On the chemical basis of thiocholine methods for demonstration of acetylcholinesterase activities

Historical landmarks in the histochemistry of the cholinergic synapse: Perspectives for future researches

Nearly one hundred years ago, acetylcholine (ACh) was proposed as a chemical agent responsible for nerve transmission at the synapse, the junction area between one neuron and its target cell. Since it has been proved that ACh played, indeed, a major role in the functioning of the nerve system in the vertebrates, cholinergic nerve transmission became a basic field of study in neuroscience. The birth of histochemistry and its ulterior developments allowed in situ localization of the molecular agents related to the functioning of the cholinergic synapse. This report presents historical landmarks in the histochemistry of major cholinergic agents (acetylcholinesterase, nicotinic acetylcholine receptor, choline acetyltransferase, and ACh), a domain which has greatly contributed to the knowledge of the nerve system. It is emphasized that despite extraordinary progresses made in this field, basic problems, such as in situ localization of ACh, still remain to be solved.

René Couteaux (1909-1999) and the morphological identification of synapses

During a historical research, we realized that René Couteaux (1909-1999) was the first histologist who stained the postsynaptic structure of the neuromuscular junction. By means of Janus Green B dye, he revealed the membranous 'subneural apparatus' related to the 'synaptic gutter'. Hence, he justified the use of the physiological term 'synapse' in histology. A few years later, Couteaux localized acetylcholinesterase activity on this subneural apparatus with a histo-enzymatic method. The histochemical staining confirmed his histological observations that the subneural apparatus of the muscle cells was distinct from the nerve terminal. Thus Couteaux not only supported Cajal's neuron theory, but also gave decisive morphological basis to the concept of the synapse, thought to be up to that time a physiological entity. These observations were performed several years before the first electron microscopic data obtained in the U.S.A. When the electron microscopy became available in Europe, Couteaux studied the ultrastructural details of the myoneural synapse. He found evidence for the presynaptic 'active zone' as a restricted zone of the thickened presynaptic membrane flanked on both sides with synaptic vesicles, some of which were observed to be opening into the synaptic cleft by exocytosis. Furthermore, the synaptic vesicles were shown to be displayed in two rows along the linearly prolonged active zone which is situated just above the 'trench-like' junctional folds of the muscle membrane. The discontinuity of the synaptic structure was confirmed by the three-dimensional observation of the intraneuronal network of neurofibrils with the first prototype of high-voltage electron microscope.

Distribution of acetylcholinesterase activity during the development of cysticercoids of Hymenolepis diminuta (Cestoda)

The distribution of acetylcholinesterase (AChE) in oncospheres and developing cysticercoids of Hymenolepis diminuta was examined. The enzyme was localized in the nervous system and in some non-nerve cells of these larvae. In oncospheres AChE was detected in hook muscles and in the binucleated medullar center that is known to enclose two neurons. At early developmental stages of the cysticercoids the enzyme was localized in the post-oncospheral hook muscles and in subtegumental muscle fibers of the cercomer. At medium and late stages of development the activity of AChE was detected in the developing nervous system and in two and, subsequently, in four populations of cells, which gradually spread over the whole internal wall of the cyst, thus forming a thin multilayer AChE-positive lining of the cyst cavity. Following withdrawal of the scolex the lining separates the parenchyma of the turned neck from the cyst tissues and remains AChE-positive during the whole life of the parasite, i.e. up to the death of the infected host. The role played by non-neural AChE associated with the cyst cavity lining is unknown, but seems to regulate both the transport of nutrients and minerals into the scolex and waste substances in the opposite direction.

Higher activities of acetylcholinesterase and choline acetyltransferase in jaw-opening than jaw-closing motoneurones in the rat

The activities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) in rat masticatory motoneurones were measured. Anterior digastric (jaw-opening) and masseter (jaw-closing) motoneurones were retrogradely labelled with the fluorescent tracers nuclear yellow and bisbenzimide, respectively. The animals were pretreated with an irreversible AChE inhibitor, diisopropyl fluorophosphate, for the measurement of AChE activities. After transcardial perfusion, serial frozen sections, 20-microm thick, of the brainstem were prepared and processed for AChE histochemical analysis. Sections of 30-microm thickness were also prepared and processed for ChAT immunohistochemical analysis using anti-ChAT antibodies and the peroxidase-antiperoxidase complex. The AChE and ChAT activities in motoneurones identified by their fluorescence were determined by measuring their absorbance in the cytoplasm at 470 and 450 nm, respectively. Each of the enzymatic activities was significantly higher in the anterior digastric than in masseter motoneurones (p < 0.001, student t-test).

Differential presynaptic and postsynaptic expression of m1-m4 muscarinic acetylcholine receptors at the perforant pathway/granule cell synapse

A family of muscarinic acetylcholine receptor proteins mediates diverse pre- and postsynaptic functions in the hippocampus. However the roles of individual receptors are not understood. The present study identified the pre- and postsynaptic muscarinic acetylcholine receptors at the perforant pathway synapses in rat brain using a combination of lesioning, immunocytochemistry and electron microscopic techniques. Entorhinal cortex lesions resulted in lamina-specific reductions of m2, m3, and m4 immunoreactivity in parallel with the degeneration of the medial and lateral perforant pathway terminals in the middle and outer thirds of the molecular layer, respectively. In contrast, granule cell lesions selectively reduced m1 and m3 receptors consistent with degeneration of postsynaptic dendrites. Direct visualization of m1-m4 by electron microscopic immunocytochemistry confirmed their differential pre- and postsynaptic localizations. Together, these findings provide strong evidence for both redundancy and spatial selectivity of presynaptic (m2, m3 and m4) and postsynaptic (m1 and m3) muscarinic acetylcholine receptors at the perforant pathway synapse.

Comparative structural analysis of neuromuscular junctions in mice at different ages

The authors studied the histochemical and ultrastructural modifications that occur in the neuromuscular junctions (NMJ) of fibularis longus muscles of mice with an age range of 3 to 21 months. Twenty-four male and female animals were killed at 3, 5, 14 and 21 months of age: 7 of them at 3 months, 4 of them at 5 month, 9 at 14 months and 4 at 21 months. The fibularis longus muscles were processed and their NMJ examined with the transmission electron microscope. The most relevant changes were associated with the degeneration and retraction of terminal axons, i.e., axons poor in synaptic vesicles with degenerated mitochondria, and exhibiting multivesicular bodies and vacuoles; exposed and widened junctional folds and cytoplasmic processes of Schwann cells located in the synaptic gutter. The presence of lysosomes or lipofuchsin in the juxtajunctional sarcoplasm was also noted. These observations suggest that the phenomena of retraction and budding occur in the NMJ with advancing age, with a predominance of events associated with degeneration, leading to profound changes in NMJ shape.

