Acetylcholinesterase and choline acetyltransferase localization patterns do correspond in cat and rat retinas

Stressing hematopoiesis and immunity: an acetylcholinesterase window into nervous and immune system interactions

Hematopoietic stem cells (HSCs) differentiate and generate all blood cell lineages while maintaining self-renewal ability throughout life. Systemic responses to stressful insults, either psychological or physical exert both stimulating and down-regulating effects on these dynamic members of the immune system. Stress-facilitated division and re-oriented differentiation of progenitor cells modifies hematopoietic cell type composition, while enhancing cytokine production and promoting inflammation. Inversely, stress-induced increases in the neurotransmitter acetylcholine (ACh) act to mitigate inflammatory response and regain homeostasis. This signaling process is terminated when ACh is hydrolyzed by acetylcholinesterase (AChE). Alternative splicing, which is stress-modified, changes the composition of AChE variants, modifying their terminal sequences, susceptibility for microRNA suppression, and sub-cellular localizations. Intriguingly, the effects of stress and AChE variants on hematopoietic development and inflammation in health and disease are both subject to small molecule as well as oligonucleotide-mediated manipulations in vitro and in vivo. The therapeutic agents can thus be targeted to the enzyme protein, its encoding mRNA transcripts, or the regulator microRNA-132, opening new venues for therapeutic interference with multiple nervous and immune system diseases.

Differential co-localization with choline acetyltransferase in nervus terminalis suggests functional differences for GnRH isoforms in bonnethead sharks (Sphyrna tiburo)

The nervus terminalis (NT) is a vertebrate cranial nerve whose function in adults is unknown. In bonnethead sharks, the nerve is anatomically independent of the olfactory system, with two major cell populations within one or more ganglia along its exposed length. Most cells are immunoreactive for either gonadotropin-releasing hormone (GnRH) or RF-amide-like peptides. To define further the cell populations and connectivity, we used double-label immunocytochemistry with antisera to different isoforms of GnRH and to choline acetyltransferase (ChAT). The labeling patterns of two GnRH antisera revealed different populations of GnRH-immunoreactive (ir) cell profiles in the NT ganglion. One antiserum labeled a large group of cells and fibers, which likely contain mammalian GnRH (GnRH-I) as described in previous studies and which were ChAT immunoreactive. The other antiserum labeled large club-like structures, which were anuclear, and a sparse number of fibers, but with no clear labeling of cell bodies in the ganglion. These club structures were choline acetyltrasferase (ChAT)-negative, and preabsorption control tests suggest they may contain chicken-GnRH-II (GnRH-II) or dogfish GnRH. The second major NT ganglion cell-type was immunoreactive for RF-amides, which regulate GnRH release in other vertebrates, and may provide an intraganglionic influence on GnRH release. The immunocytochemical and anatomical differences between the two GnRH-immunoreactive profile types indicate possible functional differences for these isoforms in the NT. The club-like structures may be sites of GnRH release into the general circulation since these structures were observed near blood vessels and resembled structures seen in the median eminence of rats.

Nonsynaptic Chemical Transmission Through Nicotinic Acetylcholine Receptors

This review attempts to organize the different aspects of nicotinic transmission in the context of nonsynaptic interactions. Nicotinic acetylcholine receptors (nAChRs) dominantly operate in the nonsynaptic mode in the central nervous system despite their ligand-gated ion-channel nature, which would otherwise be better suited for fast synaptic transmission. This fast form of nonsynaptic transmission, most likely unique to nAChRs, represents a new avenue in the communication platforms of the brain. Cholinergic messages received by nAChRs, arriving at a later phase following synaptic activation, can interfere with dendritic signal integration. Nicotinic transmission plays a role in both neural plasticity and cellular learning processes, as well as in long-term changes in basic activity through fast activation, desensitization of receptors, and fluctuations of the steady-state levels of ACh. ACh release can contribute to plastic changes via activation of nAChRs in neurons and therefore plays a role in learning and memory in different brain regions. Assuming that nAChRs in human subjects are ready to receive long-lasting messages from the extracellular space because of their predominantly nonsynaptic distribution, they offer an ideal target for drug therapy at low, nontoxic drug levels.

