Low-molecular-weight peptide stimulates cholinergic development in ventral spinal cord cultures

Establishment of pure neuronal cultures from fetal rat spinal cord and proliferation of the neuronal precursor cells in the presence of fibroblast growth factor

A primary culture system of nearly pure neuronal cells from 14-day-old fetal rat spinal cord has been developed by combining a preplating step, the use of a chemically defined serum-free medium, and borated polylysine-coated dishes that prevented the formation of cell aggregates. About 98% of the cells were found to be immunostained with neuron-specific enolase antibodies, confirming their neuronal nature. The cultures are composed essentially of a population of non-motoneurons and contain few motoneurons, characterized by their large size and multipolar aspect, the presence of acetylcholinesterase (AChE), and the intense immunoreaction for growth-associated protein GAP-43. Neuronal precursor cells are also present in these cultures and proliferate during the first 3 days. The addition of bovine brain basic fibroblast growth factor (bFGF) stimulates their proliferation over a period of 2 days, as determined by measurement of [125I]iododeoxyuridine incorporation and by immunocytochemical reaction after bromodeoxyuridine incorporation into nuclei. The proliferating cells were characterized as neurons by immunostaining against neuron-specific enolase. Recombinant human bFGF and bovine brain acidic FGF (aFGF) exerted similar effects. Other growth factors, including epidermal growth factor (EGF), transforming growth factor beta 1 (TGF-beta 1), and thrombin, were without effect on the proliferative activity of these neuronal cells. bFGF has no effect on the survival of motoneurons and on the fiber outgrowth of the whole neuronal population. However, bFGF affects the development of bipolar AChE-positive neurons, probably belonging to the non-motoneuron population. The data indicate that bFGF and aFGF are mitogens for neuroblasts from rat spinal cord in culture and that bFGF influences the development of a subpopulation of spinal neurons that are AChE-positive.

Opioids influence neurotransmitter phenotypic expression in chick embryonic neuronal cultures

There is considerable interest in the role of endogenous opioid peptides in neural growth and differentiation. In this study we used neuron-enriched cultures derived from 3-day-old chick embryos to test the effects of endogenous enkephalins on neurotransmitter phenotypic expression. Cultures were grown in serum-free chemically defined medium and were treated with either Met-enkephalin antiserum (anti-Met) to immunoneutralize enkephalins, or with naloxone, a universal opioid receptor antagonist, to block receptor-mediated actions of released endogenous opioids. The enzyme activities of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) were used as markers for cholinergic and catecholaminergic phenotypic expression, respectively. We found that cultures treated with anti-Met or naloxone exhibited strikingly different neuronal growth patterns as compared to controls. In addition, ChAT activity was enhanced by anti-Met, and TH activity by both anti-Met and naloxone. These findings lend support to the possibility that neuropeptides may be co-localized with neurotransmitters and that peptides released into the microenvironment affect neuronal phenotypic expression by differential receptor subtypes.

Growth hormone-releasing hormone and somatostatin influence neuronal expression in developing chick brain. II. Cholinergic neurons

In a previous study we have shown that in ovo administration of growth hormone-releasing hormone (GHRH) influences catecholaminergic neuronal expression as assessed by tyrosine hydroxylase activity (Dev. Brain Res., 49 (1989) 275-280). In this study we examined the effects of GHRH and somatostatin (SRIF) on cholinergic neuronal neurotransmitter expression both in ovo and in vitro. Chick embryos were administered GHRH or SRIF in ovo via the air sac on embryonic days 1, 3, 5 and 7, sacrificed at day 8 and the activity of choline acetyltransferase (ChAT) was assayed in whole brain homogenates. ChAT activity was significantly higher in peptide-treated embryos as compared to controls. Similar results were obtained when GHRH or SRIF (50 ng/50 microliters) was administered in a single dose at day 2 or 3; ChAT activity was significantly increased in peptide-treated versus control embryos. In contrast, embryos treated with GHRH or SRIF on day 1 or 5 or with growth hormone (100 ng/50 microliters) on day 3 of incubation showed no difference in ChAT activity as compared to controls. More direct effects of GHRH and SRIF were tested in neuron-enriched cultures derived from 3- (E3) or 6-day-old (E6) chick embryos. Cultures were grown in either serum-supplemented or serum-free medium for 6 days in the presence of GHRH or SRIF concentrations ranging from 0.01 to 100 nM. As observed in ovo, ChAT activity was increased in E3 cultures treated with peptides. In addition, the composition of the culture medium influenced the response to peptide treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor beta 1 is a potent survival factor for rat embryo motoneurons in culture

We have studied the effects of transforming growth factor beta 1 (TGF beta 1) on the survival of embryonic motoneurons in culture. For this purpose, E14 rat embryo motoneurons were purified to more than 90% homogeneity by cell sorting and cultured at low density on monolayers of cortex astrocytes. Subnanomolar concentrations of TGF beta 1 (40-500 pM) increased the survival of motoneurons 2-fold after 9-11 days in culture. The increase in choline acetyltransferase (ChAT) activity per culture caused by TGF beta 1 was attributable to its effects on survival. Comparable results were found with motoneurons cultured on lysed astrocytes, suggesting that the effects of the factor are not mediated by non-neuronal cells, but that motoneurons are a target for TGF beta 1.

