rewarming, ventilation can recover spontaneously (autoresuscitation). This study examined the effect of age (P0-P5) and the pons on respiratory-related output during hypothermic ventilatory arrest and recovery using a brainstem-spinal cord preparation of neonatal rats. As temperature fell, burst frequency slowed, burst duration increased, burst shape became fragmented and eventually respiratory arrest occurred in all preparations. Removing the pons had little effect on younger preparations (P0-P2). Older preparations (P4-P5) with the pons removed continued to burst at cooler temperatures compared to pons-intact preparations and burst durations were significantly longer. Episodic breathing patterns were observed in all preparations (all ages, pons on or off) at lower temperatures. At 27 °C, however, episodic breathing was only observed in younger preparations with the pons on. These data suggest that developmental changes occurring at the level of the pons underlie the loss of hypothermic tolerance and episodic breathing.

Growth restriction induced by chronic prenatal hypoxia affects breathing rhythm and its pontine catecholaminergic modulation.

Impaired transplacental supply of oxygen leads to intrauterine growth restriction, one of the most important causes of perinatal mortality and respiratory morbidity. Breathing rhythm depends on the central respiratory network modulated by catecholamines. We investigated the impact of growth restriction, using prenatal hypoxia, on respiratory frequency, on central respiratory-like rhythm, and on its catecholaminergic modulation after birth. At birth, respiratory frequency was increased and confirmed in en bloc medullary preparations, where the frequency of the fourth cervical (C4) ventral root discharge was increased, and in slice preparations containing the pre-Bötzinger complex with an increased inspiratory rhythm. The inhibition of C4 burst discharge observed in pontomedullary preparations was stronger in the growth-restricted group. These results cannot be directly linked by the tyrosine hydroxylase activity increase of A1/C1 and A2/C2 cell groups in the medulla since blockade of α1- and α2-adrenergic receptors did not abolish the difference between both groups. However, in pontomedullary preparations, the stronger inhibition of C4 burst discharge is probably supported by an increased inhibition of A5, a respiratory rhythm inhibitor pontine group of neurons displaying increased tyrosine hydroxylase activity, because blockade of α2-adrenergic receptors abolished the difference between the two groups. Taken together, these results indicate that growth restriction leads to a perturbation of the breathing frequency, which finds, at least in part, its origin in the modification of catecholaminergic modulation of the central breathing network.

Identification of proliferative progenitors associated with prominent postnatal growth of the pons.

The pons controls crucial sensorimotor and autonomic functions. In humans, it grows sixfold postnatally and is a site of paediatric gliomas; however, the mechanisms of pontine growth remain poorly understood. We show that the murine pons quadruples in volume postnatally; growth is fastest during postnatal days 0-4 (P0-P4), preceding most myelination. We identify three postnatal proliferative compartments: ventricular, midline and parenchymal. We find no evidence of postnatal neurogenesis in the pons, but each progenitor compartment produces new astroglia and oligodendroglia; the latter expand 10- to 18-fold postnatally, and are derived mostly from the parenchyma. Nearly all parenchymal progenitors at P4 are Sox2(+)Olig2(+), but by P8 a Sox2(-) subpopulation emerges, suggesting a lineage progression from Sox2(+) 'early' to Sox2(-) 'late' oligodendrocyte progenitor. Fate mapping reveals that >90% of adult oligodendrocytes derive from P2-P3 Sox2(+) progenitors. These results demonstrate the importance of postnatal Sox2(+)Olig2(+) progenitors in pontine growth and oligodendrogenesis.

Postnatal growth of the human pons: a morphometric and immunohistochemical analysis.

Despite its critical importance to global brain function, the postnatal development of the human pons remains poorly understood. In the present study, we first performed magnetic resonance imaging (MRI)-based morphometric analyses of the postnatal human pons (0-18 years; n = 6-14/timepoint). Pons volume increased 6-fold from birth to 5 years, followed by continued slower growth throughout childhood. The observed growth was primarily due to expansion of the basis pontis. T2-based MRI analysis suggests that this growth is linked to increased myelination, and histological analysis of myelin basic protein in human postmortem specimens confirmed a dramatic increase in myelination during infancy. Analysis of cellular proliferation revealed many Ki67(+) cells during the first 7 months of life, particularly during the first month, where proliferation was increased in the basis relative to tegmentum. The majority of proliferative cells in the postnatal pons expressed the transcription factor Olig2, suggesting an oligodendrocyte lineage. The proportion of proliferating cells that were Olig2(+) was similar through the first 7 months of life and between basis and tegmentum. The number of Ki67(+) cells declined dramatically from birth to 7 months and further decreased by 3 years, with a small number of Ki67(+) cells observed throughout childhood. In addition, two populations of vimentin/nestin-expressing cells were identified: a dorsal group near the ventricular surface, which persists throughout childhood, and a parenchymal population that diminishes by 7 months and was not evident later in childhood. Together, our data reveal remarkable postnatal growth in the ventral pons, particularly during infancy when cells are most proliferative and myelination increases.

