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

A qualitative and quantitative analysis of the response of the retinal ganglion cell soma after stretch injury to the adult guinea-pig optic nerve

The development of a model for focal axonal injury in the optic nerve of the adult guinea-pig has allowed a qualitative and quantitative analysis of the response of the retinal ganglion cell soma to this type of injury. Large and medium sized retinal ganglion cells show classic 'central chromatolysis' in about 30% of ganglion cells between three and seven days after injury, a high proportion of which undergo degeneration between seven and 14 days. Small ganglion cells and small neurons do not demonstrate any morphological response to stretch injury of the optic nerve. However, a small number of larger ganglion cells demonstrate enlargement of the cell soma and nucleolus together with reconstitution of the rough endoplasmic reticulum between seven and 14 days after stretch injury. We suggest that these cells are either recovering from or regenerating after a non-disruptive lesion to their axons. We suggest that some of these morphological changes parallel documented regenerative responses in peripheral/extrinsic neurons after injury to their axons. We conclude that the time course of the 'axon reaction' after stretch injury to axons is longer than that obtained after crush or transection. We provide good morphological evidence that the level of injury after application of non-disruptive mechanical strain to axons is less severe than in the former two models of axonal injury and that a proportion of damaged neurons do not die but rather demonstrate either/or recovery or a regenerative response.

Metabolic changes in axotomized fetal and early postnatal hamster facial motoneurons: an autoradiographic study

The developing facial neurons of a series of hamsters ranging in age from the 14-day fetus to the 9 day postnatal were axotomized. Postoperative times were graded for each age so that the retrograde response could be observed before any significant amount of cell degeneration or death occurred. The incorporation of tritiated uridine was followed by the autoradiographic procedure. Although grain counts, relative to control values, were significantly reduced only in the axotomized fetus and at 24 hours postoperatively in 4-day postnatal animals, there was also a repression of isotopic incorporation in all the other axotomized animals. These results support data obtained from previous work with the hamsters which indicate that it is not until after the nerve cell nucleolus reaches full cytomorphic maturity (between 15 and 20 days postnatal age in hamster facial neurons) that the axotomized neurons respond with significantly increased incorporation levels of isotope over that of control neurons.

Effects of isolation and high helium pressure on the nucleolus of sympathetic neurons in the rat superior cervical ganglion

In prokaryotes, unicellular eukaryotes and cell-free systems, pressure is known to exert an inhibitory effect on protein synthesis and RNA metabolism, the mechanism(s) of which remain to be investigated in detail. The purpose of the present in vitro study was to compare ultrastructural and quantitative changes of the nucleolus, which is the site of ribosome biogenesis, in sympathetic neurons of rat superior cervical ganglia (SCG) maintained for 2, 3 and 5 h in NCTC 109 medium and subjected to pressure or not. In control SCG (left) the nucleolus greatly increased in volume (+ 33%) 2 h after excision, in comparison with SCG fixed immediately. This overall enlargement was found to reflect a marked increase in all nucleolar components (from 16 to 87%). After 5 h, volumes of nucleolus, fibrillar centers and vacuolar component returned to control values, whereas dense fibrillar and granular components remained affected. Such early and transient changes are regarded as reflecting basic metabolic changes associated with increased nucleolar RNA that should be of primary concern to experiments using SCG transplanted in culture media. Compression under helium up to 180 atmospheric pressure for 1 h of right SCG maintained for 2 h in culture medium, was shown to induce, on the contrary, a marked decrease in nucleolar volume (-39%) and in volumes of all nucleolar components (from -36 to -51%). When they were kept at constant high pressure for 1 and 3 h a progressive recovery of volumes of nucleoli and nucleolar components was observed. Consequently, compression was shown to exert opposite effects to those of isolation of SCG. Present data are interpreted as an inhibitory effect of pressure on ribosome biogenesis. Such observations on a vertebrate neuron might open a new field in the search for cellular mechanisms underlying the effects of pressure on living organisms and especially on the nervous system.

