Dual midbrain and forebrain origins of thalamic inhibitory interneurons.

The ubiquitous presence of inhibitory interneurons in the thalamus of primates contrasts with the sparsity of interneurons reported in mice. Here, we identify a larger than expected complexity and distribution of interneurons across the mouse thalamus, where all thalamic interneurons can be traced back to two developmental programmes: one specified in the midbrain and the other in the forebrain. Interneurons migrate to functionally distinct thalamocortical nuclei depending on their origin: the abundant, midbrain-derived class populates the first and higher order sensory thalamus while the rarer, forebrain-generated class is restricted to some higher order associative regions. We also observe that markers for the midbrain-born class are abundantly expressed throughout the thalamus of the New World monkey marmoset. These data therefore reveal that, despite the broad variability in interneuron density across mammalian species, the blueprint of the ontogenetic organisation of thalamic interneurons of larger-brained mammals exists and can be studied in mice.

Individual Differences in Human Auditory Processing: Insights From Single-Trial Auditory Midbrain Activity in an Animal Model.

Auditory-evoked potentials are classically defined as the summations of synchronous firing along the auditory neuraxis. Converging evidence supports a model whereby timing jitter in neural coding compromises listening and causes variable scalp-recorded potentials. Yet the intrinsic noise of human scalp recordings precludes a full understanding of the biological origins of individual differences in listening skills. To delineate the mechanisms contributing to these phenomena, in vivo extracellular activity was recorded from inferior colliculus in guinea pigs to speech in quiet and noise. Here we show that trial-by-trial timing jitter is a mechanism contributing to auditory response variability. Identical variability patterns were observed in scalp recordings in human children, implicating jittered timing as a factor underlying reduced coding of dynamic speech features and speech in noise. Moreover, intertrial variability in human listeners is tied to language development. Together, these findings suggest that variable timing in inferior colliculus blurs the neural coding of speech in noise, and propose a consequence of this timing jitter for human behavior. These results hint both at the mechanisms underlying speech processing in general, and at what may go awry in individuals with listening difficulties.

The RNA-binding protein Celf6 is highly expressed in diencephalic nuclei and neuromodulatory cell populations of the mouse brain.

The gene CUG-BP, Elav-like factor 6 (CELF6) appears to be important for proper functioning of neurocircuitry responsible for behavioral output. We previously discovered that polymorphisms in or near CELF6 may be associated with autism spectrum disorder (ASD) in humans and that the deletion of this gene in mice results in a partial ASD-like phenotype. Here, to begin to understand which circuits might mediate these behavioral disruptions, we sought to establish in what structures, with what abundance, and at which ages Celf6 protein is present in the mouse brain. Using both a knockout-validated antibody to Celf6 and a novel transgenic mouse line, we characterized Celf6 expression in the mouse brain across development. Celf6 gene products were present early in neurodevelopment and in adulthood. The greatest protein expression was observed in distinct nuclei of the diencephalon and neuromodulatory cell populations of the midbrain and hindbrain, with clear expression in dopaminergic, noradrenergic, histaminergic, serotonergic and cholinergic populations, and a variety of presumptive peptidergic cells of the hypothalamus. These results suggest that disruption of Celf6 expression in hypothalamic nuclei may impact a variety of behaviors downstream of neuropeptide activity, while disruption in neuromodulatory transmitter expressing areas such as the ventral tegmental area, substantia nigra, raphe nuclei and locus coeruleus may have far-reaching influences on overall brain activity.

Monaural deprivation disrupts development of binaural selectivity in auditory midbrain and cortex.

Degraded sensory experience during critical periods of development can have adverse effects on brain function. In the auditory system, conductive hearing loss associated with childhood ear infections can produce long-lasting deficits in auditory perceptual acuity, much like amblyopia in the visual system. Here we explore the neural mechanisms that may underlie "amblyaudio" by inducing reversible monaural deprivation (MD) in infant, juvenile, and adult rats. MD distorted tonotopic maps, weakened the deprived ear's representation, strengthened the open ear's representation, and disrupted binaural integration of interaural level differences (ILD). Bidirectional plasticity effects were strictly governed by critical periods, were more strongly expressed in primary auditory cortex than inferior colliculus, and directly impacted neural coding accuracy. These findings highlight a remarkable degree of competitive plasticity between aural representations and suggest that the enduring perceptual sequelae of childhood hearing loss might be traced to maladaptive plasticity during critical periods of auditory cortex development.

