Development of the rat thalamus: II. Time and site of origin and settling pattern of neurons derived from the anterior lobule of the thalamic neuroepithelium

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to examine the time of origin, settling pattern, and neuroepithelial site of origin of the anterior thalamic nuclei--the lateral dorsal (lateral anterior), anterodorsal, anteroventral and anteromedial nuclei--and of two rostral midline structures--the anterior paraventricular and paratenial nuclei. The neurons of the lateral dorsal nucleus are generated over a 3-day period between days E14-E16 and their settling pattern displays a combined lateral-to-medial and dorsal-to-ventral neurogenetic gradient. The bulk of the neurons of the anteroventral nucleus are generated over a 3-day period between days E15-E17 and settle with an oblique lateral-to-medial and ventral-to-dorsal neurogenetic gradient. The bulk of the neurons of the anteromedial nucleus are generated over a 2-day period between days E16-E17 and show the same settling pattern as the anteroventral nucleus. The neurons of the anterodorsal nucleus are generated over a 3-day period between days E15-E17 and show a lateral-to-medial neurogenetic gradient. The bulk of the neurons of the central part and lateral part of the paraventricular nucleus are generated over a 2-day period (E16-E17 and E17-E18, respectively) and each part displays a ventral-to-dorsal neurogenetic gradient. Finally, the bulk of the neurons of the paratenial nucleus are generated over a 4-day period between days E15-E18 and settle with a lateral-to-medial neurogenetic gradient. Observations are presented that the anterior thalamic nuclei, constituting the distinct "limbic thalamus," derive from a discrete neuroepithelial source. This is the crescent-shaped germinal matrix lining the diencephalic (medial) wall of the hitherto unrecognized anterior transitional promontory, which we call the anterior thalamic neuroepithelial lobule. On day E16 three migratory streams leave the anterior neuroepithelial lobule and, on the basis of their labeling pattern in relation to the neurogenetic gradients of the anterior thalamic nuclei, they are identified, from dorsal to ventral, as the putative migratory streams of the anterodorsal, anteroventral, and lateral dorsal nuclei. On day E17 the putative migratory stream of the anteromedial nucleus appears to leave the same neuroepithelial region that on the previous days was the source of the anteroventral nucleus. Dorsally, two neuroepithelial patches persist after day E17 and these are identified as the putative cell lines of the anterior paraventricular and paratenial nuclei.

Development of the preoptic area: time and site of origin, migratory routes, and settling patterns of its neurons

Neurogenesis and morphogenesis in the rat preoptic area were examined with [3H]thymidine autoradiography. For neurogenesis, the experimental animals were the offspring of pregnant females given an injection of [3H]thymidine on two consecutive gestational days. Nine groups were exposed to [3H]thymidine on embryonic days E13-E14, E14-E15, E21-E22, respectively. On postnatal day P5, the percentage of labeled cells and the proportion of cells originating during 24-hr periods were quantified at four anteroposterior levels in the preoptic area. Throughout most of the preoptic area there is a lateral to medial neurogenetic gradient. Neurons originate between E12-E15 in the lateral preoptic area, between E13-E16 in the medial preoptic area, between E14-E17 in the medial preoptic nucleus, and between E15-E18 in the periventricular nucleus. These structures also have intrinsic dorsal to ventral neurogenetic gradients. There are two atypical structures: (1) the sexually dimorphic nucleus originates exceptionally late (E15-E19) and is located more lateral to the ventricle than older neurons; (2) in the median preoptic nucleus, where older neurons (E13-E14) are located closer to the third ventricle than younger neurons (E14-E17). For an autoradiographic study of morphogenesis, pregnant females were given a single injection of [3H]thymidine during gestation, and their embryos were removed either two hrs later (short survival) or in successive 24-hr periods (sequential survival). Short-survival autoradiography was used to locate the putative neuroepithelial sources of preoptic nuclei, and sequential survival autoradiography was used to trace the migratory waves of young neurons and their final settling locations. The preoptic neuroepithelium is located anterior to and in the front wall of the optic recess. The neuroepithelium lining the third ventricle is postulated to contain a mosaic of spatiotemporally defined neuroepithelial zones, each containing precursor cells for a specific structure. The neuroepithelial zones and the migratory waves originating from them are illustrated. Throughout most of the preoptic area, neurons migrate predominantly laterally. The older neurons in the lateral preoptic area migrate earlier and settle adjacent to the telencephalon. Younger neurons migrate in successively later waves and accumulate medially. The sexually dimorphic neurons are exceptional since they migrate past older cells to settle in the core of the medial preoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological and behavioral markers of environmentally induced retardation of brain development: an animal model