Organization and efferent connections of the archistriatum of the mallard, Anas platyrhynchos L.: an anterograde and retrograde tracing study

The intratelencephalic and descending connections of the archistriatum of the mallard were studied using anterograde and retrograde tracers. Autoradiography after injections of [3H]-leucine served to visualize the intratelencephalic and extratelencephalic efferent connections of the archistriatum. Horseradish peroxidase (HRP), HRP-wheatgerm agglutinin, and fluorescent tracers were used to identify the precise origin of the projections to the various terminal fields found in the anterograde experiments. Four main regions can be recognized in the archistriatum of the mallard: (1) the rostral or anterior part that is a source of contralateral intratelencephalic projections, in particular to the contralateral archistriatum; (2) the dorsal intermediate archistriatum that is the origin of a large descending fiber system, the occipitomesencephalic tract, with projections to dorsal thalamic nuclei, the medial spiriform nucleus, the intercollicular nucleus, the deep tectum, parts of the mesencephalic and bulbar reticular formation, and the subnuclei of the descending trigeminal tract. There are no direct projections to motor nuclei. This part corresponds to the somatic sensorimotor part as defined by Zeier and Karten (1971, Brain Res. 31:313-326); it also contributes to the ipsilateral intratelencephalic connections and, to a lesser degree, to contralateral intratelencephalic connections. (3) The ventral intermediate archistriatum is another region that is also a source of intratelencephalic projections, in particular of those to the lobus parolfactorius. The most lateral zone sends fibers to the septal area. (4) The caudoventral intermediate and posterior archistriatum is another region that is a source of the projections to the hypothalamus and thus corresponds to the amygdaloid part of the archistriatum as defined by Zeier and Karten; it also contributes a modest component to the occipitomesencephalic tract. The different cell populations are not spatially separated, which makes it impossible to recognize distinct subnuclei within the four main regions of the archistriatum of the mallard.

A simple enzyme histochemical method for the simultaneous demonstration of acetylcholinesterase and monoamine oxidase in fixed-frozen sections

We describe an enzyme histochemical technique for the simultaneous demonstration of acetylcholinesterase (AChE) and monoamine oxidase (MAO) (Types A, B, or A+B) in fixed-frozen sections. Several regions in the mesencephalon and brainstem were examined for both somatic and neuropil labeling. The results obtained are equivalent or superior to those obtained using previous methods for the individual localization of these enzymes. The simultaneous visualization of AChE and MAO in the same section allows the relationship of the two enzymes to be easily assessed with brightfield microscopy.

Enzyme histochemistry of cutaneous sensory nerve formations

The cutaneous sensory nerve formations belong to the structures which are studied intensely by the enzyme activity histochemistry since the early history of this technique. The histochemical localization of the activities of nonspecific cholinesterase, alkaline phosphatases, acid phosphatase, adenosine tri- and diphosphatases, adenylate cyclase, and dipeptidylpeptidase-IV in the cutaneous sensory nerve formations, mainly sensory corpuscles, is reviewed. The histochemical approach has brought new knowledge of both morphological building of these unique structures and their biochemical constituents. Taken together, the present results of enzyme histochemistry provide insight into the function of enzymes, and disclose new relationships between the sensory terminals and auxiliary structures in the cutaneous sensory nerve formations.

Distribution of choline acetyltransferase and acetylcholinesterase in vocal control nuclei of the budgerigar (Melopsittacus undulatus)

The present study used histochemical methods to map the distributions of choline acetyl transferase (ChAT) and acetylcholinesterase (AChE) in the vocal control nuclei of a psittacine, the budgerigar (Melopsittacus undulatus). The distributions of ChAT and AChE in budgerigars appeared similar to that in oscine songbirds despite evidence that these systems have evolved independently. The magnicellular nucleus of the lobus parolfactorius in budgerigars, like the area X in songbirds, contained many ChAT labeled somata, fibers, and varicosities and stained densely for AChE. In contrast, the robust nucleus of the archistriatum (RA) and the supralaminar area of the frontal neostriatum in budgerigars, like the RA and the magnicellular nucleus of the neostriatum (MAN) in songbirds, respectively, contained few or no ChAT labeled somata, fibers, and varicosities and stained lightly for AChE. The central nucleus of the lateral neostriatum in budgerigars, like the higher vocal center (HVC) in songbirds, contained no ChAT labeled somata, moderate densities of ChAT labeled fibers and varicosities, and moderate levels of AChE staining. Two nuclei, the oval nucleus of the hyperstriatum ventrale (HVo) and the oval nucleus of the anterior neostriatum (NAo), contained no ChAT labeled somata, dense ChAT labeled fibers and varicosities, and moderate to high levels of AChE staining. The HVo and the NAo have no counterparts in songbirds but may be important vocal control nuclei in the budgerigar. Cholinergic enzymes are also described in other regions which may be involved in budgerigar vocal behavior, including the basal forebrain, the torus semicircularis, and the hypoglossal nuclei (nXII).

The basal forebrain cholinergic system and object memory in the rat

Rats with near complete destruction of basal forebrain cholinergic neurons from intracerebroventricular injections of 192 IgG-saporin were trained on object discrimination problems and then retrained two weeks later to measure retention. Despite dramatic reductions of acetylcholinesterase-positive fibers in hippocampus and neocortex, these animals did not differ from controls on an analysis of savings scores. Thus, the basal forebrain cholinergic system may serve functions that support non-spatial memory but are not specifically mnemonic in nature.

Cajal-Retzius neurons in human cerebral cortex at midgestation show immunoreactivity for neurofilament and calcium-binding proteins

Along with subplate neurons, Cajal-Retzius cells (CRc) are the first neurons to be generated in the cortical anlage. Studies of their chemical content, such as neurofilament and calcium-binding proteins, might give indications on their role in cortical development at midgestation in human fetuses (20-24 gestation weeks), when the CRc are morphologically mature. Cajal-Retzius cells were immunolabeled with antibodies to subunits of neurofilament proteins SMI31 and SMI32. The SMI32 antibodies (directed against the nonphosphorylated epitope) specifically labeled the CR cell bodies, dendrites, and proximal axons in a Golgilike fashion. Specific acetylcholinesterase activity is known to be typical of all the CRc, and double labeling for SMI32 immunoreactivity and acetylcholinesterase histochemistry demonstrated that all the CRc exhibited SMI32 immunoreactivity. The SMI31 antibodies (directed against the phosphorylated epitope) exclusively labeled the CRc axons, forming a dense positive network in the deep one-half of layer 1. This plexus was much denser than the one described with the Golgi method (Marin-Padilla, 1990: J. Comp Neurol 239:89-105). Calbindin D28k, parvalbumin, and calretinin immunoreactivities were visualized in the CRc. Double-labeling experiments showed that most of the CRc contained both calbindin and calretinin and sometimes parvalbumin. These colocalizations revealed a chemical heterogeneity within the CRc population even though they were described as morphologically homogeneous. These colocalizations of calcium-binding proteins in the CRc differed from the other nonpyramidal cortical neurons where calbindin, calretinin, and parvalbumin are contained in different (mutually exclusive) neuronal populations. Based on the morphological features and differential chemical contents described for the CRc, different hypotheses on their possible role and fate are discussed.