[The brain is one of the most important sources of dopamine in general circulation during perinatal ontogenesis in rats].

This study was aimed to test our hypothesis that dopamine synthesized in the neurons of the brain is delivered to the general circulation in rats during prenatal and early postnatal periods, i.e. before the establishment of the blood-brain barrier. Using the high performance liquid chromatography, it was demonstrated that the dopamine concentration and content in the peripheral blood in fetuses and neonatal rats (i.e. before the establishment of the blood-brain barrier) greatly exceeded those in adult rats. Moreover, the establishment of the blood-brain barrier was accompanied by the significant increase of the dopamine concentration in the brain. A drop of the dopamine concentration in fetal plasma after the microsurgical lesion of the forebrain and mesencephalon (encephalectomy) are considered as direct evidence in favour of our hypothesis.

Mouse brain organization revealed through direct genome-scale TF expression analysis.

In the developing brain, transcription factors (TFs) direct the formation of a diverse array of neurons and glia. We identifed 1445 putative TFs in the mouse genome. We used in situ hybridization to map the expression of over 1000 of these TFs and TF-coregulator genes in the brains of developing mice. We found that 349 of these genes showed restricted expression patterns that were adequate to describe the anatomical organization of the brain. We provide a comprehensive inventory of murine TFs and their expression patterns in a searchable brain atlas database.

Age-related decline of serotonin transporters in living human brain of healthy males.

There is growing interest in serotonin transporter (5-HTT) function in the human brain, since alteration in 5-HTT has been suggested in a variety of neurophychiatric disorders. Age-related decline in postsynaptic 5-HT receptors has been demonstrated in postmortem human studies and in vivo imaging studies, and has been assumed to be related to changes in mental function in the normal aging process. However, few studies have investigated the aging effect on 5-HTT in human brain in vivo, since the availability of suitable ligands has been limited. To investigate the aging effect on 5-HTT in living human brain, we performed positron emission tomography (PET) scans with a selective ligand for 5-HTT, [11C](+)McN5652. We examined 28 healthy male volunteers aged between 20 and 79 years. The uptake was quantified in the thalamus and midbrain by graphical analysis with the cerebellum as a reference tissue, and binding potential (BP) was used for the index of 5-HTT binding. There was a significant age-related decline in BP in the thalamus and midbrain. The decline in [11C](+)McN5652 binding was 9.6% per decade in the thalamus and 10.5% per decade in the midbrain.

Growth hormone (GH) action in the brain: neural expression of a GH-response gene.

The presence of growth hormone (GH) binding sites and GH-receptor (GHR)-immunoreactive proteins in the brain suggests it is a target site for GH action. This could, however, reflect the presence of GH-binding proteins (GHBP) that are not linked to intracellular signal-transduction mechanisms, rather than authentic receptors. The possibility that GH has actions in the brain therefore has been examined by determining an intracellular mediator of GH action. The mechanism of GH action involves the induction of a number of specific GH-response genes. In chickens, a novel GH-responsive gene (GHRG-1) has been identified as an intracellular marker of GH action, since this gene is not expressed in GH-resistant dwarfs with dysfunctional GHRs and in normal chickens it is upregulated by exogenous GH. In normal chickens GHRG-1 mRNA is also abundant and widespread in the brain. In the cerebellum it is specifically localized in the cerebellar folia. It is present in most cells in the granular layers of the gray matter but is present in only a small number of scattered cells in the molecular layer and white matter. Intense labeling for GHRG-1 mRNA is also present in the large Purkinje cells and their dendrites at the interface between the molecular and granular layers. Labeling is also seen in the interneuronal basket cells projecting onto the Purkinje cells. In the mid-brain, cells in the ocular nerve complex and the tractus isthmo-opticus were strongly stained for GHRG-1 mRNA, with less intense staining in the central gray. In the hypothalamus, numerous small cells in periventricular locations and ependymal cells lining the III ventricle also label for GHRG-1 mRNA. These results clearly show, for the first time, the expression of a GH-responsive gene in neural tissues. Moreover, as GH- and GHR-immunoreactivity previously has been shown to be present in the same tissues expressing GHRG-1, it is possible that GH acts as an autocrine or paracrine within the CNS.

