Classical Transmitters Research Articles

Classical neurotransmitters in the ovijector of Ascaris suum: localization and modulation of muscle activity.

Ascaris suum possesses a well-developed nervous system which is regulated by a number of classical neurotransmitters including acetylcholine (ACh), gamma-aminobutyric acid (GABA), glutamate and serotonin. The vagina vera, the distal part of the ovijector, displays intrinsic, rhythmic activity which has been shown to be modulated by FMRFamide-related peptides (FaRPs) in vitro. Confocal scanning laser microscopy coupled with immunocytochemistry, and histochemical studies, revealed that the nerve plexus of the ovijector contains GABAergic and glutamatergic innervation. Although no distinctive cholinergic or serotoninergic innervation was apparent, cholinesterase activity was localized to discrete areas of the musculature of the vagina vera. The effects of classical transmitters on the activity of the vagina vera in vitro were examined. ACh was excitatory, stimulating a brief but powerful contraction of the vagina vera with a threshold for activity of 1 microM. Both GABA and glutamate were inhibitory, causing a cessation of contractile activity at high concentrations (> 10 microM). Although less potent than glutamate, GABA had more profound effects and induced longer-lasting paralysis of the tissue. The threshold concentrations for activity were 5 microM for glutamate and 10 microM for GABA. Serotonin had no consistent effect on the vagina vera. This study demonstrates that classical transmitters modulate the activity of the ovijector of A. suum.

Physiological and pharmacological studies on nematodes

Classical transmitters and neuroactive peptides act as transmitters or modulators within the central and peripheral nervous systems of nematodes, for example Ascaris suum and Caenorhabditis elegans. Acetylcholine (ACh) and gamma-aminobutyric acid (GABA) are respectively the excitatory and inhibitory transmitters onto somatic body wall muscle while 5-hydroxytrypamine (5-HT) is the excitatory transmitter onto pharyngeal muscle. 5-HT also reduces ACh-induced contractions of somatic muscle and this action of 5-HT is mediated through activation of adenylate cyclase while that on pharyngeal muscle is mediated through inositol phosphate activation. Glutamate, dopamine and octopamine also have transmitter roles in nematodes. Neuroactive peptides of the RFamide family can excite somatic muscle, for example, AF-1 (KNEFIRFamide), AF-2 (KHEYLRFamide), AF-3 (AVPGVLRFamide) and AF-4 (GDVPGVLRFamide) or inhibit and relax this muscle, for example, PF-1 (SDPNFLRFamide), PF-2 (SADPNFLRFamide) and PF-4 (KPNlRFamide). In addition PF-3 (AF-8) (KSAYMRFamide) has a biphasic action on pharyngeal muscle, excitation followed by inhibition while AF-1 only inhibits this muscle. The peptide effects can be either pre- or postsynaptic or both and are likely to be mediated through second messenger systems. In addition these peptides modulate the action of classical transmitters, particularly ACh.

The loading of neurotransmitters into synaptic vesicles

Classical (non-peptide) transmitters are stored into secretory vesicles by a secondary active transporter driven by a V-type H +-ATPase. Five vesicular neurotransmitter uptake activities have been characterized in vitro and, for three of them, the transporters involved have been identified at the molecular level using cDNA cloning and/or Caenorhabditis elegans genetics. These transporters belong to two protein families, which are both unrelated to the Na +-coupled neurotransmitter transporters operating at the plasma membrane. The two isoforms of the mammalian vesicular monoamine transporter, VMAT1 and VMAT2, are related to the vesicular acetylcholine transporter (VACHT), while a novel, unrelated vesicular inhibitory amino acid transporter (VIAAT), also designated vesicular GABA transporter (VGAT), is responsible for the storage of GABA, glycine or, at some synapses, both amino acids into synaptic vesicles. The observed effects of experimentally altered levels of VACHT or VMAT2 on synaptic transmission and behavior, as well as the recent awareness that GABAergic or glutamatergic receptors are not always saturated at central synapses, suggest a potential role of vesicular loading in synaptic plasticity.