In most neurotoxicological studies morphological assessment focuses on pathological effects, like degenerative changes in neuronal perikarya, axonopathy, demyelination, and glial and endothelial cell reactions. Similarly, the assessment of physiological and behavioral effects center on evident neurological symptoms, like EEG and EMG abnormalities, resting and intention tremor, abnormal gait, and abnormal reflexes. This paper reviews briefly another central nervous system target of harmful environmental agents, which results in behavioral abnormalities without any qualitatively evident neuropathology. This is called microneuronal hypoplasia, a retardation of brain development characterized by a quantitative reduction in the normal population of late-generated, short-axoned neurons in specific brain regions. Correlated descriptive and experimental neurogenetic studies in the rat have established that all the cerebellar granule cells and a very high proportion of hippocampal granule cells are produced postnatally, and that focal, low-dose X-irradiation either of the cerebellum or of the hippocampus after birth selectively interferes with the acquisition of the full complement of granule cells (microneuronal hypoplasia). Subsequent behavioral investigations showed that cerebellar microneuronal hypoplasia results in profound hyperactivity without motor abnormalities, while hippocampal microneuronal hypoplasia results in hyperactivity, as well as attentional and learning deficits. There is much indirect clinical evidence that various harmful environmental agents affecting the pregnant mother and/or the infant lead to such childhood disorders as hyperactivity and attentional and learning disorders. As the developing human brain is more mature at birth than the rat brain, the risk for microneuronal hypoplasia and consequent behavioral disorders may be highest at late stages of fetal development, in prematurely born and small-for-weight infants, and during the early stages of infant development. Recent technological advances in brain imaging techniques make it possible to test this hypothesis and to assess the possible relationship between the degree of retarded brain development and ensuing behavioral disorders.

Development of the precerebellar nuclei in the rat: III. The posterior precerebellar extramural migratory stream and the lateral reticular and external cuneate nuclei

Sequential thymidine radiograms from rats injected on day E15 and killed thereafter at daily intervals up to day E22 were analyzed to trace the migratory routes and settling patterns of neurons of the lateral reticular nucleus and the external cuneate nucleus. The neurons of the lateral reticular and external cuneate nuclei originate in the primary precerebellar neuroepithelium at the same site as the inferior olivary neurons but follow a different migratory route. The labeled young neurons that are produced on day E15 (the last one-third of the total) join the posterior precerebellar extramural migratory stream. The cells move circumferentially over the wall of the medulla in a ventral direction and by day E17 reach the midline and cross it beneath the inferior olive. The crossing cells apparently continue to migrate circumferentially on the opposite side. One complement of these cells begins to form a ventrolateral extramural condensation on day E19. By day E20 some cells begin to penetrate the parenchyma and settle as neurons of the lateral reticular nucleus. The settling of the lateral reticular neurons continues on the following day, and by day E22 all the cells destined for the lateral reticular nucleus have penetrated the parenchyma. A dorsomedial-to-ventrolateral neurogenetic gradient is indicated for the settling lateral reticular neurons. Another complement of migrating cells continues dorsally and forms a condensation on day E19 that we interpret as the external cuneate component of the crossed stream. These cells begin to penetrate the parenchyma on day E20, and by days E21 and E22 two components of the external cuneate nucleus are identifiable-the dorsal and ventral external cuneate nuclei. The neurons of the lateral reticular and external cuneate nuclei differ from neurons of all the other precerebellar nuclei in that their cerebellar projection is predominantly ipsilateral. We speculate that the axons of all precerebellar neurons are genetically specified to cross the midline ventrally to provide a contralateral efferent projection, but this is modified in the case of the ipsilaterally projecting lateral reticular and external cuneate neurons by the cell bodies following their neurites to the opposite side.