Genetic pathways in the developmental specification of hypothalamic neuropeptide and midbrain catecholamine systems.

The neuropeptide concept concerns the diverse and broad physiological functions of neuropeptides in behavioral adaptation. Neuropeptides like vasopressin and corticotropin-releasing hormone can coordinate multiple brain functions due to the anatomical organization of the neurons producing them. The cell bodies are focally positioned in the hypothalamus and send long-reaching efferents to limbic and brainstem areas. Likewise, midbrain dopamine systems coordinate emotional behaviors and movement control by specific connectivity of neurons in the midbrain to limbic and striatal centers, respectively. The fundament of the functions of these signalling molecules is laid out during development when transmitter identity and connectivity are specified. This is a highly controlled process involving multiple transcription factors and growth factors acting together in genetic pathways. Here, the genetic pathways enrolling in developing vasopressin, corticotropin-releasing hormone, and midbrain dopamine neurons are discussed.

Widespread expression of rat collapsin response-mediated protein 4 in the telencephalon and other areas of the adult rat central nervous system.

The rat collapsin response-mediated protein 4 (rCRMP-4) is a member of a family of proteins that are involved in axonal growth. It is found transiently in postmitotic neurons, such as those that are generated in the adult hippocampus. The authors used immunocytochemistry to investigate whether areas of the rat central nervous system (CNS) that retain postnatal neurogenesis express this protein. They found pronounced rCRMP-4 immunoreactivity in recently generated cells in the dentate granular layer, the subventricular zone, the olfactory bulbs, and the rostral migratory stream, four areas in which the production or migration of neurons occurs in adulthood. However, rCRMP-4 immunoreactivity also is expressed in many other regions of the rat brain in which there is no record of adult neurogenesis or neuronal migration, e.g., in the olfactory glomeruli and in neurons of the cerebral cortex. In the hypothalamus, intensely rCRMP-4-labeled neurons populated the supraoptic, paraventricular, and periventricular nuclei as well as the median eminence and the arcuate nucleus. Immunoreactivity for rCRMP-4 also was present in certain neurons of the interpeduncular nucleus, median raphe, superior colliculus, and scattered granule cerebellar neurons. Many of these regions are known to display axonal outgrowth and/or synaptic rearrangement in adulthood and to coexpress the polysialylated form of the neural cell adhesion molecule. Thus, the results of this study suggest that rCRMP-4 expression in the CNS is associated with cells that are migrating or are undergoing axonal growth. Nevertheless, small, rCRMP-4-immunoreactive cells were seen throughout the brain. These cells did not express neuronal, astroglial, or microglial markers, although some of them also were immunoreactive for rip antibody, suggesting an oligodendroglial lineage.

The winged helix gene, Mf3, is required for normal development of the diencephalon and midbrain, postnatal growth and the milk-ejection reflex.

The mouse Mf3 gene, also known as Fkh5 and HFH-e5.1, encodes a winged helix/forkhead transcription factor. In the early embryo, transcripts for Mf3 are restricted to the presomitic mesoderm and anterior neurectoderm and mesoderm. By 9.5 days post coitum, expression in the nervous system is predominantly in the diencephalon, midbrain and neural tube. After midgestation, the highest level of mRNA is in the mammillary bodies, the posterior-most part of the hypothalamus. Mice homozygous for a deletion of the mf3 locus on a [129 x Black Swiss] background display variable phenotypes consistent with a requirement for the gene at several stages of embryonic and postnatal development. Approximately six percent of the mf3-/- embryos show an open neural tube in the diencephalon and midbrain region, and another five percent show a severe reduction of the posterior body axis; both these classes of affected embryos die in utero. Surviving homozygotes have an apparently normal phenotype at birth. Postnatally, however, mf3-/- pups are severely growth retarded and approximately one third die before weaning. This growth defect is not a direct result of lack of circulating growth hormone or thyrotropin. Mice that survive to weaning are healthy, but they show an abnormal clasping of the hindfeet when suspended by the tail. Although much smaller than normal, the mice are fertile. However, mf3-/- females cannot eject their milk supply to feed their pups. This nursing defect can be corrected with interperitoneal injections of oxytocin. These results provide evidence that Mf3 is required for normal hypothalamus development and suggest that Mf3 may play a role in postnatal growth and lactation.

