Abstract
In culture, hippocampal neurons initially establish several shod, minor processes. The initial step in the emergence of polarity is marked by the rapid and selective growth of one of these processes, which becomes the axon. Subsequently the remaining processes become dendrites. We examined the ultrastructure of hippocampal neurons before and after the emergence of the axon. The minor processes in cells that had not yet formed axons were somewhat variable in appearance, but we found no ultrastructural feature that indicated which minor process might become the axon. The emergence of the axon was marked by several changes in its ultrastructure. The axon contained a sevenfold lower density of polyribosomes than the minor processes. In addition, axonal growth cones contained a pronounced concentration of membranous elements that resembled endoplasmic reticulum, elements that were rare in the growth cones of minor processes. Axons and minor processes did not differ in ml-crotubule density. In order to gauge how rapidly these ultra-structural changes occur, we examined cells with shod axons that, from their length, were estimated to have emerged only hours earlier. The preferential exclusion of polyribosomes from the axon and the concentration of reticular membrane in the axonal growth cone were already evident in such cells. These observations demonstrate that exclusion of ribosomes from the axon occurs early in development, about as soon as the axon can be identified. In contrast, previous work has shown that the differences in microtubule polarity orientation that distinguish mature axons and dendrites, and that have been proposed to account for the selective segregation of some constituents in neurons, first appear at a later stage of development (Baas et al., 1989). These observations also demonstrate that the accumulation of reticular membrane elements in growth cones, which has been noted previously, occurs preferentially in axonal growth cones and is closely correlated in time with the initial specification of the axon. The selective concentration of these elements in axonal growth cones could be associated with the uniquely rapid rate of axonat growth.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4301-4315 |
| Number of pages | 15 |
| Journal | Journal of Neuroscience |
| Volume | 13 |
| Issue number | 10 |
| State | Published - 1993 |
| Externally published | Yes |
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Keywords
- Axon
- Dendrite
- Growth cones
- Neurite outgrowth
- Ribosomes
- Smooth endoplasmic reticulum
ASJC Scopus subject areas
- Neuroscience(all)
Cite this
An electron microscopic analysis of hippocampal neurons developing in culture : Early stages in the emergence of polarity. / Deitch, Jeffrey S.; Banker, Gary.
In: Journal of Neuroscience, Vol. 13, No. 10, 1993, p. 4301-4315.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - An electron microscopic analysis of hippocampal neurons developing in culture
T2 - Early stages in the emergence of polarity
AU - Deitch, Jeffrey S.
AU - Banker, Gary
PY - 1993
Y1 - 1993
N2 - In culture, hippocampal neurons initially establish several shod, minor processes. The initial step in the emergence of polarity is marked by the rapid and selective growth of one of these processes, which becomes the axon. Subsequently the remaining processes become dendrites. We examined the ultrastructure of hippocampal neurons before and after the emergence of the axon. The minor processes in cells that had not yet formed axons were somewhat variable in appearance, but we found no ultrastructural feature that indicated which minor process might become the axon. The emergence of the axon was marked by several changes in its ultrastructure. The axon contained a sevenfold lower density of polyribosomes than the minor processes. In addition, axonal growth cones contained a pronounced concentration of membranous elements that resembled endoplasmic reticulum, elements that were rare in the growth cones of minor processes. Axons and minor processes did not differ in ml-crotubule density. In order to gauge how rapidly these ultra-structural changes occur, we examined cells with shod axons that, from their length, were estimated to have emerged only hours earlier. The preferential exclusion of polyribosomes from the axon and the concentration of reticular membrane in the axonal growth cone were already evident in such cells. These observations demonstrate that exclusion of ribosomes from the axon occurs early in development, about as soon as the axon can be identified. In contrast, previous work has shown that the differences in microtubule polarity orientation that distinguish mature axons and dendrites, and that have been proposed to account for the selective segregation of some constituents in neurons, first appear at a later stage of development (Baas et al., 1989). These observations also demonstrate that the accumulation of reticular membrane elements in growth cones, which has been noted previously, occurs preferentially in axonal growth cones and is closely correlated in time with the initial specification of the axon. The selective concentration of these elements in axonal growth cones could be associated with the uniquely rapid rate of axonat growth.
AB - In culture, hippocampal neurons initially establish several shod, minor processes. The initial step in the emergence of polarity is marked by the rapid and selective growth of one of these processes, which becomes the axon. Subsequently the remaining processes become dendrites. We examined the ultrastructure of hippocampal neurons before and after the emergence of the axon. The minor processes in cells that had not yet formed axons were somewhat variable in appearance, but we found no ultrastructural feature that indicated which minor process might become the axon. The emergence of the axon was marked by several changes in its ultrastructure. The axon contained a sevenfold lower density of polyribosomes than the minor processes. In addition, axonal growth cones contained a pronounced concentration of membranous elements that resembled endoplasmic reticulum, elements that were rare in the growth cones of minor processes. Axons and minor processes did not differ in ml-crotubule density. In order to gauge how rapidly these ultra-structural changes occur, we examined cells with shod axons that, from their length, were estimated to have emerged only hours earlier. The preferential exclusion of polyribosomes from the axon and the concentration of reticular membrane in the axonal growth cone were already evident in such cells. These observations demonstrate that exclusion of ribosomes from the axon occurs early in development, about as soon as the axon can be identified. In contrast, previous work has shown that the differences in microtubule polarity orientation that distinguish mature axons and dendrites, and that have been proposed to account for the selective segregation of some constituents in neurons, first appear at a later stage of development (Baas et al., 1989). These observations also demonstrate that the accumulation of reticular membrane elements in growth cones, which has been noted previously, occurs preferentially in axonal growth cones and is closely correlated in time with the initial specification of the axon. The selective concentration of these elements in axonal growth cones could be associated with the uniquely rapid rate of axonat growth.
KW - Axon
KW - Dendrite
KW - Growth cones
KW - Neurite outgrowth
KW - Ribosomes
KW - Smooth endoplasmic reticulum
UR - http://www.scopus.com/inward/record.url?scp=0027442407&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0027442407&partnerID=8YFLogxK
M3 - Article
VL - 13
SP - 4301
EP - 4315
JO - Journal of Neuroscience
JF - Journal of Neuroscience
SN - 0270-6474
IS - 10
ER -