Histochemical and cytochemical localization of acetylcholinesterase in the cerebellar cortex of the chicken

The localization of acetylcholinesterase (AChE) was studied in the cerebellar cortex of the crossbred trembler chickens by means of histo- and cytochemical methods. No essential differences between the crossbred normal and the crossbred trembler chickens were observed. The common results were as follows: Under a light microscope AChE activity was predominantly evident in the molecular layer, and secondly in the granular layer. AChE was ultrastructurally distributed principally in the cisternae of rough endoplasmic reticulum (ER) and in a part of nuclear envelope of the Purkinje, the Golgi and some of the basket and granule cells, and in a portion of the sacculus of the Golgi apparatus of the Purkinje cell only. In dendrites and the initial axon of the Purkinje cells the smooth ER also showed AChE activity. Although dendritic terminals of the Golgi cells contained AChE reaction products, the axon terminal did not. Some of the afferent terminal fibers forming the cerebellar glomerulus exhibited weakly a positive AChE reaction, while others in the vicinity did not show any AChE activity at all. However, the enzyme reaction product was localized in the intercellular spaces between a presynaptic afferent terminal and the postsynaptic granule cell dendritic terminals in the glomerulus. In addition, AChE activity was found in the form of spots in the intercellular spaces of both molecular and granular layers.     

Acetylcholinesterase in the ocellus of Apis mellifica

The ultrastructural localization of the enzyme acetylcholinesterase (AChE) in the ocellus of the honey bee (Apis mellifica) was studied by electron microscopy. High AChE activity was found both in the receptor-cell axons and in the surrounding glial cells. Second order neurones exhibited a remarkably lower anzyme activity. AChE was also detected in the intercellular spaces between the receptor-cell axons and the second order neurones. These results provide additional support to the assumed cholinergic nature of the photoreceptor cells in the insect ocellus.     

Ultrastructural localization of acetylcholinesterase in the synganglion of the tick,Dermacentor variabilis (Say)

Summary Light- and electron-microscopic enzyme cytochemistry was used to localize acetylcholinesterase (AChE) activity in the synganglion (brain) of the tick Dermacentor variabilis. High AChE activity was observed throughout the neuropil as well as adjacent to most neuronal perikarya. Intracellular activity was not observed by light microscopy. By electron microscopy, reaction product was localized at the plasma membrane of glia and neurons. Enzyme activity was not associated with the olfactory globuli neurons. In other types of neurons, small amounts of reaction product were observed in the Golgi apparatus and nuclear envelope. Large neurosecretory neurons contained activity that appeared to be associated with deep invaginations of the plasma membrane as well as intracellular membranes. AChE activity was also associated with processes of both neurons and glia. In most peripheral nerves AChE activity was associated with virtually all axons. Clearly then, AChE is associated with glia and non-cholinergic neurons as well as with presumed cholinergic neurons. The widespread localization and large amounts of AChE in the tick brain exceeds that reported for other invertebrates and vertebrates. As has been suggested for other animals, AChE in the tick brain may have functions in addition to its known role in cholinergic neurotransmission.     

Acetylcholinesterase from the motor nerve terminal accumulates on the synaptic basal lamina of the myofiber