Development of the olfactory and accessory lobes in the American lobster: an allometric analysis and its implications for the deutocerebral structure of decapods.

The allometric changes characterizing the growth of the deutocerebrum (midbrain) of the American lobster (Homarus americanus) are studied using computerized three-dimensional reconstructions of serial brain sections. During the embryogenesis of the midbrain, the paired accessory lobes (higher order processing areas) appear later than the paired olfactory lobes (primary olfactory centers), but the former grow faster from their emergence until metamorphosis. The accessory lobes, as they enlarge, shift progressively from a medial to a posterior position in the lateral deutocerebrum. In early juvenile stages the accessory lobes are one of the largest neuropils of the brain. However, these lobes stop growing in adult animals, whereas the brain and olfactory lobes continue to enlarge, albeit at a slow rate. The overall shape of the brain and the relative proportions and locations of the deutocerebral neuropils and associated cell clusters of various lobster ontogenetic stages are similar to those of selected adult decapods. In addition, the relation between deutocerebral organization and brain size seem parallel during lobster development and across crustacean species. Measurements of the brains of 13 species of decapods (illustrated in Sandeman et al. [1993] J. Exp. Zool. 265:112, plus Homarus) indicate the following trends: Small brains possess olfactory lobes but no accessory lobes, larger brains possess accessory lobes that are medial and small relative to the olfactory lobes, and the largest brains contain relatively voluminous posterior accessory lobes. These observations indicate that some differences in the organization of the deutocerebrum are related to absolute brain size in crustaceans and suggest that ontogenetic scaling of proportions may apply to the deutocerebral neuropils of decapods. Peramorphosis and paedomorphosis in the evolution of the decapod brain are considered.

Naltrexone administration effects on regional brain monoamines in developing rats.

The effects of the opioid antagonist naltrexone (NALTX) daily administration (1 mg/kg SC) from birth on the levels of dopamine (DA), serotonin (5-HT), and their respective major metabolites, in the striatum, midbrain, and hypothalamus of 7-, 14-, and 22-day-old rats were investigated. Naltrexone treatment increased the striatal HVA/DA ratio on postnatal day 7. At day 14, two subpopulations (A and B) were found among the treated animals. The subpopulation A showed decreased HVA/DA and increased DOPAC/DA ratios, whereas the subpopulation B presented a higher DA concentration. No significant effect appeared on the striatal dopaminergic system in 22-day-old pups. The serotonergic system was affected by exposure to naltrexone only from day 14. The subpopulation A showed a reduction in all the parameters measured in the three regions studied, although in the subpopulation B, lower 5-HIAA/5-HT ratios appeared in the midbrain and hypothalamus. At 22 days of age NALTX treatment elevated striatal 5-HT and 5-HIAA and the ratio of 5-HIAA/5-HT in the midbrain and hypothalamus. These data suggest an endogenous opioid modulation on the central aminergic systems during the neonatal period and point out the consequences of opioid plasticity on related neurotransmitter systems.

Antennular projections to the midbrain of the spiny lobster. III. Central arborizations of motoneurons.

The central organization of antennular motoneurons in the brain of the spiny lobster, Panulirus argus, was analyzed by combining biocytin backfills with serial reconstructions of the antennular nerves and the brain. Eighty-nine to 99 antennular motoneurons occur in each hemibrain. The somata of the motoneurons are distributed in a consistent pattern in two complex soma clusters, the ventral paired mediolateral cluster of the deutocerebrum and the dorsal unpaired median cluster of the tritocerebrum. The motoneurons arborize ipsilaterally in the lateral and median antennular neuropils and the tegumentary neuropil. The backfills indicate a minimum of five morphological types of motoneurons with different arborization patterns. The innervation pattern of the motoneurons, together with previously reported innervation patterns of antennular sensory afferents, suggest that the lateral antennular neuropil is a lower motor center driving local antennular reflexes in response to chemical and mechanical stimulation of the antennule, whereas the median antennular neuropil is a lower motor center for equilibrium responses.