Impaired acquisition in a 14-unit T-maze following medial septal lesions in rats is correlated with lesion size and hippocampal acetylcholinesterase staining

Septohippocampal cholinergic system involvement in acquisition of an aversively motivated 14-unit T-maze was evaluated in 4-month-old male Fischer-344 rats. Each rat was assigned to one of two groups that received either a bilateral electrolytic lesion to the medial septal area (MSA) or a sham operation. One week after surgery, each rat began pretraining in one-way active avoidance (footshock = 0.8 mA) consisting of 10 trials per day on each of 3 consecutive days. Criterion for successful completion of pretraining was 8/10 avoidances on the third day. On the day following completion of pretraining, each rat received 10 trials in a shock-motivated 14-unit T-maze. The performance requirement was to move through each of five maze segments within 10 s to avoid footshock (0.8 mA). A second 10-trial session was provided 24 h later. Performance measures included errors, alternation errors, runtime, shock frequency, and duration. Following maze training, each rat was sacrificed, and formalin-fixed brains were frozen for histology, which included procedures for thionin Nissl and acetylcholinesterase (AChE) staining. MSA-lesioned rats were observed to be significantly impaired on all measures of maze performance compared to sham-operated controls. Densitometric analysis of hippocampal AChE staining revealed a 30% reduction in relative AChE staining of MSA-lesioned rats compared to sham-operated controls. Lesion size was observed to be highly positively correlated with maze errors. A negative correlation of mean error score with density of AChE staining was observed for MSA-lesioned rats, but not for sham-operated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

G2-acetylcholinesterase is presynaptically localized in Torpedo electric organ

In Torpedo electric organ, much of the acetylcholinesterase (AChE) is a globular dimer (G2), anchored to the plasma membrane via covalently attached phosphatidylinositol and selectively solubilized by a bacterial phosphatidylinositol-specific phospholipase C. While the structure of this form of the enzyme is well-established, the ultrastructural localization of G2-AChE is still unclear. Selective solubilization with phosphatidylinositol-specific phospholipase C was, therefore, combined with immunocytochemistry at the electron microscope level, in order to localize G2-AChE in electric organ of Torpedo ocellata. Thin sections of electric organ were labelled with antibodies raised against Torpedo AChE, followed by gold-conjugated second antibodies, before or after exposure to the phospholipase. For comparison, the location of AChE was examined using histochemical methods. We show that (1) immunolabelling is concentrated in the synaptic clefts between nerve terminals and the innervated face of the electrocyte; (2) this labelling co-localizes with AChE histochemical reaction products; and (3) prior exposure to the phospholipase causes a decrease in AChE-associated labelling. Quantitative analysis of immunolabelling in the synaptic clefts shows that the phospholipase treatment had reduced primary labelling at or adjacent to the presynaptic membrane. Together with our earlier biochemical and immunofluorescent evidence, these results support our previous assignment of a neuronal and synaptic localization for G2-AChE in Torpedo electric organ.

Ontogeny of cholecystokinin receptors in the human striatum

The distribution of cholecystokinin binding sites was studied by receptor autoradiography in the human striatum at midgestation, birth and adulthood. In the adult, cholecystokinin receptors are inhomogeneously distributed with patches of reduced labeling. In the caudate nucleus but not in the putamen these patches match the striosomal organization as revealed by acetylcholinesterase staining. At midgestation, patches of high density of cholecystokinin receptors are in register with the dopamine D1 receptor-enriched striosomes. At birth, this striosomal organization has already evolved into the adult pattern of higher matrix level in contrast to the striosomal pattern of acetylcholinesterase staining.

Glial cells in coculture can increase the acetylcholinesterase activity in human brain endothelial cells

The elements of the cholinergic system (acetylcholinesterase and choline acetyltransferase) and butyrylcholinesterase were studied in human cortical capillary samples, brain-derived endothelial cell cultures and glial cell cultures. It was shown that the elements of the cholinergic system are present in the microvessels, but the choline acetyltransferase activity may be due to contamination with cholinergic nerve terminals since no choline acetyltransferase could be demonstrated in endothelial cell cultures. The present results revealed that the activity of acetylcholinesterase is reduced in the cortical endothelial cell cultures after longer culture times, while butyrylcholinesterase activity is not altered. In a system where endothelial cells were cocultured with embryonic human brain astroglial cells for 12 days in vitro, the acetylcholinesterase activity was increased 2-fold. These results support a glial influence on the enzyme activity of the cerebral endothelium.

[Histochemical investigations on the localization of acetylcholinesterase in the kidney of selected vertebrates]

The light and electron microscopical localization of AChE activity in the kidney of selected vertebrates was studied using the method of Karnovsky and Roots (1964) for light microscopy and the modification of the Koelle and Friedenwald's technique according to Tsuji (1974, 1984) for electron microscopy. AChE activity could be demonstrated light microscopically mainly within the glomeruli of some mammals (golden hamster, mouse, rat) and non-mammalian vertebrates (carp, frog). No activity was found in the glomeruli of guinea pig, of chicken and tortoise. In the mammalians, the strongest AChE activity could be demonstrated in the guinea pig, the lowest in the rat. A strong AChE enzyme activity was also detected within the interlobular arteries and the cells of Bowman's capsule. With the electron microscopical method AChE activity was demonstrated in mesangial cells and endothelial cells of the glomeruli (golden hamster and carp) and in the cells of Bowman's capsule (carp). Reaction product was localized within the cisterns of endoplasmic reticulum and the perinuclear space (nuclear envelope). A high amount of electron opaque material could be observed in the cells of Bowman's capsule and their lamina basalis. The functional significance of the localization of AChE activity in the glomeruli will be discussed.