Acetylcholinesterase (AChE) in skeletal muscle is concentrated at neuromuscular junctions, where it is found in the synaptic cleft between muscle and nerve, associated with the synaptic portion of the myofiber basal lamina. This raises the question of whether the synaptic enzyme is produced by muscle, nerve, or both. Studies on denervated and regenerating muscles have shown that myofibers can produce synaptic AChE, and that the motor nerve may play an indirect role, inducing myofibers to produce synaptic AChE. The aim of this study was to determine whether some of the AChE which is known to be made and transported by the motor nerve contributes directly to AChE in the synaptic cleft. Frog muscles were surgically damaged in a way that caused degeneration and permanent removal of all myofibers from their basal lamina sheaths. Concomitantly, AChE activity was irreversibly blocked. Motor axons remained intact, and their terminals persisted at almost all the synaptic sites on the basal lamina in the absence of myofibers. 1 mo after the operation, the innervated sheaths were stained for AChE activity. Despite the absence of myofibers, new AChE appeared in an arborized pattern, characteristic of neuromuscular junctions, and its reaction product was concentrated adjacent to the nerve terminals, obscuring synaptic basal lamina. AChE activity did not appear in the absence of nerve terminals. We concluded therefore, that the newly formed AChE at the synaptic sites had been produced by the persisting axon terminals, indicating that the motor nerve is capable of producing some of the synaptic AChE at neuromuscular junctions. The newly formed AChE remained adherent to basal lamina sheaths after degeneration of the terminals, and was solubilized by collagenase, indicating that the AChE provided by nerve had become incorporated into the basal lamina as at normal neuromuscular junctions.     

Fine structural localization of acetylcholinesterase activity in rat submandibular gland

Using the indirect thiocholine method, the ultrastructural localization of acetylcholinesterase (AChE) activity in the normal rat submandibular gland was studied. Cytochemical demonstration of AChE is based on coupling the hydrolysis of acetylthiocholine iodide to the precipitation of heavy metal salts. AChE-associated reaction product was selectively revealed in the perinuclear space and in the endoplasmic reticulum of the intercalated duct cells, in some cells of granular convoluted tubules, and in the striated duct epithelium, as well as in the myoepithelial cells. Although AChE activity generally occurred inside the cells, electron-dense precipitates were shown in intercellular space and in the stroma of the gland. Fine localization of AChE activity was also found in nerve bundles, predominantly between axons and between axons and Schwann cell. Our observations indicate that AChE is synthesized in the epithelium of the ducts and in the myoepithelial cells of the salivary gland. It is not known yet whether this enzyme is released from the intracytoplasmic membrane system into the extracellular space and then transported to the regions of the gland innervation. Conceivably AChE synthesized in the submandibular gland cells could also be considered an inhibitory modulator of the regulatory functions of biologically active polypeptides.     

The first optic ganglion of the bee

Each visual unit (ommatidium) of the compound eye of the honey bee contains nine retinula cells, six of which end as axons in the first synaptic ganglion, the lamina, and three in the second optic ganglion, the medulla. A technique allowing light- and electron microscopy to be performed on the same silver-impregnated sections has made it possible to follow all types of retinula axons of one ommatidium to their terminals in order to study the shape of the terminal branches with their position in the cartridge. 1. The axons of retinula cells 1-6 (numbered according to Menzel and Snyder, 1974) end as three different types of short visual fibres (svf) in the lamina; the axons of retinula cells 7-9 run through the lamina to terminate in the medulla and are known as long visual fibres (lvf). Retinula cells of each type are identified by the location of their cell bodies and by the direction of their microvilli. The retinula cells 1 and 4 (group I according to Gribakin, 1967) end as svf type 1 with three tassel-like branches in stratum B of the first synaptic region. The pair of cells 3, 6 and the pair 2, 5 (group II) end in the first synaptic region in stratum A. Cells 3 and 6 have forked endings, svf type 2, whereas cells 2 and 5 have tapered endings, svf type 3. The remaining retinula cells 7, 8 and 9 have long fibres. Nos. 7 and 8 (group III) have tapered endings and are termed lvf types 1 and 2, respectively. The 9th cell is the lvf type 3 with a highly branched ending. 2. The nine axons in the bundle from one ommatidium have relative positions which do not change from the proximal retina to the monopolar cell body layer. 3. By following silver-stained retinula cells and their corresponding axons, it is possible to describe mirror-image arrangements of fibres in the axon bundles in different parts of the eye. This correlation of numbered retinula cells with specific axon types, together with the highly organized pattern in an axon bundle, allows the correlation between histological and physiological findings on polarization and colour perception.     