Immunohistochemistry and neurochemistry of the habenulo-interpeduncular connection after partial developmental depletion of habenular cholinergic neurons in the rat.

The habenulo-interpeduncular system of the rat constitutes an interesting model to address quantitatively problems related to synaptogenesis and to the interactions between neuronal populations after selective alteration of these elements during development. In the present study this has been achieved by experimentally reducing, through gestational treatment with methylazoxymethanol acetate (MAM), the population of cholinergic neurons of the medial habenula which projects to the interpeduncular nucleus. Immunohistochemical analysis gave evidence that the topographical localization of the cholinergic and the substance P-containing populations in the medial habenula was not altered by MAM treatment. Furthermore, the topographical distribution of cholinergic fibers and terminals in the interpeduncular nucleus, which reflects the habenulo-interpeduncular projection as well as cholinergic projections coming from different sources, was substantially preserved. The same was also true concerning the terminal distribution of substance P in the interpeduncular nucleus. Quantitative radioassays demonstrated a sizable decrease of overall ChAT activity in both the habenulae and the interpeduncular nucleus. By comparison of 1 month-old and 3 month-old animals it appeared that this effect was partially reversed with age in the interpeduncular nucleus.

Control of neuronal survival by anomalous targets in the developing brain.

Described here is an aberrant parabigeminothalamic projection that follows neonatal lesions of the superior colliculus in rats, with evidence that this anomalous projection may sustain a normal number of neurons in the parabigeminal nucleus after early removal of the latter's tectal target. The aberrant projection was traced radioautographically to the tectorecipient zone of the lateral posterior nucleus after an injection of tritiated amino acid in the parabigeminal nucleus. Histochemical staining for cholinesterase revealed an anomalous patch of high enzyme activity in register with both the aberrant parabigeminothalamic projection and an abnormal retinal projection that also follows tectal lesions. Histochemical staining after either binocular enucleation or a tegmental lesion made simultaneous with the tectal ablation showed that the anomalous enzyme patch is a reliable marker of the aberrant parabigeminothalamic projection. It was also shown that the retinal projection is not needed for the formation of the anomalous parabigeminothalamic pathway. Ablation of the superior colliculus at birth failed to produce a net cell loss in the contralateral middle division of the parabigeminal nucleus after the period of natural neuronal death. Lesions extending toward the anomalous terminal field in the lateral posterior nucleus, however, prevented the survival of a normal number of neurons in the parabigeminal nucleus. When the unilateral tectal ablation was made together with a lesion of the ipsilateral posterior neocortex that produced cell loss in the thalamus, the number of neurons remaining in the middle division of the contralateral parabigeminal were linearly related to the cell content of the lateral posterior nucleus. We conclude that the anomalous target in the tectorecipient zone of the lateral posterior nucleus effectively replaces the normal projection field in the superior colliculus, with regard to the trophic requirements for neuronal survival during development of the parabigeminal nucleus.

The ontogeny of [3H]5-hydroxytryptamine binding in the lamb: effects of in vivo thyroidectomy.

The effects of congenital hypothyroidism in the late gestation ovine fetus include changes in serotonin concentrations in specific brain areas. To investigate possible ontogenic patterns of changes in 5-HT receptor function, we studied the binding characteristics of [3H]5-HT in the midbrain, hypothalamus and cerebral cortex in the late gestation ovine fetus and young lamb. We compared the binding characteristics of control fetuses to those of thyroidectomized fetuses, with or without thyroxine replacement therapy. In each of the areas examined, age-dependent changes in the receptor density (Bmax) for [3H]5-HT was observed. In cerebral cortex, Bmax was constant from 120 days gestation through the early neonatal period and increased significantly only at 25-30 days after birth. In hypothalamus, [3H]5-HT binding density decreased late in gestation (140-145 days) with a return after birth to values comparable to those at 120-125 and 130-135 days gestation. The midbrain also exhibited a significant age-dependent pattern of altered receptor density with a decrease in the 130-135 and 140-145 day gestational age groups compared to both younger and older lambs. In contrast, the affinity constant (Kd) for [3H]5-HT did not change over the ages evaluated in cerebral cortex or hypothalamus. In the midbrain, however, there was a significant increase in Kd at 1-5 days after birth compared to all other age groups. The ability of fetal thyroidectomy, with or without thyroxine replacement therapy, to alter patterns of [3H]5-HT binding was also tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Tachykinin binding sites in the interpeduncular nucleus of the rat: normal distribution, postnatal development and the effects of lesions.

