Arthur LaVelle

Developmental protein changes in normal and chromatolytic facial nerve nuclear regions

Facial neurons were severed at the stylomastoid foramen in immature (15- and 20-day-old) and adult hamsters. Four days later animals were killed under Nembutal, in accordance with either of two approaches. In one series, after perfusion with physiological saline, the medullas were immediately removed, quickfrozen in liquid nitrogen, and sectioned in a cryostat. Facial nerve nuclear regions from the experimental and control sides were dissected free from the dehydrated sections and analyzed for protein differences by micro disc electrophoresis. In another series, 3H-leucine was injected intraperitoneally 24 hr before killing by perfusion-fixation. Isotope uptake in experimental and control facial neurons was determined by autoradiography. The pattern of protein changes and the uptake of the amino acid on the chromatolytic side became progressively more dissimilar from the normal, the more mature the neurons were at the time of operation. This involved an increase in both the number of separated proteins and the uptake of labeled leucine on the experimental side. We suggest that these reactive differences may reflect two different types of metabolism, present, respectively, in immature and mature nuclear regions. The first type, present in immature and chromatolytic regions, may be concerned with the synthesis of structural proteins. The second type, present in adult normal nuclear regions, may be concerned with the synthesis of proteins for cell maintenance and function.

Ultrastructural changes in the developing nucleolus following axotomy

A large, basophilic, Feulgen-negative structure has been observed within the nucleoli of golden hamster facial motor neurons. This intranucleolar body was seen, at the electron microscopic level, to be composed of granules which are thought to be ribonucleoprotein particles. At 15 days postnatal age, this aggregation of granules had not yet be appeared. However, by 20--24 days, a small intranucleolar body had developed. At maturity, the intranucleolar body had a diameter of up to 2 mum. Facial nerve axotomy at 15 days did not appreciably alter the nucleolar morphology at 19 days; neither control (opposite side) nor experimental nucleoli contained intranucleolar bodies. Normal nucleoli developed intranucleolar bodies, however, between the ages of 20 and 24 days. After axotomy at 20 days and sacrifice at 24 days, a comparison of facial neuronal nucleoli demonstrated that while an intranucleolar body formed in the control, axotomy prevented this structure from forming at its normal time. Also, when the facial nerve of an adult hamster was axotomized and observed 4 days postoperatively, an intact intranucleolar body was not seen. Instead, the granular portions of the nucleolus appeared to have been dispersed into several small aggregates. We believe that the changes observed in granule distribution, both with development and after axotomy, are morphological indications of a qualitative and/or a quantitative change in rRNA synthesis.

Nuclear envelope invaginations in hamster facial motor neurons during development and aging

Morphometric measurements of nuclear envelope invaginations (NEI) in hamster facial motor neurons were made. These showed that the amount of NEI increased markedly between fetal life and birth to a high level that was maintained during the period of accelerated neuronal somal growth. Subsequently, the amount of NEI decreased to a plateau of low incidence that persisted through maturity and aging. This sequence of NEI formation and subsidence differs from that previously observed in a similar developing and aging series of pyramidal neurons in the same species. This may indicate, as discussed, that the presence of NEI reflects stage-specific functions that may differ depending on neuronal type.

Morphological changes of the pyramidal cell nucleolus and nucleus in hamster frontal cortex during develoment and aging

The development and aging of the nucleolus and nucleus in layer V pyramidal cells in the hamster cerebrum were studied by light and electron microscopy. The nucleoli appeared in the newborn as occasional fibrillar masses adjacent to peripherally placed bodies of chromatin. By maturity, a single, generally central, nucleolus proper with nucleolus-associated chromatin was present. Nucleolar microbodies were observed at 10, 15, 20 and 480 days, but not in the newborn, 5-or 90-day animal. An intranucleolar body was not observed at the electron at the electron-microscopy level in these pyramidal cell nucleoli at any age in this series, in contrast to the situation in large motor neurons of the facial nucleus. The nucleus progressed from an irregular shape at birth to an oval shape at maturity. At 10 days, incipient invaginations of the nuclear membrane appeared; these subsequently increased in depth and frequency in the adult. The above changes, particularly in the nucleoli, are correlated in time with changes involving the endoplasmic reticulum. The correlations may indicate different periods of metabolic activity in the hamster pyramidal neurons. Four such periods can be differentiated on the basis of cytomorphic changes which may be correlated to reported development of function. The sequence of these changes, peculiar to the developing and aging hamster pyramidal neuron, differs from that seen in large spinal and cranial motor neurons. It appears that some features of nuclear immaturity, which are lost in larger neuronal types, are retained in the adult pyramidal neuron.