Rabbit retinal ganglion cell responses to nicotine can be mediated by beta2-containing nicotinic acetylcholine receptors

Acetylcholine (ACh) affects the response properties of many retinal ganglion cells (GCs) through the activation of nicotinic acetylcholine receptors (nAChRs). To date there have been few studies directly correlating the expression of specific nAChR subtypes with the physiological and morphological characteristics of specific retinal GCs. This study was designed to correlate responses to nicotine application with immunohistochemical evidence of nAChR expression in physiologically and morphologically identified ganglion cells. Extracellular recordings were used to physiologically identify rabbit retinal GCs, based on responses to light stimulation. Cells were then tested for responses to nicotine application and/or for expression of nAChRs, as judged by immunoreactivity to mAb210, an nAChR antibody. The morphologies of many physiologically identified cells were also determined by dye injection. More than three-fourths of ganglion cells tested responded to nicotine application under cobalt-induced synaptic blockade. The nicotine sensitivity was consistent with nAChR immunoreactivity and was also correlated with specific morphological subgroups of GCs. Overall, approximately two-thirds of all physiologically identified GCs that were processed for immunohistochemistry displayed immunoreactivity. In total, 18 of 22 physiologically identified cells demonstrated both sensitivity to nicotine application under synaptic blockade and mAb210 immunoreactivity (mAb210-IR). Thus, mAb210-IR is likely to represent functional nAChRs that can modulate retinal information processing and visual functioning via direct excitation of a number of GC classes.

Dual substrate model for novel approach towards a kinetic study of acetylcholinesterase inhibition by diazinon

Limited reports as compared to other insecticides appear in the literature for acetylcholinesterase (AChE) inhibition by diazinon. In the current study, new kinetic parameters of AChE inhibition by diazinon have been investigated. The assay was done with bovine retinal AChE using two different substrate (ASCh) concentrations in the absence and presence of diazinon (0.08-1.28 mM). The optical density was monitored up to 25 min (reaction time) for the assay. New kinetic parameters k'(oms), K'(sms), k(oms), K(sms), K'(asms) and K(asms) ) were calculated from these experimental data.

Morphological and functional organization of ON and OFF pathways in the adult newt retina

Morphological and functional organization of ON and OFF pathways in the adult newt retina were examined by intracellular recording and staining techniques and immunohistochemistry. Synaptotagmin immunoreactivity discriminated three broad bands within the IPL: the distal band (sublamina I), the middle band (sublamina II) consisting of two dense punctate bands (sublaminae II(a) and II(b)), and proximal band (sublamina III). The Lucifer-yellow labeled OFF amacrine and ganglion cells send their processes mainly in sublamina I and/or II(a) where OFF bipolar cells extend their axon terminals, while ON amacrine and ganglion cells send their processes in sublamina III and/or II(b) where ON bipolar cells extend their axon terminals. Processes of ON-OFF amacrine and ganglion cells ramify broadly in the whole thickness of the IPL. Many bipolar cells responded to light spot with a transient hyperpolarization at both light onset and offset. They are probably subtypes of ON bipolar cells, because their axon terminals branch mainly in sublaminae III and/or II(b), although a few cells ramified the axon at both sublaminae II(a) and III. Two immunohistochemical markers for bipolar cells, PKC and RB-1, identified axon terminals in sublaminae III and/or II(b). From the ramification pattern of axon terminal, they are probably subtypes of ON bipolar cells. ChAT-ir amacrine cells ramified their dendrites in either sublamina I or II(b). Altogether, present studies support the general idea of segregation of ON and OFF pathways in sublaminae a and b of the IPL.

