Responses to putative second messengers and odorants in water nose olfactory neurons of Xenopus laevis

Using the whole-cell mode of the patch-clamp technique, we attempted to record inward currents in response to cAMP, inositol 1,4, 5-trisphosphate (IP(3)) and odorants from sensory neurons in the olfactory epithelium of the Xenopus laevis lateral diverticulum (water nose). Dialysis of 100 microM of IP(3) induced inward currents, while dialysis of 1 mM of cAMP into olfactory neurons did not induce any response under the voltage-clamp conditions. Changes in membrane conductance were examined by applying ramp pulses. The slope of the current-voltage (I-V) curve during the IP(3)-induced response was steeper than that after the response, indicating that IP(3) increased the membrane conductance. The water nose olfactory neurons have been shown to respond to both amino acids and volatile odorants. The slopes of I-V curves during responses to amino acids and a volatile odorant, lilial, were similar to those before the responses, suggesting that the total membrane conductance was not changed during responses to amino acids and the volatile odorant.     

Neuronal degeneration and regeneration induced by axotomy in the olfactory epithelium of Xenopus laevis

The olfactory epithelium (OE) has the remarkable capability to constantly replace olfactory receptor neurons (ORNs) due to the presence of neural stem cells (NSCs). For this reason, the OE provides an excellent model to study neurogenesis and neuronal differentiation. In the present work, we induced neuronal degeneration in the OE of Xenopus laevis larvae by bilateral axotomy of the olfactory nerves. We found that axotomy induces specific‐ neuronal death through apoptosis between 24 and 48h post‐injury. In concordance, there was a progressive decrease of the mature‐ORN marker OMP until it was completely absent 72h post‐injury. On the other hand, neurogenesis was evident 48h post‐injury by an increase in the number of proliferating basal cells as well as NCAM‐180– GAP‐43+ immature neurons. Mature ORNs were replenished 21 days post‐injury and the olfactory function was partially recovered, indicating that new ORNs were integrated into the olfactory bulb glomeruli. Throughout the regenerative process no changes in the expression pattern of the neurotrophin Brain Derivate Neurotrophic Factor were observed. Taken together, this work provides a sequential analysis of the neurodegenerative and subsequent regenerative processes that take place in the OE following axotomy. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1308–1320, 2017     

Dendritic Integration in Olfactory Sensory Neurons: A Steady-State Analysis of How the Neuron Structure and Neuron Environment Influence the Coding of Odor Intensity

Response properties of the receptor potential at steady state were analyzed in a biophysical model of an olfactory sensory neuron embedded in a multicell environment. The neuron structure was described as a set of several identical dendrites (or cilia) bearing the transduction mechanisms, joined to a nonsensory part—dendritic knob, soma, and axon. The different ionic compositions of the media surrounding the neuron sensory and nonsensory parts and the extraneuronal voltage sources, which both result from the presence of auxiliary cells, were also taken into account. Analytical solutions were found to describe how the receptor potential at the nonsensory part responds to a uniform change in the odorant-dependent conductance resulting from odorant stimulation of the sensory dendrites. We investigated the influence of various geometrical and electrical parameters on the receptor-potential response in the classical model neuron within a homogeneous environment and in the model neuron surrounded with auxiliary cells. First, it was found that the maximum amplitude of the receptor potential is independent of the neuron structure in the absence of auxiliary cells but not in their presence. In the latter case, the amplitude decreases with the length and number of sensory dendrites and with the input resistance of the nonsensory part. Second, the sensitivity (as measured by the increase in membrane conductance at half-maximum response) of the neuron model in the absence of auxiliary cells is higher, but its dynamic range is narrower than in their presence. The dynamic range is wide and the sensitivity low when the input resistance of the nonsensory part is small and the sensory dendrite is unbranched. Both sensitivity and dynamic range are higher for a longer dendrite. These results help understand the morphology of insect olfactory sensilla and can be generalized to other neuron types.     

