Shirley A. Bayer

The development of the rat spinal cord.

1 Introduction.- 2 Materials and Methods.- 2.1 Whole-Body Long-Survival (Late Fetal) Thymidine Radiograms.- 2.2 Spinal Cord Long-Survival (Adult) Thymidine Radiograms.- 2.3 Whole-Body Short Survival Thymidine Radiograms.- 2.4 Methacrylate-Embedded Embryos.- 3 A Survey of the General Features of the Spinal Cord and Its Development.- 3.1 Organization of the Spinal Cord.- 3.2 Development of the Spinal Cord.- 4 Development of Motor Neurons and the Growth of Ventral Root Fibers.- 4.1 Time of Production of Large Motor Neurons.- 4.2 Maturation and Columnar Segregation of Motor Neurons.- 4.3 Growth of Motor Fibers and Their Penetration into Somites and Limb Buds.- 4.4 Time of Origin and Maturation of the Preganglionic Motor Neurons.- 5 Development of Sensory Neurons and Growth of the Dorsal Root System.- 5.1 Time of Origin of Dorsal Root Ganglion Cells.- 5.2 Sites of Origin of the Dorsal Root Ganglia and the Spinal Boundary Caps.- 5.3 Maturation of the Dorsal Root Ganglia and of the Boundary Caps.- 5.4 Segmentation of the Boundary Caps and Dorsal Root Ganglia and the Growth of Distal Sensory Fibers.- 5.5 Growth of the Dorsal Root Fibers and of the Dorsal Funiculus.- 6 Development of Relay Neurons: The Contralaterally and Ipsilaterally Projecting Cells.- 6.1 Time of Origin of Contralaterally and Ipsilaterally Projecting Relay Neurons.- 6.2 Transverse Microsegments of the Contralaterally and Ipsilaterally Projecting Relay Neurons.- 6.3 Identity and Settling Patterns of the Sequentially Produced Relay Neurons.- 7 Development of the Interneurons of the Dorsal Horn.- 7.1 Time of Origin and the Settling of the Interneurons of the Dorsal Horn.- 7.2 Time of Origin of the Interneurons of the Dorsomedial Gray.- 8 Development of Some Glial Components of the Spinal Cord.- 9 General Discussion.- 9.1 Development of the Transverse Organization of the Spinal Cord with Some Functional Considerations.- 9.2 Development of the Longitudinal Organization of the Spinal Cord with Some Functional Considerations.- 9.3 Some Guidance Mechanisms in the Growth of Spinal Afferents and Afferents.- 10 Summary.- 11 References.- 12 Subject Index.

The hippocampus and behavioral maturation.

The morphology and connections of the hippocampus are briefly described in light of recent anatomical investigations. There is a lack of direct connections with primary sensory and motor structures, instead the hippocampus is the focal point of two loops: the direct septohippocampal loop mediated by cells of the dentate gyrus and regio inferior; and an indirect corticohippocampal loop involving the entorhinal cortex, regio superior, the mammillary body, anterior thalamic nuclei, and cingulate cortex. The literature on the effects of hippocampal lesions on behavior is briefly reviewed. It is suggested that the hippocampus facilitates response braking in the aroused animal. Accordingly, hippocampectomy leads in ambiguous appetitive learning situations to bouts of response emission even when these do not lead to or even interfere with reinforcement; in aversive conflict situations to hyperreactivity rather than defensive immobility; and, while engaged in a prepotent behavioral act, to reduced attentiveness. Septal lesions produced changes similar to those produced by hippocampectomy, while in some tests the opposite effects were obtained after cingulectomy. The different electrical patterns of the hippocampus accompanying different behavioral states are reinterpreted in light of the assumption that the hippocampus is involved in the braking of response emission in the aroused animal by facilitating the septum and inhibiting the cingulate cortex. Desynchronized high amplitude activity is assumed to represent hippocampal inactivation when voluntary activity is not in progress; synchronous slow activity (theta wave) represents the alerting of the braking system without engagement, which is set in readiness concurrently with the onset of voluntary activity; and desynchronized low amplitude is the correlate of the actual engagement of the braking system, as when responding is stopped in the passive avoidance situation. Finally, the syndromes of hippocampectomy in adults are identified as juvenile traits and the hypothesis is put forward that the function of the late-maturing hippocampus is to transform “exuberant,” “reckless,” and “inattentive” juveniles into “placid,” “cautious,” and “observant” adults. This hypothesis predicts that hippocampectomized adults will display additional juvenile traits to those already recognized, and that treatments that retard, accelerate, or prolong postnatal hippocampal development will affect behavioral maturation.