Peptide Cotransmitter Release from Motorneuron B16 inAplysia californica: Costorage, Corelease, and Functional Implications

Many neurons contain multiple peptide cotransmitters in addition to their classical transmitters. We are using the accessory radula closer neuromuscular system of Aplysia, which participates in feeding in these animals, to define the possible consequences of multiple modulators converging on single targets. How these modulators are released onto their targets is of critical importance in understanding the outcomes of their modulatory actions and their physiological role. Here we provide direct evidence that the partially antagonistic families of modulatory peptides, the myomodulins and buccalins, synthesized by motorneuron B16 are costored and coreleased in fixed ratios. We show that this release is calcium-dependent and independent of muscle contraction. Furthermore, we show that peptide release is initiated at the low end of the physiological range of motorneuron firing frequency and that it increases with increasing motorneuron firing frequency. The coordination of peptide release with the normal operating range of a neuron may be a general phenomenon and suggests that the release of peptide cotransmitters may exhibit similar types of regulation and plasticity as have been observed for classical transmitters. Stimulation paradigms that increase muscle contraction amplitude or frequency also increase peptide release from motor neuron B16. The net effect of the modulatory peptide cotransmitters released from motorneuron B16 would be to increase relaxation rate and therefore allow more frequent and/or larger contractions to occur without increased resistance to antagonist muscles. The end result of this modulation could be to maximize the efficiency of feeding.

Oxytocin, motherhood and bonding.

Release of the peptide hormone oxytocin in the brain has been shown to influence both maternal, sexual and social bonding behaviours although there are a number of species differences. This review summarizes findings on the distributions of oxytocin and oxytocin receptors in the brain, together with factors governing their expression, release of the peptide in the brain and its behavioural actions. A model of how oxytocin may act to alter maternal and socio-sexual behaviours is proposed which initially involves activation of oxytocin neurones in a single brain site, the paraventricular nucleus of the hypothalamus (PVN), following vaginal and cervical stimulation. This causes a co-ordinated release of the peptide in the PVN and its terminal projection regions for up to 1 h and this promotes different behavioural components, primarily through modulation of classical transmitter systems.

Release of classical transmitters and nitric oxide in the rat olfactory bulb, evoked by vaginocervical stimulation and potassium, varies with the oestrus cycle.

In vivo microdialysis was used to investigate the effects of ovariectomy and the oestrus cycle on vaginocervical stimulation-evoked classical transmitter and nitric oxide release in the olfactory bulb of anaesthetized (urethane) and conscious rats. During pro-oestrus/oestrus, vaginocervical stimulation (1 or 10 min) significantly increased concentrations of glutamate, aspartate, GABA, noradrenaline, dopamine and nitric oxide (citrulline) but failed to do so in met-oestrus/di-oestrus or following ovariectomy. Potassium chloride-evoked GABA, noradrenaline and nitric oxide release in the olfactory bulb was also significantly enhanced during pro-oestrus/oestrus. The effects of vaginocervical stimulation on olfactory bulb transmitter release during pro-oestrus/oestrus were significantly reduced by pelvic or vagus nerve section. Basal concentrations of classical transmitters and nitric oxide in the olfactory bulb did not vary across the oestrus cycle although noradrenaline and dopamine levels were reduced following ovariectomy. These results confirm our previous electrophysiological data showing that the olfactory bulb mitral cells are only excited by vaginocervical stimulation during pro-oestrus/oestrus. They also suggest that sex hormones acting primarily at the level of the olfactory bulb dramatically enhance the ability of vaginocervical stimulation to evoke release of both classical transmitters and nitric oxide in this region. Such alterations in neurochemical release in the olfactory bulb may be important for mediating plasticity changes underlying olfactory recognition of mates or offspring.

Study of the bidirectional transport of choline by blocking choline carriers from outside or inside brain nerve terminals.