Nonselective Suppression of Voltage-gated Currents by Odorants in the Newt Olfactory Receptor Cells

Effects of odorants on voltage-gated ionic channels were investigated in isolated newt olfactory receptor cells by using the whole cell version of the patch–clamp technique. Under voltage clamp, membrane depolarization to voltages between −90 mV and +40 mV from a holding potential (V_h) of −100 mV generated time- and voltage-dependent current responses; a rapidly (< 15 ms) decaying initial inward current and a late outward current. When odorants (1 mM amyl acetate, 1 mM acetophenone, and 1 mM limonene) were applied to the recorded cell, the voltage-gated currents were significantly reduced. The dose-suppression relations of amyl acetate for individual current components (Na⁺ current: I_Na, T-type Ca²⁺ current: I_Ca,T, L-type Ca²⁺ current: I_Ca,L, delayed rectifier K⁺ current: I_Kv and Ca²⁺-activated K⁺ current: I_K(Ca)) could be fitted by the Hill equation. Half-blocking concentrations for each current were 0.11 mM (I_Na), 0.15 mM (I_Ca,T), 0.14 mM (I_Ca,L), 1.7 mM (I_Kv), and 0.17 mM (I_K(Ca)), and Hill coefficient was 1.4 (I_Na), 1.0 (I_Ca,T), 1.1 (I_Ca,L), 1.0 (I_Kv), and 1.1 (I_K(Ca)), suggesting that the inward current is affected more strongly than the outward current. The activation curve of I_Na was not changed significantly by amyl acetate, while the inactivation curve was shifted to negative voltages; half-activation voltages were −53 mV at control, −66 mV at 0.01 mM, and −84 mV at 0.1 mM. These phenomena are similar to the suppressive effects of local anesthetics (lidocaine and benzocaine) on I_Na in various preparations, suggesting that both types of suppression are caused by the same mechanism. The nonselective blockage of ionic channels observed here is consistent with the previous notion that the suppression of the transduction current by odorants is due to the direst blockage of transduction channels.     

Analysis of Possible Involvement of Local Bioelectric Responses in Chilling Perception by Higher Plants Exemplified by <Emphasis Type="Italic">Cucurbita pepo</Emphasis>

Macroelectrodes and electrophysiological setup were used in experiments with stems of 15-day-old pumpkin (Cucurbita pepo L.) seedlings for computer-assisted data recording. It is shown that local bioelectric responses induced by graded local chilling are similar to the receptor potentials of animals. These responses increase gradually with stimulus strength and trigger the action potential generation when a temperature threshold is attained. The excitation threshold of cells in seedling stems displays the phenomenon of accommodation. Parameters of local bioelectric responses induced by intermittent cooling can undergo changes similar to sensitization-habituation patterns. The results indicate that local electrical responses may be involved in early stages of cooling perception in cells of higher plants devoid of locomotive functions.     

桔小实蝇对五种芒果气味挥发性物质的行为反应

为了探究寄主气味挥发物对桔小实蝇行为的影响,本研究应用Y型嗅觉仪测定了桔小实蝇Bactrocera dorsalis(Hendel)成虫对5种芒果气味挥发性物质(乙酸乙酯,α-蒎稀,异松油烯,3-蒈烯和石竹烯)及5种物质混合物的行为反应。结果表明,桔小实蝇雌、雄虫对5种物质及5种物质混合物的行为反应无显著性差异。结果还揭示,桔小实蝇成虫对乙酸乙酯有明显的趋性反应,对异松油烯有明显的忌避反应,而对α-蒎烯、3-蒈烯、石竹烯和5种物质的混合物均没有明显的行为定向反应。说明桔小实蝇成虫对芒果不同气味挥发物的行为反应存在差别,这可为研发桔小实蝇成虫防治新方法提供基础信息。     

Classes and narrowing selectivity of olfactory receptor neurons of Xenopus laevis tadpoles

In olfactory receptor neurons (ORNs) of aquatic animals amino acids have been shown to be potent stimuli. Here we report on calcium imaging experiments in slices of the olfactory mucosa of Xenopus laevis tadpoles. We were able to determine the response profiles of 283 ORNs to 19 amino acids, where one profile comprises the responses of one ORN to 19 amino acids. 204 out of the 283 response profiles differed from each other. 36 response spectra occurred more than once, i.e., there were 36 classes of ORNs identically responding to the 19 amino acids. The number of ORNs that formed a class ranged from 2 to 13. Shape and duration of amino acid-elicited [Ca2+]i transients showed a high degree of similarity upon repeated stimulation with the same amino acid. Different amino acids, however, in some cases led to clearly distinguishable calcium responses in individual ORNs. Furthermore, ORNs clearly appeared to gain selectivity over time, i.e., ORNs of later developmental stages responded to less amino acids than ORNs of earlier stages. We discuss the narrowing of ORN selectivity over stages in the context of expression of olfactory receptors.     