Programmed cell death: Cytochemical and X-ray microanalytical characterization of calcium compartments in neuromuscular junctions during the normal breakdown of the intersegmental muscles in the giant silkmothAntheraea polyphemus

Summary Calcium stores were cytochemically demonstrated using a combined oxalate—pyroantimonate method in the neuromuscular junctions of the degenerating intersegmental muscles in the giant silkmothAntheraea polyphemus. The elemental composition of punctate precipitates of the reaction product was determined by electron probe X-ray microanalysis of unstained thin sections by energy-dispersive spectrometry and wavelength-dispersive spectrometry. The wavelength-dispersive spectra collected over terminal axons demonstrate a significant calcium signal and a trace of antimony.During the rapid lytic phase of spontaneous muscle degeneration, the calcium punctate deposits were detected in presynaptic terminals in the following sites: the synaptic vesicles and the mitochondria. Calcium precipitates were also found in the dense bodies and the mitochondria encountered in the glial convolutions. No calcium deposit was seen in the synaptic clefts and intercellular spaces of the subsynaptic reticulum of type I and type II. A comparison of calcium to antimony ratios between the terminal axons and the sarcoplasmic lysosomes revealed highly significant differences (P<0.001). Such a variability of the calcium to antimony ratio may be related to different conditions of precipitation or antimony diffusion in the different cell compartments. It was concluded that such synaptic terminals do not appear damaged in spite of the muscle degeneration and presumably continue to perform vital functions while the muscles are no longer contractile 20 h after adult ecdysis.     

Acetylcholinesterase activity in the normal and retino-deprived optic tectum of the quail

Summary Acetylcholinesterase localization has been studied by electron microscopic histochemistry in the quail optic tectum. Ultrastructural analysis reveals that the different neuronal types in the tectum possess the metabolic pathways for AChE synthesis to different degrees. From the site of synthesis in cell bodies the enzyme spreads towards areas of neuropil. In the neuropil of AChE-rich areas a balance seems to exist between enzyme stored in dendrites (and sometimes axon terminals) and enzyme released into the extracellular spaces. Precise identification of cholinergic synapses by means of AChE localization is in most cases impossible, due to extensive spread of the enzyme through the extracellular compartments of the neuropil.Unilateral ocular ablation causes disappearance of the stratum opticum and decrease in thickness of the superficial tectal layers in the contralateral optic tectum, but only minor modifications in AChE localization. This finding is in agreement with biochemical results which show equivalence of the relative concentration of AChE in the right and left optic tectum 1 or 2 months after ablation of the right eye. The experimental evidence suggests that cholinergic mechanisms are not related to the discharge of retinal afferents on receptive tectal neurons, but more likely to intrinsic neural circuits which might be involved in the modulation of tectal activity.     

Cytodifferentiation in the Rana pipiens oocyte

Summary In early diplotene frog oocytes incubated to illustrate thiamine pyrophosphatase (TPPase) activity, reaction product is uniformly distributed within the compartments of the endoplasmic reticulum and nuclear envelope as well as within the saccules and small vesicles comprising the dictyosomes. With continued oocyte development the reaction product becomes concentrated in localized regions of the dictyosome saccules. Eventually, the enzyme is no longer apparent within the endoplasmic reticulum, but is concentrated in the cisternae of the inner dictyosome saccules. The variations noted suggest that the enzyme is synthesized early in diplotene by the endoplasmic reticulum and is subsequently transported to the Golgi apparatus where it is consistently observed at later developmental stages. TPPase activity is also present in the Golgi apparatus of follicle and theca cells as well as in ovarian epithelial cells. The enzyme is also detected in micropinocytotic vesicles contained within the cells comprising the follicle envelope and in intercellular spaces of the follicle. Horseradish peroxidase injected into the coelomic cavity is transported via micropinocytotic vesicles into and through the cells comprising the follicle envelope and in intercellular spaces. The exogenous protein is not found even after a prolonged time period in early diplotene oocytes. The protein is, however, present in large spherical and tubular vesicles in the cortex of vitellogenic oocytes approximately 500 microns in diameter. The possible functional role of the enzyme TPPase during oogenesis is discussed.This investigation was supported by a research grant from the National Science Foundation (GB-8736).     