Development of the precerebellar nuclei in the rat: IV. The anterior precerebellar extramural migratory stream and the nucleus reticularis tegmenti pontis and the basal pontine gray

Sequential thymidine radiograms from rats injected on days E16, E17, E18, and E19 and killed 2 hours after injection and at daily intervals up to day E22 were used to establish the site of origin, migratory route, and settling patterns of neurons of the nucleus reticularis tegmenti pontis and basal pontine gray. The nucleus reticularis tegmenti pontis neurons, which are produced predominantly on days E15 and E16, derive from the primary precerebellar neuroepithelium. These cells, unlike those of the lateral reticular and external cuneate nuclei, take an anteroventral subpial route, forming the anterior precerebellar extramural migratory stream. This migratory stream reaches the anterior pole of the pons by day E18. In rats injected on day E16 and killed on day E18 some of the cells that reach the pons are unlabeled, indicating that they represent the early component of neurons generated on day E15. The cells labeled on day E16 begin to settle in the pons on day E19, 3 days after their production. These cells, migrating in an orderly temporal sequence, form a posterodorsal-to-anteroventral gradient in the nucleus reticularis tegmenti pontis. Unlike the neurons of all the other precerebellar nuclei, the basal pontine gray neurons derive from the secondary precerebellar neuroepithelium. The secondary precerebellar neuroepithelium forms on day E16 as an outgrowth of the primary precerebellar neuroepithelium, and it remains mitotically active through day E19, spanning the entire period of basal pontine gray neurogenesis. The secondary precerebellar neuroepithelium is surrounded by a horizontal layer of postmitotic cells, representing the head-waters of the anterior precerebellar extramural migratory stream. In rats injected on day E18 and killed on day E19 the cells are labeled in the proximal half of the stream around the medulla but those closer to the pons are unlabeled, indicating an orderly sequence of migration. In rats injected on day E18 and killed on day E20 the labeled cells reach the pole of the pons. In the basal pontine gray the sequentially generated neurons settle in a precise order. The neurons generated on day E16 form a small core posteriorly and the neurons generated on days E17, E18, and E19 form regular concentric rings around the core in an inside-out sequence.

Development of the precerebellar nuclei in the rat: I. The precerebellar neuroepithelium of the rhombencephalon

Short-survival thymidine radiograms from rat embryos aged 13-19 days were analyzed to delineate the precerebellar neuroepithelium of the rhombencephalon. The original definition of the term "rhombencephalon" was modified to refer only to the unique dorsal portion (surface plate) of the medulla and pons where the neural groove fails to fuse and, instead, the medullary velum covers the rhomboid lumen of the fourth ventricle. Initially, the neuroepithelial tissue of the rhombencephalon consists of a pair of rostral and caudal bridgeheads: the former the primary neuroepithelium of the cerebellum and the latter the primary neuroepithelium of the octavo-precerebellar system. The spatial relationship between the cerebellar and precerebellar neuroepithelia soon changes as a result of ongoing morphogenetic events, such that the cerebellar primordium assumes a dorsal position and the precerebellar primordium a ventral position, and the distance between the two decreases. Concurrently the tela choroidea invaginates into the fourth ventricle and a secondary precerebellar neuroepithelium develops. The rostral portion of the secondary precerebellar neuroepithelium grows forward along the choroid plexus and forms the medial recess of the anterior fourth ventricle, while its caudal portion grows in the opposite direction beneath the medullary velum and forms the rostral wall of the posterior fourth ventricle. Evidence will be presented in the succeeding papers that the primary precerebellar neuroepithelium first generates the neurons of the inferior olive that migrate by a circumferential intramural (parenchymal) route to their destination. Next, the neurons of the lateral reticular and external cuneate nuclei are generated. These migrate by a posterior extramural (superficial) route and settle contralaterally. Subsequently, the primary precerebellar neuroepithelium produces the neurons of the nucleus reticularis tegmenti pontis and these form the anterior extramural migratory stream and settle ipsilaterally. Finally, the secondary precerebellar neuroepithelium produces the latest generated neurons of the basal pontine gray that follow the anterior extramural stream and settle ipsilaterally.

