Acetylcholinesterase and choline acetyltransferase activity in the developing chick spinal cord

Heat stress induced histopathology and pathophysiology of the central nervous system

The number of reports on the effects of heat stress is still increasing on account of the temperature is one of the most encountered stressful factors on the different biological systems. Because the heat stress (HS) considered a model of thermal injury to the central nervous system (CNS), the purpose of this review was to assess the histopathological changes of HS on CNS. Also, this review emphasized that the heat stress may retard partially the degree of the postnatal neurogenesis and growth of CNS. Taken together, owing to one of the most important functions of heat shock protein is to protect the organisms from the deleterious effects of temperature, thus, it can be hypothesized that the formation of heat shock proteins may be related to the deleterious effect of HS. On the other hands, the alterations of neurotransmitters in the central nervous system might be involved in the physiological and biochemical responses that occur during heat stress. The hypothalamic monoaminergic systems play an important role in the thermoregulation through regulate the heat production and heat dissipation. In addition, the disturbance in the biochemical variables due to the high temperature may be the cause of the histopathological changes and the partial retardation in CNS and the reverse is true. Thus, further studies need to be done to emphasize this concept.

A radiometric microassay for choline acetyltransferase. Some observations on the spinal cord of the chicken embryo

This paper describes cation-exchange methods for separating acetyl[3H] coenzyme A from [acetyl-3H]choline. Blanks for the routine method were approximately 0.05% of the substrate radioactivity; product recoveries were approximately 97%. The cation-exchange method was more efficient than the standard methods using either anion-exchange chromatography or periodide precipitation. The cation-exchange method was also more specific than either of the other two standard methods for estimating choline acetyltransferase (ChAT) activity. ChAT activity was detected in the chicken lumbar spinal cord on embryonic day (E) 2 1/4 with the cation-exchange method. This developmental stage is about 6 hours before the final mitosis of any neuroblast in the ventral horn. Total ChAT activity per lumbar spinal cord increased more than 10,000-fold between E 3 and E 18. Changes in ChAT activity in the lumbar spinal cord following limb-bud extirpation appeared to mirror (with a phase lag) the changes in the number of motoneurons in the lateral motor column.

Distribution of cholinergic neurons in the chick spinal cord during embryonic development. Comparison of ChAT immunocytochemistry with AChE histochemistry

The location of cholinergic neurons was studied during the development of the chick embryo spinal cord. A comparison between choline acetyltransferase (ChAT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry was performed. ChAT-positive neurons could be detected only from embryonic day 9 (E9) onwards by the FITC technique and from E12 onwards by the PAP technique. These neurons were located mainly in the medial and lateral motor columns in the ventral horn of the gray matter and some of them were observed in the intermediate region of the spinal cord. AChE-containing cell bodies were much more numerous than the ChAT immunoreactive ones and were distributed in the ventral horn of the gray matter, the intermediate gray region and mostly off the apical part of the dorsal horn. ChAT should provide a reliable and specific marker for cholinergic neurons.

Development of esterase activities in the chicken before and after hatching

The embryonic chick has long been a model for developmental biology and has often been recommended as a model system in developmental toxicology. More recently, several investigators have shown that the chick embryo also provides a good model for identifying the neurotoxic effects of environmental pollutants, especially cholinesterase-inhibiting pesticides. Although numerous studies detail the structural development of chick embryos, few describe embryonic levels of enzyme synthesis and their changes during development. In this study, the development of esterase activity in chick embryos was measured from day 9 of incubation until 46 days after hatching. Brain acetylcholinesterase (AChE) activity was detected on day 9 of incubation at a concentration of 0.364 mumoles/min/g tissue. An increase between AChE activity and age of the embryos was observed. In the liver, the nonspecific cholinesterases (ChE) and carboxylesterase activities during incubation were not different from activities after the chicks had hatched. Plasma ChE and carboxylesterase activities did not change with age after hatching. Brain neuropathy target esterase (NTE) activity was not detected on day 9 of incubation and was extremely low (6.12 nmoles/15 min/mg protein) the next day, but increased rapidly with increasing age. This study demonstrates that chick embryos have developed esterase activities in the brain and liver by day 10 of incubation and again confirms that the insensitivity of chick embryos and young chicks to organophosphorus ester-induced delayed neurotoxicity is not due to absence of NTE. In addition, the results provide baseline data for evaluating the response of embryonic and immature chicks to neurotoxicants and teratogens.

