Developmentally regulated markers in the postnatal cervical spinal cord of the opossum Monodelphis domestica

Optimized methods for rapidly dissecting spinal cords and harvesting spinal motor neurons with high survival and purity from rats at different embryonic stages

STUDY DESIGN

Experimental study, protocol optimization.

OBJECTIVES

To investigate and compare the isolation of spinal motor neurons from embryonic rats at different embryonic stages, and develop optimized methods for rapidly dissecting spinal cords and harvesting spinal motor neurons with high survival and purity.

SETTING

Guangdong Provincial Academy of Chinese Medical Sciences, Guangzhou, China.

METHODS

Embryonic rats at different embryonic stages (12-18 days) were used to isolate spinal motor neurons. Their shape and corresponding dissection procedures, time needed and skills were compared. After dissecting and dissociating spinal cords, cells were randomly divided into immunopanning group and control group, in which antibodies to p75^NTR were used or not. After plating cells, different recipe were added at different stages in serum-free culture media. Morphological features of cells were observed during development. Immunoflurorescence assay was performed to indentify motor neurons and the proportion of motor neurons in both control and immunopanning group were evaluated and compared.

RESULTS

We summarized the operation essentials for rapid isolation of spinal cords, as well as compared anatomical features and dissection procedures of embryos at different embryonic stages, which help us to better evaluate the developmental profile and isolate cells by adopting corresponding skills. Through the fast isolation procedure and optimized culture media, cells grow in good viability. Moreover, compared with control group, the purity of spinal motor neurons in the immunopanning group was significantly increased, reaching a proportion of over 95%.

SPP1 expression in spinal motor neurons of the macaque monkey

In the macaque cerebral cortex, the SPP1 (secreted phosphoprotein 1) gene is mainly expressed in corticospinal neurons. In this study, we found that SPP1 was principally expressed in motor neurons in lamina IX of the macaque spinal cord. The expression level varied among different spinal segments and correlated positively with neuron size. The expression was weak in Errγ-positive neurons, presumably gamma motor neurons, and in neurons in sacral Onuf's nucleus. These results suggest that SPP1 is a molecular characteristic of spinal motor neurons and is preferentially expressed in neurons with high conduction velocities.

Neurotrophic factors improve motoneuron survival and function of muscle reinnervated by embryonic neurons

Motoneuron death can occur over several spinal levels with disease or trauma, resulting in muscle denervation. We tested whether cotransplantation of embryonic neurons with 1 or more neurotrophic factors into peripheral nerve improved axon regeneration, muscle fiber area, reinnervation, and function to a greater degree than cell transplantation alone. Sciatic nerves of adult Fischer rats were cut to denervate muscles; 1 week later, embryonic ventral spinal cord cells (days 14-15) were transplanted into the tibial nerve stump as the only source of neurons for muscle reinnervation. Factors that promote motoneuron survival (cardiotrophin 1; fibroblast growth factor 2; glial cell line-derived neurotrophic factor; insulin-like growth factor 1; leukemia inhibitory factor; and hepatocyte growth factor) were added to the transplant individually or in combinations. Inclusion of a single factor with the cells resulted in comparable myelinated axon counts, muscle fiber areas, and evoked electromyographic activity to cells alone 10 weeks after transplantation. Only cell transplantation with glial cell line-derived neurotrophic factor, hepatocyte growth factor, and insulin-like growth factor 1 significantly increased motoneuron survival, myelinated axon counts, muscle reinnervation, and evoked electromyographic activity compared with cells alone. Thus, immediate application of a specific combination of factors to dissociated embryonic neurons improves survival of motoneurons and the long-term function of reinnervated muscle.

Culture of porcine fetal pancreatic neurons

OBJECTIVES

Pancreatic neurons have not been cultured commonly. Cultured neurons can be continuously observed, and their external environment is easy to be controlled. We report here a simple method for separating and cultivating neuronal cells from pancreas.

METHODS

Pancreata of fetal swine were digested with collagenase. Clusters were collected with a sieve and digested with trypsin. Digested clusters were collected and cultured in Dulbecco modified Eagle medium containing serum and basic fibroblast growth factor. Cultured cells were investigated morphologically.