Development of the precerebellar nuclei in the rat: II. The intramural olivary migratory stream and the neurogenetic organization of the inferior olive

Sequential thymidine radiograms from rats labeled on days E13 and E14, and killed at daily intervals thereafter, were analyzed to trace the migratory route and settling pattern of neurons of the inferior olive. Long-survival thymidine radiograms from perinatal rats injected on day E14 were used to subdivide the inferior olivary complex on the basis of neurogentic criteria. The inferior olivary neurons originate on days E13 and E14 in the primary precerebellar neuroepithelium. The olivary neurons labeled on day E14 (the late generated components) translocate into the inferior olivary premigratory zone on day E15. On day E16 these cells join the olivary migratory stream, which follows an intramural circumferential path between the gray and white matters of the medulla. By day E17 the olivary migratory stream is reduced to a small band near the corpus of the inferior olive, which has been settled by this time by neurons generated on day E13. As a result, the unlabeled cells are situated on day E17 dorsomedially and the labeled cells ventrolaterally. The regional segregation of neurons forming subdivisions of the inferior olive begins on day E18, and by day E19 the major subdivisions are all recognizable. In thymidine radiograms from perinatal rats injected on day E14, four neurogenetic components can be distinguished in the inferior olive, those composed: (1) of unlabeled cells (generated on day E13), (2) of predominantly unlabeled cells, (3) of predominantly labeled cells (generated on day E14), and (4) of labeled cells. By combining these neurogenetic differences with the morphological features of the inferior olivary complex, we propose a modification of the currently accepted classification. The four major divisions of the inferior olive are the successively produced posterodorsal olive, anterolateral (principal) olive, posteroventral olive, and anteroventral olive. The location and configuration of these divisions are illustrated in relation to the traditional classification both in the coronal and the sagittal plane.

A comparison of oral midazolam, nitrazepam and placebo in young and elderly subjects

Twelve young and twelve elderly subjects received a single dose orally of midazolam 15 mg, nitrazepam 5 mg and placebo in a double-blind, crossover comparison. Midazolam acted rapidly, producing a deep sleep at 1 h in fifteen subjects compared to two after Nitrazepam and none after placebo. No comparison of psychomotor tests was possible at this time, but such tests showed that there was no detectable subjective or objective psychomotor impairment at 4 h postdose with either drug. However, the EEG scores strongly suggested that volunteers were more sleepy at 8 h after nitrazepam in comparison to placebo or midazolam. Both groups appeared to handle the drug in a similar manner, there being no significant differences between the groups in the plasma concentration time curves of nitrazepam, or midazolam. The elderly had higher concentrations of alpha-hydroxymidazolam. This accounted for a small proportion of the total plasma benzodiazepine concentration, and the mean area under the curve for midazolam and metabolite was not significantly different in the old from that in the young.

A new Chlamydia psittaci strain, TWAR, isolated in acute respiratory tract infections

During a 2 1/2-year period, we studied 386 University of Washington students with acute respiratory disease, to determine whether a Chlamydia psittaci strain, here designated TWAR, is an important respiratory pathogen. Serologic evidence of recent TWAR infection was found in 13 students, and the organism was isolated from 8 of these. TWAR infection occurred in 12 percent of the students who had pneumonia (9 of 76), 5 percent of those with bronchitis (3 of 63), and 1 percent of those with pharyngitis (1 of 150). The TWAR infections occurred throughout the study period. Pharyngitis, often accompanied by laryngitis, was a common first symptom. Clinically, the infections resembled those with Myco-plasma pneumoniae; therefore, the patients were given courses of erythromycin used for the treatment of M. pneumoniae infections. This therapy proved to be inadequate. The limited data available suggest that the TWAR strain is a "human" C. psittaci that is spread from human to human, without a bird or animal host.

Lamellar ichthyosis with episodic psoriasiform reaction pattern

The skin of a girl born with the typical appearance of "collodion baby," evolved into an exfoliative erythroderma that clinically was lamellar ichthyosis. However, biopsy specimens done in early infancy showed psoriasis. Over the ensuing sixteen years she has continued to have clinical lamellar ichthyosis with rare occasions of febrile episodes and superficial pustules. Some biopsy specimens have been diagnosed as showing lamellar ichthyosis, while others have again shown psoriasis.

