Appearance and development of neuron-specific enolase immunoreactivity in organotypic cultures of mouse embryo otocysts

Characterization of different neuron populations in mouse statoacoustic ganglion cultures

Statoacoustic ganglion (SAG) cells were grown in primary culture and the appearance of different neuronal phenotypes was investigated. Analysis criteria were shape, size and staining for the immunocytochemical markers: neurofilament proteins (NF-200 kDa), neuron-specific enolase (NSE), calretinin, a calcium-binding protein and substance P, a neurotransmitter. Cultures were prepared from dissociated SAG cells of 13 gestation-day-old mouse embryos. Neurons were identified and counted after 7 days in vitro. At this stage, neurons were organized in small clusters forming an extensive network of neurites grown on a layer of fibroblasts and glia. Most neurons identified by NF or NSE immunoreactivity showed a typical adult-like bipolar profile. The diameters of the neurons were between 5.62 and 17.00 microns and displayed a normal distribution (mean: 10.6 microns). Two distinct subpopulations were identified by the expression of calretinin and substance P. Calretinin-immunoreactive neurons were large and very rare and had a mean diameter of 11.3 microns; the distribution of substance P was more extensive than that of calretinin and identified a population of small neurons with a mean diameter of 8.9 microns. The distributions of these two markers in SAG cultures were consistent with in vivo results. In conclusion, dissociated SAG cell cultures appear to be a suitable model for analyzing the development of the immunocytochemical and functional characteristics of the neurons of this inner ear ganglion.

The development of laminar staining for neuron-specific enolase in the rat somatosensory cortex

The expression of the enzyme neuron-specific enolase (NSE) in the central nervous system (CNS) has been used as a developmental marker based on observations that it is expressed shortly after the arrival of afferent inputs. The immunostaining pattern of NSE was examined in the laminae of the somatosensory cortex of the rat and the relationship of this staining pattern with previous data on the timing of afferent and efferent arrival was determined. Male rat pups were sacrificed on postnatal days 1 (24 h after birth), 3, 5, 8, 10, 12, 15 and 20, and as an adult (over 90 days of age). Sections were stained with an anti-NSE antibody using the avidin-biotin immunocytochemical method. Sections from day 1 animals revealed stained cells in the subplate layer and cortical plate, presumably in cells destined to form layers VI and V. By day 8 there was staining in layers II, III, V and VI, the same layers that exhibited staining in the adult rat. This appears consistent with the arrival of afferents and efferents which is completed by approximately postnatal day 7. On day 10, there was a change in the staining pattern: cell staining in layer VI was decreased and then increased gradually up to adult levels by day 20. A stable pattern of NSE staining was not observed previous to day 20. These results suggest that changes in NSE expression following the initial arrival of afferents may relate to maturation of the neurons.

In vitro differentiation of mouse embryo statoacoustic ganglion and sensory epithelium

Interactions between the statoacoustic ganglion and sensory vestibular epithelia have been investigated using different methods of organ and tissue cultures taken from mouse embryos on gestation day 13. Ultrastructural and biochemical observations of the degree of maturation of vestibular sensory cells and ganglion neurons grown in co-culture showed that these structures are able to replicate their in vivo ontogenic maturation and form specific 'functional' links, although anomalies in development were noted. The completion of ultrastructural sensory hair cell development in isolated otocyst organotypic culture is in agreement with previous findings supporting the hypothesis that nerve fibers do not exert any direct trophic influences on the survival and maturation of sensory epithelia. Morphological and immunocytochemical observations of vestibular and cochlear ganglion neuron differentiation in isolated cultures showed that these neurons can differentiate without their peripheral and central target structure. Possible interactions at earlier stages cannot be excluded. Further studies are needed to determine whether interactions between hair cells and ganglion cells can modulate their in vitro maturation under different experimental conditions.