Electron microscopic and histochemical observations on different types of nerve endings in the extraocular muscles of the rat

Summary Nerve endings in the extraocular muscles of the rat were submitted to histochemical tests for formalin-induced fluorescence and carboxylic esterases. Acetylthiocholine, butyrylthiocholine and -naphthyl acetate were used as substrates and iso-OMPA, 284C51, eserine and E-600 as inhibitors. The ultrastructure of the endings was studied with the electron microscope.Both single and multiple nerve terminals were observed in all six extraocular muscles. The single terminals of myelinated axons were comparable in their light and electron microscopic structure with the typical motor end plates of other striated muscles, and like these they exhibit acetylcholinesterase (AChE), non-specific cholinesterase (ns. ChE) and non-specific esterase (ns. E) activity. These endings were apposed to twitch-type muscle fibres.The multiple terminals were classified with the light microscope into two types. The larger type was 1/3 of the size of the motor end plate; 2–5 endings innervated the same muscle fibre; subneural infoldings were weakly developed and possessed only slight AChE and ns. ChE and probably no ns. E activity. No subneural lamellae were visible under the light microscope in the smaller type, which also possessed AChE and ns. ChE and was composed of 10–20 small dots dispersed along a single muscle fibre. The Schwann cells along nerve fibres leading to these two types of multiple endings exhibited ns. ChE but not AChE and ns. E activity.The ultrastructure of the two types of multiple endings was principally similar. The main difference, compared with the motor end plate, was that these endings were derived from unmyelinated axons which either make synaptic contacts along their course with the muscle fibre at variable distances (smaller-type) or these terminals were grouped closely together (larger-type).A few dense-core vesicles were observed in these unmyelinated nerves and in their terminals which were considerably smaller than those in the motor end plate. They were not always separated from each other by sarcoplasm and teloglia (larger-type) and contained also empty vesicles. The secondary synaptic clefts were often sparse and irregular or even absent, but the typical myoneural postsynaptic electron density was always observed. These multiple endings, in contrast to the motor end plate, were apposed only to muscle fibres with slow contraction.No catecholamine containing nerve endings were observed in the extraocular muscles. These observations indicate that the rat extraocular muscles have a double cholinergic innervation.The author wishes to express his gratitude to Professor Antti Telkkä, M. D., Head of the Electron Microscope Laboratory, University of Helsinki, for permission to avail himself of the electron microscope facilities.     

Vasoactive intestinal peptide (VIP)-like immunoreactivity in the human sympathetic ganglia

Vasoactive intestinal peptide immunoreactive (VIP-IR) nerve fibres and terminals, neurons and small granule containing cells were observed in human lumbal sympathetic ganglia. Electron-microscopically VIP-IR was localized in the large dense-cored vesicles in nerve terminals and on the membranes of the Golgi complexes in the neurons. A small population of principal ganglion cells was surrounded by VIP-IR nerve terminals. Most of these neurons contained acetylcholinesterase (AChE) enzyme but were not tyrosine hydroxylase-immunoreactive (TH-IR). All VIP-IR ganglion cells and most of the nerve fibres contained AChE but not TH-IR. It appears that in human sympathetic ganglia VIP is localized in the cholinergic neurons and nerve fibres and that the VIP-IR nerve terminals innervate mainly the cholinergic subpopulation of the sympathetic neurons.     

