Effect of taurine on neurotransmitter release from insect synaptosomes

Distribution of taurine and other free amino acids in the visual pathway of the crayfish procambarus clarkii

1. Free taurine showed an in homogenous distribution along the neuropiles associated with the visual processing pathway in the eyestalk and brain of the freshwater crayfish Procambarus clarkii.2. Within the eyestalk, taurine was statistically significant (P < 0.001), more Concentrated in the retina(photo reccptor layer) lamina ganglionaris region than in the medulla extema-medulla interna and medulla terminalis regions; 64% of the total content (45% in terms of total concentration) of taurine in the eyestalk was localized in the retina-lamina ganglionaris zone.3. Regarding other free amino acids also identified, and considering the whole eyestalk, taurine concentration was comparable with those of alanine and glycine, but statistically significantly higher than glutamate, GABA and aspartate. In the brain (cerebroid ganglion) taurine, alanine, glycine, glutamate and GABA concentrations, albeit not identical, were not statistically significantly different; only the aspartate concentration was significantly lower (P < 0.001).4. These results show that taurine is a major constituent in the anterior part of the crayfish central nervous system and support the notion that this free amino acid could play a physiologically important role in the crustacean visual pathway.

Manipulation of host behavior by parasitic insects and insect parasites

Parasites often alter the behavior of their hosts in ways that are ultimately beneficial to the parasite or its offspring. Although the alteration of host behavior by parasites is a widespread phenomenon, the underlying neuronal mechanisms are only beginning to be understood. Here, we focus on recent advances in the study of behavioral manipulation via modulation of the host central nervous system. We elaborate on a few case studies, in which recently published data provide explanations for the neuronal basis of parasite-induced alteration of host behavior. Among these, we describe how a worm may influence the nervous system of its cricket host and manipulate the cricket into committing suicide by jumping into water. We then focus on Ampulex compressa, which uses an Alien-like strategy for the sake of its offspring. Unlike most venomous hunters, this wasp injects venom directly into specific cerebral regions of its cockroach prey. As a result of the sting, the cockroach remains alive but immobile, but not paralyzed, and serves to nourish the developing wasp larva.

Nitric oxide: a co-modulator of efferent peptidergic neurosecretory cells including a unique octopaminergic neurone innervating locust heart

Our findings suggest that nitric oxide (NO) acts as peripheral neuromodulator in locusts, in which it is commonly co-localized with RF-like peptide in neurosecretory cells. We also present the first evidence for NO as a cardio-regulator in insects. Putative NO-producing neurones were detected in locust pre-genital free abdominal ganglia by NADPH-diaphorase histochemistry and with an antibody against NO synthase (NOS). With both methods, we identified the same 14 somata in each examined ganglion: two dorsal posterior midline somata; six ventral posterior midline somata; and three pairs of lateral somata. A combination of NOS-detection methods with nerve tracing and transmitter immunocytochemistry revealed that at least 12 of these cells were efferent, of which four were identified as peptidergic neurosecretory cells with an antiserum detecting RFamide-like peptides. One of the latter was unequivocally identified as an octopaminergic dorsal unpaired median (DUM) neurone, which specifically projected to the heart ("DUM-heart"). Its peripheral projections revealed by axon tracing appeared as a meshwork of varicose endings encapsulating the heart. NOS-like immunoreactive profiles were found in the heart nerve. NO donors caused a dose-dependent increase in heart rate. This cardio-excitatory effect was negatively correlated to resting heart rate and seemed to be dependent on the physiological state of the animal. Hence, NO released from neurones such as the rhythmically active DUM-heart might exert continuous control over the heart. Possible mechanisms for the actions of NO on the heart and interactions with other neuromodulators co-localized in the DUM-heart neurone (octopamine, taurine, RF-amide-like peptide) are discussed.