Biochemical and morphological differentiation of acetylcholinesterase-positive efferent fibers in the mouse cochlea

We have compared the biochemical expression of cholinergic enzymes with the morphological differentiation of efferent nerve fibers and endings in the cochlea of the postnatally developing mouse. Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) are present in the newborn cochlea at specific activities 63% and 25%, respectively, of their mature levels. The relative increases in ChAT, in AChE, and in its molecular forms over the newborn values start about day 4 and reach maturity by about day 10. The biochemical results correlate well with the massive presence of nerve fibers stained immunocytochemically for ChAT and AChE or enzymatically for AChE in the inner and outer hair cell regions. Ultrastructral studies, however, indicate the presence of only few vesiculated fibers and endings in the inner and outer hair cell regions. The appearance of large, cytologically mature endings occurs only toward the end of the third postnatal week. The discrepancy may be resolved in the electron microscopy using the enzymatic staining for AChE. Labeling is seen on many nonvesiculated fibers and endings in the hair cell regions, suggesting that the majority of the efferent fibers in the perinatal organ may be biochemically differentiated but morphologically immature. The results may imply that the efferents to inner and outer hair cells develop earlier than indicated by previous ultrastructral studies. Moreover, the pattern of development suggests that in the cochlea, as in other tissues, the biochemical differentiation of the efferent innervation may precede the morphological maturation.

Early expression of acetylcholinesterase activity in functionally distinct neurons of the zebrafish

The first expression and distribution of acetylcholinesterase (AChE) activity was studied among a distinct population of early neurons in embryonic zebrafish by using histochemical and retrograde labeling techniques. AChE first appeared in the nervous system in the primary motoneurons of the rostral spinal cord when the embryo had nine somites, approximately 14 hours postfertilization. Subsequent expression of AChE activity in the spinal cord proceeded in a rostral-to-caudal sequence. Cranial neurons expressed AChE activity shortly after it appeared in the rostral spinal cord. Several hours later, near the end of the first day, primary neurons in the hind-brain and spinal cord all contained AChE, including sensory neurons, reticulospinal interneurons, and primary motoneurons. AChE activity was also detected in the nucleus of the medial longitudinal fasciculus. Presumptive cranial ganglia transiently expressed AChE activity between 14 and 24 hours of development. These results, combined with previous observations that examined the time of origin and axogenesis of primary neurons, suggest that primary neurons in the embryonic zebrafish contain AChE before they sprout axons. The primary neurons appear to follow a common sequence of development consisting of a withdrawal from the cell division cycle, the expression of AChE, and axogenesis. Although this sequence is followed by all primary neurons, lack of a rostral-to-caudal sequence in the time of birth and variability in the time of axon outgrowth demonstrate that the relative timing of these three events is not rigidly programmed in individual neurons. Moreover, the very early expression of AChE in such diverse cell types suggests that it may have a developmental role in addition to its function in transmitter metabolism.

The effects of nerve growth factor on the development of septal cholinergic neurons in reaggregate cell cultures

Recent studies suggest that nerve growth factor is present within the central nervous system where it may exert selective trophic effects on cholinergic neurons. We have measured the effects of nerve growth factor on septal cholinergic neurons in three-dimensional reaggregating cell cultures, a system which closely simulates the cellular environment in situ. Septal cells obtained from 15-day-old mouse embryos were dissociated into a single cell suspension and then allowed to reaggregate in culture in a rotary incubator shaker. After 17 days in culture, half of the reaggregates from a flask were sonicated for measurement of choline acetyltransferase activity, and the remaining reaggregates were processed for acetylcholinesterase histochemistry. Addition of nerve growth factor to medium containing septal reaggregates resulted in greater than a three-fold increase in choline acetyltransferase activity and in the number of acetylcholinesterase-positive cells, as well as an enhancement in the staining of acetylcholinesterase-positive fibers. All of these effects of nerve growth factor could be neutralized by antibodies to nerve growth factor. In order to evaluate the possible role of endogenous hippocampal-derived nerve growth factor, antiserum to nerve growth factor was added to the culture media containing septal-hippocampal coaggregates. After 21 days in culture, the presence of nerve growth factor antibodies did not qualitatively affect the pattern or density of cholinergic fibers observed. Synapse formation between cholinergic axons and hippocampal target cells was still in evidence as revealed by electron microscopy. However, there was a modest decrease in choline acetyltransferase activity (20%) and cholinergic cell number (30%) when compared with coaggregates grown in culture medium either without nerve growth factor antiserum or with non-immune serum. The magnitude of these effects was markedly less than the effects observed when exogenous nerve growth factor was added to septal cells grown alone in reaggregate culture. These results suggest that nerve growth factor may play a role during central cholinergic development, but that additional trophic mechanisms are likely to be required.