Deficiency of acetylcholine receptors in a case of end-plate acetylcholinesterase deficiency: a histochemical investigation

A young boy is described who, since early infancy, suffered from weakness of predominantly proximal limb muscles. Electromyography revealed impairment of neuromuscular transmission. There were no antibodies against acetylcholine receptors. The amplitude of miniature end-plate potentials was reduced. Neuromuscular junctions showed somewhat coarse postsynaptic junctional folds and degeneration products in the synaptic clefts and in postsynaptic areas. Using qualitative and semiquantitative histochemical methods, at light- and electronmicroscopical levels, acetylcholinesterase (AChE) activity and acetylcholine receptors (AChRs) were demonstrated to be deficient. This patient demonstrates that the clinical picture of congenital myasthenia may closely resemble a congenital myopathy. The findings provide evidence that AChR deficiency offers protection from some of the effects of AChE deficiency. The clinical features of AChE deficiency depend, not only on the level of residual enzyme activity, but also on the degree of AChR reduction, if present.

Effects of delayed transplantation of cultured Schwann cells on axonal regeneration from central nervous system cholinergic neurons

The introduction of transplants consisting of cultured Schwann cells and their associated extracellular matrix (Sc/ECM) into a central nervous system (CNS) lesion cavity facilitates axonal regeneration from injured, adult mammalian neurons with subsequent reinnervation of their appropriate target (Kromer and Cornbrooks: Proceedings of the National Academy of Sciences of the United States of America 82:6330-6334, 1985). In the present study, the effects of a delayed transplantation procedure on the time course of this regenerative response were evaluated. For these experiments, bilateral CNS lesions were created between the septum and hippocampus by removing the fimbria-fornix pathway. Lesion cavities received either no transplants, transplants of collagen, or Sc/ECM transplants at the time the lesion was created or 6 days later. When no transplants or transplants of collagen were used, axonal sprouts extended for very short distances into the lesion cavity. These axons were not preferentially associated with the collagen transplants nor maintained at long post-lesion survival times. In animals that received Sc/ECM transplants, the number of sprouting axons and the progression of axonal growth along the transplants was much more extensive than for the collagen transplants. Although more axons were detected in cavities that received transplants immediately after the fimbria-fornix lesion, axonal regeneration along the transplants was similar regardless of whether there was a delay in transplanting the Schwann cells. By using histochemical techniques to identify acetylcholinesterase (AChE), regenerating AChE-positive axons were first detected in the cavity at 3 days post-transplantation, were associated with the Sc/ECM transplants by 5 days, and crossed the cavity within 8 days post-transplantation. Regenerating, neurofilament-positive axons crossed the CNS-Sc/ECM transplant interfaces in association with laminin-positive, glial fibrillary acidic protein-positive cellular pathways. Upon reaching the caudal end of the Sc/ECM transplant, the cholinergic axons abandoned the transplant and oriented directly toward the adjacent hippocampus. Both the simultaneous and delayed transplantation paradigms demonstrated a similar reinnervation pattern of AChE-positive fibers in the hippocampus, but there was a more rapid penetration and more extensive arborization of fibers in animals receiving the delayed transplants. Cholinergic fibers initially invaded the dentate gyrus molecular layer and hilus between 8 and 14 days post-transplantation. By 45 days post-transplantation, AChE-positive axons were detected throughout the dentate gyrus and regio inferior, but few fibers were present in regio superior of the hippocampus.(ABSTRACT TRUNCATED AT 400 WORDS)

Human nerve growth factor prevents degeneration of basal forebrain cholinergic neurons in primates

Basal forebrain cholinergic neurons respond to nerve growth factor (NGF), and it has been suggested that the administration of NGF might prevent their degeneration in patients with Alzheimer's disease. One major prerequisite to be fulfilled before the consideration of clinical trials of NGF in patients with Alzheimer's disease is the demonstration that human NGF affects basal forebrain cholinergic neurons in primates. In the present study, we used a recombinant human nerve growth factor (rhNGF), which we previously showed to be active on rat basal forebrain cholinergic neurons, in nonhuman primates with a unilateral transection of the fornix (a well-established model for the induction of retrograde degenerative changes in septal cholinergic neurons). After the lesion, one group of animals received rhNGF and a second group received vehicle solution for 2 weeks. In animals receiving vehicle, the medial septal nucleus ipsilateral to the lesion showed reductions in number (55%) and size of cell bodies immunoreactive for NGF receptor and choline acetyltransferase. In Nissl stains, many cells showed reduced size and basophilia. The rhNGF completely prevented alterations in the number and size of NGF receptor- and choline acetyltransferase-immunoreactive neurons in the medial septal nucleus and reversed atrophy in a subpopulation of large, basophilic medial septal nucleus neurons, as identified by Nissl stains. The effects of rhNGF were identical to those of mouse NGF, which we have previously used in the same primate lesion paradigm. The restoration of the phenotype of injured cholinergic septal neurons by rhNGF in the monkey raises the possibility that this factor may be used to ameliorate acetylcholine-dependent memory impairments that occur in aged nonhuman primates. In concert, results of the present investigation provide critical information for the future use of NGF in patients with neurological disorders that affect NGF-responsive cells in the peripheral and central nervous systems.

Effects of sciatic nerve transplants after fimbria-fornix lesion: examination of the role of nerve growth factor

At two weeks post-transplantation, sciatic nerves inserted into the lesioned septo-hippocampal pathway contain NGF levels more than twice that of normal nerves. These transplanted nerves also contain regenerating cholinergic axons. Moreover, transplanted animals exhibit septal NGF levels that are significantly greater than in animals with lesions only. These results suggest a role for NGF in the ingrowth of axons into the transplants and in the increase in ChAT(+) septal neurons previously observed at this post-transplant time.

The bed nucleus-amygdala continuum in human and monkey

The cytoarchitecture and distributions of seven neuropeptides were examined in the the bed nucleus of the stria terminalis (BST), substantia innominata (SI), and central and medial nuclei of the amygdala of human and monkey to determine whether neurons of these regions form an anatomical continuum in primate brain. The BST and centromedial amygdala have common cyto- and chemo-architectonic characteristics, and these regions are components of a distinct neuronal complex. This neuronal continuum extends dorsally, with the stria terminalis, from the BST and merges with the amygdala; it extends ventrally from the BST through the SI to the centromedial amygdala. The cytoarchitectonics of the BST-amygdala complex are heterogeneous and compartmental. The BST is parcellated broadly into anterior, lateral, medial, ventral, supracapsular, and sublenticular divisions. The central and medial nuclei of the amygdala are also parcellated into several subdivisions. Neurons of central and medial nuclei of the amygdala are similar to neurons in the lateral and medial divisions of the BST, respectively. Neurons in the SI form cellular bridges between the BST and amygdala. The BST, SI, and amygdala share several neuropeptide transmitters, and patterns of peptide immunoreactivity parallel cytological findings. Specific chemoarchitectonic zones were delineated by perikaryal, peridendritic/perisomatic, axonal, and terminal immunoreactivities. The results of this investigation demonstrate that there is a neuronal continuity between the BST and amygdala and that the BST-amygdala complex is prominent and discretely compartmental in forebrains of human and monkey.