The role of reinforcement in reactive self-monitoring

The role of reinforcement in reactive self-monitoring was investigated. Subjects for this study were three mentally retarded adults employed in a sheltered workshop. Changes in productivity rates in a party hat assembly task across experimental conditions (reinforcements, self-monitoring, and self-monitoring plus reinforcement) were evaluated. Findings showed that while reinforcement alone increased productivity, it was to a lesser degree and with less consistency than when combined with self-monitoring. In addition, self-monitoring alone did not increase productivity. These results support the Rachlin and Nelson and Hayes hypotheses that reactive effects of self-monitoring are dependent upon environmental contingencies. The results also showed that self-monitoring increases the salience of reinforcement.

Cranial CT findings in sclerosteosis

Sclerosteosis or Van Buchem's disease is a rare genetic craniotubular hyperostosis that becomes evident in early childhood and is associated with progressive involvement of the skull. The pathologic changes in the cranium noted on CT are described in three cases. Although the disease is incurable, CT is useful to display the morbid anatomy of the cranium before palliative surgery.

Embryonic development of the rat cerebellum. II. Translocation and regional distribution of the deep neurons

In thymidine radiograms and plastic-embedded sections, the migration of cerebellar deep neurons was traced from their germinal source to their final settling sites. The route proved to be roundabout and three developmental events could be distinguished during the process. First, between days E14 and E16, transversely oriented cells of the nuclear transitory zone move in an arc from the ventrolateral neuroepithelium of the lateral cerebellar primordium in a medial direction. Second, between days E16 and E18, the cells of the rostral component of the nuclear transitory zone assume a longitudinal orientation. We postulated that this is the period of axonogenesis, the longitudinally oriented cells issuing efferents that join the superior cerebellar peduncle ipsilaterally and the transversely oriented cells (representing the neurons of the caudal fastigial nucleus) sending decussating fibers to the uncinate fasciculus (the hook bundle of Russell). Third, between days E18 and E21, the earlier-produced superficial cells of the nuclear transitory zone and the later-produced deep cells of the cortical transitory zone (the young Purkinje cells) exchange positions. The descent of the deep neurons is in the direction of the fibers of the inferior cerebellar peduncle, which becomes distributed throughout the cerebellum on day E17. The ascent of the Purkinje cells is in the direction of the external germinal layer, which begins to spread from caudal to rostral on day E17. The three deep nuclei, the lateral (dentate), interpositus, and medial (fastigial), can be distinguished before their descent into the depth of the cerebellum, and by day E22 a small-celled and a large-celled subdivision is identifiable in each nucleus.

Embryonic development of the rat cerebellum. I. Delineation of the cerebellar primordium and early cell movements

Short-survival and long-survival thymidine radiograms, and methacrylate-embedded tissue from normal and X-irradiated rat embryos were used to delineate the neuroepithelial source of the cerebellum and trace the earliest cell movements. The cerebellar anlage, crescent shaped, is demarcated by two ventricular landmarks, the anterior extension of the tela choroidea of the fourth ventricle and the embryonic cerebellar fissure. The cerebellar tela choroidea extends from the medullary fourth ventricle posteromedially to the lateral recess of the pontine fourth ventricle anterolaterally. The embryonic cerebellar fissure begins caudally as a single midline incision beneath the fused posterior cerebellar primordium, then splits to follow the unfused cerebellar halves, first separating each from the isthmus then from the pons. The cerebellar primordium is divided into three parts. The lateral cerebellar primordium caps the lateral recess of the fourth ventricle; it is contiguous with the pons medially and separated ventrally from the anlage of the cochlear nuclei by the tela choroidea. The subisthmal cerebellar primordium is situated beneath the isthmus, medially lining the isthmus canal. Laterally and posteriorly, it is continuous with the lateral and postisthmal primordia. The postisthmal cerebellar primordium caps the postisthmal recess of the fourth ventricle and extends to the medullary fourth ventricle. As we shall describe later, each of these primordia is a source of different components of the developing cerebellum. Most cells of the superficially located nuclear transitory zone are labeled with 3H-thymidine administered on day E14 but not thereafter. A high proportion of the cells of the deeper cortical transitory zone could still be labeled on day E15. This supports the assumption made earlier that the first is composed of differentiating deep neurons, the second of Purkinje cells. The cells of the nuclear transitory zone originate in the lateral cerebellar primordium near the junction with the tela choroidea prior to the formation of the germinal trigone and migrate in a superficial position medially. Beginning on day E16, the nuclear transitory zone splits into two components. One has transversely oriented cells that seem to be the source of a decussating fiber tract, presumably the hook bundle of Russell. The other is composed of longitudinally oriented cells that apparently contribute fibers to the ipsilateral superior cerebellar peduncle. The translocation of the cells of the nuclear transitory zone from the cerebellar surface to its depth, to form the deep nuclei, and the radial migration of the cells of the cortical transitory zone to the surfa

