Unscheduled DNA synthesis refers to DNA synthesis not followed by cell division. Previous studies have suggested that this phenomenon may occur in neurons from peripheral myenteric ganglia in conditions of functional hyperstimulation. In order to verify these observations, we have carried on an immunohistochemical study on myenteric neurons from the hypertrophic intestinal loops upstream from a partial obstruction (an experimental condition that induces a relevant increase of the neuronal workload) after labelling with two different markers: the proliferating cell nuclear antigen (PCNA), that is specifically expressed in cell nuclei during the S-phase, and the protein gene product 9.5 (PGP 9.5), a specific marker of nerve cells. While no myenteric neuron immunopositive for the anti-PCNA antibody was found in the control intestine, in the hypertrophic myenteric ganglia some neurons were positive for PCNA. These results provide an unequivocal evidence on the existence of unscheduled DNA synthesis in myenteric neurons from the hypertrophic intestine.
A morphological analysis of types and sub-types of neurons from dorsal root ganglia at different spinal levels was carried out by combined light and electron microscopy in Podarcis sicula. Two neuron types were recognized: small dark cells (type D) and large light cells (type L). Type L cells were further sub-divided into three sub-types (L1, L2, L3) on the basis of entity and distribution of neurofilaments. Percentage distribution of neuron types did not vary in relation to the spinal level. On the contrary, differences were found in the percentage of the three type L neuron sub-types; a higher percentage of cells very rich in neurofilaments (L2, L3) was found in dorsal root ganglia from the cervical and the lumbar spinal levels. Results are discussed in relation to the spinal-level-related extent of innervation territory of dorsal root ganglia.
Some nerve cells of the Auerbach's myenteric plexus of the intestine of the adult rat, which hypertrophied following a surgically induced stenosis, began DNA synthesis unrelated to mitotic division. The cytophotometric analysis confirmed and quantified the amount of synthesis revealed by autoradiography with tritiated thymidine uptake. Numerous nerve cells show a DNA content exceeding the diploid level. Only a few of these show twice the diploid content. The significance of the DNA synthesis is discussed.
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