RESULTS

Cultured cells formed spiderweblike colonies. These cells were distinguished into Schwann cells and 2 types of neurons. The neurons were positive on immunocytochemical staining with antigrowth-associated protein-43 and cytochemical staining for cholinesterase. One type of neuron was located in the central cluster and had very long processes extending radially. The other type of neuron was sparsely scattered, had long processes, and was connected to other neurons. The neurotransmitter of these neurons was concluded to be acetylcholine.

CONCLUSIONS

Using our method, neuronal cells were readily cultured from pancreatic tissue. These cells will be useful in elucidating the physiology and pharmacology of pancreatic neurons.

Development of neurons expressing estrogen receptor α transiently in facial nucleus of prenatal and postnatal rat brains

The transient expression of estrogen receptor alpha (ERalpha) in the facial nucleus of rats during development was already reported. However, how and whether the receptor functions physiologically in the nucleus of developing rats are as yet unclear. In this study, we applied a retrograde tracer into one of the possible target muscles of the motoneurons in the nucleus, that is, the transverse auricular muscle (Mta), and examined whether ERalpha-immunopositive neurons take up the tracer. Because it is probable that neurogenesis, apoptosis, and maturation may be associated with the transient expression of ERalpha, we attempted to analyze the neurons expressing the receptor in the nucleus. We found that ERalpha-immunopositive neurons in the medial facial subnucleus innervate mostly the Mta. Quantitative analyses showed that the number of motoneurons projecting to the Mta remained the same throughout the ages examined, whereas that of ERalpha-immunopositive neurons decreased between postnatal days 6 and 11. Apoptosis and neurogenesis in the nucleus were not affected by the expression of ERalpha during development. ERalpha expression coincided with the maturation of neurons in the nucleus. Thus, it is possible that ERalpha expression in the facial nucleus during development plays important roles in the development of motoneurons and/or external pinna muscles.

Primary sensory afferent innervation of the developing superficial dorsal horn in the South American opossum Monodelphis domestica

The development of the primary sensory innervation of the superficial dorsal horn (SDH) was studied in postnatal opossums Monodelphis domestica by using DiI labelling of primary afferents and with GSA-IB(4) lectin binding and calcitonin gene-related peptide (CGRP) immunoreactivity to label primary afferent subpopulations. We also compared the timing of SDH innervation in the cervical and lumbar regions of the spinal cord. The first primary afferent projections to SDH emerge from the most lateral part of the dorsal root entry zone at postnatal day 5 and project around the lateral edge of the SDH toward lamina V. Innervation of the SDH occurs slowly over the second and third postnatal weeks, with the most dorsal aspect becoming populated by mediolaterally oriented varicose fibers before the rest of the dorsoventral thickness of the SDH becomes innervated by fine branching varicose fibers. Labelling with GSA-IB(4) lectin also labelled fibers at the lateral edge of the dorsal horn and SDH at P5, indicating that the GSA-IB(4) is expressed on SDH/lamina V primary afferents at the time when they are making their projections into the spinal cord. In contrast, CGRP-immunoreactive afferents were not evident until postnatal day 7, when a few short projections into the lateral dorsal horn were observed. These afferents then followed a pattern similar to the development of GSA-IB(4) projects but with a latency of several days. The adult pattern of labelling by GSA-IB(4) is achieved by about postnatal day 20, whereas the adult pattern of CGRP labelling was not seen until postnatal day 30. Electron microscopy revealed a few immature synapses in the region of the developing SDH at postnatal day 10, and processes considered to be precursors of glomerular synapses (and thus of primary afferent origin) were first seen at postnatal day 16 and adopted their definitive appearance between postnatal days 28 and 55. Although structural and functional development of forelimbs of neonatal Monodelphis is more advanced than the hindlimbs, we found little evidence of a significant delay in the invasion of the spinal cord by primary afferents in cervical and lumbar regions. These observations, together with the broadly similar maturational appearance of histological sections of rostral and caudal spinal cord, suggest that, unlike the limbs they innervate, the spinal regions do not exhibit a large rostrocaudal gradient in their maturation.

