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PubMed1994

Early development of the forebrain and midbrain: a longitudinal ultrasound study from 7 to 12 weeks of gestation.

The purpose of this longitudinal study was to describe embryonic development in vivo. Twenty-nine healthy pregnant women were examined five times with transvaginal ultrasound between 7 and 12 weeks of gestation. Brain structures such as the hemispheres, the choroid plexus of the lateral ventricles, the diencephalon, and the mesencephalon were identified and, if possible, measured. It was possible to identify the cavities of the hemispheres, the diencephalon and the mesencephalon during week 7. The choroid plexus of the lateral ventricles became visible during week 8. The growth of the length, width and height of the hemispheres and the choroid plexus of the lateral ventricles was curvilinear, that of the mesencephalon and diencephalon was linear except for the width of the diencephalon. The width of the diencephalon, the future third ventricle, was 1.1 mm during week 7. It decreased to 0.8 mm at 12 weeks. Apart from the rhombencephalon, the cavity of the diencephalon was the large dominating brain structure during embryonic development. In early fetal life the cerebral hemispheres took over this dominance. The study was in full agreement with descriptions in the embryological literature, both concerning the anatomical features and their chronological formation.

Journal Article↗

PubMed1995

Precocious invasion of the optic stalk by transient retinopetal axons.

This study demonstrates that the fetal optic nerve contains a conspicuous population of transient retinopetal axons. Implants of the carbocyanine dye, DiI, were made into the retina or diencephalon of fetal ferrets to label the retinopetal axons retrogradely or anterogradely, respectively, and sections were immunostained for beta-tubulin to label the early differentiating axons in the optic nerve. Dye implants into the optic nerve head, but not the retinal periphery, retrogradely labeled somata in the ventrolateral diencephalon, provided the implants were made before embryonic day (E) 30. When dye implants were made into the ventrolateral diencephalon, these same retinopetal axons were anterogradely labeled, coursing through the optic nerve but never invading the retina. The axons course as 2-5 fascicles from their cells of origin and turn laterally to enter the optic nerve where it joins the future hypothalamus. The retinopetal cells can be retrogradely labeled as early as E20, before optic axons have left the retina. The optic nerve and fiber layer are immunoreactive for beta-tubulin on E24 and thereafter, whereas on E20 and E22, they are immunonegative. Yet at these early embryonic ages, immunopositive fascicles of axons course from the diencephalon into the optic stalk, confirming the precocious nature of the retinopetal projection. Implants of dye made into the future optic nerve head at these very early stages also retrogradely label retinopetal cells in the future chiasmatic region. These cells are distributed primarily on the side ipsilateral to the midline, but a few can be found contralateral to it. Both these, as well as the retinopetal axons arising from the ventrolateral diencephalon, may serve a transient guidance function for later developing optic axons.

Afferent Pathways↗

PubMed1994

Increased extracellular serotonin in rat brain after systemic or intraraphe administration of morphine.

The effect of morphine on serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the CNS of unanesthetized rats was investigated by microdialysis. Morphine was administered either subcutaneously, by local perfusion into the diencephalon, or by intraraphe microinjection. Systemic administration of morphine resulted in a significant increase in both extracellular 5-HT and 5-HIAA in the diencephalon. The effect of morphine on 5-HT was dose dependent during local perfusion of the diencephalon with inhibitors of uptake or monoamine oxidase. Systemic morphine also produced significant increases in extracellular 5-HT in the striatum and hippocampus during uptake inhibition. The site of opioid effects on 5-HT was tested by locally perfusing morphine into the diencephalon. This had no effect on 5-HT or 5-HIAA. In contrast, intraraphe injection of morphine caused a dose-dependent increase in extracellular 5-HT and 5-HIAA in the diencephalon. These results suggest that systemic morphine induces an increase in 5-HT release in widespread areas of the forebrain. This appears to be due to an effect on 5-HT cell bodies and not on 5-HT nerve endings in projection sites.

Animals↗

PubMed1978

The diencephalic course of regenerating retinotectal fibres in Xenopus tadpoles.

