Proliferating ability, morphological development and acetylcholinesterase activity of the neural tube cells in early chick embryos. An electron microscopic study

The role of thyroid hormone on phenylhydrazine hydrochloride mediated inhibitory effects on blood acetylcholinesterase: An in vivo and in vitro study

A novel phenomenon of protective counteraction by thyroid hormone has been demonstrated in phenylhydrazine hydrochloride (PHH) induced insult on blood acetylcholinesterase (AChE, EC 3.1.1.7) activity, in both, in vivo and in vitro conditions. Injection of PHH (20 microg/g) to juvenile male rats for three consecutive days caused a 48% decrease (p < 0.001) in the total blood AChE activity on the third day (i.e. 24 h after injections for three consecutive days) in comparison to the control animals. Simultaneous injections of thyroxine (T4) 1 or 2 microg/g with PHH (20 microg/g) showed a recovery in AChE activity by 27% (p < 0.02) and 55% (p < 0.001), respectively, in comparison to the only PHH-injected animals. T4 at 1, 2 and 4 microg/g doses showed unchanged levels in comparison to the untreated controls. In our in vitro system, incubations of the RBCs in PHH (2 mM) containing medium also showed an inhibition of 44% (p < 0.001) of the RBC membrane AChE activity in comparison to the control conditions. A recovery of 23-81% of the enzyme activity was observed after simultaneous use of T4 (1 nM-100 nM) or T3 (0.1 nM-100 nM), or triiodothyroacetic acid (TRIAC) (100 nM) with PHH (2 mM) in a dose-dependent manner with a potency profile of T3 > T4 > TRIAC. Incubation of RBCs only with T4, T3, or TRIAC at 0.1-100 nM concentration did not cause any alteration in the membrane AChE activity in comparison to control conditions. Thus, thyroid hormone distinctly demonstrated a counteraction or protective nature of action on the PHH-induced inhibition of total blood and RBC membrane AChE activity.

The key role of butyrylcholinesterase during neurogenesis and neural disorders: an antisense-5'butyrylcholinesterase-DNA study

The wide tissue distribution of butyrylcholinesterase (BChE) in organisms makes specific roles possible, although no clear physiologic function has yet been assigned to this enzyme. In vertebrates, it appears e.g. in serum, hemopoietic cells, liver, lung, heart, at cholinergic synapses, in the central nervous system. in tumors and not at least (besides acetylcholinesterase, AChE) in developing embryonic tissues. Here, a functional role of BChE can be found in regulation of cell proliferation and the onset of differentiation during early neuronal development--independent of its enzymatic activity. For studies concerning this point, we have established a strategy for a specific and efficient inhibition of BChE to investigate how the expected decrease of enzyme and, therefore, the manipulation of cellular cholinesterase-equilibrium influences embryonic neurogenesis--among others to gain information about the significance of noncholinergic, activity-independent and cell growth functions of BChE. The antisense-5'BChE-DNA strategy is based on inhibition of BChE mRNA transcription and protein synthesis. For this, the BChE gene is cloned into a suitable vector system; this is done in antisense-orientation, so that a transfected cell will produce their own antisense mRNA to inhibit gene expression. For such investigations in neurogenesis, the developing retina is a good model and we are able to create organotypic, three-dimensional retinal aggregates in vitro (retinospheroids) using isolated retinal cells of 6-day-old chicken embryos. Using this in vitro retina and "knock out" of BChE gene expression, we could show a key role of BChE during neurogenesis. The results are of great interest because in tumorigenesis and some neuronal disorders, the BChE gene is amplified or abnormally expressed. It has to be discussed how the antisense-5'BChE strategy can play a role in the development of new and efficient therapy forms.

