Neurogenesis in the olfactory tubercle and islands of Calleja in the rat.

Neurogenesis in the rat olfactory tubercle and islands of Calleja was examined with [(3)H]thymidine autoradiography. Animals in the prenatal groups were the offspring of pregnant females given an injection of [(3)H]thymidine on two consecutive gestational days. Ten groups of embryos (E) were exposed to [(3)H]thymidine on E12-E13, E13-E14 4 E21-E22, respectively.

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.

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.

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.

Neurogenesis in the rat neostriatum.

Neurogenesis in the rat neostriatum was examined with [(3)H]thymidine autoradiography. For the animals in the prenatal groups, the initial [(3)H]thymidine exposures were separated by 24 h; they were the offspring of pregnant females given two injections on consecutive embryonic (E) days (E13-E14, E14-E15, … E21-E22). For the animals in the postnatal (P) groups, the initial [(3)H]thymidine exposures were separated by 48 h, each group receiving four consecutive injections (P0-P3, P2-P5, P4-P7).

3H-thymidine-radiographic studies of neurogenesis in the rat olfactory bulb.

Neurogenesis in the rat olfactory bulb was examined with 3H-thymidine-radiography. For the animals in the prenatal groups, the initial 3H-thymidine exposures were separated by 24 h; they were the offspring of pregnant females given two injections on consecutive embryonic (E) days (E12-E13, E13-E14, . .

Neurons in the rat dentate gyrus granular layer substantially increase during juvenile and adult life.

Volumetric estimates of the total number of granule cells in rats 30, 120, 200, and 365 days old increase linearly by approximately 35 to 43 percent between 1 month and 1 year. Total volume of the granular layer also grows linearly during that time. These results demonstrate a numerical increase in a neuronal population during adulthood in the mammalian brain.

Changes in the total number of dentate granule cells in juvenile and adult rats: a correlated volumetric and 3H-thymidine autoradiographic study.

The total number of granule cells in the dentate gyrus was estimated in 17 male rats, four each aged 30, 120, and 200 days, and five aged 365 days. There is a substantial 35-43% linear increase between 1 month and 1 year. Two parameters of the granular layer are involved in the numerical change.

Development of the brain stem in the rat. V. Thymidine-radiographic study of the time of origin of neurons in the midbrain tegmentum.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day E12 and 13 (E12 j3) until the day before parturition (E21 k2) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (no longer labeled) on specific embryonic days was determined quantitatively in 18 regions of the midbrain tegmentum. The neurons of the oculomotor and trochlear nuclei are generated concurrently on days E12 and 13.

Time of origin of neurons of the rat superior colliculus in relation to other components of the visual and visuomotor pathways.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day 12 and 13 (E12 + E13) until the day before parturition (E21 + 22) in order to label all the multiplying precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labelled) on specific days was determined in the separate layers of the superiorr colliculus. Neurogenesis begins with layers V and IV on day E12; the bulk (87%) of these cells are generated on day E13.

Time of origin of neurons of the rat inferior colliculus and the relations between cytogenesis and tonotopic order in the auditory pathway.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day 12 and 13 (E12+13) until the day before parturition (E21+22) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labelled) on specific embryonic days was determined quantitatively in six vertical strips of the inferior colliculus. It was established that the neurons of the inferior colliculus are produced between days E14 and the perinatal period in an orderly sequence: the earliest generated cells are situated rostrally, laterally and ventrally in the principal nucleus, the latest generated cells are situated caudally, medially and dorsally in the pericentral nucleus.

Development of the brain stem in the rat. IV. Thymidine-radiographic study of the time of origin of neurons in the pontine region.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day 12 and 13 (E12 + 13) until the day before parturition (E21 + 22) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labeled) on specific embryonic days was determined quantitatively in 14 nuclei of the pontine region. Peak production time of neurons of the trigeminal mesencephalic nucleus was on day E11 or earlier, with a small proportion generated on day E12.

Development of the brain stem in the rat. III. Thymidine-radiographic study of the time of origin of neurons of the vestibular and auditory nuclei of the upper medulla.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational days 12 and 13 (E12 + 13) until the day before parturition (E21 + 22). In adult progeny of the injected rats the proportion of neurons generated on specific embryonic days was determined quantitatively in the vestibular and auditory nuclei of the upper medulla. In the vestibular nuclei, neurons are generated between days E11 and E15 in an overlapping sequential order, yielding a lateral-to-medial and a rostral-to-caudal internuclear gradient.

Development of the brain stem in the rat. II. Thymidine-radiographic study of the time of origin of neurons of the upper medulla, excluding the vestibular and auditory nuclei.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational days 12 and 13 (E12 + 13) until the day before birth (E21 + 22). In radiographs from adult progeny of these rats the proportion of neurons generated on specific days was determined in the major nuclei of the upper medulla, with the exception of the vestibular and auditory nuclei. The neurons of the motor nuclei are generated over a brief period.

Development of the brain stem in the rat. I. Thymidine-radiographic study of the time of origin of neurons of the lower medulla.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational days 12 and 13 (E12 + 13) until the day before birth (E21 + 22). In adult progeny of the injected rats the proportion of neurons generated on specific days was determined quantitatively in the major nuclei of the lower medulla. The earliest generated cells form two motor nuclei: the hypoglossal and dorsal vagal nuclei.

Development of the diencephalon in the rat. VI. Re-evaluation of the embryonic development of the thalamus on the basis of thymidine-radiographic datings.

The development of the thalamus was examined in normal and X-irradiated embryos from day 13 (E13) to the day before birth (E22). The differentiating, radioresistant neurons of the lateral habenular nucleus, derived from a portion of the superior neuroepithelial lobule (SL1), were settling by day E15 and by this time the habenulopeduncular tract was forming. The neurons of the reticular nucleus, derived from the middle neuroepithelial lobe, began to settle on day E15 but a massive migration was still evident on day E16.

Development of the diencephalon in the rat. V. Thymidine-radiographic observations on internuclear and intranuclear gradients in the thalamus.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational days 13 and 14 (E13 + 14) until the day before birth (E21 + 22). Internuclear and intranuclear cytogenetic gradients were examined in radiograms of the thalamus sectioned in the coronal, sagittal and horizontal planes. There was a precise and segregated lateral-to-medial gradient between and within the habenular nuclei.