The normal retinotectal path in the diencephalon of Xenopus tadpoles is widely distributed in the form of a wedge of fibres extending from the central grey to the outer margin of the diencephalon. Regenerating optic nerve fibres were shown, by silver-staining and proline autoradiography, to follow an abnormal path up the extreme lateral edge of the diencephalon. Study of tadpoles at various stages of development, and of optic nerves allowed to regenerate for various periods, indicates that all new incoming optic fibres pass up the lateral edge of the diencephalon. The inner/outer order of the fibres in the normal diencephalon thus reflects the radial distribution of the retinal cells of origin.

Animals↗

PubMed1987

Extra-axonal environment and fibre directionality in the early development of the chick embryo optic chiasm: a light and scanning electron microscopic study.

The events that occur during the early development of the optic chiasm of the chick embryo have been studied by light and scanning electron microscopy. In developmental stages previous to the arrival of the first optic fibres in the floor of the diencephalon, as well as during the arrival of the leading fibres, extracellular spaces can be seen in the diencephalon ventral wall. These spaces are defined by external cell prolongations which end in a foot-shaped formation. During stages 25 and 26 a prechiasmic degenerative centre appears in the area immediately rostral to the early chiasm, leading to a notable degree of disorganization in the diencephalon wall. This centre appears to be related to the reorganization of the system of external cell processes and extracellular spaces which become progressively more irregularly distributed, coinciding with the arrival of the first optic fibre fascicles to the midline of the floor of the diencephalon. The optic fibre fascicles change their latero-medial directionality in the medial-most regions of the ventral diencephalon, where their course becomes rostrocaudal. This reorientation of the optic fibres seems to be mediated by primitive glial cells which first appear in the ventrorostral region of the early chiasm (previously occupied by the system of external cell processes and extracellular spaces) in stage 26, increasing in number from this stage on. The morphology of the primitive glial cells is laminar in nature and the cells are seen to be densely packed together with no large extracellular spaces between them.

Animals↗

PubMed1977

Biochemical differentiation of aggregating cell cultures of different fetal rat brain regions.

Rotation-mediated aggregating cell cultures of mechanically dissociated fetal rat brains divided into three (telencephalon, mesencephalon-diencephalon and rhombencephalon), or two (telencephalon and mesencephalon-diencephalon plus rhombencephalon) parts were examined for their biochemical differentiation by measuring the specific activities of choline acetyltransferase, acetylcholinesterase, glutamic acid decarboxylase, tyrosine 3-monooxygenase, aromatic L-amino acid decarboxylase, catechol methyltransferase and monoamine oxidase. The results showed that such parts yielded cultures that were relatively enriched for acetylcholine-synthesizing (telencephalon) or catecholamine-synthesizing (mesencephalon-diencephalon and mesencephalon-diencephalon plus rhombencephalon) enzymes. For cultures which were derived from two brain divisions, the sum of the total activity for each enzyme in the parts after 30 days equalled that in whole brain cultures derived from the same group of embryos, suggesting that development of these enzymes was unaffected by division of the brain in two. In experiments to determine the effects of culture conditions on this development, chronic administration of certain drugs was found to selectively influence the specific activity of certain neurotransmitter metabolizing enzymes. Thus, in cultures of whole brain, ascorbic acid (0.2 mM) decreased tyrosine 3-monooxygenase and aromatic L-amino acid decarboxylase while other enzymes were slightly increased; and in cultures of telencephalon and mesencephalon-diencephalon plus rhombencephalon, N6, O2'-dibutyryladenosine 3',5'-cyclic phosphate (0.2 mM) decreased the specific activities of choline acetyltransferase acetylcholinesterase, glutamic acid decarboxylase and monoamine oxidase. These results demonstrate the feasibility of growing these cultures for pharmacological studies in developmental neurobiology.

Acetylcholinesterase↗

PubMed1990

Pluripotentiality of the 2-day-old avian germinative neuroepithelium.