Regulation of cholinesterase gene expression affects neuronal differentiation as revealed by transfection studies on reaggregating embryonic chicken retinal cells

In the embryonic chicken neuroepithelium, butyrylcholinesterase (BChE) as a proliferation marker and then acetylcholinesterase (AChE) as a differentiation marker are expressed in a mutually exclusive manner. These and other data indicate a coregulation of cholinesterase expression, and also possible roles of cholinesterases during neurogenesis. Here, both aspects are investigated by two independent transfection protocols of dissociated retina cells of the 6-day-old chick embryo in reaggregation culture, both protocols leading to efficient overexpression of AChE protein. The effect of the overexpressed AChE protein on the re-establishment of retina-like three-dimensional networks (so-called retinospheroids) was studied. In a first approach, we transfected retinospheroids with a pSVK3 expression vector into which a cDNA construct encoding the entire rabbit AChE gene had been inserted in sense orientation. As detected at the mRNA level, rabbit AChE was heterologously overexpressed in chicken retinospheroids. Remarkably, this was accompanied by a strong increase in endogenous chicken AChE protein, while the total AChE activity was only slightly increased. This increase was due to chicken enzyme, as shown by species-specific inhibition studies using fasciculin. Clearly, total AChE activity is regulated post-translationally. As an alternative method of AChE overexpression, transfection of spheroids was performed with an antisense-5'-BChE vector, which not only resulted in the down-regulation of BChE expression, but also strongly increased chicken AChE transcripts, protein and enzyme activity. Histologically, a higher concentration of AChE protein (as a consequence of either AChE overexpression or BChE suppression) was associated with an advanced degree of tissue differentiation, as detected by immunostaining for the cytoskeletal protein vimentin.

Expression of the cholinergic signal-transduction pathway components during embryonic rat heart development

BACKGROUND

Previous studies showed that acetylcholinesterase (AChE) activity is present in the downstream (arterial) part of the embryonic chick and rat heart, but its functional significance was unclear. To establish whether other components of a cholinergic signal-transduction pathway are present in the embryonic heart, we localised the mRNAs encoding choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and the muscarinic receptor isoforms (mAChRs; m1-m5).

METHODS

Messenger RNA detection and localisation by in situ hybridisation and reverse transcriptase-polymerase chain reaction were employed.

RESULTS

Expression of ChAT and AChE mRNAs was observed from 15 embryonic days onward in the neural tissue covering the dorsocranial wall of the atria. Muscarinic receptors (m1, m2, m4) were observed at the same localisation as AChE and ChAT mRNAs, both during embryogenesis and after birth. In addition, m1 and m4 mAChRs showed a low level of expression in the atrial myocardium during the fetal period. No expression of the m3 or the m5 mAChRs was observed in or near the embryonic hearts. ChAT, AChE, and mAChRs (m1, m2, m4) mRNAs always colocalised in the cardiac ganglia. However, none of these mRNAs was found at a detectable level in the outflow tract and/or the ventricular trabeculations.

CONCLUSIONS

The AChE activity in the arterial part of the embryonic heart is probably synthesised elsewhere and subserves a function different from the hydrolysis of locally produced acetylcholine.

Cholinesterases and peanut agglutinin binding related to cell proliferation and axonal growth in embryonic chick limbs

Embryonic cholinesterases are assigned important functions during morphogenesis. Here we describe the expression of butyrylcholinesterase and acetylcholinesterase, and the binding of peanut agglutinin, and relate the results to mitotic activity in chick wing and leg buds from embryonic day 4 to embryonic day 9. During early stages, butyrylcholinesterase is elevated in cells under the apical ectodermal ridge and around invading motoraxons, while acetylcholinesterase is found in the chondrogenic core, on motoraxons and along the ectoderm. Peanut agglutinin binds to the apical ectodermal ridge and most prominently to the chondrogenic core. Measurements of thymidine incorporation and enzyme activities were consistent with our histological findings. Butyrylcholinesterase is concentrated near proliferative zones and periods, while acetylcholinesterase is associated with low proliferative activity. At late stages of limb development, acetylcholinesterase is concentrated in muscles and nonexistent within bones, while butyrylcholinesterase shows an inverse pattern. Thus, as in other systems, in limb formation butyrylcholinesterase is a transmitotic marker preceding differentiation, acetylcholinesterase is found on navigating axons, while peanut agglutinin appears in non-invaded regions. These data suggest roles for cholinesterases as positive regulators and peanut-agglutinin-binding proteins as negative regulators of neural differentiation.