Histochemical profiles of motoneurons innervating muscle fibres with different activity patterns in the zebrafish, Brachydanio rerio

Enzyme histochemical profiles of spinal motoneurons in the zebrafish were determined. Five enzymes of glucose metabolism were chosen: glucose-6-phosphate dehydrogenase (G6PDH), hexokinase (HK), phosphofructokinase (PFK), succinate dehydrogenase (SDH) and NADH tetrazolium reductase (NADH-TR). Motoneurons were traced with Fluorogold and classified as those that innervate white muscle fibres (W-MNs) and those that innervate red and intermediate muscle fibres (R/I-MNs). The average enzyme activities per volume of tissue in the somata of both populations differed at most by 25%. Both the average soma volume and the average number of muscle fibres innervated are three times larger for the W-MNs than for the R/I-MNs. This suggests that the total amount of enzyme activity within a neuron soma matches target size. In the R/I-MNs, the activities of SDH and NADH-TR were closely correlated (correlation coefficient, r = 0.99; p less than 0.05) and HK activity correlated well with G6PDH activity (r = 0.94; p less than 0.05), but not with PFK (r = 0.64; p greater than 0.05). In the W-MNs, there was no correlation between SDH and NADH-TR (r = -0.59; p greater than 0.05) or between HK and G6PDH (r = 0.50; p greater than 0.05) and the correlation coefficient between HK and PFK activity was close to zero (r = 0.04; p greater than 0.05). It was concluded that in the R/I-MNs, which are continuously active, firing activity is fuelled by oxidative metabolism. We suggest that in the W-MNs glucose is stored in the form of glycogen and that, despite high levels of NADH-TR present, the energy for intermittent firing activity is provided by glycolysis.

Axotomy induces nerve growth factor receptor immunoreactivity in spinal motor neurons

Expression of the nerve growth factor receptor (NGF-R) mRNA in adult motor neurons is increased by axonal injury. The present study was designed to examine, by immunocytochemistry, the onset, course, and specificity of NGF-R up-regulation following distal or proximal crush of the sciatic nerve. Lesions at both levels induced the appearance of NGF-R-like immunoreactivity in motor neurons beginning on day two postaxotomy. NGF-R-like immunoreactivity was present exclusively in axotomized neurons, as verified by the near complete colocalization of immunoreactive NGF-R with a fluorescent retrograde tracer injected at the crush site. NGF-R expression was closely linked with disconnection of cells from the target; one week after muscle reinnervation, NGF-R immunoreactivity was no longer detectable in animals with distal injuries. These results extend the previous findings of axotomy-induced expression of NGF-R mRNA to the level of the receptor. Furthermore, our observations are consistent with the hypothesis that target-derived factors participate in the regulation of NGF-R gene expression in adult motor neurons.

Recombinant human nerve growth factor prevents retrograde degeneration of axotomized basal forebrain cholinergic neurons in the rat

Cholinergic neurons in the basal forebrain magnocellular complex (BFMC) respond to nerve growth factor (NGF) during development and in adult life, and it has been suggested that the administration of NGF might ameliorate some of the abnormalities that occur in neurological disorders associated with degeneration of this population of neurons. A prerequisite for the introduction of NGF in clinical trials is the availability of active recombinant human NGF (rhNGF). The present investigation was designed to test, in vivo, the efficacy of a preparation of rhNGF. Axons of cholinergic neurons of the BFMC in the rat were transected in the fimbria-fornix; this manipulation alters the phenotype and, eventually, causes retrograde degeneration of these neurons. Our investigation utilized two lesion paradigms (resection and partial transection of fibers in the fimbria-fornix), two different strains of rats, and two delivery systems. Following lesions, animals were allowed to survive for 2 weeks, during which time one group received intraventricular mouse NGF (mNGF), a second group received rhNGF, and a third group received vehicle alone. In animals receiving vehicle, there was a significant reduction in the number (resection: 70%; transection: 50%) and some reduction in size of choline acetyltransferase- or NGF receptor-immunoreactive cell bodies within the medial septal nucleus ipsilateral to the lesion. Treatment with either mNGF or rhNGF completely prevented these alterations in the number and size of cholinergic neurons. The rhNGF was shown to be equivalent in efficacy with mNGF. Thus, rhNGF is effective in preventing axotomy-induced degenerative changes in cholinergic neurons of the BFMC. Our results, taken together with the in vitro effects of rhNGF (42), indicate that an active rhNGF is now available for further in vivo studies in rodents and primates with experimentally induced or age-associated lesions of basal forebrain cholinergic neurons. These investigations provide essential information for the consideration of future utilization of rhNGF for treatment of human neurological disorders, including Alzheimer's disease.

Ultrastructural localization of [125I]neurotensin binding sites to cholinergic neurons of the rat nucleus basalis magnocellularis

The distribution of specifically-labeled neurotensin binding sites was examined in relation to that of cholinergic neurons in the rat nucleus basalis magnocellularis at both light and electron microscopic levels. Lightly prefixed forebrain slices were either labeled with [125I](Tyr3) neurotensin alone or processed for combined [125I]neurotensin radioautography and acetylcholinesterase histochemistry. In light microscopic radioautographs from 1-microns-thick sections taken from the surface of single-labeled slices, silver grains were found to be preferentially localized over perikarya and proximal processes of nucleus basalis cells. The label was distributed both throughout the cytoplasm and along the plasma membrane of magnocellular neurons all of which were found to be cholinesterase-positive in a double-labeled material. Probability circle analysis of silver grain distribution in electron microscopic radioautographs confirmed that the major fraction (80-89%) of specifically-labeled binding sites associated with cholinesterase-reactive cell bodies and dendrites was intraneuronal. These intraneuronal sites were mainly dispersed throughout the cytoplasm and are thus likely to represent receptors undergoing synthesis, transport and/or recycling. A proportion of the specific label was also localized over the nucleus, suggesting that neurotensin could modulate the expression of acetylcholine-related enzymes in the nucleus basalis. The remainder of the grains (11-20%) were classified as shared, i.e. overlied the plasma membrane of acetylcholinesterase-positive neuronal perikarya and dendrites. Extrapolation from light microscopic data, combined with the observation that shared grains were detected at several contact points along the plasma membrane of cells which also exhibited exclusive grains, made it possible to ascribe these membrane-associated receptors to the cholinergic neurons themselves rather than to abutting cellular profiles. Comparison of grain distribution with the frequency of occurrence of elements directly abutting the plasma membrane of neurotensin-labeled/cholinesterase-positive perikarya indicated that labeled cell surface receptors were more or less evenly distributed along the membrane as opposed to being concentrated opposite abutting axon terminals endowed or not with a visible junctional specialization. The low incidence of labeled binding sites found in close association with abutting axons makes it unlikely that only this sub-population of sites corresponds to functional receptors. On the contrary, the dispersion of labeled receptors seen here along the plasma membrane of cholinergic neurons suggests that neurotensin acts primarily in a paracrine mode to influence the magnocellular cholinergic system in the nucleus basalis.