In a previous study using chick/quail chimeric embryos with homotopic transplants (Martinez & Alvarado-Mallart, 1989b), we have delimited in the 2-day-old avian embryo the areas of the neural tube giving rise to optic tectum and mesencephalic grissea as well as to isthmic grissea and cerebellum: respectively, "mesencephalic" and "metencephalic" alar plates. To investigate the determination or the competence of these areas, portions of these germinative neuroepithelia from a quail embryo were transplanted in substitution for other areas of the chick neural tube. The analysis of the chimeric brains was done by comparing alternating transverse sections stained for cytoarchitecture and with two different techniques to recognize transplanted versus host cells: either the Feulgen and Rossenbeck DNA histochemical reaction and/or immunohistochemical methods with a monoclonal antibody recognizing quail but not chick cells. The eventual visual innervation of the quail graft was analyzed in many cases by injecting anterograde axonal tracers in the eye contralateral to the graft. The results are as follows: (1) caudal metencephalon transferred to mesencephalon maintained in all cases its presumptive cerebellar phenotype, whereas (2) rostral metencephalon transferred to mesencephalon changed its fate to a tectal phenotype but maintained its cerebellar fate when transferred to diencephalon; (3) caudal mesencephalon maintained its tectal fate in 65% of the cases when transferred to diencephalon, whereas (4) rostral mesencephalon transferred to a cerebellar domain changed its fate and became influenced by the surrounding structures in all cases, but only in 85% of the cases when it was transplanted to diencephalon; (5) the in situ host diencephalon, isolated from its normal environment by a mesencephalic graft, is competent to change its fate and express a mesencephalic phenotype. These results demonstrate that at least some regions of the germinative neuroepithelium from either metencephalon, mesencephalon, and diencephalon are still pluripotent in the 2-day-old avian embryo and that their fate seems to be under the influence of the surrounding structures. Rostral mesencephalon and rostral metencephalon have been more easily influenced by environmental factors than their caudal counterparts, suggesting that regions providing instructive positional factors exist within the 2-day-old germinative neuroepithelium. These regions might play an important role in the determination of the various segments of the neural tube.

Animals↗

PubMed1990

Reduction of thyrotropin-releasing hormone concentrations in central nervous system of African lungfish during estivation.

Thyrotropin-releasing hormone (TRH) has been implicated as an important modulator of arousal state in mammals. Changes in the content of TRH in several brain regions accompany hibernation in the ground squirrel. In the present study, the involvement of TRH in the regulation of arousal was further investigated in the African lungfish, Protopterus annectens, which contain high concentrations of TRH throughout its central nervous system and enter a hibernation-like state, estivation. Lungfish were divided into three groups. Group 1 was fed normally, group 2 was starved while aquatic, and group 3 was allowed to enter into a state of estivation. After 3 months, the lungfish were sacrificed and the concentrations of TRH, norepinephrine, dopamine, and serotonin were determined in the telencephalon, diencephalon, medulla, and spinal cord. In estivation, there was a significant decline in the concentration of TRH in the diencephalon, with no alteration in other regions. Starvation had no effect on regional TRH concentrations. The concentration of norepinephrine, dopamine, and serotonin did not change in estivation; however, a significant elevation of norepinephrine in the diencephalon and dopamine in the telencephalon was observed in starvation. Starvation and estivation were associated with significant declines in the protein content of the diencephalon and medulla. The estivation-linked decline in TRH in the diencephalon of the lungfish is similar to the decrease in TRH content in the hypothalamus in hibernating ground squirrels. These findings lend further support to the importance of TRH in the regulation of arousal state.

Adaptation, Physiological↗

PubMed1983

Changes in brain amines associated with cancer anorexia.

Analysis of indole amine metabolism within acute (Walker 256 carcinosarcoma) and chronic (methycholanthrene-induced sarcoma) animal models of cancer anorexia demonstrated elevated levels of plasma free tryptophan, whole brain tryptophan, serotonin and 5-hydroxyindoleacetic acid in anorectic tumor-bearing rats. Whole brain levels of catecholamines were not changed within either tumor line. Regional central nervous system determination of tryptophan metabolism in rats bearing Walker 256 tumors revealed elevated tryptophan in the hypothalamus, corpus striatum, mesencephalon, diencephalon, cerebellum and cortex, increased serotonin in the diencephalon and cerebellum and elevated 5-hydroxyindoleacetic acid in the diencephalon, hippocampus, pons-medulla, cerebellum and cortex. Although tryptophan was significantly increased only in the corpus striatum and diencephalon of the more chronic methycholanthrene tumor model, serotonin concentration was elevated in the corpus striatum, diencephalon, hippocampus, pons-medulla, cerebellum and cortex, while levels of 5-hydroxyindoleacetic acid were significantly increased in all these areas as well as in the mesencephalon. Since similar changes in indole activity were not observed in pair-fed control rats, it is concluded that the elevated serotonin and 5-hydroxyindoleacetic acid levels in tumor-bearing rats did not result from undernutrition alone. Assay of regional catecholamines revealed few food-relevant changes, with norepinephrine being elevated in the corpus striatum and decreased in the pons-medulla of tumor-bearing rats. Therefore, these experiments suggest that the increased serotonin metabolism observed in tumor-bearing rats may be involved in the etiology of the anorexia of cancer.