Dopaminergic neurons in the retina of Xenopus laevis: amacrine vs. interplexiform subtypes and relation to bipolar cells

Presumed dopaminergic neurons were visualized in the retina of the clawed frog, Xenopus laevis, by anti-tyrosine hydroxylase (TH) immunoreactivity. The studied cells constitute a uniform population with perikarya at the junction of inner nuclear (INL) and inner plexiform (IPL) layers. Each cell body gives rise to 4–6 relatively stout processes (0.5–2.0 m in diameter) which run for up to 1.2 mm in strata 4–5 of the IPL. These processes have a very asymmetric distribution in the horizontal plane of the retina. A dense plexus of TH fine fibers is distributed uniformly in stratum 1 of the IPL. TH cells are distributed evenly but sparsely (16–20 cells/mm²) across the retina. About 20% of the TH neurons emit 1–3 distally directed fine processes, the majority of which extend < 20 m, which barely suffices to reach the outer plexiform layer (OPL). Other longer processes are typically unbranched; some reach the OPL, others run tangentially in the INL. The axon terminals of Golgi-impregnated bipolar cells are characterized according to the strata of the IPL in which they arborize. About 80% are confined either to strata 1–2 or 3–5, conforming to the off and on zones defined by Famiglietti and Kolb (1976). The remainder appear to end in both zones, some extending across the entire width of the IPL. EM examination showed that TH processes receive bipolar synaptic input in both distal and proximal portions of the IPL.     

Addition of Signal Leader Sequences to the N-Termini of Olfactory Receptor Proteins Enhances Their Expression in Xenopus Oocyte

Several recent papers have reported the difficulties in expressing olfactory receptor proteins (ORs) in heterologous systems, and proposed that some sequences in ORs have negative effects on their efficient expression. To obtain an efficient expression system of ORs, we modified N-terminal sequences of ORs through the addition of exogenous sequences. Three kinds of sequences, designated as 5HT, V, and VL, were used. 5HT and V corresponded to the signal leader (SL) sequences of 5HT₃R and VIPR, respectively. VL corresponded to the first extracellular region of VIPR containing the SL sequence and three potential asparagine- (Asn-) linked glycosylation sites. The myc epitope was also added to the C-termini of the sequences. Several ORs including I7 of rat, GUST43 of rat, Y1 of medaka, FOR1-3 of pufferfish, 47E of carp, and ODR-10 of nematode were subjected to the modifications, and the RNAs encoding modified ORs were injected into Xenopus oocytes. The membrane fraction of the oocytes were analyszed by Western blotting to examine the expression of the proteins. In the cases of ORs modified with 5HT and V, only ODR-10 and 47E, both of which have more than two Asn-linked glycosylation sites in their extracellular regions, were detected as the bands of predicted molecular weights. On the other hand, most of the ORs modified with VL showed the bands of predicted molecular weights. These results suggest that SL sequences together with potential Asn-linked glycosylation sites have positive effects on the expression of ORs in heterologous systems.     

研究: 外膝状体神经元的亮度反应与感受野ON-OFF反应的关系

外膝体是视觉信息进入新皮层的主要通路,其编码亮度信息的神经机制还不清楚.我们采用随机呈现的连续快速变化(50 Hz)的均匀亮度刺激,显著地提高了猫外膝体神经元对均匀亮度的反应强度,通过反相关算法抽提出神经元的亮度反应函数.约81%的神经元的亮度反应函数为单调性上升或下降,有19%的神经元亮度反应函数为V型.通过分析这些神经元对亮度上升和下降的反应强度与感受野ON和OFF反应强度的关系,表明83%的神经元对亮度的反应模式是由其感受野ON-OFF反应的相对强度决定的,其余17%则与其感受野ON-OFF区的兴奋和抑制的变化相关.这些结果揭示了外膝体神经元编码亮度变化的机制.     