Chicken retinospheroids as developmental and pharmacological in vitro models: acetylcholinesterase is regulated by its own and by butyrylcholinesterase activity

The phylo- and ontogenetically related enzymes butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are expressed consecutively at the onset of avian neuronal differentiation. In order to investigate their possible co-regulation, we have studied the effect of highly selective inhibitors on each of the cholinesterases with respect to their expression in rotary cultures of the retina (retinospheroids) and stationary cultures of the embryonic chick tectum. Adding the irreversible BChE inhibitor iso-OMPA to reaggregating retinal cells has only slight morphological effects and fully inhibits BChE expression. Unexpectedly, iso-OMPA also suppresses the expression of AChE to 35%-60% of its control activity. Histochemically, this inhibition is most pronounced in fibrous regions. The release of AChE into the media of both types of cultures is inhibited by iso-OMPA by more than 85%. Control experiments show that AChE suppression by the BChE inhibitor is only partially explainable by direct cross-inhibition of iso-OMPA on AChE. In contrast, the treatment of retinospheroids with the reversible AChE inhibitor BW284C51 first accelerates the expression of AChE and then leads to a rapid decay of the spheroids. After injection of BW284C51 into living embryos, we find that AChE is expressed prematurely in cells that normally express BChE. We conclude that the cellular expression of AChE is regulated by the amount of both active BChE and active AChE within neuronal tissues. Thus, direct interaction with classical cholinergic systems is indicated for the seemingly redundant BChE.

Formation of neuroblastic layers in chicken retinospheroids: the fibre layer of Chievitz secludes AChE-positive cells from mitotic cells

The significance of the classical subdivision of the retinal primitive neuroepithelium into an outer and an inner neuroblastic layer by the transient fibre layer of Chievitz (LOC) is little understood. We examine here the formation of neuroblastic layers by regenerating fully laminated retinospheroids from dissociated cells of the embryonic chick eye margin in rotary culture. By tracing cellular processes with the fibre-specific F11-antibody in retinospheroids, we occasionally find, in addition to an outer and an inner plexiform layer, a cell-free F11-positive LOC homologue, subdividing the inner nuclear layer. Moreover, we demonstrate that the LOC precisely separates postmitotic AChE-positive cells of the inner retina from an AChE-negative outer part holding all BrdU-labelled mitotic cells. These in vitro data suggest that the inner neuroblastic layer is exclusively composed of AChE-positive cells, thus representing a primary differentiation zone of the retina.

Cranial nerve growth in birds is preceded by cholinesterase expression during neural crest cell migration and the formation of an HNK-1 scaffold

The expression of the neural crest cell (NCC) markers acetylcholinesterase (AChE) and the HNK-1-epitope is compared from the emigration of cephalic NCC until the formation of the cranial nerves V-X in chicken and quail hindbrain. We show that NCC transiently express acetylcholinesterase (AChE) activity during their emigration; NCC migrate into butyrylcholinesterase (BChE)-positive areas of the cranial mesenchyme. Along these migratory tracks that foreshadow the course of later projecting cranial nerves, BChE increases strongly in cells that may represent immature Schwann cells. Both AChE and BChE, but not HNK-1, are expressed in the ectodermal placodes. In NCC, HNK-1 is expressed strongly only when they approach their destination sites. Their intense expression of HNK-1 then leads to the establishment of tunnel-shaped HNK-1 matrices, within which G4-positive cranial neurites begin to extend. We conclude that AChE and HNK-1 expression in cephalic NCC serve different functions, since AChE is related to their migration, and HNK-1 to their aggregation and the formation of an extracellular neurite scaffold.