Development of the Cranial Nerve Ganglia and Related Nuclei in the Rat

1 Introduction.- 2 Materials and Methods.- 2.1 Whole-Body Thymidine Radiograms.- 2.2 Paraffin- and Methacrylate-Embedded Embryos.- 3 Development of the Trigeminal Ganglion in Relation to the Trigeminal Nuclei.- 3.1 Time of Origin of Trigeminal Ganglion Cells.- 3.2 Fate of the Two Components of the Trigeminal Anlage.- 3.3 Development of the Trigeminal Nuclei of the Upper Medulla.- 4 Development of the Facial Ganglion in Relation to the Facial Motor Nucleus.- 4.1 Time of Origin of Facial Ganglion Cells.- 4.2 Embryonic Development of the Facial Ganglion.- 4.3 Development of the Facial Motor Nucleus and Nerve.- 5 Development of the Vestibular Ganglion in Relation to the Vestibular Nuclei.- 5.1 Time of Origin of Vestibular Ganglion Cells.- 5.2 Embryonic Development of the Vestibular Ganglion.- 5.3 Embryonic Development of the Vestibular Nuclei.- 6 Development of the Glossopharyngeal and Vagal Ganglia in Relation to the Solitary and Ambiguus Nuclei.- 6.1 Time of Origin of Glossopharyngeal and Vagal Ganglion Cells.- 6.2 Embryonic Development of the Glosso pharyngeal and Vagal Ganglia.- 6.3 Development of some Medullary Nuclei Associated with the Glossopharyngeal and Vagal Nerves.- 7 An Aspect of the Development of the Hypoglossal Nucleus and Nerve.- 8 General Discussion.- 8.1 Sequence of Production of Motor Neurons, Ganglion Cells, and Sensory Neurons of the Cranial Nerves.- 8.2 Placodal Origin of Ganglion Cells.- 8.3 Nerve-Specific Boundary Caps and Their Possible Role in the Guidance of Afferents and Efferents.- 8.4 Sites of Neuron Production, Routes of Migration, and the Relation Between Cytogenetic Zones and Neuroepithelial Zones in the Medulla.- 9 Summary.- Abbreviations.- References.

The development of the rat hypothalamus

1 Introduction.- 2 Materials and Methods.- 3 An Overview of the Organization of the Hypothalamus.- 4 Delineation of the Hypothalamic Primordium of the Third Ventricle Neuroepithelium.- 5 Development of the Reticular Hypothalamus: The First Wave.- 5.1 The Lateral Hypothalamus.- 5.2 The Entopeduncular Nucleus.- 5.3 The Zona Incerta.- 6 Development of the Core Hypothalamus: The Second Wave.- 6.1 Development of the Preoptic Area.- 6.2 Development of the Anterior Hypothalamus: Rostral Region.- 6.2.1 The Anterior Hypothalamic Nuclei.- 6.2.2 The Paraventricular Nucleus.- 6.2.3 The Supraoptic Nucleus.- 6.2.4 The Problem of the Bed Nucleus of the Stria Terminalis.- 6.3 Development of the Anterior Hypothalamus: Caudal Region.- 6.3.1 The Ventromedial Nucleus.- 6.3.2 The Dorsomedial Nucleus.- 6.4 Development of the Posterior Hypothalamus: Ventral Region.- 6.4.1 The Subthalamic Nucleus.- 6.4.2 The Tuberal Magnocellular Nucleus.- 6.4.3 The Premammillary Nuclei.- 6.5 Development of the Posterior Hypothalamus: Dorsal Region.- 6.5.1 The Supramammillary Nucleus.- 6.5.2 The Posterior Area Nuclei.- 6.6 Development of the Mammillary Body.- 7 Development of the Midline Hypothalamus: The Third Wave.- 7.1 The Suprachiasmatic Nucleus.- 7.2 The Arcuate Nucleus.- 7.3 The Periventricular Field.- 8 Development of the Specialized Linings of the Third Ventricle.- 9 Development of Some Glial Components of the Hypothalamus.- 10 General Discussion.- 11 Summary.- References.

