Choline acetyltransferase induction in cultured neurons: dissociated spinal cord cells are dependent on muscle cells, organotypic explants are not

New organotypic model to culture the entire fetal rat spinal cord

We have developed a system for culturing separately the entire longitudinally-cut ventral and dorsal parts of the whole spinal cord of 12-14 day rat embryos, either on polylysine-collagen mixture or co-cultured with human muscle. At the time of explanation and throughout the period of culturing (up to 21 days) choline acetyltransferase (ChAT) activity in dorsal macroexplants (D-MEs) was negligible (2% of that in the ventral macroexplants (V-MEs)). During culturing neuronal survival was evaluated by measurements of ChAT and enolase. The densities and lengths of neuronal processes outgrowing from the MEs were measured in living and fixed cultures. In the latter, immunocytochemical and cytochemical stainings, allowing visualization of neurites, were evaluated by computerized video image analysis. The ChAT activity in the MEs cultured under our two experimental conditions differed only during the first few days of culturing, being significantly higher in the V-MEs co-cultured with muscle as compared to those cultured on a polylysine-collagen mixture. After 3 weeks of culturing, ChAT activity was not statistically different. However, the co-cultured muscle fibers definitely influenced: (a) neurite outgrowth, (b) the expression of neurofilament proteins and (c) the ability to maintain cultured MEs long-term. This new system allows study of motor neurons and the influence on them of putative growth, survival and maturation factors in a tissue culture milieu that more closely resembles in vivo conditions than other culture systems. Our established parameters can now serve as a basis for such studies.

The use of cell and tissue culture techniques in the study of regulatory peptides

Cell and tissue culture preparations have a number of general advantages for the study of biological processes: cells are more accessible for study, diffusion delays and barriers to applied substances are minimised, the humoral and cellular components of the culture environment can be controlled and progressive changes in intracellular and intercellular events can be directly monitored. These significant advantages mean that culture preparations can provide unique opportunities for investigation of the properties and functions of regulatory peptides. Culture preparations also have disadvantages and not all cultures are suitable for use in all types of experiments; therefore, the choice of preparation must be made accordingly. Here we describe different types of culture preparation and give examples where cultures have been used to examine peptide synthesis, storage, secretion and receptor localisation, as well as the short-term and trophic actions of regulatory peptides.

Cultured rat spinal cord neurons: interaction with motor neuron disease immunoglobulins

Conditions have been developed for the culture of rat spinal cord neurons in serum-free media supplemented with hormones and growth factors. Neurons were identified by immunofluorescence-labeled anti-neurofilament antibody, and their growth was monitored by assay of choline acetyltransferase and cholinesterase activities. Activities of these enzymes were considerably higher than those of comparable cultures in serum supplemented media in which there were visibly many more nonneuronal cells. Serum immunoglobulins from patients with motor neuron disease showed enhanced binding to rat spinal cord cells maintained in both serum-supplemented and serum-free media, as compared with those from normal healthy individuals. Enhanced binding was more marked with the latter cells, presumably because of the higher proportion of neuronal cells in these cultures. Serum immunoglobulins from patients with other neurologic disorders showed a similar binding to that of the normal controls. The results demonstrate the presence of an immune response to spinal cord cell membrane components in patients with motor neuron disease, although whether the response is primary or secondary in the disease process remains unclear.