A nucleolus-associated coiled body.

SummaryOne or two threadlike structures frequently have been observed attached to nucleoli in facial motor neurons of the golden hamster. These round-to-oval structures, called ‘coiled bodies’, were seen at 15, 19, and 24 days postnatal and in the adult, both in normal neurons and in chromatolytic neurons which had been axotomized 4 days previously. With one exception, the coiled bodies were seen to be attached via fibrillar material to the nucleolar periphery. Although the numbers of coiled bodies may be altered during neuronal maturation and as a result of axon section, the bodies revealed no structural alterations that could be attributed to developmental age or to experimental trauma.

Nuclear envelope invaginations in hamster pyramidal cells during development and aging

Nuclear envelope invaginations were observed in pyramidal cell nuclei of the hamster frontal cortex during development and aging. These invaginations which began to appear at 10 day did not recede at maturity as has been observed in certain other cell types, but persisted in the adult hamster and during subsequent aging. Morphometric data showed a significant increase in the number of nuclear envelope invaginations and in their length per unit of the nucleus. This increase was positively correlated with age until 500 days and is suggestive of a continued high metabolic activity that did not subside following the rapid growth phase of the pyramidal neurons.

Tritiated leucine incorporation in the developing hamster facial nucleus with injury: an autoradiographic study.

Abstract Tritiated leucine incorporation was examined after axotomy of the hamster facial nerve in development in an attempt to correlate structural maturation of the nucleolus with levels of competence in the metabolic response to axon section. Changes in neuronal tritiated leucine incorportation were characterized by autoradiographic examination of the facial neuronal population after axotomy as specific stages in nucleolar development. The ability to increase incorporation over the normal as a result of injury in development coincided with the time of final nucleolar maturation, between 20 and 24 days postnatal age. Thus, there was a correlation between a specific morphologic event, the appearance of the adult nucleolar configuration, and the appearance of the mature protein metabolic response to injury of increased leucine incorporation.

Tritiated leucine incorporation in the developing hamster facial nucleus with injury: A liquid scintillation study ☆

Tritiated leucine incorporation was examined after either crush or axotomy of the hamster facial nerve at specific stages in the maturation of the neuronal nucleolus. Changes in the neuronal metabolic response to injury in development were demonstrated with liquid scintillation examination of tritiated leucine incorporation into the trichloroacetic acid (TCA)-insoluble and TCA-soluble fractions derived from whole reactive and normal facial nuclear groups. Changes in incorporation seen in the developmental sequence were attributed to actual changes in neuronal protein metabolism, and not to changes in the amino acid pool, glial changes or hyperemic capillary changes. The ability to increase leucine incorporation over the normal as a result of injury in development coincided with the time of final nucleolar maturation in the facial motor neurons, beginning at approximately 20 days postnatal age. Thus, there is a correlation between a specific morphological event, the attainment of the mature nucleolar configuration, and the acquisition of the mature synthetic capacity as indicated by the ability to respond to injury in the mature manner.

An unusual nucleolar ring-like structure in axotomized hamster facial motoneurons

Structures consisting of connecting rings surrounding a fibrillar core were observed within nucleoli of developing normal and axotomized hamster facial motoneurons. A few appeared in the nucleoplasm, attached to coiled bodies. Their peculiar structure and temporal association with neuronal maturation may reflect a transient state of ribosomal RNA transcription.