Development of the enteric nervous system in the moth. I. Diversity of cell types and the embryonic expression of FMRFamide-related neuropeptides

The enteric nervous system (ENS) of the larval moth Manduca sexta consists of two small ganglia and several nerve networks that lie superficially along the alimentary tract. Within this system are approximately 600 neurons that exhibit a spectrum of biochemical and morphological characteristics and that express these features in a definable sequence during development. The accessibility of both the neural and nonneural components of the moth ENS throughout embryogenesis makes it a potentially useful model in which to examine the developmental regulation of transmitter phenotype. In this paper, we have focused on the differentiation of the enteric plexus (EP) cells, a heterogeneous population of enteric neurons that are distributed across the foregut-midgut boundary. Unlike many neurons of the CNS in insects, the cells of the enteric plexus are not uniquely identifiable. While the total number of EP cells is constant, their locations vary significantly from animal to animal. However, several distinct classes of neurons can be identified within this population on the basis of morphology and transmitter phenotype, including one class that contains substances related to the molluscan peptide Phe-Met-Arg-Phe-amide (FMRFamide). Expression of this FMRFamide-like material within the enteric plexus is position-specific, occurring only in neurons on the midgut and not in those on the foregut. FMRFamide-like immunoreactivity first appears in approximately one-third of these cells at 65% of development; this pattern is retained without apparent modification throughout subsequent embryonic and postembryonic development. In the following paper, we describe the sequence of stereotyped cell migration that precedes the expression of this peptidergic phenotype and that underlies the formation of the enteric plexus during embryogenesis.

Time course of neocortical graft innervation by AChE-positive fibers

Acetylcholinesterase (AChE)-containing axons are the only extrinsic fibers projecting to the adult cortex that readily innervate embryonic cortical grafts up to normal densities without prior manipulation of the host brain. In the present paper we compare the time course of AChE-positive fiber innervation in the normal mouse cortex with that seen in neocortical grafts by using AChE histochemistry as a marker for presumed cholinergic fibers. Donor tissue was taken at two different stages of gestation; before (embryonic days 12-14, or E12-14) and after (E17-19) the cortical plate is formed. Three features are analyzed: 1) the distribution and density of AChE-containing fibers, 2) the presence of AChE-positive cells, and 3) the distribution of butyrylcholinesterase (BuChE)-positive elements. The modification of Koelle's method used for AChE localization showed AChE-positive fibers in developing parietal neocortex as early as E18-19. The distribution of AChE-labeled fibers in the normal cortex achieves the mature pattern by the end of the third postnatal week. The rate of innervation of transplants takes longer and depends on the age of the donor tissue. Tissue from both donor ages first showed AChE-positive fibers crossing the host-transplant interface by 7 days postsurgery. E17-19 tissue approaches the density of AChE-positive fibers in the normal adult cortex by 15 weeks after grafting, whereas the E12-14 donor tissue does not approach normal innervation densities until after 20 weeks. While the degree of innervation in the E12-14 donor tissue never equalled the surrounding adult cortex within our range of survival times, a few of the E17-19 transplants did develop densities equal to that of the host cortex. AChE-positive cells are first detectable in the normal parietal cortex on the day of birth, peak by the end of the first postnatal week, and then decline in number to the low levels of the mature cortex after the second postnatal week. Grafted cells in E12-14 tissue stain lightly for AChE by 7 days postsurgery, achieve maximal densities by 3 weeks, and become markedly reduced in number and density by 10 weeks. Cells in E17-19 tissue are lightly reactive by 7 days postsurgery, reach maximal numbers by 2 weeks postsurgery, and become similar in number and density to those seen in the mature cortex after 4 weeks. The appearance of BuChE-reactive blood vessels, neurons, and glia in both normal development and in the transplants is described and discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth patterns of primary cultures dissociated from 3-day-old chick embryos: morphological and biochemical comparisons