Vasoactive intestinal peptide (VIP)-like immunoreactivity in the human sympathetic ganglia

Summary Vasoactive intestinal peptide immunoreactive (VIP-IR) nerve fibres and terminals, neurons and small granule containing cells were observed in human lumbal sympathetic ganglia. Electron-microscopically VIP-IR was localized in the large dense-cored vesicles in nerve terminals and on the membranes of the Golgi complexes in the neurons. A small population of principal ganglion cells was surrounded by VIP-IR nerve terminals. Most of these neurons contained acetycholinesterase (AChE) enzyme but were not tyrosine hydroxylase-immnoreactive (TH-IR). All VIP-IR ganglion cells and most of the nerve fibres contained AChE but not TH-IR. It appears that in human sympathetic ganglia VIP is localized in the cholingergic neurons and nerve fibres and that the VIP-IR nerve terminals innervate mainly the cholinergic subpopulation of the sympathetic neurons.     

Electron microscope localization of acetylcholinesterase and butyrylcholinesterase in the superior cervical ganglion of the cat. I. Normal ganglion

The distributions of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the superior cervical ganglion (SCG) of the cat were determined by electron microscopy (EM) with the bis- (thioacetoxy)aurate (I), or Au(TA)2, method. Before the infusion of fixative, one of the enzymes was selectively, irreversibly inactivated in vivo, as confirmed by light microscope (LM) examination of sections of the stellate ganglion stained by the more specific copper thiocholine method. Physostigmine-treated controls, for inhibition of AChE or BuChE, were stained concomitantly with tissue for enzyme localization by the Au(TA)2 method for EM examination in each experiment. It was concluded that most of the AChE of the cat SCG is present in the plasma membranes of the preganglionic axons and their terminals, and in the dendritic and perikaryonal plasma membranes of the postsynaptic ganglion cells. BuChE is confined largely to the postsynaptic neuronal plasma membranes. Reasons for the discrepancies between the localizations found by the present direct EM observations and those deduced earlier from LM comparisons of normal and denervated SCG are discussed. It is proposed that a trophic factor released by the preganglionic terminals is probably required for the synthesis of postsynaptic neuronal AChE, and that BuChE may serve as a precursor of AChE at that site.     

Evolution and ultrastructure of the bovine spermatogonia precursor cell line

We have used a cytochemical technique to investigate the distribution of acetylcholinesterase (AChE) activity in the deutocerebrum of the brain of the sphinx moth Manduca sexta. To distinguish between extra-and intracellular pools of the enzyme, some brains were treated prior to histochemical staining with echothiophate, an irreversible AChE inhibitor which penetrates cell membranes very slowly and, therefore, inhibits only extracellular AChE. In the antennal nerve, fascicles of presumably mechanosensory fibers show echothiophateinsensitive AChE activity. They bypass the antennal lobe and project to the antennal mechanosensory and motor center of the deutocerebrum. In the antennal lobe, fibers in the coarse neuropil, cell bodies in the lateral cell group, and all glomeruli exhibit AChE activity. In most ordinary glomeruli, echothiophate-sensitive AChE activity is concentrated in the outer cap regions, corresponding to the terminal arborizations of olfactory afferents. A previously unrecognized glomerulus in the ventro-median antennal lobe shows uniform and more intense AChE-specific staining that the other glomeruli. No AChE activity appeared to be associated with malespecific pheromone-sensitive afferents in the macro-glomerular complex. About 67 interneurons with somata in the lateral cell group of the antennal lobe show echo-thiophate-insensitive AChE activity. These neurous seem to be members of two types of antennal-lobe projection neurons with fibers passing through the outer-antenno-cerebral tract to the protocerebrum. AChE-stained arborizations of these neurons appear to invade all glomeruli, including three distinguishable subunits of the male-specific macroglomerular complex. In echothiophate-treated animals, the projections of one of these types of fiber form large terminals in the lateral horn of protocerebrum, which partly protrude into the adjacent glial cell layer. The results suggest that extracellularly accessible AChE is associated with ordinary olfactory receptor terminals but apparently not with pheromone-sensitive afferents. Intracellular AChE appears to be present in antennal mechanosensory fibers and in two types of olfactory projection neurons of the antennal lobe. The study provides further evidence for cholinergic neurotransmission of most antennal afferents. The AChE-containing interneurons might be cholinergic as well or use the enzyme for functions unrelated to hydrolysis of acetylcholine.Abbreviations ACh acetylcholine - AChE acetylcholinesterase - AL antennal lobe - AMMC antennal mechanosensory and motor center - ChAT choline acetyltransferase - IACT inner antenno-cerebral tract - MGC macroglomerular complex     