Developmental discord among markers for cholinergic differentiation: in vitro time courses for early expression and responses to skeletal muscle extract

The effects of skeletal muscle extract on the development of CAT, ACh synthesis, high affinity choline uptake, and AChE activities were studied in dissociated ventral spinal cord cultures prepared from 14-day gestational rat embryos. In the absence of muscle extract, the development of CAT and AChE follow biphasic time courses in which they show initial declines followed by periods of steadily increasing activity. In contrast, ACh synthesis and high affinity choline uptake both gradually increase throughout the entire culture period. The presence of muscle extract both prevents the initial decline of CAT and AChE as well as stimulates the rates of development of all four cholinergic markers; however, the degrees and time courses of stimulation differ markedly. The effects of muscle extract on the kinetic and pharmacological properties of ACh synthesis and choline uptake in rat ventral cord cultures were also investigated. Cells treated with muscle extract for 2 days express both high affinity (Km = 1.6 microM) and low affinity (Km = 22 microM) choline uptake mechanisms. Control cells, on the other hand, express only low affinity uptake at this stage but develop a high affinity uptake mechanism by Day 7. During this time both ACh synthesis and high affinity choline uptake become increasingly sensitive to inhibition by hemicholinium-3. These results demonstrate that skeletal muscle factors enhance the development of cholinergic properties in embryonic spinal cord cultures. However, differences in sensitivity to muscle extract concentration, time courses of development, and degrees of stimulation suggest that these changes may involve distinct cellular mechanisms which are differentially affected by skeletal muscle factors.

Monoclonal antibodies to and immunoaffinity purification of choline acetyltransferase from bovine brain

Three hybridomas producing monoclonal antibodies to bovine brain choline acetyltransferase (ChAT) have been established by fusion of the spleen cells from a mouse immunized with purified enzyme with myeloma NS-1 cells. All three clones produced IgGl antibodies that reacted with enzyme protein denatured with sodium dodecyl sulfate. By using one of the monoclonal antibodies, a rapid and efficient immunoaffinity purification procedure of bovine ChAT has been established. Immunoblot analysis and immunoaffinity purification indicated that bovine ChAT is a single 68-kilodalton protein. The monoclonal antibodies will offer us a good tool to isolate the cDNA clones encoding ChAT.

Structural specificity of peptides influencing neuronal survival during development

Vasoactive intestinal peptide (VIP) has been shown to increase the survival of developing neurons grown in dissociated spinal cord cultures. This result was evident when synaptic activity was blocked with tetrodotoxin (TTX) during a critical period of development (days 7-21 after plating). Other neuropeptides, with a close sequence homology to VIP, have now been tested for their effects on neuronal survival in culture. Within the critical period, the survival of spinal cord neurons was significantly decreased (30-35%) after incubation with 1 nM peptide histidyl-isoleucine amide (PHI-27) or 0.1 nM growth hormone releasing factor (GRF). Neuronal cell death produced by these peptides did not exceed that observed from tetrodotoxin treatment alone. Secretin had no detectable effect on neuronal survival at any of the concentrations tested. In tetrodotoxin-treated cultures, PHI-27 and GRF prevented the neuronal cell death produced by TTX, but only at concentrations greater than 0.1 microM. In contrast, VIP significantly increased neuronal survival at concentrations less than 0.01 nM. The presence of 0.1 nM PHI-27 significantly decreased the effectiveness of VIP in preventing TTX-mediated neuronal cell death. Addition of PHI-27 or VIP, with or without TTX, to one month-old cultures produced no significant change in the number of neurons compared to control cultures. These studies indicate that the survival-promoting effect of VIP is highly structure-dependent and that this action appears to be confined to a critical period of development.

Somatostatin enhances neurite outgrowth and electrical coupling of regenerating neurons in Helisoma

The present study tested the ability of 3 peptides (somatostatin, arginine-vasopressin (AVP) and arginine-vasotocin (AVT)) to enhance neurite outgrowth from regenerating Helisoma neurons. The buccal ganglia from Helisoma were incubated either short-term in saline or longer-term (2-5 days) in medium and the extent of neurite outgrowth (induced by nerve crush) by a buccal neuron (neuron 5) was determined. Neurite outgrowth was consistently enhanced by both somatostatin and its extended analog somatostatin, but was unaffected by either AVT or AVP. The enhanced outgrowth due to somatostatin was associated with stronger electrical synapse formation between the two neurons 5, this being attributable to lower coupling resistance rather than a change in non-junctional resistance. Both the enhancement of neurite outgrowth and the increased efficacy of electrical coupling due to somatostatin were prevented by a somatostatin inhibitor. An immunohistochemical survey produced evidence for neurons containing a somatostatin-like peptide in both the cerebral ganglia and the enteric nervous system of Helisoma. It is concluded that somatostatin can act neurotrophically in the nervous system.