Embryonic development of the rat cerebellum. III. Regional differences in the time of origin, migration, and settling of Purkinje cells

The time of origin, site of origin, migratory path and settling pattern of the Purkinje cells of the cerebellar hemispheres, anterior vermis, and posterior vermis were investigated in thymidine radiograms and plastic-embedded materials from rat embryos ranging in age from 15 to 22 days. In the hemispheres there is a rostral-to-caudal cytogenetic gradient: the Purkinje cells of lobulus simplex, crus I, and crus II are produced earlier than the Purkinje cells of the paramedian lobule and paraflocculus, followed by the Purkinje cells of the flocculus. The Purkinje cells of the vermis, in general, are generated later than those of the hemispheres, and with a reverse gradient from caudal to rostral: the Purkinje cells of the posterior vermis (lobules X-VI) being produced ahead of the Purkinje cells of the anterior posteriorly directed wedge of early-produced Purkinje cells through the vermis. Evidence was obtained that the Purkinje cells of the hemispheres derive from the lateral cerebellar primordium capping the lateral recess of the fourth ventricle anteriorly. The Purkinje cells of the anterior vermis originate from the subisthmal cerebellar primordium medially lining the isthmal canal. The Purkinje cells of the posterior vermis originate in the postisthmal cerebellar primordium overlying the tela choroidea caudally. The young Purkinje cells migrate from the neuroepithelium to the surface of the cerebellum in a strictly caudal-to-rostral order, paralleling the spread of the EGL superficially from posteroventral to anterodorsal. This pattern is independent of the time of origin of Purkinje cells. In the posterior vermis the earliest-settling Purkinje cells of the uvula follow a short radial course, and a discrete Purkinje layer is formed 3 days after they are generated. In the anterior vermis the Purkinje cells of lobulus centralis, which follow an anterodorsal migratory course, are still settling on day E22, 7 days after their production, presumably awaiting the fusion of the cerebellar base anteriorly. The fissura prima forms medially at the interface region of Purkinje cells derived from the postisthmal and subisthmal cerebellar primordia. For 1-2 days after their settling, the Purkinje cells of the newly forming lobules can be distinguished by certain cytological criteria from the Purkinje cells in the more caudally-situated, earlier-settled lobules.

Potential use of biaromatic L-phenylalanyl derivatives as therapeutic agents in the treatment of sickle cell disease

N-Phenylacetyl-L-phenylalanine (PAP) and L-phenylalanyl-3-aminopyridine ( PAPA ) are biaromatic agents with properties that make them suitable candidates for the development of a useful therapeutic agent for the treatment of sickle cell disease. PAP and PAPA are taken up by the erythrocyte to give intra-/extracellular concentration ratios of 2.2 and 1.5, respectively, after a 2-hr exposure period. The intracellular buildup of PAP and PAPA produces moderate decreases in the mean corpuscular hemoglobin concentration (MCHC) of 6 and 10%, respectively, at 3 mM and a further decline in MCHC with increased concentration. Both PAP and PAPA increase the deoxy-Hb S solubility, CS. If the solubility in the absence of the agent is COS, PAP and PAPA have CS/COS values of 1.21 and 1.14 at 20 mM, respectively, compared with a value of 1.06 for L-phenylalanine itself. Filterability assays of partially dexygenated homozygous sickle cells shows an increase in cell flexibility of 7 to 16 times more than that of untreated cells when these agents are present at 3-6 mM. These results are largely due to the reduction in the Hb S polymer content of the treated cells. At 3 mM or less, both PAP and PAPA delay the onset of gelation in reversible sickle cells for time periods that are likely to be therapeutically useful.