Differential mtDNA damage patterns in a transgenic mouse model of Machado-Joseph disease (MJD/SCA3).

Mitochondrial dysfunction has been associated with late onset neurodegenerative disorders, among which is Machado-Joseph disease (MJD/SCA3). In a previous study, using a transgenic mouse model of MJD, we reported a decrease in mitochondrial DNA (mtDNA) copy number and an accumulation of the 3876-bp deletion with age and with phenotype development. We extended this study by analyzing the pattern of mtDNA depletion and the accumulation of the 3876-bp deletion in 12 older transgenic (TG) and 4 wild-type (wt) animals, and by investigating the accumulation of somatic mutations in the D-loop region in 76 mice (42 TG and 34 wt). mtDNA damage was studied in TG and wt mice at different ages and tissues (blood, pontine nuclei, and hippocampus). Results for older mice demonstrate an accumulation of the mtDNA 3867-bp deletion with age, which was more pronounced in TG animals. Furthermore, the tendency for mtDNA copy number decrease with age, in all analyzed tissues of TG and wt animals, was also confirmed. No point mutations were detected in the D-loop, neither in TG nor wt animals, in any of the tissues analyzed. Due to the absence of mtDNA somatic mutations, we can suggest that mtDNA point mutation accumulation cannot be used to monitor the development and progression of the phenotype in this mouse model and likely in any MJD mice model. The present results further confirm not only the association between mtDNA alterations (copy number and deletions) and age, but also between such alterations and the expression of the mutant ataxin-3 in TG mice.

Developmental study of the distribution of hypoxia-induced factor-1 alpha and microtubule-associated protein 2 in children's brainstem: comparison between controls and cases with signs of perinatal hypoxia.

Perinatal asphyxia and hypoxia are common causes of morbidity in neonates. Prenatal birth associated with hypoxemia often results in several disorders because of the lack of oxygen in the brain. Survival rates from perinatal hypoxia have improved, but appropriate treatments for recovery are still limited, with great impact on patients, their families, society in general and health systems. The aim of this work is to contribute to a better understanding of the cellular mechanisms underlying the brainstem responses to hypoxia. For this purpose, distributions of two proteins, hypoxia-inducible factor-1 alpha (HIF-1α) and microtubule-associated protein 2 (MAP-2) were analyzed in brainstems of 11 children, four of them showing neuropathological evidence of brain hypoxia. They were included in control or hypoxic groups, and then in several subgroups according to their age. Immunohistochemical labeling for these proteins revealed only cell bodies containing HIF-1α, and both cell bodies and fibers positive for MAP-2 in the children's brainstems. The distribution of HIF-1α was more restricted than that of MAP-2, and it can be suggested that the expression of HIF-1α increased with age. The distribution pattern of MAP-2 in the medulla oblongata could be more due to age-related changes than to a response to hypoxic damage, whereas in the pons several regions, such as the nucleus ambiguus or the solitary nucleus, showed different immunolabeling patterns in controls and hypoxic cases. The distribution patterns of these two proteins suggest that some brainstem regions, such as the reticular formation or the central gray, could be less affected by conditions of hypoxia.

Four-dimensional analysis of nucleogenesis of the pontine nucleus in the hindbrain.