Cholinesterases during development of the avian nervous system

1. Long before onset of synaptogenesis in the chicken neural tube, the closely related enzymes butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are expressed in a mutually exclusive manner. Accordingly, neuroblasts on the ventricular side of the neural tube transiently express BChE before they abruptly accumulate AChE while approaching the outer brain surface. 2. By exploiting AChE as a sensitive and early histochemical differentiation marker, we have demonstrated complex polycentric waves of differentiation spreading upon the cranial part of the chicken neural tube but a smooth rostrocaudal wave along the spinal cord. Shortly after expression of AChE, these cells extend long projecting neurites. In particular, segmented spinal motor axons originate from AChE-positive motoneurones; they navigate through a BChE-active zone within the rostral half of the sclerotomes before contacting BChE/AChE-positive myotome cells. At synaptogenetic stages, cholinesterases additionally are detectable in neurofibrillar laminae foreshadowing the establishment of cholinergic synapses. 3. In order to elucidate the functional significance of cholinesterases at early stages, we have investigated specific cholinesterase molecules and their mechanisms of action in vivo and in vitro. A developmental shift from the low molecular weight forms to the tetramers of both enzymes has been determined. In vitro, the addition of a selective BChE inhibitor leads to a reduction of AChE gene expression. Thus, in vivo and in vitro data suggest roles of cholinesterases in the regulation of cell proliferation and neurite growth. 4. Future research has to show whether neurogenetic functioning of cholinesterases can help to understand their reported alterations in neural tube defects, mental retardations, dementias and in some tumours.

Cholinesterases preceding major tracts in vertebrate neurogenesis

The role of acetylcholinesterase (AChE) in neurotransmission is well known. But long before synapses are formed in vertebrates, AChE is expressed in young postmitotic neuroblasts that are about to extend the first long tracts. AChE histochemistry can thus be used to map primary steps of brain differentiation. Preceding and possibly inducing AChE in avian brains, the closely related butyrylcholinesterase (BChE) spatially foreshadows AChE-positive cell areas and the course of their axons. In particular, before spinal motor axons grow, their corresponding rostral sclerotomes and myotomes express BChE, and both their neuronal source and myotomal target cells express AChE. Since axon growth has been found inhibited by acetylcholine, it is postulated that both cholinesterases can attract neurite growth cones by neutralizing the inhibitor. Thus, the early expression of both cholinesterases that is at least partially independent from classical cholinergic synaptogenesis, sheds new light on the developmental and medical significance of these enzymes.

Developmental maps of acetylcholinesterase and G4-antigen of the early chicken brain: long-distance tracts originate from AChE-producing cell bodies

After approaching the outer surface of the neuroepithelium, postmitotic cell bodies abruptly start to synthesize acetylcholinesterase (AChE). Their easy histochemical detection allows us to trace sensitively spatiotemporal patterns of differentiation processes of the chicken nervous system. To investigate the relationship between postmitotic AChE production and the first formation of neurites, AChE histochemistry is combined here with immunohistochemistry using the neurite-specific G4-antibody. Spatial computer reconstructions from double-stained serial sections of whole brains of H.H. stages 10-20 demonstrate that G4-neurite expression spatio-temporally follows the expression of AChE in its complex polycentric pattern closely, the details of which have been described earlier. By comparing both differentiative steps at the single cell level reveals that a great majority (if not all) of the G4-positive neurites originate from AChE-positive cell bodies. Based on both the computer reconstructions as well as single cell analysis, including [3H]-thymidine pulse-experiments followed by autoradiography, we conclude, that AChE expression precedes formation of G4-neurites by about 15 h. In addition, the reconstructions provide the first detailed maps of G4-fiber tract formation and shows that G4-neurites form fascicles, most of which travel over long distances to targets within or without the central nervous system (CNS). This is the first demonstration for the entire young chicken brain which verifies that AChE-expressing cells, generally, are those that will establish efferents to distant targets.

Ontogeny of acetylcholinesterase, substance P and calcitonin gene-related peptide-like immunoreactivity in chick dorsal root ganglia

The distribution of acetylcholinesterase and of two neuropeptide (substance P and calcitonin gene-related peptide) immunoreactivities has been investigated in sensory neurons of lumbosacral dorsal root ganglia during chick embryo development, combining immunolocalization of neuropeptides with simultaneous histochemical detection of acetylcholinesterase, in order to study co-localization of the two peptides and their relations with acetylcholinesterase. Acetylcholinesterase at E7 of development appears in only a few neurons, usually the larger ones located in the lateroventral region of the ganglia. As development proceeds the number of neurons and intensity of staining increase. Until E12-13 acetylcholinesterase positivity is limited to the region of the ganglion containing larger neurons. At later stages (E20) it spreads progressively, leading to staining of cells over the whole ganglion. Substance P-like immunoreactivity appears at E6 and for calcitonin gene-related peptide at E7. These immunoreactivities progressively increase with development, remaining limited to the small neuron compartment of the dorsomedial region of the ganglion. Immunoreactivity for both neuropeptides reaches a maximum around E10-13 and then declines. Using simultaneous double immunostaining, calcitonin gene-related peptide and substance P-like immunoreactivities are largely co-localized, although their distribution is not completely coincident. Neuropeptide-positive cells are usually devoid of any acetylcholinesterase activity until E15. They become positive for the enzyme at later stages. The significance of acetylcholinesterase expression in sensory neurons and the possible relation of its appearance and neuron size is discussed.