Parasitoid wasp sting: A cocktail of GABA, taurine, and β-alanine opens chloride channels for central synaptic block and transient paralysis of a cockroach host

The wasp Ampulex compressa injects venom directly into the prothoracic ganglion of its cockroach host to induce a transient paralysis of the front legs. To identify the biochemical basis for this paralysis, we separated venom components according to molecular size and tested fractions for inhibition of synaptic transmission at the cockroach cercal-giant synapse. Only fractions in the low molecular weight range (<2 kDa) caused synaptic block. Dabsylation of venom components and analysis by HPLC and MALDI-TOF-MS revealed high levels of GABA (25 mM), and its receptor agonists beta-alanine (18 mM), and taurine (9 mM) in the active fractions. Each component produces transient block of synaptic transmission at the cercal-giant synapse and block of efferent motor output from the prothoracic ganglion, which mimics effects produced by injection of whole venom. Whole venom evokes picrotoxin-sensitive chloride currents in cockroach central neurons, consistent with a GABAergic action. Together these data demonstrate that Ampulex utilizes GABAergic chloride channel activation as a strategy for central synaptic block to induce transient and focal leg paralysis in its host.

Regulatory role of nitric oxide over extracellular taurine in the hippocampus of freely moving rats

We have studied the effects of drugs which manipulate nitric oxide (NO) levels as well the effect of N-methyl-d-aspartate (NMDA) infusion on extracellular taurine in rat hippocampus using in vivo microdialysis. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) increased dialysate taurine in a concentration-dependent manner, and this effect was blocked by the inhibitor of soluble guanylate cyclase1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ). NMDA (100 microM) increased hippocampal taurine release, an effect that was reversed by the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5; 10 microM). The non-selective nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (L-NAME; 100 microM and 1.0 mM) increased extracellular taurine in a concentration-dependent manner while 7-nitroindazole (7-NI), a relatively selective neuronal NOS (nNOS) inhibitor, at the same concentrations decreased extracellular taurine. L-NAME (1.0 mM) infused prior to NMDA did not alter the effect of NMDA on extracellular taurine having an effect essentially identical to that seen with L-NAME infused alone. In contrast, when 7-NI was infused for 30 min prior to NMDA, taurine levels were no longer increased above basal. This suggests to us that taurine efflux is mediated by two different mechanisms: an NMDA-evoked, 7-NI-sensitive pathway which may be dependent on cyclic guanosine monophosphate formation, and an L-NAME-modulated mechanism which presumably involves other members of the NOS group of enzymes than nNOS alone.

Biochemical and histological changes in the brain of the cricket Nemobius sylvestris infected by the manipulative parasite Paragordius tricuspidatus (Nematomorpha)

Hairworms (nematomorpha) alter the behaviour of their insect hosts, making them commit 'suicide' by jumping into an aquatic environment required by the adult parasite for the continuation of its life cycle. To explore the physiological and neuronal basis of this behavioural manipulation, we first performed a biochemical study to quantify different neurotransmitters or neuromodulators (monoamines and amino acids) in the brain of crickets (Nemobius sylvestris) uninfected and infected by the hairworm Paragordius tricuspidatus. We also analysed several polyamines and amino-acids having no known neuromodulatory function. The presence/absence of the parasite explained the largest part of the variation in compound concentrations, with infected individuals displaying on average lower concentrations than uninfected individuals. However, for three amino acids (taurine, valine and tyrosine), a significant part of the variation was also correlated with the manipulative process. In order to compare neurogenesis between infected and uninfected crickets, we also performed a histological study on mushroom bodies in the cricket's brain. The mitotic index exhibited a two-fold increase in infected crickets as compared with uninfected crickets. This is the first study to document changes in the brain of insects infected by nematomorphs.

Colocalisation of taurine- with transmitter-immunoreactivities in the nervous system of the migratory locust

The expression of taurine immunoreactivity (TAU-IR) by neurones immunoreactive for octopamine (OA-IR), gamma-aminobutyric acid (GABA-IR), and the C-terminal peptide sequence arginine-phenylalanine (RFamide-IR) was investigated in the migratory locust (Locusta migratoria). TAU-IR is colocalised with OA-IR in the dorsal unpaired median neurones, which are efferent neuroparacrine cells. TAU-IR is not, however, expressed by OA-IR interneurones in the thoracic ganglia and brain. The only other TAU-IR somata found with peripheral axons are the medial neurosecretory cells in abdominal ganglia that project to the neurohaemal organs. These cells exhibit RFamide-IR. The majority of TAU-IR somata in the thoracic abdominal nervous system exhibit GABA-IR. These cells correspond to populations of identified local and intersegmentally projecting inhibitory interneurones. TAU-IR is not, however, exhibited by the well-known GABAergic common inhibitor neurones, which have peripherally projecting axons. This differential distribution of TAU-IR in basically two, functionally different, neuronal subsets (efferent neurosecretory and neuroparacrine cells, inhibitory interneurones) conforms with the concept of taurine acing as a depressive agent to limit excitation during stressful conditions.