Neurite-promoting activities for embryonic spinal neurons and their developmental changes in the chick

Spinal motoneurons may depend upon muscle-derived factors for axon outgrowth and stabilization at two principal stages of their development: during the initial invasion of the differentiating muscle masses in the embryo and during the perinatal regression of multiple innervation. Using a bioassay involving the measurement of neurite outgrowth from 4.5-day embryonic chick spinal neurons in dissociated cell culture, neurite-promoting activities were detected both in medium conditioned over embryonic chicken myotubes in vitro (embryonic muscle-conditioned medium) and in soluble extracts of chick leg muscle prepared 3-5 days after hatching (postnatal muscle extract). The molecules responsible for these two activities had physicochemical properties that distinguished them both from each other and from some other reported neurite-promoting factors. The factor in embryonic muscle-conditioned medium, although active on uncoated tissue culture wells, bound with only low affinity to tissue culture plastic under cell culture conditions. It was inactivated by incubation with trypsin, and was essentially found only in media conditioned by muscle and liver cells. The factor in PNME, on the other hand, bound to plastic culture wells and was found in extracts of a variety of tissues. Its concentration in postnatal leg muscle was developmentally regulated: the specific activity increased approximately 10-fold between hatching and Day 3 (maximum value: 3200 units/mg protein) and then fell back to nearly its original levels by Day 7. Evidence is presented that the observed effects of these two neurite-promoting factors did not result from differential survival in vitro of different cell subpopulations. Possible roles for the two active factors during motoneuron development are discussed.

Development of cholinergic properties in nerve cell cultures in the presence of brain extract

Cells dissociated from cerebral hemispheres of 6-day-old chick embryos were cultured either in standard nutrient medium or in the presence of a brain extract from 8-day-old chick embryo. Morphological observations showed the development of bipolar and multipolar neurons in both culture conditions and acetylcholinesterase activity was found in all neuronal cells. Brain extract stimulated the morphological maturation of neurons, expressed by the formation of fiber bundles, fine structural maturation and development of synapses rich in clear vesicles. Furthermore, acetylcholinesterase and choline acetyltransferase activities were higher in the cultures treated with brain extract. In these cultures, the values of choline acetyltransferase activity reached a peak at 10 days and then decreased. These observations are discussed with particular reference to proliferation, maturation and degeneration of cholinergic neurons.

Induction of cholinergic expression in developing spinal cord cultures

The induction of choline acetyltransferase (ChAT) by cAMP derivatives was studied in dissociated spinal cord cultures. Dibutyryl cAMP (dbcAMP) and 8-bromo cAMP (1 mM) produced a 2-3-fold stimulation of ChAT activity in developing cultures whereas 8-bromo cGMP had no effect. A phosphodiesterase inhibitor, 3-isobutyl-l-methylxanthine, also increased (2-fold) ChAT activity in immature cultures. Significant elevations in ChAT were detected after 2 h incubation with dbcAMP. Maximum enzyme induction was observed 24 h after dbcAMP supplementation to the culture medium. Developmental studies revealed that ChAT could be induced on days 2-16 in culture. The largest induction of ChAT activity was observed on day 7 in culture. After day 19, when control enzyme activity attained levels of mature cultures, cAMP-mediated ChAT induction was no longer observed. Cycloheximide and actinomycin D blocked ChAT induction whereas basal enzyme activity remained unaffected. Culture protein content was not changed after 1-day exposure to dbcAMP. 125I-Tetanus toxin fixation after dbcAMP treatment revealed a 20% decrease from control in neuronal surface during days 7-9 in culture. These data indicated that cAMP derivatives produced a rapid increase in cholinergic expression during a specific period of development in spinal cord cultures. There appears to be specificity to this effect, as total neuronal surface does not respond in the same manner as ChAT activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracts of skeletal muscle increase neurite outgrowth and cholinergic activity of fetal rat spinal motor neurons

A soluble extract of rat skeletal muscle increased neurite outgrowth and cholinergic activity of dissociated ventral spinal neurons in culture. The effects were concentration-dependent, saturable, and labile in the presence of heat or trypsin. The morphological enhancement was produced only by skeletal muscle extract and decreased with developmental age, whereas the cholinergic enhancement was produced by extracts of cerebral cortex and cardiac and skeletal muscle and did not change with age. These changes were specific for ventral cord neurons, but no species specificity was observed with respect to the muscle source or the neuronal target.