The human amygdaloid complex: a cytologic and histochemical atlas using Nissl, myelin, acetylcholinesterase and nicotinamide adenine dinucleotide phosphate diaphorase staining

We examined the distribution of acetylcholinesterase and nicotinamide adenine dinucleotide phosphate diaphorase enzyme activity in the human amygdala using histochemical techniques. Both methods revealed compartments of higher or lower enzyme activity, in cells or neuropil, which corresponded to the nuclear subdivisions of the amygdala as defined with classical Nissl and myelin methods. The boundaries between the histochemical compartments were usually so sharp that the identification of these nuclear subdivisions was enhanced. There was also variation of staining intensity within many of the nuclear subdivisions, such as the lateral and central nuclei, anterior amygdaloid area and the intercalated groups. This histochemical difference corresponded to more subtle differences in Nissl and myelin staining patterns, and suggests further structural subdivisions of potential functional significance. We present a revised scheme of anatomical parcellation of the human amygdala based upon serial analysis with all four techniques. Our expectation is that this will allow the delineation of a clearer homology between the cytoarchitectonic subdivisions of the human amygdala and those of experimental animals.

Non-specific cholinesterase activity of the developing peripheral nerves and its possible function in cells in intimate contact with growing axons of chick embryo

The results presented here demonstrate non-specific cholinesterase (nChE) activity in the developing peripheral nerves of chick embryos at stages 25-26 according to Hamburger and Hamilton (1951, J. Morphol. 88, 49-92). Under the light microscope the use of simultaneous staining for nChE activity and silver proteinate impregnation revealed the axons to be surrounded by cells exhibiting nChE activity in the main nerve trunks and in the growing tips of nerves. Nerve branches arising from the main nerve trunks contained cells with positive reaction for nChE activity, too. Electron-dense particles of the reaction product indicating nChE activity were found in the rough endoplasmic reticulum and in the perinuclear envelope of cells in close contact with growing nerve fibers and their growth cones. The same distribution of nChE activity was found in cells which were located near to nerve fasciculi but without direct contact with axons. Surprisingly, the cells in close contact with axons and their growth cones exhibited the end product of nChE activity in the outer part of their plasma membrane. The cells enveloping axons within the nerve trunks were apparently Schwann cells, while those around the growth cones at nerve tips could be identified as Schwann cells and/or mesenchymal cells of the hindlimb. The nChE reaction product was also detected in the axolemma of nerve fibers and their growth cones. The distribution of nChE activity in the developing peripheral nerves of chick embryos suggests that these molecules may influence the process of axonal elongation and locomotion. Several possible mechanisms of nChE action on growing axons can be presumed: (i) intracellular Ca2+ level regulation; (ii) providing an adhesive substrate; and (iii) butyrate production affecting the cell metabolism and the distribution of neurotubules and neurofilaments. It is also assumed that nChE molecules are involved in the interactions of nerve fibers with Schwann cells and/or mesenchymal cells as well as in interneuronal interactions.