Nuclei in the central nervous system are 3D aggregates of neurons that have common physiological properties, functionalities, and connectivities. To form specific nuclei, neurons migrate from their birthplace towards the presumptive nuclear region where they change their dynamics to aggregate and rearrange into a distinct 3D structure, a process that we term nucleogenesis. Nuclei, together with the laminar structure, form the basic cytoarchitectonic unit for information processing. However, in contrast to much-studied laminar structures, the neuronal dynamics that contribute to the aggregation process to form nuclei are poorly understood. Here, we analyze nucleogenesis by observing the mouse precerebellar pontine nucleus (PN), and provide the first 4D view of nucleogenesis by tracking neuronal behaviors along the three spatial axes over time. Early- and late-born PN neurons were labeled by in utero electroporation and their behaviors on cultured brain slices were recorded by time-lapse imaging. We find that when PN neurons migrate medially into the nuclear region, many of them switch to migrate radially and laterally, to populate the dorsal and lateral PN regions, respectively. The tendency to switch to radial migration is much less in later-born neurons, whereas that to switch to lateral migration is comparable between the two groups. In contrast to the radial and mediolateral axes, very few PN neurons switch to migrate rostrocaudally. These results could thus provide a framework for understanding the mechanisms that regulate this complex yet important process.

Reduced effect of stimulation of AMPA receptors on cerebral O2 consumption in a rat model of autism.

Previous work demonstrated that basal alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor activity did not contribute to the elevated regional cerebral O2 consumption in the brains of Eker rat (an autism-tuberous sclerosis model). We tested the hypothesis that increased stimulation of AMPA receptors also would not augment cerebral O2 consumption in the Eker rat. Three cortical sites were prepared for administration of saline, 10⁻4 and 10⁻³ M AMPA in young (4 weeks) male control Long Evans and Eker rats (70-100 g). Cerebral blood flow (¹4C-iodoantipyrine) and O2 consumption (cryomicrospectrophotometry) were determined in isoflurane anesthetized rats. Receptor levels were studied through Western analysis of the GLuR1 subunit of the AMPA receptor. We found significantly increased cortical O2 consumption (+33%) after 10⁻4 M AMPA in control rats. The higher dose of AMPA did not further increase consumption. In the Eker rats, neither dose led to a significant increase in cortical O2 consumption. Regional blood flow followed a similar pattern to oxygen consumption but cortical O2 extraction did not differ. Cortical AMPA receptor protein levels were significantly reduced (-21%) in the Eker compared to control rats. Both O2 consumption and blood flow were significantly elevated in the pons of the Eker rats compared to control. These data demonstrate a reduced importance of AMPA receptors in the control of cortical metabolism, related to reduced AMPA receptor protein, in the Eker rat. This suggests that increasing AMPA receptor activity may not be an effective treatment for children with autism spectrum disorders as they also have reduced AMPA receptor number.

Development of the human abducens nucleus: a morphometric study.

BACKGROUND: The abducens nucleus directly innervates the lateral rectus muscle and plays a role in controlling conjugate horizontal eye movements. Although the neuronal cytoarchitecture of the abducens nucleus has been extensively investigated in various species of vertebrates, few studies have been undertaken in humans, especially in fetuses or neonates. DESIGN/SUBJECTS: We examined 12 human brains from preterm infants aged 20-43 postmenstrual weeks to document the histology and morphometry of the abducens nucleus. The brain was processed into celloidin-embedded serial sections stained with the Klüver-Barrera and other conventional methods. RESULTS: The nucleus was identified as a mass of cells as early as 20 weeks. Its neurons were clearly distinguished from glial cells due to droplet-like, clear nuclei containing prominent nucleoli and surrounded by a basophilic perikaryon. Neurons of various sizes and shapes were intermingled within the nucleus, although larger neurons were located towards the center of the nucleus. Immature granular or reticular Nissl bodies were seen at 20-21 weeks. Tigroid, coarse Nissl bodies appeared around 28-29 weeks in larger neurons, although in smaller neurons Nissl bodies were dispersed or concentrated peripherally. Morphometric results were: (1) the nuclear volume exponentially increased with age between 20 and 43 weeks; (2) the histograms of neuronal profile areas showed a non-normal distribution trailing toward the right and widening with age; (3) the geometric average of neuronal profile areas increased linearly with age. CONCLUSION: Our study suggests that the human abducens nucleus enlarges more quickly toward the end of gestation, and comprises heterogeneous groups of neurons.

Pre- and postsynaptic properties of glutamatergic transmission in the immature inhibitory MNTB-LSO pathway.