Cultures were prepared by dissociating 3-day-old whole chick embryos and plating the dispersed cells on poly-L-lysine-coated dishes in Dulbecco's Modified Eagle's Medium with 10% fetal calf serum. By 48 hr in culture, aggregates and neuritic sprouting were observed. Long neuritic bundles connecting cell aggregates were evident by 4 days in culture. Consistent patterns throughout the lifespan of the cultures were contacts between neurites, and flat isolated cells, presumptively glial, emerged. Throughout the lifespan of the cultures, the cholinergic cell population was characterized histochemically by the method of Karnovsky and Roots and biochemically by assaying choline acetyltransferase. By 4 days in culture, all aggregates showed light cholinesterase-positive staining; however, with days in culture, several aggregates had no staining, and some positive-stained aggregates were interconnected with other aggregates showing only spotted positive staining. Choline acetyltransferase activity showed a developmental profile in agreement with the histological findings. The early presence of choline acetyltransferase activity is taken as indication of the early commitment of cholinergic neurons.

Alpha-bungarotoxin binding to the myotome and choline acetyltransferase activity in the rabbit embryo

We have previously found incomplete sarcomeres and acetylcholinesterase activity in the myoblasts of the myotome of the rabbit at day 13 of gestation. We now report that an acetylcholine (ACh)-synthesizing enzyme and the nicotinic receptor are present at this stage as well. A study of the myotome using [125I]alpha-bungarotoxin shows that the mononucleated myoblasts have alpha-bungarotoxin binding sites before they migrate away to form multinucleated myotubes. Choline acetylcholinesterase activity and/or a different ACh-synthesizing enzyme are found at early stages of development, even before the spinal nerve has formed. An ACh-synthesizing enzyme is present in the notochord, a neural tube-dorsal root ganglion preparation, as well as in rows of myotomes separated from the latter preparation. Assays of isolated myotomes with very little adherent mesenchyme indicate that the enzyme is located either within the myotome or in its immediate vicinity. Cholinergic components, therefore, are associated with the mononucleated myoblasts of the myotome before they fuse to form myotubes and before they receive their permanent innervation.

Cholinergic enzyme activity in neurons of the developing anuran spinal cord

Cholinergic enzyme activity was investigated over the course of spinal cord development from early larval (tadpole) stages to adult life in bullfrogs (Rana catesbeiana). Acetylcholinesterase (AChE) activity examined histochemically in spinal neurons and AChE and choline acetyltransferase (ChAT) activities were measured biochemically in axons of developing hindlimb motoneurons. At early larval stages, only spinal neurons born during embryonic life (primary neurons) showed histochemical evidence of AChE activity. Hindlimb motoneuron somata did not show AChE activity until mid-larval stages. AChE and ChAT activities were found in hindlimb motoneuron axons at the earliest stages examined, when the hindlimb consists of a small bud of undifferentiated mesenchyme. Activities of both enzymes show steady increases over the course of development until climax, when activities maintain a plateau until metamorphosis is complete. Total activities of both enzymes increase as the adult frog grows, although ChAT activity shows a much greater proportional increase than AChE activity.