Amino Acids↗

PubMed1989

Effects of idebenone on metabolism of monoamines and cyclic AMP formation in rats.

Idebenone, 6-(10-hydroxydecyl)-2,3-dimethoxy-5-methyl-1,4-benzoquinone, at a dose of 100 mg/kg (i.p.) markedly increased the level of 5-hydroxyindole-3-acetic acid (5-HIAA) in several brain regions without affecting monoamine contents in normal rats. In rats with cerebral ischemia, idebenone (10 mg/kg, i.p.) normalized the decreased levels of 5-HIAA in the cerebral cortex, hippocampus, diencephalon and brain stem. A 5-hydroxytryptamine (serotonin, 5-HT) biosynthesis inhibitor, DL-p-chlorophenylalanine (PCPA, 150 mg/kg, i.p.) decreased the levels of 5-HT to one-third of the control level 24 h after administration. Idebenone (10, 30, or 100 mg/kg, i.p.), administered 24 h after the treatment with PCPA, accelerated the PCPA-induced 5-HT decreased in the hippocampus, diencephalon and brain stem in a dose-dependent manner. Idebenone (100 mg/kg, i.p.) stimulated the release of 5-HT in the dorsal hippocampus as determined by in vivo differential pulse voltammetry. Idebenone, like p-chloroamphetamine (PCA), stimulated 5-HT release from slices of hippocampus and diencephalon, and the formation of cyclic AMP in a concentration-dependent manner in rat diencephalon slice. This stimulation was almost completely blocked by methysergide, a 5-HT receptor blocker. Idebenone slightly and PCA markedly inhibited 5-HT uptake into hippocampus slices. The mechanism of the 5-HT releasing actions of idebenone in the hippocampal slices may be mediated through endogenous calcium. These results suggest that idebenone has an enhancing effect on the turnover of 5-HT in the hippocampus, diencephalon, and brain stem of rats.

Animals↗

PubMed1991

Establishment of rostrocaudal polarity in tectal primordium: engrailed expression and subsequent tectal polarity.

In the E4 (embryonic day 4) chick tectal primordium, engrailed expression is strong at the caudal end and gradually weakens toward the rostral end. We used quail-chick chimeric tecta to investigate how the caudorostral gradient of engrailed expression is established and whether it is correlated with the subsequent rostrocaudal polarity of tectal development. To examine the positional value of the tectal primordium, we produced ectopic tecta in the diencephalon by transplanting a part of the mesencephalic alar plate heterotopically. In the ectopic tectum, the gradient of the engrailed expression reversed and the strength of the expression was dependent on the distance from the mes-diencephalon junction; the nearer the ectopic tectum was to the junction, the weaker the expression was. Consequently, the pattern of the engrailed expression in the host and ectopic tecta was nearly a mirror image, suggesting the existence of a repressive influence around the mes-diencephalon junction on the engrailed expression. We examined cytoarchitectonic development in the ectopic tecta, which normally proceeds in a gradient along the rostrocaudal axis; the rostral shows more advanced lamination than the caudal. In contrast, the caudal part of the ectopic tecta (near to the mes-diencephalon junction) showed more advanced lamination than the rostral. In both the host and ectopic tecta, advanced lamination was observed where the engrailed expression was repressed, and vice versa. Next we studied the correlation between engrailed expression and retinotectal projection from a view of plasticity and rigidity of rostrocaudal polarity in the tectum. We produced ectopic tecta by anisochronal transplantations between E3 host and E2 donor, and showed that there is little repressive influence at E3 around the mes-diencephalon junction. We then made chimeric double-rostral tectum (caudal half of it was replaced by rostral half of the donor tectum) or double-caudal tectum at E3. The transplants kept their original staining pattern in hosts. Consequently, the chimeric tecta showed wholly negative or positive staining of engrailed protein on the grafted side. In such tecta retinotectal projection pattern was disturbed as if the transplants retained their original position-specific characters. We propose from these heterotopic and anisochronal experiments that the engrailed expression can be a marker for subsequent rostrocaudal polarity in the tectum, both as regards cytoarchitectonic development and retinotectal projection.