Development of acetylcholinesterase-positive neuronal pathways in the cochlea of the mouse

Development of the cholinergic enzymes, choline acetyltransferase (ChAT) and AChE, and of the AChE-positive innervation in the cochlea was studied biochemically and morphologically in the postnatal mouse up to 26 days. Both ChAT and AChE are already present at birth in levels comparable to 50 and 20% of near-adult values, respectively. Increases in the enzymatic activities occur mainly during the second postnatal week. ChAT increases primarily in the basal turn; the specific activities in the basal and mid turns become about equal and at least twice of the values found in the apex. AChE increase continues throughout the entire cochlea; at all times its activity is highest in the base and lowest in the apex. In the light microscope, AChE-positive fibres are seen to enter the organ in the intraganglionic bundle during late foetal development and travel upwards via radial bundles. The fibres destined for outer hair cells usually differentiate first and take a separate route. They either cross the prospective tunnel of Corti directly or take a spiral course in front of inner pillar cells to form the inner pillar bundle. The tunnel fibres are radially oriented and provide the innervation to outer hair cells in narrow vertical sectors. In most cases, the outer hair cells are being innervated by the 4th day. Between the 4th and the 6th day, the tunnel fibres reach the outer hair cells in the third row; the first and second outer spiral bundles are formed. The AChE-positive innervation of the inner spiral bundle and plexus forms in short segments, and the bundle may be still discontinuous even by the 6th day. By the 12th day the innervation is complete. In the electron microscope, the stain for AChE may allow identification of growing efferent fibres before their ultrastructural differentiation. Both ChAT and AChE activities are early markers of the differentiating efferent system. An ingrowth of the cholinergic fibres to the entire cochlea occurs before birth. The greatest increase of AChE occurs between the 4th and 10th day, relating in time to efferent synaptogenesis.

Aberrant phosphorylation of neurofilaments accompanies transmitter-related changes in rat septal neurons following transection of the fimbria-fornix

Lesions of the fimbria-fornix (FF) have been reported to cause retrograde changes in neurons of the medial septal nucleus (MSN). To analyze the nature and time course of these events, we investigated changes in cytoskeletal elements (phosphorylated and non-phosphorylated neurofilament (NF) proteins) and transmitter-related enzymes (choline acetyltransferase (ChAT) in MSN neurons following FF transection. During the first week postlesion, ChAT immunoreactivity and size of many perikarya were reduced. Irregular, swollen cholinergic fibers appeared first at postlesion day 2 in caudal septum and soon spread rostrally, reaching rostral septum by day 7. A few perikarya developed abnormal accumulations of phosphorylated NFs. At postlesion days 7-10, many neurons did not stain for ChAT. Phosphorylated NFs were present in many perikarya. At this time, cell loss was apparent in Nissl-stained material. Cholinergic cell loss continued through postlesion weeks 6-8 but at a much slower rate than during the first week. Phosphorylated NF accumulations in MSN perikarya persisted until postlesion week 6, disappearing thereafter. Double-immunostaining procedures showed that MSN neurons expressed both ChAT and phosphorylated NF immunoreactivity at postlesion day 3; however, at days 7 and 14, cells that accumulated phosphorylated NFs did not stain for ChAT. The results of this study indicate that FF transection leads to perikaryal shrinkage with loss of ChAT immunoreactivity, perikaryal phosphorylation of NFs, cholinergic fiber abnormalities, and cell loss. Recent evidence suggests that reduction of transmitter markers and aberrant phosphorylation of NFs may be involved in the pathogenesis of several neurodegenerative disorders, including Alzheimer's disease. Therefore, FF transection provides a useful animal model for further investigations of complex disorders of the central nervous system that involve degeneration of transmitter-specific pathways.

Electron microscopical study of non-specific cholinesterase activity in simple lamellar corpuscles of glabrous skin from cat rhinarium: a histochemical evidence for the presence of collagenase-sensitive molecular forms and their secretion

The distribution of nCHE activity was studied histochemically in simple lamellar corpuscles (SLCs) of glabrous skin from cat rhinarium. The Schwann cells forming myelin sheaths in preterminal part of SCLs exhibited no positive reaction for nCHE activity. Prevalent reaction product was localized extracellularly in the inne core enveloping terminal portion of unmyelinated sensory axon. A dot-like shaped reaction product was deposited in the basal lamina of the inner core cells and their cytoplasmic lamellae or was scattered in enlarged interlamellar spaces. Only small amount of fine end product was found to be associated with the plasma membrane of inner core lamellae. Fine reaction product for nCHE activity was consistently localized in perinuclear and rER cisternae and saccules of the Golgi apparatus of inner core cells. Some vesicles around rER and the Golgi apparatus, ones beneath the plasma membrane, and tubular-like cisternal profiles oriented towards the surface contained nCHE end product, as well. The intracellular and extracellular localization of nCHE reaction product suggests that this enzyme behaves in cat SLCs as a secreted rather than as an integral membrane protein. A large amount of dot-like reaction product in the interlamellar spaces disappeared if the skin sections were treated with collagenase before incubation in the medium for histochemical detection of nCHE activity. The decrease of nCHE end product in SLCs of the skin sections after collagenase digestion was corroborated by means of light microdensitometer and electrometrical measurement. The histochemical detection and electrometrical measurement revealed that the majority of the reaction product in the interlamellar spaces of inner core corresponds with the nCHE molecules sensitive to collagenase treatment and they are probably counted among asymmetrical molecular forms.

Topographic, non-collateralized basal forebrain projections to amygdala, hippocampus, and anterior cingulate cortex in the rhesus monkey

Projections of the basal forebrain magnocellular complex to the limbic telencephalon of the primate were studied by combining double-retrograde tracing with immunocytochemistry. Tracers were injected into anterior cingulate cortex and hippocampus or into hippocampus and amygdala. Retrogradely labeled populations of neurons were topographically arranged but intermingled peripherally. Double-labeled neurons, found only after amygdala-hippocampus injections, were very rare. Approximately 30% of hippocampopetal, 50-70% of amygdalopetal, and 50-90% of cingulopetal neurons were cholinergic; percentages varied among different regions of basal forebrain. These findings further support the concept of a system with a highly organized efferent circuitry.

