The muscarinic receptor-mediated action of acetylcholine in the gastrulating chick embryo

Impact of the electric shock on the embryonic development and physiological traits in chicks embryo

The objective of this study was to investigate the impact of stimulating the embryo during the dormancy in the incubation period. 450 eggs (Ross 308) were allocated in four treatments each with three replicates. The treatments were as follows: T1 control (without shock), T2 Shocked (40) Millivolts (mV), T3 Shocked (50) (mV), T4 Shocked (75) (mV). A different voltage device was used to shock the egg, after marking the eggs with a line of iron filings to ensure electrical conductivity, eggs were shocked at different times three times a day. The results showed that the percentage of embryonic weight increased significantly and the percentage of albumin decreased significantly and the percentage of shells for experimental treatments during the seven days of incubation compared to the control treatment. The significant increase in the percentage of embryonic weight and amniotic sac and liquid and a significant decrease in the percentage of albumin and yolk compared to the control treatment at 14 and 17 days of incubation for experimental treatment. Significant increase in neurophysiological traits of neurons, brain weight for T2, T3 and especially T4 concluded that electrical stimulation had a positive effect on the embryo.

Detection and characterisation of NAD(P)H-diaphorase activity in Dictyostelium discoideum cells (Protozoa)

In Dictyostelium discoideum (D. discoideum), compounds generating nitric oxide (NO) inhibit its aggregation and differentiation without altering cyclic guanosine monophosphate (cGMP) production. They do it by preventing initiation of cyclic adenosine monophosphate (cAMP) pulses. Furthermore, these compounds stimulate adenosine diphosphate (ADP)-ribosylation of a 41 kDa cytosolic protein and regulate the glyceraldehyde-3-phospate dehydrogenase activity. Yet, although D. discoideum cells produce NO at a relatively constant rate at the onset of their developmental cycle, there is still no evidence of the presence of nitric oxide synthase (NOS) enzymes. In this work, we detect the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity in D. discoideum and we characterise it by specific inhibitors and physical-chemical conditions that allegedly distinguish between NOS-related and -unrelated NADPH-d activity.

Control of cell proliferation by neurotransmitters in the developing vertebrate retina

In the developing vertebrate retina, precise coordination of retinal progenitor cell proliferation and cell-cycle exit is essential for the formation of a functionally mature retina. Unregulated or disrupted cell proliferation may lead to dysplasia, retinal degeneration or retinoblastoma. Both cell-intrinsic and -extrinsic factors regulate the proliferation of progenitor cells during CNS development. There is now growing evidence that in the developing vertebrate retina, both slow and fast neurotransmitter systems modulate the proliferation of retinal progenitor cells. Classic neurotransmitters, such as GABA (gamma-amino butyric acid), glycine, glutamate, ACh (acetylcholine) and ATP (adenosine triphosphate) are released, via vesicular or non-vesicular mechanisms, into the immature retinal environment. Furthermore, these neurotransmitters signal through functional receptors even before synapses are formed. Recent evidence indicates that the activation of purinergic and muscarinic receptors may regulate the cell-cycle machinery and consequently the expansion of the retinal progenitor pool. Interestingly, GABA and glutamate appear to have opposing roles, inducing retinal progenitor cell-cycle exit. In this review, we present recent findings that begin to elucidate the roles of neurotransmitters as regulators of progenitor cell proliferation at early stages of retinal development. These studies also raise several new questions, including how these neurotransmitters regulate specific cell-cycle pathways and the mechanisms by which retinal progenitor cells integrate the signals from neurotransmitters and other exogenous factors during vertebrate retina development.