Animals↗

PubMed1975

Central sites of naloxone-precipitated shaking in the anesthetized, morphine-dependent rat.

Naloxone hydrochloride, an opiate antagonist, administered via the intracranial or parenteral route precipitates shaking behavior in the morphine-dependent rat. We made localized bilateral injections of naloxone HCl, 1.5 mug/rat, into 60 subcortical sites of the pentobarbital-anesthetized, morphine-dependent rat and found that two circumscribed areas of the brain, the medial hypothalamus and the periaqueductal-4th ventricular spaces, were selectively sensitive to naloxone-precipitated shaking. In the nondependent rat, morphine injections into the anterior diencephalon inhibited the shaking response to ice water; injections of morphine into the medial diencephalon were less effective. However, naloxone antagonized the morphine-inhibited shaking more effectively when injections of naloxone were made in the medial diencephalon than when injections were made in the anterior diencephalon. These results suggest that the reciprocal relationship of morphine and morphine-naloxone effects on shaking behavior may be regulated by topographically different structures in the diencephalon.

Animals↗

PubMed2000

Morphologic fate of diencephalic prosomeres and their subdivisions revealed by mapping cadherin expression.

The expression of four cadherins (cadherin-6B, cadherin-7, R-cadherin, and N-cadherin) was mapped in the diencephalon of chicken embryos at 11 days and 15 days of incubation and was compared with Nissl stains and radial glial topology. Results showed that each cadherin is expressed in a restricted manner by a different set of embryonic divisions, brain nuclei, and their subregions. An analysis of the segmental organization based on the prosomeric model indicated that, in the mature diencephalon, each prosomere persists and forms a coherent domain of gray matter extending across the entire transverse dimension of the neural tube, from the ventricular surface to the pial surface. Moreover, the results suggest the presence of a novel set of secondary subdivisions for the dorsal thalamus (dorsal, intermediate, and ventral tiers and anteroventral subregion). They also confirm the presence of secondary subdivisions in the pretectum (commissural, juxtacommissural, and precommissural). At most of the borders between the prosomeres and their secondary subdivisions, changes in radial glial fiber density were observed. The diencephalic brain nuclei that derive from each of the subdivisions were determined. In addition, a number of previously less well-characterized gray matter regions of the diencephalon were defined in more detail based on the mapping of cadherin expression. The results demonstrate in detail how the divisions of the early embryonic diencephalon persist and transform into mature gray matter architecture during brain morphogenesis, and they support the hypothesis that cadherins play a role in this process by providing a framework of potentially adhesive specificities.

Animals↗

PubMed1988

The first appearance of the future cerebral hemispheres in the human embryo at stage 14.

Thirty-five embryos of stage 14 (32 days) were studied in detail and graphic reconstructions of four of them were prepared. Characteristic features of this stage include the beginning formation of the future cerebral hemispheres and the cerebellar plates. The ventral boundary between telencephalon medium and diencephalon is the preoptic recess. Although a velum transversum is not yet distinguishable as a dorsal boundary, its site is indicated by a change in the thickness of the roof of the forebrain. As the cerebral vesicles (future hemispheres) begin to evaginate, a di-telencephalic sulcus and a corresponding lateral ventricle and ventricular ridge (torus hemisphericus) develop. The telencephalic wall is mainly ventricular layer but three areas show advanced differentiation: olfactory area, future amygdaloid body (which lies at first mainly in the diencephalon), and primordium of the hippocampus. The telencephalon is growing in length, and the forebrain now occupies almost one quarter of the total length of the brain. The two neuromeres of the diencephalon are no longer as clearly delineated. The floor of D1 presents a thickened chiasmatic plate; that of D2 includes the infundibulum, which is closely related to the adenohypophysial pouch. The ventricular surface of D1 presents elevations for the dorsal and ventral thalami, separated by the sulcus medius. Other features of the diencephalon include the ventricular eminence (medial ventricular ridge) of the basal nuclei and the hypothalamic cell cord, from which the preopticohypothalamotegmental tract arises. The roof of D2 contains the evaginating part of the synencephalon. The mesencephalic angle continues to diminish. Two neuromeres, M1 and M2, are still distinguishable. The oculomotor nucleus emits nerve fibres, as does also the trochlear nucleus, which lies in the isthmic segment. Some extracerebral oculomotor fibres are present, but decussating and extracerebral trochlear fibres have not yet appeared. In the region of the tectum, two nuclei are discernible, and will form the medial tectobulbar tract and the mesencephalic root of the trigeminal nerve, respectively. The medial longitudinal fasciculus is present. A "median ventricular formation" is sometimes found in the mesencephalic roof. The cerebellum is the widest part of the brain. Two neuromeres (isthmic segment and Rh1) are involved in its formation. Most of the cerebellar plate has differentiated an intermediate layer, and the future rhombic lip is discernible. Indications of an efferent fibre system are present. In addition to the cerebellum, the rhombencephalon includes Rh1 to Rh7, and RhD.(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗

PubMed1982

Neurogenesis in the chick ventral lateral geniculate and ectomammillary nuclei: relationship of soma size to birthdate.

This study had 3 objectives: to determine if there are gradients of neuron production in the chick diencephalon and mesencephalon, to determine if large neurons are produced before small neurons, and to determine the period of neurogenesis in the ventral lateral geniculate nucleus (GLv) and ectomammillary nucleus (EMN). Tritiated thymidine autoradiography and a cumulative labeling analysis were used in determining neuron birthdates. In our studies the diencephalon, mesencephalon, and EMN did not exhibit clearcut gradients of neuron proliferation. The GLv possessed an inside to outside laminar gradient and a more subtle caudal to rostral gradient of neurogenesis. There was a consistent negative correlation between neuron size and embryonic age among nuclear groups of the diencephalon, in general, and within the GLv and EMN in particular. The neurons of the GLv and EMN were produced from the third to the seventh day of incubation. It was concluded that there is an irregular sequence of production of nuclear groups in the diencephalon and mesencephalon rather than a series of recognizable neurogenetic gradients. Neuron size, however, is an important factor in predicting the order of neuron production.

Aging↗

PubMed1990

GABA and glycine as putative transmitters in subcortical pathways to the pontine nuclei. A combined immunocytochemical and retrograde tracing study in the cat with some observations in the rat.

Using the retrograde tracers horseradish peroxidase-wheatgerm agglutinin and gold particles conjugated to wheatgerm agglutinin apo-horseradish peroxidase in combination with an antiserum against glutaraldehyde-fixed GABA, it was examined whether the pontine nuclei of the cat receive projections from GABA-like immunoreactive neurons in the brainstem, diencephalon, or deep cerebellar nuclei, contributing to the GABA-like immunoreactive fibre plexus previously demonstrated in the pontine nuclei [Brodal et al. (1988) Neuroscience 25, 27-45]. Following tracer injections that covered both the pontine nuclei and the reticular tegmental nucleus in two cats, it was found that 125 out of 1166 (10.7%) and 29 out of 294 (9.9%) retrogradely labelled neurons in the cerebellar nuclei were GABA-like immunoreactive. In the same two experiments only six out of 2029 (0.3%) and 10 out of 1398 (0.7%) retrogradely labelled neurons in the brainstem and diencephalon were GABA-like immunoreactive. Among the regions in the brainstem and diencephalon known to project to the pontine nuclei, double-labelled cells were seen in the reticular formation, the periaqueductal gray, and the nucleus praepositus hypoglossi, but not in the zona incerta or the anterior pretectal nucleus, regions that have been shown to contain glutamate decarboxylase-like immunoreactive neurons projecting to the pontine nuclei in the rat [Border et al. (1986) Brain Res. Bull. 17, 169-179]. In order to test whether this is due to species differences, the same experimental approach was used in the rat, and it was found that 54 out of 3249 (1.7%) retrogradely labelled neurons in the brainstem and diencephalon were double-labelled. Notably, in the zona incerta 2% of the retrogradely labelled cells were also GABA-like immunoreactive, and in the reticular formation there was a higher proportion of double-labelled cells than was found in the cat. Additional sources were identified, that may contribute to the GABA-like immunoreactive fibre plexus in the pontine nuclei of the rat. This, in conjunction with the previous finding that the pontine nuclei of the rat contain only very few putative GABAergic neurons [Border and Mihailoff (1985) Expl Brain Res. 59, 600-614; Brodal et al. (1988) Neuroscience 25, 27-45], lead to the suggestion that the GABA-like immunoreactive fibre plexus in the pontine nuclei of the rat is predominantly of extrinsic origin, possibly representing a mosaic of the terminal fields of several subcorticopontine projections.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Regional expression of the Wnt-3 gene in the developing mouse forebrain in relationship to diencephalic neuromeres.