Distinct ONE-GC transduction modes and motifs of the odorants: Uroguanylin and CO2

In a subset of the olfactory sensory neurons ONE-GC^$ membrane guanylate cyclase is a central component of two odorant-dependent cyclic GMP signaling pathways. These odorants are uroguanylin and CO₂. The present study was designed to decipher the biochemical and molecular differences between these two odorant signaling mechanisms. The study shows (1) in contrast to uroguanylin, CO₂ transduction mechanism is Ca²⁺-independent. (2) CO₂ transduction site, like that of uroguanylin-neurocalcin δ, resides in the core catalytic domain, aa 880-1028, of ONE-GC. (3) The site, however, does not overlap the signature neurocalcin δ signal transduction domain, ⁹⁰⁸LSEPIE⁹¹³. Finally, (4) this study negates the prevailing concept that CO₂ uniquely signals ONE-GC activity (Sun et al. [19]; Guo et al. [21]). It demonstrates that it also signals the activation of photoreceptor membrane guanylate cyclase ROS-GC1. These results show an additional new transduction mechanism of the membrane guanylate cyclases and broaden our understanding of the molecular mechanisms by which different odorants using a single guanylate cyclase can regulate diverse cyclic GMP signaling pathways.     

树叶凋落物的分解速率对酸性矿山废水污染的响应

按照广东大宝山矿酸性矿山废水对横石水河的酸性污染梯度,从上游到下游在横石水河及其支流设置7个污染样点、3个清洁样点,利用孔径为0.5 mm的分解网袋采集了2种树叶(藜蒴,Castanopsis fissa;荷木,Schima superba),研究树叶凋落物在不同污染梯度下的分解状况.结果表明,随着pH值逐渐升高,水体重金属浓度逐渐降低,2种树叶的分解速率逐渐加快,各污染样点的分解速率均显著低于清洁样点的分解速率(P<0.05),其中藜蒴和荷木的树叶凋落物在清洁点I点的分解速率分别比距离污染源头最近、污染最重的样点A快6.5和10.5倍.回归分析表明,2种树叶的分解速率均与河流的pH值呈正相关.与河流的Cu、Cd、Zn、Pb 4种重金属浓度呈负相关,即河流pH值越低,重金属含量越高,树叶分解速率越慢.说明树叶凋落物的分解速率对水质变化是比较敏感的,可以作为评价河流生态系统完整性的一个参数.     

昆虫感觉气味的细胞与分子机制研究进展

昆虫作为地球上最为成功的类群,已经成功地进化了精细的化学感受系统,通过化学感受系统适应各种复杂的环境,保持种群的繁荣。自1991年在动物中发现嗅觉受体基因以来,关于昆虫感受化学信息的周缘神经系统的分子和细胞机制方面的进展十分迅速。文章主要就昆虫周缘神经系统的感受化学信息的分子和细胞机制进行综述。首先对昆虫感觉气味的细胞机制的研究进展进行简要介绍。昆虫嗅觉神经元在感受化学信息过程中起着极为重要的作用,昆虫嗅觉神经元上表达的嗅觉受体不同而执行着各异的功能。各种嗅觉神经元对于化学信息的感受谱有较大的区别;嗅觉神经元对化学信息类型、浓度、流动动态等产生相应的电生理特征反应。研究表明同一种神经原可以感受多种化学信息,而一种化学信息也可以被多种神经原所感受。由神经原对化学信息感受所形成的特征组合就是感受化学信息的编码。其次较为详细地论述与昆虫感受气味分子相关的一些蛋白质的研究进展。气味分子结合蛋白是一类分子量较小、水溶性的蛋白,主要位于化学感受器神经原树突周围的淋巴液中。在结构上的主要特征是具有6个保守的半光氨酸和由6个α螺旋组成的结合腔。自1981年发现以来,已经在40余种昆虫中发现上百种。由于研究手段的不断进步,已经对该类蛋白的表达特征、结合特性以及三维结构和结合位点进行了大量的研究,提出了多个可能的功能假说,在诸多的假说中,较为广泛接受的是气味分子结合蛋白在昆虫感觉气味的过程中,是与疏水性的气味分子相结合,并将气味分子运输到嗅觉神经原树突膜上的嗅觉受体上。这些处于树突膜上的嗅觉受体则是昆虫感觉气味过程中的另一个十分重要的蛋白质。目前,已经在果蝇、按蚊、蜜蜂和家蚕等10余个昆虫种类中发现上百个嗅觉受体蛋白基因。这类蛋白是跨膜蛋白,一般具有7个跨膜区,整个蛋白的氨基酸残基在400～600个。昆虫的嗅觉受体蛋白的N-端在胞内,而C-端在胞外,这与G耦联蛋白不同。而且,昆虫的一个嗅觉神经元可以表达1～3个嗅觉受体蛋白,也与哺乳动物的一个神经元只表达一种受体蛋白有所不同。每种嗅觉受体可以感受多种气味分子,而一种气味分子可以被多个嗅觉受体所感知,这样组成了感受化学信息的编码谱。最近采用基因敲除技术和膜片钳技术研究发现,昆虫的嗅觉受体蛋白在信号传导中也有特殊性,即嗅觉受体可以直接作为离子通道,而引起动作电位。还有近来的研究表明,神经膜蛋白对于果蝇的性信息素感受神经元感受性信息素cVA是必要的。实际上,昆虫对于化学信息的感受和信号的转导,并不是上述蛋白单独起作用完成的,而是多种蛋白相互作用的结果。论文最后对该领域研究内容进行了展望。     