Acetylcholinesterase in the development of chick dorsal root ganglia

Acetylcholinesterase is expressed in chick dorsal root ganglia neurons very early in development. Since the physiological role of the enzyme in these cells is still obscure, it appeared of interest to investigate its modifications in the course of development. The specific activity of acetylcholinesterase in chick dorsal root ganglia increases, during in ovo development, from day E5 to day E13; after day E13 there is a decrease. Conversely, when acetylcholinesterase activity was expressed on a per ganglion basis, a continuous increase in the level of the enzyme until day E20 was observed. Acetylcholinesterase is a polymorphic enzyme and its molecular forms have different cellular localizations. Two globular forms, a tetramer (G4) and a dimer (G2), are present in the ganglia, as in chick brain. G4 is the major form at day E5, where it represents about 85% of the activity. This form shows a progressive decrease since day E8, and at day E20 exhibits activity levels similar to those of G2. It is known that acetylcholinesterase-producing cells are also able to release the enzyme in the extracellular space. We determined the release of acetylcholinesterase by cultured dorsal root ganglia neurons at various developmental stages: acetylcholinesterase release is significantly increased at day E20, as compared to younger stages, and 90% of the enzyme released is G4.

Independent spatial waves of biochemical differentiation along the surface of chicken brain as revealed by the sequential expression of acetylcholinesterase

AChE-positive cells suddenly amass in a superficial layer of the neuroepithelium; this layer finally covers, in a sheat-like manner, the entire surface of the embryonic chicken brain. This feature is functionally not understood; however, it appears shortly after the neurons become postmitotic, and the lateral extensions of this layer can easily be traced using histochemistry on serial brain sections. The layer can therefore be exploited to delineate spatially the waves of onset of biochemical tissue differentiation. We have studied whole brains between stages 11 and 30 and provide the first complete spatial schemes of brain differentiation based on computer-reconstructed, two- and three-dimensional maps. The brain does not differentiate in one smooth coherent wave, but instead five separate primary AChE-activation zones are detected: the first originating at stage 11 ("rhombencephalic wave"), the second at the same time ("midbrain wave"), the third at stage 15 ("tectal wave"). A fourth zone develops later, at stage 18, from the bottom part of the telencephalon to the top. Retinal development also starts at stage 18. In a given area, it appears that AChE-development shortly precedes that of the formation of major fiber tracts. AChE might therefore represent a prerequisite for fiber growth and pathfinding.

Segment-related, mosaic neurogenetic pattern in the forebrain and mesencephalon of early chick embryos: I. Topography of AChE-positive neuroblasts up to stage HH18

Histochemical mapping of AChE-positive neuroblasts in sectioned and whole-mounted preparations of the chick embryo mesencephalon and prosencephalon allows a correlation of early neural tube morphogenesis (segmentation, longitudinal compartmentation) with the heterochronic pattern of neurogenesis. One significant finding is that the initial appearance of neuroblasts in the forebrain does not follow neuromeric segmentation, but evolves in parallel with it. Early neuroblasts appear as separate, distinct groups within specific matrix territories at the center of the transverse neuromeric segments. Neighbouring segments display different spatiotemporal patterns of neurogenesis. Overall gradients of differentiation in the rostrocaudal and ventrodorsal directions are absent, whereas a clear-cut segment-related, mosaic pattern becomes evident. Notwithstanding this, gross regularities of heterochrony in the neurogenetic behavior of the different segments lead to a definition of elemental longitudinal compartments of the forebrain and mesencephalon (floor, paramedian, basal, and alar regions) on the basis of precocious differentiation of the basal region and retarded differentiation of the paramedian and alar regions.

Cholinergic traits in rat mandibular processes observed by electron microscopy

Cholinergic traits in rat mandibular processes were examined histochemically, under the electron microscope, at early developmental stages (Stages 20 to 23, by Christie's nomenclature). The histochemical reaction for detection of enzymes was performed by the thiocholine method. Nonspecific cholinesterase (EC 3.1.1.8) activity was found in ectomesenchymal cells, vascular endothelial cells, and in some epidermal cells at stages 20 and 21. The enzymatic activity was localized in the perinuclear and endoplasmic reticular cisternae. At stage 22, the number of cells with enzymatic activity decreased gradually, except in the case of the capillary endothelial cells. At stage 23, when the trigeminal nerve fiber was obvious in the mandibular processes, nonspecific cholinesterase activity was restricted to some of the endothelial cells and trigeminal ganglionic cells. In contrast, acetylcholinesterase activity was found on the membrane of trigeminal nerve fiber. Thus, the transient, nonspecific, cholinesterase activity, found in rat mandibular processes, may serve some functions in transmission, lipid metabolism or destruction of toxic cholinesters during the period that precedes organogenesis.