Postnatal Development of the Hippocampal Dentate Gyrus Under Normal and Experimental Conditions

Recent studies using [3H] thymidine autoradiography produced convincing evidence that in the development of a particular brain region the small, short-axoned cells come into existence after the larger long-axoned cells. Indeed, in an altricial rodent, the rat, the granular nerve cells of the olfactory bulb, hippocampus, cerebellum, and cochlear nucleus are formed exclusively or predominantly after birth (Altman and Das, 1965a). There are indications that these short-axoned neurons (microneurons) arise from late-forming secondary germinal matrices (like the subependymal layer of the forebrain ventricles and the external germinal layer of the cerebellar cortex), in contrast to the long-axoned neurons (macroneurons) which originate from the periventricular primary matrix, the neuroepithelium (Altman, 1969). We do not as yet have an adequate explanation of the delayed formation of microneurons but the importance of these elements in the maturation of brain functions is indicated by behavioral studies. For instance, interference with the postnatal acquisition of cerebellar granule cells by experimental means produces behavioral deficits comparable to those seen after decerebellation (Wallace and Altman, 1969a,b; Altman et al., 1971; Brunner and Altman, 1973).

Neurogenesis in the rat primary olfactory cortex

Neurogenesis in the rat primary olfactory cortex was examined with [3H]thymidine autoradiography. The experimental animals were the offspring of pregnant females given an injection of [3H]thymidine on two consecutive gestation days. Nine groups of embryos were exposed to [3H] thymidine on E13–E14, E14–E15, … E21–E22, respectively. On P60, the percentage of labeled cells and the proportion of cells originating during 24 hr periods were quantified at selected anatomical levels of the anterior and posterior piriform cortex, dorsal lateral peduncular cortex, and posterior two‐thirds of the ventral agranular insular cortex. Throughout most of the primary olfactory cortex, deep cells are generated earlier than superficial cells: the ‘dinside‐out’ pattern. Neurons in the anterior (prepiriform) cortex are located lateral to the caudal anterior olfactory nucleus and olfactory tubercle, and are generated mainly between E14 and E18 in a caudal (older) to rostral (younger) neurogenetic gradient. Neurons in the posterior (periamygdaloid) cortex are located lateral to the caudal olfactory tubercle and amygdala, and are generated mainly between E14 and E17 simultaneously along the rostrocaudal plane. Superficial cells in the piriform cortex have some additional neurogenetic gradients; ventromedial cells forming transition zones with either the olfactory tubercle or amygdala originate earlier than cells located dorsally and laterally. In the posterior piriform cortex, younger neurons are located at middle dorsoventral levels while older neurons lie above and below. Neurons in the dorsolateral peduncular cortex originate between E14 and E20 in a caudal to rostral gradient of neurogenesis; caudal parts also have a lateral to medial neurogenetic gradient. The most lateral part of the dorsolateral peduncular cortex is unique and does not have the typical ‘inside‐out’ cortical neurogenetic gradient. Neurons in the ventral agranular insular cortex (area 13) originate mainly between E15 and E17 in combined caudal to rostral and ventral to dorsal neurogenetic gradients. The neurogenetic gradients in the primary olfactory cortex, along with patterns of neurogenesis throughout the olfactory projection field are related to the termination patterns of afferents from the main olfactory bulb.