Responses of the ciliates tetrahymena and paramecium to vertebrate odorants and tastants

The ciliates Tetrahymena and Paramecium respond to strong depolarizing stimuli with Ca(2+)-based action potentials, ciliary reversals, and consequent bouts of backward and forward swimming called "avoidance reactions" (ARs). We found that several representative tastants and odorants cause repetitive ARs in Tetrahymena and Paramecium at low (nM to microM) concentrations. Tetrahymena responded well to capsaicin, quinine, quinacrine, denatonium benzoate, eugenol, piperine, chloroquine, carvacrol, allyl isothiocyanate (AITC), and menthol. Chemosensory adaptation was seen with carvacrol, eugenol, quinacrine, and capsaicin. Cross-adaptation was seen between some of these compounds, suggesting possible similarities in their chemosensory transduction or adaptation pathways. Paramecium only responded well to AITC, quinacrine, piperine, and eugenol (with the effective concentration for 50% response [EC(50)] values in the microM range) while chemosensory adaptation was only seen to eugenol in Paramecium, suggesting possible species differences. Tetrahymena and Paramecium may have primitive receptors that can recognize these and other compounds or some of these compounds can act independently of specific receptors.     

Possible coupling of prostaglandin E receptor EP(1) to TRP5 expressed in Xenopus laevis oocytes

We previously reported that the prostaglandin E(2) (PGE(2)) receptor subtype EP(1) is coupled to intracellular Ca(2+) mobilization in CHO cells, which is dependent on extracellular Ca(2+) in a pertussis toxin-insensitive manner [H. Katoh, et al., Biochim. Biophys. Acta 1244 (1995) 41-48]. However, it remains unknown about the signal transduction involved in this response. To investigate the mechanism regulating Ca(2+) mobilization mediated by EP(1) receptors in detail, we performed a series of experiments using the Xenopus laevis oocyte expression system and found that endogenous G(q) and/or G(11), and not G(i1) is involved in the Ca(2+) mobilization induced by PGE(2). We further investigated the receptor-activated Ca(2+) channel (RACC)-related response by introducing mRNA for mouse transient receptor potential 5 (TRP5), a possible candidate for the RACC, and found effective coupling between them. These results suggest that the EP(1) receptors induce Ca(2+) mobilization via G(q) and/or G(11) and Ca(2+) influx via TRP.     

Transport and membrane binding of the glutamine analogue 6-diazo-5-oxo-L-norleucine (DON) in Xenopus laevis oocytes