The lateral superior olive (LSO) integrates excitatory inputs driven by sound arriving at the ipsilateral ear with inhibitory inputs driven by sound arriving at the contralateral ear in order to compute interaural intensity differences needed for localizing high-frequency sound sources. Specific mechanisms necessary for developmental refinement of the inhibitory projection, which arises from the medial nucleus of the trapezoid body (MNTB), have only been partially deciphered. The demonstration that immature MNTB-LSO synapses release glutamate has led to a model in which early glutamate neurotransmission plays a major role in inhibitory plasticity. We used whole cell electrophysiology in acute auditory brain stem slices of neonatal rats to examine glutamatergic transmission in the developing MNTB-LSO pathway. Unexpectedly, AMPA receptor (AMPAR)-mediated responses were prevalent at the earliest ages. We found a salient developmental profile for NMDA receptor (NMDAR) activation, described both by the proportion of total glutamate current and by current durations, and we found evidence for distinct release probabilities for GABA/glycine and glutamate in the MNTB-LSO pathway. The developmental profile of NMDAR is consistent with the possibility that the inhibitory MNTB-LSO pathway experiences a sensitive period, driven by cochlear activity and mediated by GluN2B-containing NMDARs, between postnatal days 3 and 9. Differing neurotransmitter release probabilities could allow the synapse to switch between GABA/glycinergic transmission and mixed glutamate/GABA/glycinergic transmission in response to changing patterns of spiking activity.

Developmental expression of oxytocin receptors in the neonatal medulla oblongata and pons.

The distribution of oxytocin receptors (OTRs) in the postnatal brain stem of rats was examined by immunohistochemistry. Fibrous or rounded shaped OTR-immunoreactive structures were distributed densely in sensory nuclei, such as the gracile nucleus, the solitary nucleus, and the spinal trigeminal nucleus, evenly in the reticular formation of the medulla oblongata and pons, and moderately in the locus coeruleus during the neonatal period, but disappeared by postnatal day 10. Few OTR-immunoreactive structures were distributed in motor nuclei. Many rounded OTR-immunoreactive structures were discovered layered and partially overlapping with GM-130-immunoreacivity in the neuronal Golgi apparatus, which was confirmed by electron microscopy. The present study suggests that a transient type of OTR may be functioning in neuronal development during the neonatal period.

Hedgehog-responsive candidate cell of origin for diffuse intrinsic pontine glioma.

Diffuse intrinsic pontine gliomas (DIPGs) are highly aggressive tumors of childhood that are almost universally fatal. Our understanding of this devastating cancer is limited by a dearth of available tissue for study and by the lack of a faithful animal model. Intriguingly, DIPGs are restricted to the ventral pons and occur during a narrow window of middle childhood, suggesting dysregulation of a postnatal neurodevelopmental process. Here, we report the identification of a previously undescribed population of immunophenotypic neural precursor cells in the human and murine brainstem whose temporal and spatial distributions correlate closely with the incidence of DIPG and highlight a candidate cell of origin. Using early postmortem DIPG tumor tissue, we have established in vitro and xenograft models and find that the Hedgehog (Hh) signaling pathway implicated in many developmental and oncogenic processes is active in DIPG tumor cells. Modulation of Hh pathway activity has functional consequences for DIPG self-renewal capacity in neurosphere culture. The Hh pathway also appears to be active in normal ventral pontine precursor-like cells of the mouse, and unregulated pathway activity results in hypertrophy of the ventral pons. Together, these findings provide a foundation for understanding the cellular and molecular origins of DIPG, and suggest that the Hh pathway represents a potential therapeutic target in this devastating pediatric tumor.

Developmental changes in intrinsic excitability of principal neurons in the rat medial nucleus of the trapezoid body.

The calyx of Held synapse is a giant axosomatic synapse that has a fast relay function within the sound localization circuit of the brainstem. In the adult, each principal neuron of the medial nucleus of the trapezoid body (MNTB) is contacted by a single calyx terminal. In rodents, the calyx of Held synapse forms around the third postnatal day (P3). Here, we studied the developmental changes in the intrinsic excitability of the principal neurons during the first postnatal week by making whole-cell recordings from brainstem slices. In slices from P0-1 rats, about 20% of the principal neurons were spontaneously active, whereas after P3, no spontaneously active cells were observed. Already at P0, principal neurons received both glutamatergic and GABAergic/glycinergic inputs. The occurrence of spontaneous action potentials depended upon the presence of spontaneous glutamatergic inputs; summation of only a few quanta was enough to reach action potential threshold. The main cause for this high excitability was a high resting membrane resistance, which decreased at least four-fold during the first postnatal week. A relatively slow decay of synaptic currents and a relatively depolarized membrane potential may have contributed as well. We conclude that the decrease in the excitability of principal neurons in the MNTB matches the increase of the strength of the synaptic inputs resulting from the formation and maturation of the calyx of Held synapse during the first postnatal week. This decrease in excitability will make it progressively more difficult for non-calyceal inputs to trigger action potentials.