Quantitative analysis of the combination dose-effects of taurine and taurine analogues on the phosphorylation of an approximately 44-Kd protein present in a mitochondrial subfraction of rat heart

Combinations of taurine and analogues of taurine that partially contain the N-C-C-S moiety within a semirigid saturated ring structure were tested for their effects on the phosphorylation of an approximately 44-Kd protein present in the mitochondrial fraction of rat heart. (+/-)Piperidine-3-sulfonic acid (PiP), an inhibitor of the phosphorylation of the approximately 44-Kd protein with activity approximately similar to that of taurine, was observed to be mutually exclusive with taurine, i.e., to have a similar mode of action. The combination of taurine plus PiP in a fixed ratio mixture of 1:1 was slightly antagonistic at all concentrations. (+/-)Aminotetrahydrothiopyran-1,1-dioxide (APS), a sulfone derivative of taurine with a net positive charge, also has approximately the same inhibitory activity as taurine. However, APS was mutually nonexclusive with taurine when tested in combination and thus appears to act independently of taurine. Taurine plus APS in a fixed ratio mixture of 3:1 was highly antagonistic at low concentrations of the mixture, approached an additive relation at 50% saturation, and became synergistic at high concentrations of the mixture. Three analogues of taurine, pyridine-3-sulfonic acid (PyS), quinoline-8-sulfonic acid (QS), and 2-aminobenzenesulfonic acid (ABS), that have the basic taurine structure (N-C-C-S) partially in a semirigid unsaturated ring structure stimulate the phosphorylation of the approximately 44-Kd protein. Due to the unsaturated ring structure, these analogues of taurine have a net negative charge at physiologic pH and are not zwitterions. When PyS, QS, or ABS was titrated in the presence of a fixed concentration of taurine (10 mM), there was a competitive relation even though their electronic nature is quite different than that of taurine. The combination of QS plus PyS (1:5) appears to progress through a transition from being synergistic at low concentrations of the fixed ratio mixture, additive at 50% saturation, and finally antagonistic at high concentration of the fixed ratio mixture.

Purification of toxic peptides and the amino acid sequence of CSTX-1 from the multicomponent venom of Cupiennius salei (Araneae:Ctenidae)

The venom of the wandering spider Cupiennius salei was analysed biochemically by gel filtration, cation exchange chromatography, RP-HPLC, IEF, SDS-PAGE and TLC-electrophoresis. The native venom contains high levels of Na+, K+, Ca2+, histamine and taurine. It shows considerable activity of hyaluronidase, but not proteolytic activity. Thirteen peptides (CSTX-1 to CSTX-13) with an apparent mol. wt between 2.6 and 12.5 kDa causing differently strong toxic, effects were purified. Toxicity data of the crude venom (insects and mouse) are given and compared with the toxicity of CSTX-1, which causes most of the crude venom's toxicity. CSTX-1 has a mol. wt of 8352.6 and its amino acid sequence of 74 amino acids is given.

Taurine-like immunoreactivity in octopaminergic neurones of the cockroach, Periplaneta americana (L.)

Taurine (2-aminoethanesulphonic acid) is reported to interact with the octopaminergic system. The distribution of taurine-like immunoreactivity (-LIR) in relation to octopamine-like immunoreactive dorsal unpaired median (DUM) neurones was investigated with the aim of revealing possible colocalization of these two neuromediators. The specificity of the anti-taurine serum used was demonstrated by dot blot immunoassay and by use of preabsorption controls. There was no crossreactivity with octopamine. The specificity of the octopamine antiserum employed has been described elsewhere. Taurine-LIR could be demonstrated in large dorso-median cells in the suboesophageal and the mesothoracic ganglion as well as in the abdominal ganglia. In addition taurine-LIR is distributed in numerous other regions of the ganglia. A comparison of the immunostaining for taurine and octopamine indicates that several of the taurine-like immunoreactive (-LI) neurones are probably members of the octopamine-immunoreactive DUM cell population. These taurine-LI neurones resemble octopamine-LI DUM cells in soma position and size as well as in the projections of their primary neurites. Colocalization of octopamine-LIR and taurine-LIR within the same neuronal element could be shown by alternate immunostaining of consecutive sections. It is probable that all octopamine-LI DUM neurones also exhibit taurine-LIR, and the possible physiological significance of this coexistence is discussed.