The Human Brain During the Second Trimester

INTRODUCTION Organization of the Atlas Specimens Photography and Computer Processing Identification of Brain Structures Major Developmental Brain Structures in the Second Trimester The Cortical Stratified Transitional Field References GW24 CORONAL Low Magnification Plates High Magnification Cortex Plates GW23 SAGITTAL Low Magnification Plates High Magnification Cortex Plates GW23 HORIZONTAL Low Magnification Plates High Magnification Plates GW20 CORONAL Low Magnification Plates High Magnification Cortex Plates High Magnification Corpus Callosum Plates GW20 SAGITTAL Low Magnification Plates High Magnification Cortex Plates High Magnification Cerebellum Plates GW17 CORONAL Low Magnification Plates High Magnification Plates High Magnification Cortex Plates GW17 SAGITTAL Low Magnification Plates High Magnification Cortex Plates High Magnification Cerebellum Plates GW17 HORIZONTAL Low Magnification Plates High Magnification Plates GW13 CORONAL Low Magnification Plates High Magnification Plates High Magnification Cortex Plates

The effects of X-irradiation on the postnatally-forming granule cell populations in the olfactory bulb, hippocampus, and cerebellum of the rat

Beginning on the second postnatal day, either two (2X group), four (4X group) or six (6X group) daily or alternate daily exposures to low-level X-irradiation (150–200 r) were used to interfere with the acquisition of granule cells in the olfactory bulb, hippocampus, and cerebellum of the rat. At 60 days of age, the relationship between post-irradiation recovery and permanent granule cell loss was assessed with two quantitative techniques. First, the total number of granule cells was determined to estimate the magnitude of permanent loss. Secondly, the number of labeled granule cells were counted on day 60 after a 3H-thymidine injection given on either day 15 or on day 20 to estimate differential rates of cell proliferation during the recovery period. n nPermanent loss of granule cells was sustained in all regions by all schedules of irradiation. The time for the most effective exposures was earlier in the hippocampus and olfactory bulb than in the cerebellum. In all regions, both the irradiated groups and the controls showed a decrease in the level of cell proliferation between 15 and 20 days. The number of cells that could be labeled after either the 15 or 20 day injection was below control levels for all groups in the hippocampus, at control levels for all groups in the cerebellum, and either at (2X and 4X) or below (6X) control levels in the olfactory bulb. These results are discussed in the light of the formation time of the granule cells in each region.

Neurogenesis of the magnocellular basal telencephalic nuclei in the rat.

Neurogenesis in the magnocellular basal telencephalic nuclei of the rat was examined with [3H]thymidine autoradiography. The experimental animals were the offspring of pregnant females given two injections of [3H]thymidine on consecutive embryonic (E) days (E12–E13, E13–E14, … E21–E22). On postnatal day (P) 60, the percentage of labeled cells and the proportion of cells originating during 24 h periods were quantified at several anatomical levels throughout the magnocellular basal telencephalic nuclei. The neurons of the horizontal limb of the diagonal band originate mainly between E13 and E16 in a combined rostral‐to‐caudal and lateral‐to‐medial gradient. The neurogenetic gradients in the horizontal limb are continued by generation patterns of cells in the vertical limb of the diagonal band‐medial septal complex, the large cells in the polymorph layer of the olfactory tubercle, and the large cells of the anterior amygdaloid area. The substantia innominata originates between E13 and E17 in combined caudal‐to‐rostral and lateral‐to‐medial gradients. The globus pallidus originates between E13 and E17 in combined caudal‐to‐rostral, ventral‐to‐dorsal and medial‐to‐lateral gradients. The entopeduncular nucleus originates between E12 and E14 in a ‘sandwich’ gradient where neurons in the core of the nucleus are older than those in either the anterior or posterior ends. There is an overall superficial (ventral) to deep (dorsal) neurogenetic gradient between the magnocellular basal nuclei present at any given rostrocaudal level. An important finding is that neurogenetic gradients in the individual components of the magnocellular basal nuclei are alike (with the possible exception of the entopeduncular nucleus) indicating they are part of a single system. Finally, evidence is presented that neurogenetic gradients in the magnocellular basal telencephalic neurons can be correlated with their anatomical projections to the cerebral cortex.

The human brain during the third trimester

This is the second volume of a five-volume set of atlases on the developing human central nervous system. With no other atlases available on the development of the human spinal cord and the brain during the third trimester, the first two volumes of the series fill a large void in current knowledge. Easy to use, the second volume provides low and high magnification photographs of brain sections arranged in two parts: a high resolution black and white image on the left and a ...ghost... image on the right page with unabbreviated labels. This volume provides a user-friendly survey of the complex structural changes that occur during late prenatal human brain development.