Quantitative development and molecular forms of acetyl- and butyrylcholinesterase during morphogenesis and synaptogenesis of chick brain and retina

The embryonic development of total specific activities as well as of molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and of butyrylcholinesterase (BChE, EC 3.1.1.8) have been studied in the chick brain. A comparison of the development in different brain parts shows that cholinesterases first develop in diencephalon, then in tectum and telencephalon; cholinesterase development in retina is delayed by about 2-3 days; and the development in rhombencephalon [not studied until embryonic day 6 (E6)] and cerebellum is last. Both enzymes show complex and independent developmental patterns. During the early period (E3-E7) first BChE expresses high specific activities that decline rapidly, but in contrast AChE increases more or less constantly with a short temporal delay. Thereafter the developmental courses approach a late phase (E14-E20), during which AChE reaches very high specific activities and BChE follows at much lower but about parallel levels. By extraction of tissues from brain and retina in high salt plus 1% Triton X-100, we find that both cholinesterases are present in two major molecular forms, AChE sedimenting at 5.9S and 11.6S (corresponding to G2 and G4 globular forms) and BChE at 2.9S and 10.3S (G1 and G4, globular). During development there is a continuous increase of G4 over G2 AChE, the G4 form reaching 80% in brain but only 30% in retina. The proportion of G1 BChE in brain remains almost constant at 55%, but in retina there is a drastic shift from 65% G1 before E5 to 70% G4 form at E7.(ABSTRACT TRUNCATED AT 250 WORDS)

Early phenobarbital-induced alterations in hippocampal acetylcholinesterase activity and behavior

Early exposure to phenobarbital (PhB) causes marked destruction of large neurons which are then forming both in the hippocampus and in the cerebellum. Such exposure to PhB also reduces the achievements of mice in hippocampus-related behaviors such as radial 8-arm maze performance. Experimental evidence suggests that these behaviors are partially mediated by cholinergic transmission. We studied the performance of mice, exposed to PhB prenatally or neonatally, in radial 8-arm maze. Both treatments caused significant impairments in the animals' performance in the maze. Acetylcholinesterase (AChE) and pseudocholinesterase (pChE) activities were studied in the hippocampus and cerebellum of mice who were exposed to PhB prenatally or neonatally. These enzymes are involved both in cholinergic transmission and in neuronal development. A significant decrease (13-16%, P less than 0.01) in hippocampal AChE specific activity was found between days 15 and 22 in animals exposed to PhB neonatally. The total hippocampal activity of AChE was also greatly reduced (25-39%, P less than 0.01) during that period as a result of both the reduction in specific activity and a reduction in hippocampal weight of the treated animals. These alterations were transient and were not detected in adulthood. No changes in hippocampal AChE or pChE activities were found in animals treated prenatally. Cerebellar AChE and pChE activities were not altered after prenatal nor after neonatal exposure to PhB. It is possible that the short-term effect of neonatal treatment on AChE specific activity might mediate the long-term impairments in hippocampus-related behaviors.

Ultrastructural localization of cholinesterase during chondrogenesis and myogenesis in the chick limb bud

Cholinesterase (ChE) is transiently expressed in undifferentiated embryonic cells. In the chick limb bud ChE-activity was found in the apical ectodermal ridge and in the subridge mesenchyme. The reaction was localized in the perinuclear cisterna, in an extensive network of narrow profiles of endoplasmic reticulum (ER), and in the Golgi complex. The chondroblasts emerging from the subridge mesenchyme, also showed strong ChE-activity. During differentiation the enzyme first disappeared from the Golgi zone. Then, the narrow ChE-positive ER was successively replaced by ChE-negative extended rough ER characteristic for the differentiated chondrocyte. The myoblasts showed weak ChE-activity with the same ultrastructural localization as in other mesenchymal cells. After fusion the myotubes exhibited strong ChE-activity in the perinuclear cisterna and the developing sarcoplasmic reticulum. In later stages of myogenesis the myoblasts were closely attached to the myotubes and had lost their ChE-activity. During mitosis of ChE-positive cells, ChE-activity was retained in fragments of perinuclear cisterna and ER. In ChE-active mesenchymal cells and chondroblasts we observed specialized contact zones between ER and plasma membrane. ChE-active cisternae of ER run parallel to the plasma membrane with a gap of approximately 10-15 nm. We discuss a possible function of a cholinergic system during morphogenesis.