Formation and maturation of the calyx of Held.

Sound localization requires precise and specialized neural circuitry. A prominent and well-studied specialization is found in the mammalian auditory brainstem. Globular bushy cells of the ventral cochlear nucleus (VCN) project contralaterally to neurons of the medial nucleus of the trapezoid body (MNTB), where their large axons terminate on cell bodies of MNTB principal neurons, forming the calyces of Held. The VCN-MNTB pathway is necessary for the accurate computation of interaural intensity and time differences; MNTB neurons provide inhibitory input to the lateral superior olive, which compares levels of excitation from the ipsilateral ear to levels of tonotopically matched inhibition from the contralateral ear, and to the medial superior olive, where precise inhibition from MNTB neurons tunes the delays of binaural excitation. Here we review the morphological and physiological aspects of the development of the VCN-MNTB pathway and its calyceal termination, along with potential mechanisms that give rise to its precision. During embryonic development, VCN axons grow towards the midline, cross the midline into the region of the presumptive MNTB and then form collateral branches that will terminate in calyces of Held. In rodents, immature calyces of Held appear in MNTB during the first few days of postnatal life. These calyces mature morphologically and physiologically over the next three postnatal weeks, enabling fast, high fidelity transmission in the VCN-MNTB pathway.

Synaptic changes underlying the strengthening of GABA/glycinergic connections in the developing lateral superior olive.

Before hearing onset, the topographic organization of the auditory GABA/glycinergic pathway from the medial nucleus of the trapezoid body (MNTB) to the lateral superior olive (LSO) is refined by synaptic silencing and strengthening. The synaptic mechanisms underlying the developmental strengthening of maintained MNTB-LSO connections are unknown. Here we address this question using whole-cell recordings from LSO neurons in slices prepared from prehearing mice. Minimal and maximal stimulation techniques demonstrated that during the first two postnatal weeks, individual LSO neurons lose about 55% of their initial presynaptic MNTB partners while maintained single-fiber connections become about 14-fold stronger. Analysis of MNTB-evoked miniature events indicates that this strengthening is accompanied by a 2-fold increase in quantal amplitude. Strengthening is not caused by an increase in the probability of release because paired pulse ratios (PPRs) increased from 0.7 in newborn animals to 0.9 around hearing onset, indicating a developmental decrease rather than increase in release probability. In addition, a possible soma-dendritic relocation of MNTB input seems unlikely to underlie their strengthening as indicated by analysis of the rise times of synaptic currents. Taken together, we conclude that the developmental strengthening of MNTB-LSO connections is achieved by a 2-fold increase in quantal size and an 8-fold increase in quantal content.

Timing and mechanism of a window of spontaneous activity in embryonic mouse hindbrain development.

Spontaneous activity (SA) in the developing vertebrate brain is required for correct wiring of circuits and networks. In almost every brain region studied to date, SA is recorded during a period of synaptogenesis, and may deploy ionic mechanism(s) that are not expressed in the adult structure. Eventually the conditions in the immature neurons that allow SA are replaced with ion channels found in the mature neuron; this replacement may itself require SA. In the embryonic (E) 11.5 mouse hindbrain, SA is initiated by a subgroup of serotonergic neurons derived from former rhombomeres 2 and 3; SA events propagate rostrally and caudally along the midline, and into the lateral hindbrain. In this review, I describe the properties of mouse hindbrain SA and the developmental window during which it is expressed, summarize the known mechanisms by which SA arises, and describe other brain regions where this SA is similar (chick hindbrain) or influential (mouse midbrain).

Postnatal changes in morphology and dendritic organization of neurones located in the area of the Kölliker-Fuse nucleus of rat.

The Kölliker-Fuse nucleus (KF) is an integral part of the central pattern generator for breathing and shows postnatal development of synaptic functions and cyto-architectural structure. Here, we analyzed the postnatal changes in cell morphology of biocytin-labelled KF neurones. Developmental analyses revealed an increasing size of somas and dendritic length. These changes were accompanied by changes in the orientation of the main dendritic branches from a diffuse orientation in neonates to a predominant medio-lateral orientation in juveniles. These developmental changes may allow for synaptic contacts with multiple ascending fibre tracts required for the processing of multi-modal respiratory inputs in the KF.