Regulation of choline acetyltransferase in primary cell cultures of spinal cord by neurotransmitter L-norepinephrine

Neurotransmitter L-norepinephrine increased up to 8-fold the activity of choline acetyltransferase (CAT), the enzyme responsible for the synthesis of acetylcholine, in mouse spinal cord cells in culture grown for several days. The increase of CAT activity by L-norepinephrine was mediated by a beta-adrenergic receptor in the same manner as the response of intracellular cyclic AMP. Derivatives of cyclic AMP caused an increase of CAT activity to the level similar to that of L-norepinephrine. A cyclic AMP phosphodiesterase inhibitor, 3-isobutyl-1-methyl xanthine (IBMX), enhanced the elevation of CAT activity by L-norepinephrine. These results indicate that L-norepinephrine stimulated the synthesis of CAT molecules via the action of cyclic AMP. The pretreatment of cells with 5-fluoro-2'-deoxyuridine (FdU) markedly diminished the numbers of satellite cells and, in parallel, the responses of CAT activity to L-norepinephrine. The increase of cyclic AMP by L-norepinephrine was also reduced by pretreatment of the cells with FdU. In contrast, co-cultures of spinal cord with heart muscle markedly (30-fold) stimulated CAT activity both with and without pretreatment of FdU. The addition of L-norepinephrine and co-cultures with heart muscle showed an additive effect. These observations indicate that the stimulatory effect of L-norepinephrine on CAT activity is mostly, if not only, mediated via the interaction with satellite cells, and that the increase of CAT activity by L-norepinephrine is based on a mechanism different from that of co-cultures with heart muscle cells.

Survival and neurite growth of chick embryo spinal cord cells in serum-free culture

Cell survival and neurite growth were investigated in serum-free spinal cord cell cultures on polyornithine coating (PORN). Cells were obtained from 6- or 7-day-old chick embryos. Isolated spinal cord cells required promoting factors for their survival and neurite growth. The survival-promoting factors were initially present in spinal cord cells. High density cultures, co-cultures with spinal cord explants, and spinal cord extract promoted survival of isolated spinal cord cells in MEM with no additives. Other tissue extracts (brain, liver, heart and skeletal muscle), serum, and serum-free conditioned medium (SF-CM) of muscle or glioma C6 cells also promoted survival. The active substances in the brain extract and SF-CM were shown to be protein and were separated into 3 fractions (approximately molecular weight 150,000, 70,000, 40,000) by gel filtration chromatography. Survival and neurite growth were suggested to be promoted by different factors because: (1) survival was promoted by both tissue extract and SF-CM, but neurite growth was promoted only by SF-CM; (2) the neurite growth-stimulating activity of SF-CM was lost following dialysis and heat (100 degrees C, 2 min) treatment; however, the survival-promoting activity was not. It was also suggested that spinal cord cells produce neurite growth promoting factors, but did not initially contain these factors.

Neuronal maturation in mammalian cell culture is dependent on spontaneous electrical activity

Fetal mouse spinal cord (SC) and dorsal root ganglion (DRG) neurons undergo a process of maturation in cell culture lasting a month or more. We have investigated the role of electrical activity in this maturational process with the use of tetrodotoxin (TTX), the specific blocker of the voltage-sensitive sodium channel responsible for action potential generation. This agent completely eliminates the spikes and related synaptic activity which occur abundantly in untreated cultures. Such blockade of electrical activity in the cultures, when begun early (day 1 or day 8 in vitro), results in a 85-95% reduction in the number of large SC neurons, without affecting DRG neuron numbers. TTX treatment initiated when cultures are mature (day 70) has no significant effect on either DRG or SC neurons. Intermediate effects are obtained when treatment is initiated at day 35 in vitro. The activity of the nerve-specific enzyme choline acetyltransferase, is significantly decreased by early TTX treatment, while DNA and protein content of the cultures (primarily contributed by glial and fibroblastic cells) is not affected.