Differential effects of axotomy on immature and mature hamster facial neurons: a tritiated-uridine autoradiographic study

In this study, tritiated-uridine incorporation was autoradiographically examined following axotomy of hamster facial motor neurons (HFMN) at the critical development age of 15 days postnatal and in the adult. The postoperative times selected were 0.5, 1, 2, and 4 days. In the 15-day operative series, no changes in incorporation were observed at any of the postoperative times, except at 4 days postoperative, when there was a decrease in tritiated-uridine incorporation in the axotomized neurons relative to the controls. In the adult operative series there were no changes in incorporation at 0.5 or 1 day postoperative, relative to the controls. At 2 days postoperative in the adult, there was a transient increase in tritiated-uridine incorporation that returned to control levels by 4 days postoperative. When axotomized and control cytoplasmic/nuclear grain densities were compared, no changes were found in either operative series. These results of the time course of axotomy-induced changes in RNA synthesis in HFMN corroborate our previous findings of an age-dependent reactive sequence in HFMN and lend support to the hypothesis that the young neurons are synthesizing at peak capacity related to final growth and cannot be stimulated further by axotomy. As discussed, the transient increase in RNA levels in the adult, the lack of any changes in the rate of transfer of RNA from the nucleus to the cytoplasm, and the decrease in RNA levels in the 15-day neurons may be related to the presence of an unusual intranucleolar body within the nucleolus of HFMN that contains ribosomal precursors.

Differential effects of axotomy on immature and mature hamster facial neurons: a time course study of initial nucleolar and nuclear changes

The early nuclear and nucleolar responses at 0.5, 1, 2 and 4 days after axotomy were observed in neurons just before and after the completion of nuclear maturation. Axotomy of hamster facial motor neurons at a postnatal age of 15 days did not produce any changes within the nucleus that were significantly different from those of control cells. In addition, no significant changes were evident in the adults at 0.5 and 1 day after axotomy. At postoperative days 2 and 4, however, the adult neurons showed enlargement of the nucleus and nucleolus. Nucleolonemal strands became more rounded and distinct, and the large cluster of granules located centrally in the nucleolus disaggregated. The irregularly distributed clumps of nucleolus-associated chromatin dispersed to form a thin shell about the nucleolar periphery. In adults at postoperative day 4, the nucleoplasmic granules became more homogeneous and less distinctly outlined than normal. The peak of both nucleolar and nuclear responses coincided at 2 days after injury in the adult, i.e. 2 days before the previously documented chromatolytic peak at 4 days after injury. These studies on the ultrastructural level support our previous hypothesis that the 15-day neurons are synthesizing at peak capacity related to their rapid growth phase and cannot be stimulated further by axotomy. The adult neurons, however, do undergo a metabolic reorganization for regenerative synthesis, and the nucleolar and nuclear changes observed are indicative of transcriptive alterations involving the underlying genome.

Alkaline ribonuclease activity is increased in rat sympathetic ganglia after nerve injury

Ribonuclease activity at pH 7.1 ("alkaline" ribonuclease) was determined in homogenates of rat superior cervical ganglion up to 5 days after postganglionic nerve injury under optimal conditions of assay. Measurements were performed in the presence and absence of the sulfhydryl blocking agent, N-ethylmaleimide, to assess the proportion of "alkaline" ribonuclease apparently bound to endogenous inhibitor. Total ribonuclease activity per ganglion was stimulated 1.3 fold by 1 day after injury and remained elevated over the 5 day period. Free ribonuclease activity accounted for about 60% of the observed increase in total activity at day 1, but had returned to control level by day 3. At day 3 the entire 90% increase in total activity was attributable to ribonuclease bound to endogenous inhibitor (i.e. latent activity). These changes are occurring at times after nerve injury when marked alterations in RNA turnover have been observed, implicating "alkaline" ribonucleases in the control of RNA metabolism during nerve regeneration.

Effect of ethanol on nucleolar structure: a cytological indication of change in RNA/protein synthesis

The effects of chronic ethanol ingestion on an organelle known to be involved in protein synthesis were studied cytologically in nerve cells of the adult hamster. Twenty-six animals were administered standard laboratory chow and either tap water (controls) or a 15% ethanol solution (experimentals) for a period of 7 weeks. Brains were perfusion-fixed, sectioned transversely, and stained with buffered thionin for microscopic analysis. Reported here are changes in an RNA-rich intranucleolar body (INB) seen in facial motor neurons and cerebellar Purkinje cells of the golden hamster. After chronic ethanol ingestion, the size and frequency of the INB increased significantly in both cell populations. Theoretical considerations are discussed concerning the correlation between this apparent storing of nucleolar RNA/RNP and the biochemical evidence of other investigators for ethanol-induced alterations in RNA/protein synthesis and utilization in neurons.

A difference in the nucleoli of Purkinje cells of the nodular lobe of the hamster cerebellum

Purkinje cells of the hamster cerebellum typically contain a large, single, centrally located nucleolus. Strikingly different are Purkinje cells concentrated in the nodular cortex, which characteristically contain several small, pale-staining nucleoli, most of which are peripherally located, in contact with the nuclear envelope. These atypical cells are also smaller, their Nissl bodies stain less intensely, and their nuclear envelopes appear more invaginated. Functional differences are implicit.