Targeted three-dimensional immunohistochemistry reveals localization of presynaptic proteins Bassoon and Piccolo in the rat calyx of Held before and after the onset of hearing.

Bassoon and Piccolo contribute to the cytomatrix of active zones (AZ), the sites of neurotransmitter release in nerve terminals. Here, we examined the 3D localization of Bassoon and Piccolo in the rat calyx of Held between postnatal days 9 and 21, the period of hearing onset characterized by pronounced structural and functional changes. Bassoon and Piccolo were identified by immunohistochemistry (IHC) on slices of the brainstem harboring calyces labeled with membrane-anchored green fluorescent protein (mGFP). By using confocal microscopy and 3D reconstructions, we examined the distribution of Bassoon and Piccolo in calyces delineated by mGFP. This allowed us to discriminate calyceal IHC signals from noncalyceal signals located in the spaces between the calyceal stalks, which could mimic a calyx-like distribution. We found that both proteins were arranged in clusters resembling the size of AZs. These clusters were located along the presynaptic membrane facing the principal cell, close to or overlapping with synaptic vesicle (SV) clusters. Only about 60% of Bassoon and Piccolo clusters overlapped, whereas the remaining clusters contained predominantly Bassoon or Piccolo, suggesting differential targeting of these proteins within a single nerve terminal and potentially heterogeneous AZs functional properties. The total number of Bassoon and Piccolo clusters, which may approximate the number of AZs, was 405 +/- 35 at P9 and 601 +/- 45 at P21 (mean +/- SEM, n = 12). Normalized to calyx volume at P9 and P21, the density of clusters was similar, suggesting that the absolute number of clusters, not density, may contribute to the functional maturation associated with hearing onset.

Magnetic resonance imaging and diffusion-weighted imaging of normal-appearing white matter in children and young adults with tuberous sclerosis complex.

INTRODUCTION: Patients with tuberous sclerosis complex (TSC) frequently present with neurocognitive deficits which may be related to impaired white matter maturation. The purposes of our study were (a) to evaluate the white matter maturation in children and young adults with TSC by comparing the apparent diffusion coefficient (ADC) values of normal-appearing white matter (NAWM) with age-matched healthy controls and (b) to determine the association of NAWM-ADC values with the severity of neurological symptoms in TSC patients. METHODS: Twenty-three TSC patients who underwent magnetic resonance imaging/diffusion-weighted imaging between January 2000 and January 2009 were studied. ADC values of NAWM were measured in the frontal, parietal, occipital lobes, and in the pons. ADC data were compared with age-matched normative data derived from healthy controls. Patients were neurologically scored by a pediatric neurologist. Two-sample t tests and linear regression were conducted using STATA software. RESULTS: ADC values of NAWM were higher in TSC patients compared with healthy controls; the increase, however, only reached statistical significance in the frontal white matter and pons in the age group between 96 and 144 months and in the right parietal and occipital white matter in the age group above 144 months. There was no significant change in neurological severity score per unit increase in ADC measurement. CONCLUSION: ADC values of NAWM appear increased in TSC patients. The abnormal ADC values suggest that myelination may be delayed/impaired in TSC patients, which could explain global neurocognitive deficits. Larger prospective studies, including diffusion tensor imaging, are necessary to validate our results.

Cerebellar haemorrhages and pons development in extremely low birth weight infants.

UNLABELLED: Neuropathological and Magnetic Resonance Imaging (MRI) studies showed a high frequency of posterior fossa abnormalities in preterms. To assess whether cerebellar haemorrhages (CH) diagnosed with ultrasound and/or MRI affect pons development in ELBW infants. The anteroposterior diameter of the pons was measured manually on the midline sagittal T1 MR image in 75 ELBW babies consecutively scanned at term postmenstrual age. Subjects with CH were identified and compared to babies with no posterior fossa bleeding. Nine ELBW infants with CH (CH-Group: median gestational age -GA- 26 wks, range 23-27; birth weight -BW- 680 g, 425-980) were compared with 66 babies with normal cerebellum (Control-Group: GA 28 wks, 23-33; BW 815 g, 430-1000). The two groups were comparable for BW (p=0.088) while GA was significantly shorter in CH babies (p=0.005). The pontine diameter was significantly lower in CH-Group compared to Control-Group (12.8 +/- 2.2 vs 14.8 +/- 1.2 mm; p<0.001). CONCLUSIONS: Cerebellar haemorrhages seem to affect the development of the pons in ELBW with the youngest GA.