Muscarinic calcium mobilization in the regenerating retina of adult newt

We used optical recording with a Ca(2+)-sensitive dye, fura2, in living slice preparations from the newt retina at different stages of regeneration. ACh produced the most pronounced [Ca2+]i rise in progenitor cells and premature ganglion cells of the earlier stage of retinal regeneration, but less pronounced Ca2+ response in ganglion cells just before, or at the beginning of, synaptogenesis. The [Ca2+]i rise to ACh was mediated by mAChRs. This was shown by inhibition of the ACh-induced Ca2+ response with a preincubation of the mAChR antagonist atropine as well as with direct stimulation of the [Ca2+]i rise by the mAChR agonist muscarine. This muscarine-induced [Ca2+]i rise was more greatly suppressed by the M1 and/or M3 preferring mAChR antagonists than by the M2 preferring mAChR antagonist. The [Ca2+]i rise due to muscarine was not suppressed in the absence of extracellular Ca2+, but suppressed in part in the presence of the L-type voltage-gated Ca2+ channel blockers, verapamil or nicardipine. Furthermore, thapsigargin (TG), a Ca-ATPase inhibitor, abolished the muscarine-induced [Ca2+]i rise in the absence of extracellular Ca2+. These results suggest that the mAChR-mediated [Ca2+]i rise is mainly a result of a release of Ca2+ from intracellular stores. TG produced a slow rise in the resting level of [Ca2+]i. This [Ca2+]i raise was suppressed as extracellular Ca2+ was omitted, whereas a rapid rise in [Ca2+]i occurred when extracellular Ca2+ was reintroduced, suggesting the occurrence of the capacitative Ca2+ influx in the progenitor cells and premature ganglion cells of the regenerating newt retina.

Transient muscarinic calcium mobilisation in transdifferentiating as in reaggregating embryonic chick retinae

Two independent in vitro regeneration systems of the embryonic chick retina (E4-5) were used to study the mobilisation of intracellular calcium by the neurotransmitters acetylcholine (ACh) and glutamate, as measured by Fura-2 fluorescence changes. Retinal pigment epithelium (RPE) explants under the influence of basic fibroblast growth factor transdifferentiate into a retina-like tissue with normal laminar organisation, while rosetted spheres reaggregated from fully dispersed cells of the embryonic retina will achieve only an inferior tissue organisation, characterised by regions of an inverted retina [Layer et al., Neuroreport 12 (2001) A39-46]. ACh induced a pronounced Ca(2+) response in young explants, and a similar but less pronounced response in reaggregates; this response decreased almost entirely after 1 week in culture. In contrast, a Ca(2+) response to glutamate became detectable later, continuously increasing during this period. The response to ACh was strictly mediated by muscarinic ACh receptors (mAChRs), since it was inhibited by preincubation with atropine, but not tubocurarine; correspondingly, it was mimicked by muscarine, but not nicotine. Studies with mAChR blockers, preferentially acting on the m1-, m2-, or m3-receptor subtypes, suggested that the muscarine-induced Ca(2+) response is mediated by m1- and/or m3-type mAChRs, but not by the m2-type. These results show that (i) similar to the in vivo retina, in both a transdifferentiating and a reaggregating system an early muscarinic Ca(2+) response is active, which (ii) roughly parallels periods of cell proliferation, and (iii)-as evidenced by the reaggregates-does not depend on any tissue pre-organisation. In contrast, a response to glutamate becomes prominent only when tissue differentiation commences. This is the first demonstration of a physiological response in regenerating chick retinas, supporting their validity as models both of retinal development and regeneration.

Perturbations in choline metabolism cause neural tube defects in mouse embryos in vitro

A role for choline during early stages of mammalian embryogenesis has not been established, although recent studies show that inhibitors of choline uptake and metabolism, 2-dimethylaminoethanol (DMAE), and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3), produce neural tube defects in mouse embryos grown in vitro. To determine potential mechanisms responsible for these abnormalities, choline metabolism in the presence or absence of these inhibitors was evaluated in cultured, neurulating mouse embryos by using chromatographic techniques. Results showed that 90%-95% of 14C-choline was incorporated into phosphocholine and phosphatidylcholine (PtdCho), which was metabolized to sphingomyelin. Choline was oxidized to betaine, and betaine homocysteine methyltransferase was expressed. Acetylcholine was synthesized in yolk sacs, but 70 kDa choline acetyltransferase was undetectable by immunoblot. DMAE reduced embryonic choline uptake and inhibited phosphocholine, PtdCho, phosphatidylethanolamine (PtdEtn), and sphingomyelin synthesis. ET-18-OCH3 also inhibited PtdCho synthesis. In embryos and yolk sacs incubated with 3H-ethanolamine, 95% of recovered label was PtdEtn, but PtdEtn was not converted to PtdCho, which suggested that phosphatidylethanolamine methyltransferase (PeMT) activity was absent. In ET-18-OCH3 treated yolk sacs, PtdEtn was increased, but PtdCho was still not generated through PeMT. Results suggest that endogenous PtdCho synthesis is important during neurulation and that perturbed choline metabolism contributes to neural tube defects produced by DMAE and ET-18-OCH3.