Neurotransmitter enzymes in telencephalon, brain stem and cerebellum during the entire life span of the mouse

Neurochemical analysis of neuronal function was undertaken by measuring the activities of cholinacetyltransferase (CAT), acetylcholinesterase (AChE), and glutamic acid decarboxylase (GAD), in the telencephalon, brain stem and cerebellum of the mouse. Cholinergic activity was first expressed in the 10-day embryonic brain stem, which showed a relatively high CAT activity at birth. Postnatal brain stem development was characterized by a rapid and parallel increase in CAT and AChE. Although AChE peaked at 1 month, CAT activity was no achieved until 1 year. Acetylcholine synthesis was initiated in the 12-day embryonic telencephalon and a steady age-related increase in CAT was maintained until birth. A lag in both CAT and AChE activities was recorded during the first week of postnatal telencephalon development. Cerebellar CAT was low at birth, and increased irregularly to reach a maximum by 1 month. In contrast, postnatal cerebellar AChE activity increased steadily over the same time period. The GABA-ergic neuronal system matured rapidly in each brain region, and was unaffected by aging. Although the brain stem precociously expressed cholinergic activity, it wa the region most susceptible to deterioration during aging. Telencephalon CAT activity was unaffected by aging and in the cerebellum, a significantly reduced level of CAT was only found in truly senescent animals. The decreased cholinergic function during senescence was not due to either increased proteolysis or to alteration in the molecular form of the cholinergic enzymes.

Development of the multiple molecular forms of acetylcholinesterase in chick paravertebral sympathetic ganglia: an in vivo and in vitro study

The development of acetylcholinesterase (AChE) activity and the distribution of this enzyme among its multiple forms was studied in both tissue extracts and dissociated cell cultures of chick paravertebral sympathetic ganglia. In agreement with previous findings, total AChE (expressed either per ganglion or per microgram protein) increased in vivo between the time of formation of the paravertebral chain (embryonic day 7; E7) to hatching (E20-E21). After this time, enzyme activity changed much more slowly. Sucrose gradient sedimentation analysis of AChE in ganglia of post-hatching chicks revealed multiple forms of AChE with S values of approximately 6.5, 11 and 19.5. Developmental studies showed that 6.5 S and 11 S forms are present as early as day E7. Much of the pre-hatching increase in total AChE is due to increased levels of the 6.5 S form of the enzyme. By hatching, this form comprised approximately 85-90% of the total AChE activity. In contrast, during the first week after hatching, the activity of the 11 S form increased several-fold while that of the 6.5 S remained approximately unchanged. The 19.5 S form, which is thought to be associated with the synaptic membrane, was not detected prior to day E17 and reached adult levels (2-3% of total AChE activity) by the first week after hatching. Development of AChE was also studied in dissociated cell cultures of embryonic ganglia. Essentially all the AChE activity in such cultures was found to be associated with the neurons. Total AChE activity of cultured E11 ganglia increased in a pattern which was both qualitatively and quantitatively similar to that which occurred in vivol. Furthermore, it was found that development of both the 6.5 and 11 S forms of AChE took place in vitro. In cultures of E8, E11, E15 and E19 ganglia, the distribution of activity between the two forms after various times in vitro was similar to that which was found for in vivo ganglia at an equivalent embryonic stage. Such changes were not affected by the elimination of nonneuronal cells from the cultures. Two aspects of in vitro development, however, differed from that which occurred in vivo. First, an increase in 11 S AChE did not occur at ages equivalent to the first week post-hatching. Second, the 19.5 S form did not develop (even after several weeks) in cultures of E8, E11 and E15 ganglia, nor was this form (which was removed during dissociation of the ganglia) regenerated in cultures of E19 ganglia. Such findings suggest that the pattern of development of AChE and its multiple forms in chick sympathetic neurons is in part intrinsically programmed into these cells at an early stage of development as well as in part regulated by extrinsic signals that these cells receive from their chemical and cellular environment.

Acetylcholine synthesis by mesencephalic neural crest cells in the process of migration in vivo

Specific to the vertebrate embryo, the neural crest is a transitory structure whose constituent cells migrate extensively through the developing animal and ultimately give rise to many distinct cell types, including the components of the peripheral nervous system. The earliest clear indices of their differentiation have so far been detected only when cells from the crest have reached their destination. This is exemplified by the acquisition of the ability to synthesise and store catecholamines; absent from crest cells before and during their dorso-ventral migration, this ability appears concomitantly with their aggregation into the primary sympathetic ganglia. The chronology of cholinergic maturation, however, is less well defined. Appropriate biochemical markers are demonstrable as soon as parasympathetic or enteric ganglia are formed, but the lack of a suitable cytochemical method is a major obstacle to the identification of any cholinergic cells before then. Although acetylcholinesterase (AChE) is present in migrating neural crest, choline acetyltransferase (CAT), the enzyme catalysing acetylcholine (ACh) synthesis, is a much more relevant correlate, and definitive evidence for cholinergic differentiation should include the demonstration of ACh-synthesising activity in intact cells or their extracts. We show here that neural crest, as soon as it begins migration, can synthesise ACh.

