Histochemical study of biogenic monoamines in early (“Prenervous”) and late embryos of sea urchins

Abstract

Treatment of the embryos of sea urchins with glyoxylic acid results in the appearance of luminescence which is indicative of the presence of biogenic monoamines. At the early stages of development (cleavage divisions, blastula, gastrula) the histochemical method reveals a tryptamine-like substance which is first found in all embryonic cells and later is concentrated mainly in the cells of the primary gut and ciliary bands. At the stages of prism and pluteus there appear neuron-like cells containing dopamine. The inhibitors of monoamine oxidase and neurotoxins reliably increase the histochemical reaction to monoamines only in late embryos which suggests a change in the properties of monoaminergic systems in the course of embryogenesis.

Morphogenetic roles of acetylcholine.

“…In sea urchin embryos, cell movements occurring during gastrulation and postgastrulation stages appear to be regulated by ACh and biogenic monoamines (5)(6)(7)(8)(9)(10). Specific antagonists of receptors for these neurotransmitters act as inhibitors of morphogenetic cell movements during specific phases of gastrulation.…”

“…The ability of both 5-HT and ACh to affect gastrulating sea urchin embryos suggests that receptors for these neurotransmitters are expressed at the time of gastrulation by cells of the primary gut and mesenchyme (5,6). Histochemical evidence has demonstrated the presence of acetylcholinesterase (AChE) during sea urchin gastrulation where it is localized predominantly in the primary gut, which is the site of the most active cell movements (7,10).…”

Transmitters in Blastomere Interactions

“…Similar situation is suggested in case of cholinergic interaction of gametes that both contain acetylcholine and corresponding receptors, taking part in the fertilization [96,107]. The second was the astonishing fact that the main way of transmitter inactivation in the embryonic cells are the transport of the transmitter molecules to outer medium because of low activity or absence of MAO (enzyme of serotonin and catcholamine degradation) [96,108]. Recently the absence of the expression of MAO A at early stages of Xenopus development was shown [85].…”

Changes in the physiological roles of neurotransmitters during individual development

“…This is particularly evidenced by the transmitter specialization of cells just mentioned, which arises in sea urchins and other animals with the standard type of development (including vertebrates) during and immediately after gastrulation [26,61,64,69,82]. Additionally, antagonists of various neurotransmitters act in different ways on the morphogenetic movements of cells during gastrulation, and the sensitivity of these cells to different groups of antagonists appears non-synchronously [7,51].…”

“…5-HT is synthesized or at least accumulated in motor cells of sea urchin and mollusk larvae, disappearing from other ectodermal cells. Acetylcholine, which is involved in regulating embryonic motor function in sea urchins, is also of non-neural origin [1,34,50,69]. In embryos and larvae of holobranch mollusks [1,20], 5-HT receptors are located on the surfaces of motor cells and are similar to classical 5-HT2 receptors.…”