Enhancement of passive avoidance learning through small doses of intra-amygdaloid physostigmine in the young rat. Its relation to the development of acetylcholinesterase

Passive avoidance learning was studied in young rats 7-20 days old, in control conditions and after bilateral injections of physostigmine into the lateral amygdaloid nucleus. Acquisition in controls was possible from postnatal Day 8 on, progressed markedly after Day 11, and nearly reached maturity by Day 20. Physostigmine differentially altered acquisition depending on the dose: facilitation with low doses, no effect with moderate doses, and impairment with high doses. Enhanced learning through small doses of physostigmine was observed at all ages from Day 8 on, and was greater with 0.2 microgram than with 0.1 microgram. Maturation of the cholinergic innervation of the amygdaloid region was also studied between Days 9-20 using acetylcholine-esterase histochemistry. The results suggest that passive avoidance learning is dependent on amygdaloid cholinergic mechanisms early in life. In addition, very immature cholinergic systems, which are known to be uninfluenced by anticholinergic agents, react to anticholinesterases.

Patterns of cholinesterase staining during neural crest cell morphogenesis in mouse and chick embryos

Cholinesterase (ChE) activity has been reported previously in nonneuronal tissues of a variety of avian and mammalian embryos. We report here a comparison study of ChE staining in chick and mouse embryos. Transmission electron microscopy was used to study the distribution of this activity in neuroepithelial, neural crest, somite, and ectodermal cells. Our cytochemical studies show that the distribution of nonspecific ChE staining in these tissues during neurulation is similar in the two species but that acetylcholinesterase (AChE) staining, previously shown to be intense in the chick, is absent in the mouse; the only cells showing the presence of this enzyme at these stages of development in mouse are blood cells. However, AChE staining does appear later in the brain, in neural tissues derived from the neural crest and, perhaps, in some migratory neural crest cells. The differences between AChE distribution in these two species (and that reported previously in the rabbit) indicate that the timing of first appearance of AChE is unrelated to neuroepithelial morphogenesis or to neural crest cell motility. The correlation between nonspecific cholinesterases and morphogenetic movements, however, is supported by these studies.

A comparison of the localization of acetylcholinesterase in the rat brain as demonstrated by enzyme histochemistry and immunohistochemistry

The localization of acetylcholinesterase (AChE) as revealed either by enzyme-histochemical or by immunohistochemical methods was compared in distinct regions of the rat brain. In general, the localization of AChE observed was nearly the same, whether revealed by histochemical demonstration of its catalytic activity or by immunohistochemical detection of the enzyme molecule itself, in all regions investigated. Penetration problems of the antibodies, however, arose on strong myelin sheaths of the facial nerve, for instance, where no immunohistochemical staining was found though there was a relatively strong histochemical reaction. These problems could be partly solved by increasing the normal concentration of Triton X-100 added to the immunohistochemical solutions (0.1%) to 2.5%. Furthermore, it seems that sites containing low amounts of AChE could be better detected by the enzyme-histochemical method, whereas the depiction of structures (particularly of nerve fibres) was somewhat sharper with the immunohistochemical method.

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.

Identification of trophic factors and transplanted cellular environments that promote CNS axonal regeneration

As indicated in this review, we have begun to elucidate cellular environments and trophic factors that promote the regeneration of adult mammalian CNS neurons. In the present paradigm, bilateral aspiration lesions of the fornix-fimbria are used to axotomize septal neurons and transect the septal cholinergic projection to the dorsal hippocampus in order to evaluate the influence of trophic factors, such as NGF, on neuronal survival and the ability of cellular transplants of PNS tissue to promote axonal regeneration in vivo. Initial results demonstrate that NGF is a potent trophic molecule that prevents retrograde degeneration of septal cholinergic neurons. Observations from transplantation studies demonstrate that viable Schwann cells obtained from PNS nerve grafts or Schwann cell-ECM cultures provide a favorable cellular milieu for CNS regeneration. These cellular transplants induce a remarkable sprouting response from septal cholinergic neurons and promote the rapid elongation of septal axons that reinnervate the denervated hippocampus. In stark contrast to the Schwann cell-laden transplants, transplants including only ECM channels synthesized by cultured Schwann cells do not promote axonal regeneration within the time periods that we have examined. Therefore, we hypothesize that viable Schwann cells are crucial for the process of regeneration because they contribute both trophic and tropic factors to the injured CNS neurons. The significant early sprouting phenomenon associated with transplants containing Schwann cells strongly suggests that soluble Schwann cell-synthesized factors induce axon elongation and possibly enhance the survival of injured septal neurons. The trophic factors probably function in a manner similar, if not identical, to the action of NGF on axotomized septal neurons. Moreover, Schwann cells appear to provide tropic signals, such as LAM or a LAM-NGF complex, that can act, when in the proper stereoconfiguration, to promote the elongation and orientation of regenerating axons. Thus, our current data indicate that in order to promote optimal axonal regeneration from injured CNS neurons, both trophic and tropic factors must be supplied from exogenous sources.

Polymorphous geniohyoid muscles of mice, rats and hamsters

The geniohyoid has been characterized as a parallel-fibred muscle extending from the mandibular symphysis to the hyoid body. Motor end-plate staining of dissected whole muscles showed that only in the hamster does the geniohyoid architecture correspond to the usual description of simple parallel fibres. In rats and mice, the muscle was complex with two banks of myofibres separated by a tendinous intersection. Geniohyoid was attached mainly to a basihyal raphe shared by the sternohyoid. A septate geniohyoid may be a primitive feature of mammals because it also exists in the opossum and tree shrew. The segmental disposition of the geniohyoid in rats and mice reflects its serial homology with other compound ventral muscles, such as sternohyoid and rectus abdominis. Architectural patterns of myofibres and connective tissue were distinctive for each species.