TRANSPORT, TURNOVER AND DISTRIBUTION OF CHOLINE ACETYLTRANSFERASE AND ACETYLCHOLIN-ESTERASE IN THE VAGUS AND HYPOGLOSSAL NERVES OF THE RABBIT

Abstract— The transport, distribution and turnover of choline O -acetyltransferase (ChAc, EC 2.3.1.6) and acetylcholinesterase (AChE, EC 3.1.1.7) in the vagus and hypoglossal nerves were studied in adult rabbits. The enzymes accumulated proximally and distally to single and double ligatures on both nerves and thus indicated both a proximo-distal and retrograde flow of the enzymes. Double ligature experiments indicated that only 5–20 per cent of the enzymes were mobile in the axon. The rate of accumulation of both enzymes above a single ligature corresponded to the slow rate of axonal flow provided that all the enzymes were mobile, but to an intermediate or fast flow if only a small part of the enzymes was transported. The distribution of ChAc along the hypoglossal neurons was studied and only 2 per cent of ChAc was confined to cell bodies, 42 per cent was localized to the main hypoglossal nerve trunks and 56 per cent to the preterminal axons and axon terminals in the tongue. The ratio of AChE to ChAc was about 3 in the hypoglossal nerve and 32 in the vagus nerve.
Transection of the hypoglossal nerve was followed by a decrease in the activity of ChAc in the hypoglossal nucleus and nerve and in the axons and their terminals in the tongue. The activity of AChE decreased in the hypoglossal nucleus and nerve but not in the tongue. The half-life of ChAc in preterminal axons and terminals of the hypoglossal nerve was estimated to be 16-21 days from the results obtained on transport, axotomy and distribution of the enzyme. Intracisternal injection of colchicine inhibited the cellulifugal transport of both enzymes and led to an increase in enzyme activity in the hypoglossal nucleus.     

The first optic ganglion of the bee

The nine receptor cells in each ommatidium of the worker bee end as six short visual fibres in the lamina and as three long visual fibres in the medulla. Behavioural and physiological evidence for regional variation in spectral sensitivity prompted observations on the morphology of the visual units. The distribution, branching pattern, diameter and the arrangement of axonal protusions of the characteristic receptor-cell axons were studied in various regions of the lamina. The six short visual fibres and two of the long visual fibres in each laminar cartridge are uniform over the total eye surface. Only the receptor axons of the ninth cell a UV and polarised light-sensitive cell, show obvious regional variation. In view of the regional constancy in morphology of eight of the nine receptor-cell axons, the regional variations in spectral sensitivity demand either functional subdivision of morphologically indistinguishable photoreceptors (e.g., content of different visual pigments) or a highly complex connectivity pattern of their axons in the first optic ganglion.     

Fiber analysis of human ventral and dorsal roots on the basis of different acetylcholinesterase activity]

Marked differences in the AChE activity of myelinated nerve fibers of ventral and dorsal roots could be established in human post mortem material. After a fixation time of 3 h and a critical incubation period of 24 h, in the mean 96% of the myelinated ventral root but only 4% of dorsal root fibers showed reaction product, detectable by the light microscope. The percentage of stained fibres varies, to some extent, in the different segments. Groups of very thin myelinated fibres within the ventral roots between the segments C-8 and L-3, showing a conspicuous high enzyme activity, are interpreted as pre-ganglionic sympathetic fibres; similar elements in the sacral ventral roots may represent parasympathetic fibres. The method of Karnovsky, applied under conditions established in this study, can be used for analysis of fibre types in a given human peripheral nerve.     