Regulation of acetylcholinesterase activity by retinoic acid in a human neuroblastoma cell line

The ability of retinoic acid (RA) to modulate acetylcholinesterase (AChE) activity in a human neuroblastoma cell line (LN-N-5) was examined. The specific activity of AChE was significantly increased 3 days after exposure of LA-N-5 to RA and reached its maximum values after 9 or more days of culturing. Dose-response experiments demonstrated that large increases of AChE occurred at RA concentrations between 10(-7) and 10(-6) M with maximum AChE values detected at 10(-6)-10(-5) M. Increased AChE activity paralleled neurite outgrowth in LA-N-5 cultures. These findings demonstrate that RA can regulate specific AChE activity in human neuroblastoma cells in a manner consistent with neuronal maturation.

Comparative localization of acetylcholinesterase and pseudocholinesterase during morphogenesis of the chicken brain

The histochemical localization of specific acetylcholinesterase (AcChoEase) and nonspecific cholinesterase (BtChoEase) is described during the early morphogenesis of the whole chicken head with main emphasis on the visual system. It is found that: (i) Expression of AcChoEase is an early differentiation event in the entire brain. Its pattern of first appearance on the external part of the neuroepithelium correlates with the general spatio-temporal pattern of differentiation. AcChoEase thus represents an early differentiation marker. (ii) The late pattern of AcChoEase (at E18), reflecting at least partially the distribution of synaptic AcChoEase shows no direct correlation to the distributions found at early stages when synapses are not yet formed. This argues for a nonsynaptic function of the early appearing AcChoEase. (iii) BtChoEase in early nervous tissue is diffusely localized on the ventricular side of the neural tube. At later stages it becomes concentrated on the ependymal layer as well as along fibers reaching from this inner layer outwards. Minor activities appear in specific external layers of tectum and retina. (iv) During the course of differentiation the enzymes express pronounced graded distributions within the areas where they are detectable. (v) Mesenchymal and epidermal BtChoEase is abundant in the entire head. Prominent amounts of activity are expressed on the rostral epidermis, along the eye cup next to the sclera, and on the rostro-dorsal surrounding of the optic nerves. The results are discussed in the light of possible morphogenetic functions of these enzymes.

Acetylcholinesterase activity in neural crest cells of the early chick embryo

The appearance and distribution of AChE activity in the neural crest cells of the chick embryo were histochemically investigated. Prior to closure of the neural tube, neural crests were not demonstrated and most of the cells constituting the neural plate and the more lateral ectoderm were AChE-negative. With the closure of the neural tube, the neural crests assumed the form of a cell mass in its mid-dorsal portion and AChE activity was demonstrated in some elements of both tube and crests. The neural crest cells beginning to migrate ventrally or laterally were AChE-positive, and some showed intense enzymatic activity. Electron microscopically, the neural crest cells and the cells migrating from the neural crest displayed AChE activity in the cisternae of the nuclear envelope and in a few r-ER profiles, but were morphologically undifferentiated. As assessed by 3H-thymidine autoradiography, these cells possessed the potential to proliferate. These findings indicate that with the formation of the neural tube and neural crest, cells constituting these structures begin to differentiate with respect to AChE activity and that the enzyme appears in the neural crest cells before the onset of neuronal differentiation.

Choline acetyltransferase in the chick limb bud

In embryonic tissues a primitive cholinergic system is transiently expressed during morphogenesis. In the chick limb bud expression of the primitive cholinergic system in mesenchyme and central chondrogenic core precedes the appearance of the definitive cholinergic system in nerve and muscle. Here we show that, parallel to the expression of cholinesterase in mesenchyme and chondroblasts, embryonic cells are capable of acetylcholine synthesis. Choline acetyltransferase (ChAT) activity was measured by the radiometric assay of Fonnum (1975).