Choline acetyltransferase and acetylcholinesterase in the normal, developing and regenerating newt retinas

The presence of the choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) was demonstrated in the adult newt retina using immunocytochemical and histochemical techniques. Within the inner plexiform layer (IPL), two ChAT-positive bands were detected at relative depths of 0-15% and 45-60% of the total thickness (100%) of the IPL. AChE-positive band occupied approximately 0-60% of the IPL width with an intensive AChE-positive band at a depth of 20-40% within the IPL. Localizations of maximum ChAT and AChE activity were not exactly the same in the IPL of the mature retina. To elucidate whether retinal regeneration follows the same sequence of cellular differentiation steps that occur in retinal development, we examined the time course of appearance of the cholinergic neurons and AChE activity in both developing and regenerating retinas. The ChAT-positive cells were first detected in the retina just before or at the beginning of the morphological development of the IPL in both developing and regenerating retinas. AChE activity first became detectable in somata located at the most proximal layer of the retina before the ChAT-positive cells could be detected and well before the IPL developed in both developing and regenerating retinas. During subsequent development and regeneration, the outer plexiform layer, the IPL, and somata close to either side of the IPL became AChE-positive. The fact that the time course of the appearance of ChAT and AChE molecules during regeneration was similar to that observed during development suggests that common mechanisms may control both the development and the regeneration of the newt retina.

Colocalization of GLUT3 and choline acetyltransferase immunoreactivity in the rat retina

Toward elucidating the functional aspects ofGLUT3, a primary neuronal glucose transporter isoform in the vertebrate central nervous system, this study examined its expression in cholinergic amacrine cells made identifiable by the presence of acetylcholine-synthesizing enzyme, choline acetyltransferase (ChAT), in the rat retina. Double-immunofluorescence staining of adult rat retinal tissue with anti-GLUT3 and anti-ChAT antibodies revealed characteristic stratified GLUT3 immunoreactivity (GLUT3-IR) in the inner plexiform layer (IPL) that was identical to the arborization pattern of ChAT-positive neuronal processes there. In addition, approximately 30-50% of intensely GLUT3-immunoreactive cell bodies in the inner nuclear layer and ganglion cell layer showed ChAT-IR, while the majority of ChAT-positive cell bodies were also intensely GLUT3 immunoreactive. Analysis at the cellular level using retinal cells in culture revealed similar findings. These results collectively indicate that cholinergic amacrine cells constitute the major component of GLUT3-expressing cells in the rat retina. It is expected that the link demonstrated here between GLUT3 expression and cholinergic amacrine cell population will provide clues for further analyzing GLUT3 function in the retina.

Correlations between cholinergic neurons and muscarinic m2 receptors in the rat retina

Acetylcholine is well established as the neurotransmitter of starburst amacrine cells in the vertebrate retina but their function is poorly understood. We compared the distribution of muscarinic m2 receptors in the rat retina with the localization of the starburst cell processes. mAChR2 immunoreactivity appeared in a central band in the inner plexiform layer, which did not co-localize with the processes of the cholinergic amacrine cells. We found co-labelling of VAChT and ChAT making it highly unlikely that there are undetected cholinergic neurons in rat retina. Most mAChR2 receptors were located far from the cholinergic neurons, suggesting that most of them are unlikely to be associated with conventional cholinergic synapses.

Differential effects of acetylcholine on neuronal activity and interactions in the auditory cortex of the guinea-pig

During normal brain operations, cortical neurons are subjected to continuous cholinergic modulations. In vitro studies have indicated that, in addition to affecting general cellular excitability, acetylcholine also modulates synaptic transmission. Whether these cholinergic mechanisms lead to a modulation of functional connectivity in vivo is not yet known. Herein, the effects were studied of an iontophoretic application of acetylcholine and of the muscarinic agonist, carbachol, on the ongoing activity and co-activity of neurons simultaneously recorded in the auditory cortex of the anaesthetized guinea-pig. Iontophoresis of cholinergic agonists mainly affected the spontaneous firing rates of auditory neurons, affected autocorrelations less (in most cases their central peak areas were reduced), and rarely affected cross-correlations. These findings are consistent with cholinergic agonists primarily affecting the excitability of cortical neurons rather than the strength of cortical connections. However, when changes of cross-correlations occurred, they were usually not correlated with concomitant changes in average firing rates nor with changes in autocorrelations, which suggests a secondary cholinergic effect on specific cortico-cortical or thalamo-cortical connections.