During early vertebrate development, a series of neuromeres divides the central nervous system from the forebrain to the spinal cord. Here we examine in more detail the expression of Wnt-3, a member of the Wnt gene family of secreted proteins, in the developing diencephalon, in comparison to the expression of the homeobox gene Dlx-1. In 9.5-day mouse embryos, Wnt-3 is expressed in a restricted area of the diencephalon before any morphological signs of subdivisions appear. Around embryonic day 11.5, Wnt-3 expression becomes restricted to one of the neuromeres of the diencephalon, the dorsal thalamus. Dlx-1 is expressed in a non-overlapping area immediately anterior to and abutting the Wnt-3 expressing domain, corresponding to the ventral thalamus. In addition, Wnt-3 is expressed in the midbrain-hindbrain region. In the adult mouse, Wnt-3 and Dlx-1 are expressed in subsets of neural cells derived from the original areas of expression in the diencephalon. Taken together, our results suggest that Wnt-3 and Dlx-1 provide positional information for the regional specification of neuromeres in the forebrain. The continued expression of these genes in the adult mouse brain suggests a distinct role in the mature CNS.

Aging↗

PubMed2004

Territorial aggression, circulating levels of testosterone, and brain aromatase activity in free-living pied flycatchers.

Testosterone (T) is a critical endocrine factor for the activation of many aspects of reproductive behavior in vertebrates. Castration completely eliminates the display of aggressive and sexual behaviors that are restored to intact level by a treatment with exogenous T. There is usually a tight correlation between the temporal changes in plasma T and the frequency of reproductive behaviors during the annual cycle. In contrast, individual levels of behavioral activity are often not related to plasma T concentration at the peak of the reproductive season suggesting that T is available in quantities larger than necessary to activate behavior and that other factors limit the expression of behavior. There is some indication from work in rodents that individual levels of brain aromatase activity (AA) may be a key factor that limits the expression of aggressive behavior, and in agreement with this idea, many studies indicate that estrogens produced in the brain by the aromatization of T may contribute to the activation of reproductive behavior, including aggression. We investigated here in pied flycatcher (Ficedula hypoleuca) the relationships among territorial aggression, plasma T, and brain AA at the peak of the reproductive season. In a first experiment, blood samples were collected from unpaired males holding a primary territory and, 1 or 2 days later, their aggressive behavior was quantified during standardized simulated territorial intrusions. No relationship was found between individual differences in aggressive behavior and plasma T or dihydrotestosterone levels but a significant negative correlation was observed between number of attacks and plasma corticosterone. In a second experiment, aggressive behavior was measured during a simulated territorial intrusion in 22 unpaired males holding primary territories. They were then immediately captured and AA was measured in their anterior and posterior diencephalon and in the entire telencephalon. Five males that had attracted a female (who had started egg-laying) were also studied. The paired males were less aggressive and correlatively had a lower AA in the anterior diencephalon but not in the posterior diencephalon and telencephalon than the 22 birds holding a territory before arrival of a female. In these 22 birds, a significant correlation was observed between number of attacks/min displayed during the simulated territorial intrusion and AA in the anterior diencephalon but no correlation was found between these variables in the two other brain areas. Taken together, these data indicate that the level of aggression displayed by males defending their primary territory may be limited by the activity of the preoptic aromatase, but plasma T is not playing an important role in establishing individual differences in aggression. Alternatively, it is also possible that brain AA is rapidly affected by agonistic interactions and additional work should be carried out to determine whether the correlation observed between brain AA and aggressive behavior is the result of an effect of the enzyme on behavior or vice versa. In any case, the present data show that preoptic AA can change quite rapidly during the reproductive cycle (within a few days after arrival of the female) indicating that this enzymatic activity is able to regulate rapid behavioral transitions during the reproductive cycle in this species.

Aggression↗