Inhibitors of choline uptake and metabolism cause developmental abnormalities in neurulating mouse embryos

BACKGROUND

Choline is an essential nutrient in methylation, acetylcholine and phospholipid biosynthesis, and in cell signaling. The demand by an embryo or fetus for choline may place a pregnant woman and, subsequently, the developing conceptus at risk for choline deficiency.

METHODS

To determine whether a disruption in choline uptake and metabolism results in developmental abnormalities, early somite staged mouse embryos were exposed in vitro to either an inhibitor of choline uptake and metabolism, 2-dimethylaminoethanol (DMAE), or an inhibitor of phosphatidylcholine synthesis, 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH(3)). Cell death following inhibitor exposure was investigated with LysoTracker Red and histology.

RESULTS

Embryos exposed to 250-750 microM DMAE for 26 hr developed craniofacial hypoplasia and open neural tube defects in the forebrain, midbrain, and hindbrain regions. Embryos exposed to 125-275 microM ET-18-OCH(3) exhibited similar defects or expansion of the brain vesicles. ET-18-OCH(3)-affected embryos also had a distended neural tube at the posterior neuropore. Embryonic growth was reduced in embryos treated with either DMAE (375, 500, and 750 microM) or ET-18-OCH(3) (200 and 275 microM). Whole mount staining with LysoTracker Red and histological sections showed increased areas of cell death in embryos treated with 275 microM ET-18-OCH(3) for 6 hr, but there was no evidence of cell death in DMAE-exposed embryos.

CONCLUSIONS

Inhibition of choline uptake and metabolism during neurulation results in growth retardation and developmental defects that affect the neural tube and face.

Synthesis of the Signal Molecule Acetylcholine during the Developmental Cycle of PARAMECIUM PRIMAURELIA (Protista, Ciliophora) and its Possible Function in Conjugation

We recently discovered, in mating-competent Paramecium primaurelia, the presence of functionally related molecules of the cholinergic system: the neurotransmitter acetylcholine (ACh), both its nicotinic and muscarinic receptors and its lytic enzyme acetylcholinesterase (AChE). Our results on the inhibition of mating-cell pairing in vivo in mating-competent cells treated with cholinomimetic drugs support the hypothesis that the cholinergic system plays a role in cell-to-cell adhesion. To investigate the possible function of the signal molecule ACh in conjugation in P. primaurelia, we attempted to detect the intracellular sites of ACh synthesis by localizing the ACh biosynthetic enzyme choline acetyltransferase (ChAT). Using immunocytochemical and histochemical methods, we have demonstrated the presence and activity of ChAT principally on the surface membrane of mating-competent cells and of mature but non-mating-competent cells. No evidence for ChAT activity was found in immature cells. Immunoblot analysis revealed the presence of immunoreactive bands, ranging in molecular mass from 42 to 133kDa, as reported for ChAT isolated from higher organisms. In vivo experiments showed that inhibition of ChAT activity by Congo Red, known to be a potent competitive inhibitor of acetyl coenzyme A, did not affect mating-cell pairing. Conversely, inhibition of AChE with BW284c51 or eserine, which block enzyme activity by reacting with a specific serine within the catalytic centre, significantly inhibited mating-cell pairing. Our results suggest that ACh has a negative modulating effect on conjugation in P. primaurelia.