Interneurone bursts are spontaneously associated with muscle contractions only during early phases of mouse spinal network development: a study in organotypic cultures

For a short time during development immature circuits in the spinal cord and other parts of the central nervous system spontaneously generate synchronous patterns of rhythmic activity. In the case of the spinal cord, it is still unclear how strongly synchronized bursts generated by interneurones are associated with motoneurone firing and whether the progressive decline in spontaneous bursting during circuit maturation proceeds in parallel for motoneurone and interneurone networks. We used organotypic cocultures of spinal cord and skeletal muscle in order to investigate the ontogenic evolution of endogenous spinal network activity associated with the generation of coordinate muscle fibre contractions. A combination of multiunit electrophysiological recordings, videomicroscopy and optical flow computation allowed us to measure the correlation between interneurone firing and motoneurone outputs after 1, 2 and 3 weeks of in vitro development. We found that, in spinal organotypic slices, there is a developmental switch of spontaneous activity from stable bursting to random patterns after the first week in culture. Conversely, bursting recorded in the presence of strychnine and bicuculline became increasingly regular with time in vitro. The time course of spontaneous activity maturation in organotypic slices is similar to that previously reported for the spinal cord developing in utero. We also demonstrated that spontaneous bursts of interneurone action potentials strongly correlate with muscular contractions only during the first week in vitro and that this is due to the activation of motoneurones via AMPA-type glutamate receptors. These results indicate the occurrence in vitro of motor network development regulating bursting inputs from interneurones to motoneurones.

Spinal circuits formation: a study of developmentally regulated markers in organotypic cultures of embryonic mouse spinal cord

In this study, we have addressed the issue of neural circuit formation using the mouse spinal cord as a model system. Our primary objective was to assess the suitability of organotypic cultures from embryonic mouse spinal cord to investigate, during critical periods of spinal network formation, the role of the local spinal cellular environment in promoting circuit development and refinement. These cultures offer the great advantage over other in vitro systems, of preserving the basic cytoarchitecture and the dorsal-ventral orientation of the spinal segment from which they are derived [Eur J Neurosci 14 (2001) 903; Eur J Neurosci 16 (2002) 2123]. Long-term embryonic spinal cultures were developed and analyzed at sequential times in vitro, namely after 1, 2, and 3 weeks. Spatial and temporal regulation of neuronal and non-neuronal markers was investigated by immunocytochemical and Western blotting analysis using antibodies against: a) the non-phosphorylated epitope of neurofilament H (SMI32 antibody); b) the enzyme choline acetyltransferase, to localize motoneurons and cholinergic interneurons; c) the enzyme glutamic acid decarboxylase 67, to identify GABAergic interneurons; d) human eag-related gene (HERG) K(+) channels, which appear to be involved in early stages of neuronal and muscle development; e) glial fibrillary acidic protein, to identify mature astrocytes; f) myelin basic protein, to identify the onset of myelination by oligodendrocytes. To examine the development of muscle acetylcholine receptors clusters in vitro, we incubated live cultures with tetramethylrhodamine isothiocyanate-labeled alpha-bungarotoxin, and we subsequently immunostained them with SMI32 or with anti-myosin antibodies. Our results indicate that the developmental pattern of expression of these markers in organotypic cultures shows close similarities to the one observed in vivo. Therefore, spinal organotypic cultures provide a useful in vitro model system to study several aspects of neurogenesis, gliogenesis, muscle innervation, and synaptogenesis.

Isolation and culture of motor neurons from the newborn mouse spinal cord

A protocol for the isolation and culture of motor neurons from postnatal day 1 mouse spinal cord is described. After 72 h in culture, phase contrast microscopy reveals healthy cells with motor neuronal morphology and extensive neuritic processes. These neurons express the 75-kDa low-affinity neurotrophin receptor (p75NTR) and choline acetyltransferase (ChAT), both proteins are specifically expressed by neonatal and embryonic motor neurons in vivo. This protocol can be adapted for various postnatal motor neuron assays.

Effects of target tissue on growth of snail neurones in collagen gel culture

The aim of this study was to assess the effect of potential target tissue on regenerating neurones of the snail Lymnaea stagnalis using the three-dimensional collagen gel culture system. Mammalian type I collagen supported the regenerative outgrowth of snail neurones, and the neurofilament antibody SMI31 specifically labelled regenerating processes both within the gel and those growing over the surface of the ganglia. Using these techniques we tested the effect of co-culturing ganglia with either additional nervous tissue, previously shown to produce trophic substances, or buccal muscle on both the amount and direction of outgrowth. We conclude that, under the conditions used, neither target tissue provided trophic or tropic support in collagen gel cultures.