Release of GABA and taurine from brain slices

In brain slices the mechanisms of release of GABA have been extensively studied, but those of taurine markedly less. The knowledge acquired from studies on GABA is, nevertheless, still fragmentary, not to speak of that obtained from the few studies on taurine, and firm conclusions are difficult, even impossible, to draw. This is mainly due to methodological matters, such as the diversity and pitfalls of the techniques applied. Brain slices are relatively easy to prepare and they represent a preparation that may most closely reflect relations prevailing in vivo, since the tissue structure and cellular integrity are largely preserved. In our opinion the most recommendable method at present is to superfuse freely floating agitated slices in continuously oxygenated medium. Taurine is metabolically rather inert in the brain, whereas the metabolism of GABA must be taken into account in all release studies. The use of inhibitors of GABA catabolism is discouraged, however, since a block in GABA metabolism may distort relations between different releasable pools of GABA in tissue. It is not known for sure how well, and homogeneously, incubation of slices with radioactive taurine labels the releasable pools but at least in the case of GABA there may prevail differences in the behavior of labeled and endogenous GABA. It is suggested therefore that the results obtained with radioactive GABA or taurine should be frequently checked and confirmed by analyzing the release of respective endogenous compounds. The spontaneous efflux of both GABA and taurine from brain slices is very slow. The magnitude of stimulation of GABA release by homoexchange is greater than that of taurine under the same experimental conditions. However, the release of both amino acids is generally enhanced by a great number of structural analogs, the most potent being those which are simultaneously the most potent inhibitors of uptake. This may result in part from inhibition of reuptake of amino acid molecules released from slices but the findings may also signify that the efflux of GABA and taurine is at least partially mediated by the membrane carriers operating in an outward direction. It is thus advisable not to interpret that stimulation of release in the presence of uptake inhibitors solely results from the block of reuptake of exocytotically released molecules, since changes in the carrier-mediated transport are also likely to occur upon stimulation. The electrical and K+ stimulation evoke the release of both GABA and taurine. The evoked release of GABA is several-fold greater than that of taurine in slices from the adult brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Taurine-like immunoreactivity in photoreceptor cells and mushroom bodies: a comparison of the chemical architecture of insect nervous systems

Taurine is one of the most abundant amino acids found in the tissues of insect nervous systems. The distribution of taurine-like immunoreactivity was investigated in compound eyes, ocelli and mushroom bodies of Drosophila and Locusta. A comparison to the previously described taurine-like immunoreactivity in the brain of worker honeybees (J. Comp. Neurol., 268 (1988) 60-70) showed that the photoreceptor cells of all three insect species are immunoreactive. Immunoreactive mushroom body intrinsic Kenyon cells were also found in all three species. The intensity of the immunoreactivity was however graded, depending on the species. While the majority of Kenyon cells were stained in Apis and Drosophila, the immunoreactivity of the locust mushroom body was mainly confined to the intrinsic neurons originating in the accessory calyx.

Inhibition by taurine of the phosphorylation of specific synaptosomal proteins in the rat cortex: effects of taurine on the stimulation of calcium uptake in mitochondria and inhibition of phosphoinositide turnover

It has been previously observed that taurine inhibits PKC-activated phosphorylation of specific proteins including a approximately 20k Mr protein in rat cortical synaptosomes. In the present study, the mechanism of the above effects of taurine were investigated. In an intrasynaptosomal cytosol fraction obtained by subcellular fractionation, taurine did not have inhibitory effects on protein phosphorylation. However, taurine did inhibit the phosphorylation of the approximately 20k Mr protein in a reconstituted preparation containing intrasynaptosomal cytosol and mitochondria. Experiments measuring calcium uptake demonstrated that taurine increased the accumulation of 45Ca2+ in the mitochondrial fraction in incubation systems both in the absence and presence of added ATP. In addition, taurine inhibited the accumulation of 32P-labeled phosphatidic acid in synaptosomes indicative of a reduction in the levels of diacylglycerol. These results suggest that taurine may inhibit specific protein phosphorylation both by reducing cytosolic calcium levels and by inhibiting the turnover of phosphoinositides. These effects of taurine on the signal transduction cascade involving PKC and phosphoinositide metabolism indicate a potential biological role for taurine in the nervous system.