Ultrastructural localization of non-specific cholinesterase activity in rat muscle spindles

Electron microscopical localization of non-specific cholinesterase activity was studied in the encapsulated part of rat hindlimb muscle spindles. After incubation of the muscle tissue in a medium containing butyrylthiocholine bromide as substrate and BW284c51 as the specific inhibitor of acetylcholinesterase, a distinct electron-dense precipitate corresponding to non-specific cholinesterase activity was found along the whole length of muscle spindles. The richest source of non-specific cholinesterase activity were the motor end-plates present in the polar and juxtaequatorial regions. Much smaller amounts of reaction deposits were found at the secondary sensory terminals in the juxtaequatorial zones. The primary sensory terminals in the equatorial zone contained only low amounts of the reaction product. A fine homogeneous reaction product was localized in the narrow spaces between Schwann cell processes or in gaps between the Schwann cell, and axonal and muscle membranes. A granular precipitate was localized on the basal lamina in the synapse region of motor terminals or covering Schwann cell processes and sensory terminals with adjacent intrafusal muscle fibres. Our results suggest that most of non-specific cholinesterase in muscle spindles is synthesized by the Schwann cells; but a small amount can also be synthesized by fibroblast-like cells forming the inner capsule of muscle spindles. Non-specific cholinesterase thus coexists with acetylcholinesterase at motor end-plates, but is single at sensory terminals. The function of non-specific cholinesterase in sensory receptors is still not clear. It seems most probable that non-specific cholinesterase in muscle spindles may play a role in the maintenance of the external milieu around nerve endings, especially in the sensory region.

Preliminary evidence for a cholinergic-like system in lichen morphogenesis

Membrane acetylcholinesterase activity is considered to be a marker for a cholinergic system. When temporarily expressed in differentiating cells other than the nervous or muscular ones, it may play a role in morphogenesis. In the lichen Parmelia caperata (L.) Ach., acetylcholinesterase is histochemically localized mainly in the cell walls and/or membranes of both symbionts just where they proliferate and form well-organized propagation structures, the soredia. The enzyme activity is first detected in a few algae undergoing aplanosporogenesis and later in medullary hyphae that reach the dividing algae by elongating perpendicularly to the thallus surface. This histochemical pattern that is associated with algal proliferation and oriented hyphal growth is characteristic of early morphogenesis of the soredia; when fully differentiated, they consist of an inner dividing alga and an outer hyphal envelope, both showing cholinesterase activity. Substrate specificity and inhibitor sensitivity of the histochemical staining indicate an acetylcholinesterase-like activity. However, extracts of the thallus areas where soredia develop give four bands of cholinesterase activity on disc electrophoresis: the two cathodal bands have the characteristics of acetylcholinesterase, the others of pseudocholinesterase. One of the latter hydrolyses propionylthiocholine very rapidly. The findings suggest that in lichen symbiosis, a cholinergic-like system participates in regulating morphogenetic processes such as cell division, oriented tip growth and alga-fungus membrane interactions. Environmental stimuli, particularly light, might trigger the development of soredia by modulating the activity of the cholinergic mechanism.

Interaction of 125I-labeled botulinum neurotoxins with nerve terminals. I. Ultrastructural autoradiographic localization and quantitation of distinct membrane acceptors for types A and B on motor nerves

The labeling patterns produced by radioiodinated botulinum neurotoxin (125I-BoNT) types A and B at the vertebrate neuromuscular junction were investigated using electron microscopic autoradiography. The data obtained allow the following conclusions to be made. 125I-BoNT type A, applied in vivo or in vitro to mouse diaphragm or frog cutaneous pectoris muscle, interacts saturably with the motor nerve terminal only; silver grains occur on the plasma membrane, within the synaptic bouton, and in the axoplasm of the nerve trunk, suggesting internalization and retrograde intra-axonal transport of toxin or fragments thereof. 125I-BoNT type B, applied in vitro to the murine neuromuscular junction, interacts likewise with the motor nerve terminal except that a lower proportion of internalized radioactivity is seen. This result is reconcilable with the similar, but not identical, pharmacological action of these toxin types. The saturability of labeling in each case suggested the involvement of acceptors; on preventing the internalization step with metabolic inhibitors, their precise location became apparent. They were found on all unmyelinated areas of the nerve terminal membrane, including the preterminal axon and the synaptic bouton. Although 125I-BoNT type A interacts specifically with developing terminals of newborn rats, the unmyelinated plasma membrane of the nerve trunk is not labeled, indicating that the acceptors are unique components restricted to the nerve terminal area. BoNT types A and B have distinct acceptors on the terminal membrane. Having optimized the conditions for saturation of these binding sites and calibrated the autoradiographic procedure, we found the densities of the acceptors for types A and B to be approximately 150 and 630/micron 2 of membrane, respectively. It is proposed that these membrane acceptors target BoNT to the nerve terminal and mediate its delivery to an intracellular site, thus contributing to the toxin's selective inhibitory action on neurotransmitter release.

Matrix models. Essential tools for microscopic cytochemical research

An overview is given of the preparation and use of model systems for cytochemistry, dealing with quantitative as well as qualitative aspects. Descriptions are given of the various possibilities to prepare cytochemical matrix models, ranging from macroscopic and microscopic films, to models with more cell-like dimensions as agarose beads, artificial cells and erythrocyte ghosts. Such models allow the study of a large variety of cytochemical processes. Their potentialities are demonstrated in a number of specific applications, comprising: the study of the influence of fixation on cellular processes, reaction specificity and reaction kinetics, quality of reagents and biochemical calibration in cytochemical staining; factors influencing localization of the specific endproduct in enzyme cytochemistry; immunocytochemistry and hybridocytochemistry.

A histochemical method for the demonstration of acetylcholinesterase activity using semipermeable membranes

The "direct coloring" thiocholine method of Karnovsky and Roots (1964) for the demonstration of acetylcholinesterase (AChE) activity was modified and adapted to the technique of semipermeable membranes. In this way it is possible to demonstrate histochemically both the bound as well as the soluble part of AChE activity. The localization of the reaction product is very distinct. Microdensitometric investigations of results of this method showed a linear increase of the amount of reaction product up to an incubation time of 180 min and section thickness up to 24 micron. The medium supplemented with buffer (instead of agar) can be used for the demonstration of AChE activity in cryostat sections adherent to slides and is also very suitable for the detection of multiple forms of AChE in polyacrylamide or agarose gels.

Interspecific cell markers and cell lineage in birds

A cell marking technique based on the structural differences existing between the interphase nucleus in two closely related species of birds, the chick and the Japanese quail, is described. In all embryonic and adult cell types of the quail, a large mass of heterochromatin is associated with the nucleolus making quail and chick cells easy to identify at the single cell level after application of any DNA-specific staining procedure and also at the electron microscope level. This method has been largely used to construct chimeras in ovo and to study dynamic processes such as cell migrations or cell lineage segregation during ontogeny. Recently monoclonal antibodies specific for either quail or chick antigenic determinants (for example, class II MHC antigens) have been prepared, increasing the interest of the quail-chick chimera system as an experimental model.