Development of high affinity choline uptake and associated acetylcholine synthesis in the rat fascia dentata

The ontogenic development of hemicholinium-sensitive, high affinity choline uptake and the synthesis of acetylcholine from exogenous choline have been studied in particulate preparations of the rat fascia dentata. Between 6 days of age and adulthood the rate of high affinity choline uptake increases 3-fold, when expressed with respect to protein, and 125-fold, when expressed independently of protein. This process develops most rapidly during the period around 16-17 days of age, similar to the ontogenesis of choline acetyltransferase activity. This observation supports the idea that cholinergic septohippocampal boutons develop mainly at this time. Unlike choline acetyltransferase activity, the velocity of high affinity choline uptake increases to as much as 161% of the adult value at about 30 days of age. It is suggested that at 25-31 days of age a relatively high endogenous septohippocampal firing rate increases the rate of choline uptake. At 6 days of age we detected no synthesis of acetylcholine from the accumulated choline. Uptake-synthesis coupling develops mainly between 6 and 13 days of age, earlier than any other presynaptic cholinergic property. Acetylcholine synthesis from exogenous choline develops in paralled with high affinity choline uptake, but developmental increases in uptake velocity result in comparable increases in synthesis rate only after a delay of several days. Some limiting factor other than choline acetyltransferase activity appears to link the accumulation of exogenous choline to acetylcholine synthesis during development.

Acetylcholinesterase distribution in chick spinal cord cultures. A light and electron microscope study

Explants of 10--12 day chick embryo spinal cord were cultured by coverslip-roller tube method for 3-80 days. The cellular and subcellular localization of acetylcholinesterase activity in cultured neurons was studied by the thiocholine techniques of Karnovsky and Roots and Lewis and Shute. At the light microscopic level, acetylcholinesterase was demonstrated in the neurons of both ventral and dorsal horn regions. Occasionally neurons migrated in the outgrowth zone exhibited strong intracellular activity. At the electron microscopic level, acetylcholinesterase activity was found in the nuclear envelope, granular endoplasmic reticulum and the Golgi apparatus of the neurons. No enzyme reaction was detected in the glial cell cytoplasm.

The appearance of acetylcholinesterase in the myotome of the embryonic rabbit. An electron microscope cytochemical and biochemical study

Acetylcholinesterase (AChE) activity has been studied in the myoblast of skeletal muscle of the 9-13 day fetal rabbit. Cytochemical activity is present in the nuclear envelope and the endoplasmic reticulum, including its derivatives the subsurface reticulum and the sarcoplasmic reticulum. End product is also found in the Golgi complex of the more differentiated myoblasts. The formation of reticulum-bound acetylcholinesterase in the myoblast appears to be independent of nerve-muscle contact, since the enzyme is present before the outgrowth of the spinal nerve. The nerve lacks cytochemical end product until the myoblast is well differentiated. Possible mechanisms of spontaneous muscle contraction have been discussed. A second type of myotomal cell, which exhibits a poorly localized end product of AChE activity, has been described. The ready solubility of the enzyme or diffusibility of its end product suggests that the enzyme may be a lyoesterase. This cell may be the precursor of the morphologically undifferentiated cell which is closely apposed to the myotubes in later stages of skeletal muscle development. Biochemical studies show a significant increase in AChE activity in the dermomyotome by day 12, when many of the myoblasts are well differentiated and the second type of myotomal cell is prominent. Cytochemical studies have indicated that many of the cells in the sample lack reaction product of enzymic activity, whereas others are very active. Biochemical values, therefore, reflect the amount of enzyme in the dermomyotome as a whole, but give little information on the enzymic content of individual cells.