Thermodynamic investigation of camel retina acetylcholinesterase inhibition by cyclophosphamide

The present work addresses the estimation of energy parameters such as Gibb's free energy change (delta G), enthalpy change (delta H); entropy change (delta S) and activation energy (E a) of acetylcholinesterase (AChE, EC 3.1.1.7) from camel retina in the absence and presence of the antineoplastic drug cyclophosphamide (CP). A spectrophotometric method was used for the determination of AChE activity, which was the basis for determination of these parameters. The PZ factor (number of sterically and energetically favorable collisions occurring between CP and AChE) have also been studied in this investigation. The energy parameters obtained in the present investigation were compared with the values reported elsewhere.

The inhibitory effect of cyclophosphamide on camel retina acetylcholinesterase activity

Kinetic parameters for the effect of cyclophosphamide (CP) on the camel retina acetylcholinesterase (AChE) activity were investigated for the first time in the present study. It was found that 18 micrograms of retina protein and an incubation time of 4.0 min were suitable conditions for linear of AChE activity. The CP effect was independent of time of incubation with AChE before the addition of substrate, which shows it reversible action. Moreover, dilution data prove that CP is a reversible inhibitor of camel retina AChE. Cyclophosphamide (0.2-2.4 mM) inhibited activity of camel retina in a concentration-dependent fashion, the IC50 being about 1.17 mM. The Michaelis constant (K(m)) for the hydrolysis of acetylthiocholine iodide was found to be 0.106 mM and the Vmax was 0.765 mumol/min/mg protein. Dixon as well as Lineweaver-Burk plots and their secondary replots indicated that the nature of the inhibition was of the pure noncompetitive type. The value of Ki was estimated as 0.763 mM by the primary Dixon and secondary replots of the Lineweaver-Burk plot.

Acetylcholinesterase in the developing ferret retina

The function of acetylcholinesterase (AChE) is to terminate the action of acetylcholine at the cholinergic synapse. Recent evidence suggests additional roles for acetylcholinesterase as a peptidase and/or a protease which is expressed by growing neurites as part of their invasion of developing neural structures. We report the localization of acetylcholinesterase in developing ferret retina. AChE histochemical staining is seen in the developing inner plexiform layer (IPL) of ferret retina at birth (post-natal day zero, PO), the earliest developmental stage examined. Transient expression is seen at the border between the ganglion cell layer and the nerve fiber layer at P14 and P21. A small amount of transient expression is seen in the outer plexiform layer (OPL) at this age as well. By P28, the transient expression in the OPL is at its peak, and is found at photoreceptor terminals and associated with apparent horizontal cell axons. Labeling is also seen intracellularly in the inner nuclear layer (INL), at the OPL/INL border, suggesting that horizontal cells are the source of the transient AChE expression in the OPL. Overt synaptic profiles also appear in the inner plexiform layer (IPL) at P21 and P28. About 2 days layer, the eyes open and the photoreceptor outer segments are fully developed. By 2 weeks later, at P42, the AChE staining pattern in the retina has taken on its adult appearance: no reaction product in the outer retina; intracellular reaction product in the Golgi apparatus of a subset of amacrine and displaced amacrine cells which manufacture AChE; and extracellular reaction product at both synaptic and non-synaptic sites in the IPL. These data are consistent with a role for AChE as a peptidase early in development, and as an enzyme essential in the termination of synaptic action at mature synapses.