Tachykinin binding sites in the basal midbrain were labeled in adult and neonatal rats using 125I-Bolton Hunter (BH) substance P (SP) and 125I-BH eledoisin as ligands. In the adult, binding was very low in the tegmentum and raphe adjacent to the interpeduncular nucleus (IPN). Within the IPN, no binding with either ligand was seen in the target subnuclei of the habenular SP and substance K projections, the lateral subnuclei and the cap of the rostral subnucleus. Labeling with 125I-BH-SP was very light and was restricted primarily to the central subnucleus of the IPN while 125I-BH-eledoisin labeling was very dense over the dorsal, the ventral sector of the rostral, the intermediate and the central subnuclei. Lesions of major afferents to the IPN, the fasciculus retroflexus or the locus coeruleus, had no effect on the distribution or density of the binding of either ligand. In rats 0, 4 or 7 days or age, 125I-BH-SP binding was very dense in the ventral tegmental region, the raphe and in the dorsal, rostral and central subnuclei. 125I-BH-eledoisin binding was extremely dense in the raphe and in the dorsal, rostral, intermediate and central subnuclei but was less dense in the ventral tegmentum. Adult levels of binding in the midbrain were established by 11 days of age. Neonatal lesions restricted to the fasciculus retroflexus had no effect on the density of labeling with either ligand in animals allowed to reach adulthood.

Axonal growth and target selection during development: retinal projections to the ventrobasal complex and other "nonvisual" structures in neonatal Syrian hamsters.

In newborn hamsters, there is a direct retinal projection to the ventrobasal complex, the principal thalamic somatosensory nucleus. The projection decreases precipitously between the second and third postnatal days. A few retinofugal axons remain dorsally along the lateral border of the nucleus on day 4, and none are present thereafter. In neonatal hamsters, retinofugal axons project to additional "nonvisual" nuclei including the periventricular and anterior nuclei of the hypothalamus, zona incerta, substantia nigra, inferior colliculus, pons, and mesencephalic tegmentum. Some of these connections remain in adult hamsters, although in apparently reduced density or relative volume, while others disappear. The contribution of transient connections to the normal morphological or functional development of the brain remains to be clarified. The combined results of this and other studies show that the normally transient retino-ventrobasal projection is a substrate for abnormal connections in that it can be permanently stabilized by appropriate neurosurgery on the day of birth.

Developmental sequence in the origin of descending spinal pathways. Studies using retrograde transport techniques in the North American opossum (Didelphis virginiana).

The origin of descending pathways to thoracic and cervical levels of the spinal cord has been investigated with retrograde tracing techniques in a series of pouch young and adult opossums. The opossum was chosen because it is born in a very immature state, 12-13 days after conception, and has a protracted development in an external pouch. A few neurons in the pontine reticular formation and nucleus coeruleus were labeled by horseradish peroxidase (HRP) injections of the thoracic cord as early as postnatal day (PND) 3. By PND 5, similar injections labeled neurons in the same areas as well as in the medullary reticular formation, the raphe nuclei of the caudal pons and medulla, the spinal trigeminal nuclei, the vestibular complex, the accessory oculomotor nuclei and the interstitial nucleus of Cajal. When Nuclear Yellow (NY) was employed, neurons were also labeled in the red nucleus, the hypothalamus and possibly in the nucleus of the solitary tract. Regardless of the technique employed, neurons in the dorsal column nuclei were not labeled by thoracic injections until at least PND 14. Axons from the nucleus ambiguus, the fastigial and interposed nuclei of the cerebellum as well as the intermediate and deep layers of the superior colliculus reach cervical levels of the cord, where they are specifically targeted, by at least PND 17. They do not significantly overgrow those levels during development. Corticospinal axons are the last of the major descending pathways to innervate the spinal cord. Cortical neurons cannot be labeled by cervical injections of either HRP or NY until at least PND 30. Evidence for transient brainstem-spinal and corticospinal projections was obtained.