Summary We have examined transport and membrane binding of 6-diazo-5-oxo-l-norleucine (DON, a photoactive diazo-analogue of glutamine) and their relationships to glutamine transport in Xenopus laevis oocytes. DON uptake was stereospecific and saturable (V _max of 0.44 pmol/oocyte · min and a K _m of 0.065 mm). DON uptake was largely Na^u+ dependent (80% at 50 m DON) and inhibited (>75%) by glutamine and arginine (substrates of the System B^0,+ transporter) at 1 mm. Glutamine and DON show mutual competitive inhibition of Na⁺-dependent transport. Preincubation of oocytes in medium containing 0.1 mm DON for 24 or 48 hr depressed the V _max for System B^0,+ transport (as measured by Na⁺-dependent glutamine uptake), this effect was highly specific (neither d-DON nor the System B^0,+ substrates glutamine and d-alanine showed any independent effect) and required Na⁺ ions. Glutamine (1 mm in preincubation medium) protected transport from inhibition by DON. The possibility that specific inactivation of System B^0,+ by DON reflects attachment of DON to the transporter was tested by examining the binding of [¹⁴C]DON to Xenopus oocyte membranes. Oocytes incubated in 100 mm NaCl in the presence of [¹⁴C]DON for up to 48 hr showed 2.4-fold higher ¹⁴C-binding to membranes than oocytes incubated in choline chloride. Na⁺-dependent DON binding (31 ± 11 fmol/g membrane protein) was suppressed by external glutamine, arginine or alanine and was largely confined to a membrane protein fraction of 48–65 kDa (as assessed by SDS-polyacrylamide gel electrophoresis). The present studies indicate that DON and glutamine uptake in oocytes are both mediated by System B^0,+ and demonstrate that DON binding to a particular membrane protein fraction is associated with inactivation of the transporter, offering the prospect of using [¹⁴C]DON as a covalent label for the transport protein in order to facilitate its isolation and subsequent biochemical characterization.This work was supported by The Wellcome Trust, Action Research for the Crippled Child, Ajinomoto GmbH, Pfrimmer GmbH, the Rank Prize Funds, the Medical Research Council and the University of Dundee. We are grateful to Dr. C.I. Pogson (Wellcome Research Laboratories) and Drs. J.C. Ellory and B. Elford (University of Oxford) for gifts of [¹⁴C]DON.     

Calcium oscillations in the olfactory nonsensory cells of the goldfish, Carassius auratus

Background

The olfactory nonsensory cells contribute to the maintenance of normal functions of the olfactory epithelium (OE). Specifically, the ciliated nonsensory cells of teleosts play important roles in the odorant detection by OE in aqueous environment. Their cilia show strong beating activities and cause water flow at the OE surface, making the detection of odorants by OE more efficient. Because intracellular Ca²⁺ level has been reported to play an important role in ciliary beating, the ciliary beating activity may be regulated by intracellular Ca²⁺ dynamics of these ciliated nonsensory cells.

Methods

We performed Ca²⁺ imaging experiments to analyze the Ca²⁺ dynamics in acutely dissociated OE cells of the goldfish. Furthermore, we examined the contribution of the Ca²⁺ dynamics to the ciliary beating frequency (CBF) at the surface of the intact OE.

Results

Olfactory nonsensory cells showed both spontaneous intracellular Ca²⁺ oscillations and propagating intercellular Ca²⁺ waves. Application of 2-aminoethoxydiphenylborate (2-APB), which antagonizes IP₃-induced Ca²⁺ release from intracellular stores suppressed these Ca²⁺ oscillations. Furthermore, 2-APB application to the intact OE lamellae resulted in the decrease of CBF at the surface of the OE.

Conclusions

These results indicate that spontaneous intracellular calcium oscillations persistently up-regulate the ciliary beating at the surface of the OE in teleosts.

General significance

Ciliary beating activity at the surface of OE can be regulated by the Ca²⁺ dynamics of olfactory nonsensory cells. Because this ciliary movement causes inflow of external fluid into the nostril, this regulation is suggested to influence the efficiency of odorant detection by OE.     

Solubilization and Biochemical Characterization of the Melatonin Deacetylase from Xenopus laevis Retina

Abstract: Melatonin deacetylase, an enzyme activity recently discovered in the Xenopus laevis retina, regulates local melatonin levels. The deacetylase occurs in retina, retinal pigment epithelium, and skin, all sites of melatonin action, and is widely distributed among vertebrates. We have solubilized the enzyme from Xenopus retina and pigment epithelium using nonionic detergents, and have developed a specific enzyme assay. We have characterized the enzyme and now report that the deacetylase is relatively specific for melatonin and is inhibited by the melatonin precursor N -acetylserotonin and the product of the deacetylase, 5-methoxytryptamine. Inhibition of deacetylase activity by eserine (physostigmine) suggests a relationship between deacetylase and cholinesterase activities. However, among a variety of cholinesterase inhibitors tested, only eserine inhibits the deacetylase. Furthermore, eserine is much less potent as an inhibitor of the deacetylase than the cholinesterases, and purified cholinesterases failed to deacetylate melatonin. We also show that melatonin deacetylase and aryl acylamidase (an enzyme related to cholinesterases) activities are differentially extractable from Xenopus ocular tissues, and that they exhibit different pH optima and inhibition profiles. Our results provide an initial characterization of the Xenopus retinal melatonin deacetylase, and indicate that deacetylase activity is distinct from cholinesterase and aryl acylamidase activities.