Time of neuron origin in the diencephalon of the mouse. An autoradiographic study

Abstract

Time of origin of neurons of thalamus ventralis, thalamus dorsalis, and epithalamus was determined autoradiographically at three transverse levels in adults which received thymidine-H3 once during gestation. A ventrodorsul gradient in the entire region demonstrates a wave of neuron origin in the forebrain, probably rostrocaudal originally but revectored by rearrangement of neuromeres 1-111. A caudorostrul gradient in dorsal thalamus similarly may represent redirection of a n earlier ventrodorsal one. A lateromedial gradient in dorsal thalamus and epithalamus (opposite that i n cortex) may reflect lateral displacement of neuroblasts (or their nuclei) by younger elements. Large neurons generally arise before small ones, as seen in epithalamus; the two habenular nuclei illustrate programmed origin of large and small neurons and glia consecutively, with progressively restricted potentiality by the primitive ependyma. Phylogenetically, slight differences in duration of proliferation might radically alter the numbers of small neurons. Although dorsal thalamic nuclei "appear" in external germinal and mantle layers, their neuroblasts originate in primitive ependyma; time of origin accords with subsequent recognition of nuclei and appearance of thalamocortical connections. Massive proliferation (from the 10th to 15th days of gestation) and the gradients overshadow nuclear differences and demonstrate a developmental unity in the dorsal thalamus. The findings further validate Herrick's diencephalic zones and suggest some orderly mechanism, probably at the molecular level, underlying generation of the neurons in this complex brain region.The improved resolution brought to morphogenetic studies by autoradiography with titiated thymidine has initiated a systematic regional analysis of brain development with this technique. It is now possible to trace the history of individual neurons from proliferative through migratory stages to ultimate disposition in the mature brain. A label affixed premitotically to a neuron precursor is p e fmunent; once a neuroblast Ieaves its germinal center, it loses the capacity to divide. Moreover, a rigorous schedule of proliferative events within the matrix layer of the neuraxis facilitates selective labeling by appropriate timing of radioactive thymidine injections. Thus, the identities of neurons originating as end products of germinal cell division at a given developmental stage may be ascertained by noting their positions in the adult brain. Neighboring neurons, originating earlier or later, remain nonradioactive.Exploiting this technique, Angevine ('65), Taber Pierce ('66, '67) and Hinds ('67, '68a,b) and elaborate timetables of neuronal birthdates for the components of the hippocampal formation, various nuclear complexes of the brain stem, and olfactory bulb, respectively. For the latter two regions, moreover, examination of serial embryonic stages following the stage at which thymidine-H3 was administered permitted isolation and day-by-day tracing of the paths of young neurons.The...

Neonatal Nonhandling andIn UteroPrenatal Stress Reduce the Density of NADPH-Diaphorase-Reactive Neurons in the Fascia Dentata and Ammon’s Horn of Rats

“…This has been observed in various species (mouse: Angevine, 1965; monkey: Rakic and Nowakowski, 1981;rat: Altman and Das, 1965;cat: Purpura and Pappas, 1968), including human. On the basis of their analysis of the Yakovlev collection, Kretschmann et al (1986) concluded that the maximum rate of growth of the human hippocampal formation occurs at approximately 2 months postnatally.…”

Spatiotemporal patterns of secretomotor neuron generation in the parvicellular neuroendocrine system 1Published on the World Wide Web on 3 June 1997. 1

“…This is a particularly difficult problem because different eggs associated with a litter are fertilized at different times, often ranging up to some 20 h in mice [58], so that somewhat different patterns are observed even in animals from the same litter. Thus, some workers have resorted to illustrating birthdate maps for several different animals from the same litter or from mothers injected with [ 3 H]thymidine on the same day of gestation [6]. Because conservative criteria were employed here for brightly BrdUlabeled nuclei, numbers of positive cells were low in individual animals, making detailed comparisons between animals uninformative.…”

Axonal ribosomes and mRNAs associate with fragile X granules in adult rodent and human brains

“…The persistent expression of the translational machinery in axons of adult rat CA3 neurons, which are born exclusively in the prenatal period (27), indicates that axonal translation functions in mature, circuit-integrated axons. However, this observation does not resolve whether FXG-associated translational machinery is also present in growing axons prior to synaptogenesis.…”