Light- and electron-microscopic studies on acetylcholinesterase activity in Auerbach's plexus of the developing rat colon

The distal portions of rat colon from 14-, 16-, 18-, and 21-day fetuses, newborns, and adults were histochemically examined for acetylcholinesterase (AChE) activity by light and electron microscopy. The specificity of AChE activity in Auerbach's plexus was confirmed by specific and/or nonspecific cholinesterase inhibition tests. Enzyme activity was first detectable after 18 days of gestation and became stronger with age. The reaction product was demonstrated by electron microscopy in and between the plasma membranes of the nerve fibers and their terminals. Ganglion cells also showed positive activity in the plasma membrane, nuclear envelope, and rough endoplasmic reticulum. The distribution pattern of the reaction product in fetal and newborn rat colons was basically the same as in adult rat colon. Therefore, the localization of AChE activity is considered to be a good marker for identifying premature ganglion cells in Auerbach's plexus, and the degree of AChE staining is a good indication of the degree of maturation of the plexus.     

A developmental and ultrastructural study of the optic chiasma in Xenopus

The structure of the optic chiasma in Xenopus tadpoles has been investigated by light and electron microscopy. Where the optic nerve approaches the chiasma, a tongue of cells protrudes from the periventricular cell mass into the dorsal part of the nerve. Glial processes from this tongue of cells ensheath fascicles of optic axons as they enter the brain. Coincident with this partitioning, the annular arrangement of axons in the optic nerve changes to the laminar organization of the optic tract. Beyond the site of this rearrangement, all newly growing axons accumulate in the ventral-most part of the nerve and pass into the region between the periventricular cells and pia which we have called the 'bridge'. This region is characterized by a loose meshwork of glial cell processes, intercellular spaces and the presence of both optic and nonoptic axons. In the bridge, putative growth cones of retinal ganglion cell axons are found in the intercellular spaces in contact with both the glia and with other axons. The newly growing axons from each eye cross in the bridge at the midline and pass into the superficial layers of the contralateral optic tracts. As the system continues to grow, previous generations of axon, which initially crossed in the existing bridge, are displaced dorsally and caudally, forming the deeper layers of the chiasma. At their point of crossing in the deeper layers, these fascicles of axons from each eye interweave in an intimate fashion. There is no glial segregation of the older axons as they interweave within the chiasma.     

Cytochemical Localization of Adenosine Triphosphataes Activity During Cytomixis in Pollen Mother Cells of David Lily and Its Relation to the Intercellular Migrating Chromatin Substance

Standard lead precipitation procedures have been used to examine the localization of ATPase activity during cytomixis in pollen mother cells of Lilium davidii var. willmottiae (Wilson) Roffill. Before cytomixis, cells at this stage of development show ATPase activity on plasma membrane, in the endoplasmic reticulum, dictyosomes, plastids, plasmodesmata, and in part of the groundplasm; however, there is no ATPase activity on the chromatin and nucleolus. During cytomixis, the chromatin substance begin to transfer from one cell to an adjacent cell, reaction product indicating ATPase activity is observed associated with the chromatin and nucleolus. ATPase activity is also found with the cistenae of both endoplasmic reticulum and dictyosomes, and some plastids. There is no deposition of ATPase reaction product associated with the plasm membrane and intercellular spaces. After cytomixis, the chromatin is little or no deposition of enzyme reaction product. ATPase activity, however, is consistenlly found within the intercellular space and on the plasm membrane, and also occur in the endoplasmic reticulum, dictyosome and plastid. The presence or absence of ATPase activity in the cell structure of pollen mother cells before, during or after eytomixis is discussed in relation to the active uptake or export of water for short-distance transport. It is also suggested that the intensive ATPase activity in the nucleus during cytomixis of pollen mother cells is evidence for a transport system involved in the active movement of the intercellular migrating ebromatin substance.