Membrane carriers can operate bidirectionally. We studied, in rat neocortex synaptosomes, the choline carrier by comparing the ability of the transport inhibitor hemicholinium-3, present outside or inside the nerve terminals, to prevent uptake and release of [(3)H]choline. Because hemicholinium-3 is membrane-impermeable, it was previously entrapped into synaptosomes during homogenization of brain tissue. External and internalized hemicholinium-3 produced similar maximal inhibition (80-90%) of [(3)H]choline uptake. Also comparable (approximately 30 nM) are the potency of externally applied hemicholinium-3 and the estimated potency of the entrapped inhibitor. Exposure to ouabain elicited release of both [(3)H]acetylcholine and [(3)H]choline from synaptosomes prelabeled with [(3)H]choline. The ouabain (300 microM)-evoked release of [(3)H]choline only was blocked by externally added (IC(50) approximately 10 nM) or internalized (estimated IC(50) approximately 5 nM) hemicholinium-3. Release of previously taken up [(3)H]choline elicited by 100 microM external choline (homoexchange) was prevented by external (IC(50) approximately 30 microM) or entrapped (estimated IC(50) approximately 20 microM) hemicholinium-3. The results suggest that the choline carriers fit into the alternating-access model proposed for classical transmitter transport. Entrapping nonpermeant ligands into synaptosomes could allow investigation of the inward-facing conformation of native transporters and how cytoplasmic ligands affect the bidirectional transport of neurotransmitters.

Measurement of cholecystokinin release in vivo in the rat spinal dorsal horn

The microdialysis technique, used to monitor extracellular levels of transmitter substances in the central nervous system of laboratory animals as a reflection of transmitter release, is based on the ability of neurotransmitters to diffuse in the extracellular fluid from the site of release and to cross a semipermeable dialysis membrane. Even though the surgical procedure is not very complicated, the detection of released substances in the recovered dialysate may be difficult. Especially, the measurement of neuropeptide release is limited by the low extracellular concentration and of low recovery as compared to, for example, monoamines. Thus, for example, cholecystokinin (CCK), which is the most abundant neuropeptide in the central nervous system, is found at concentrations that are several orders of magnitude lower than those of classical transmitters. Therefore a highly sensitive detection method is of utmost importance. In the dorsal horn of the spinal cord CCK is found mainly in interneurons and in terminals of descending fibers. CCK seems to be involved in nociceptive transmission and CCK attenuates morphine-induced antinociception. We here describe in vivo microdialysis in the lumbar dorsal horn of the rat with subsequent quantification of the level of CCK-like immunoreactivity (-LI) by a highly sensitive radioimmunoassay. Theme: Neurotransmitters, modulators, transporters, and receptors Topic: Peptides: anatomy and physiology

Galanin and NPY, two peptides with multiple putative roles in the nervous system.

In the present brief overview we summarize results from several studies focusing on two neuropeptides, galanin and neuropeptide Y (NPY) in discrete neuronal systems, where they coexist with classic transmitters. On the basis of studies in different animal models we propose that these peptides may be involved in regulation of certain CNS functions and that drugs acting on their receptors may be of use in new therapeutic strategies. At the spinal level galanin and NPY are regulated in DRG neurons by nerve injury and in dorsal horn neurons by inflammation. It is possible that this leads to attenuation of pain sensitivity. Moreover, both peptides may exert trophic effects, for example to enhance regeneration. In the hypothalamic arcuate nucleus NPY and its receptors are part of the feeding circuitry, and we suggest that derangement of these NPY neurons may at least in part underlay the lethal phenotype of anorectic mice, which die 22 days postnatally after showing decreased food intake and growth retardation. Expression of NPY and NPY receptors is changed in the hippocampus of mice comparatively early after prion inoculation, indicating that this peptide system is affected in this spongiform degenerative disease in a region of importance for learning and memory. Finally, galanin is co-localized with classic monoamine transmitters in two central systems, the dorsal raphe serotonin neurons and the locus coeruleus noradrenergic neurons. In both cases galanin causes hyperpolarization (at high concentrations) and prolongs monoamine-induced outward currents (at low concentrations), thus modulating activity in two systems of importance for many brain functions including mood regulation. It may therefore be interesting to analyse to what extent drugs affecting galaninergic transmission also may be efficient in the treatment of, for example, depression.

Immunocytochemical evidence of vesicular localization of the orphan transporter Rxt1 in the rat spinal cord

Rxt1, a member of the Na +/Cl − orphan transporter family, exhibits numerous features suggesting a role as plasma membrane transporter. Despite numerous attempts, its substrate has not yet been identified, although immunocytochemical studies have shown that Rxt1 distribution generally matches that of glutamate or GABA. In order to further characterize Rxt1, its detailed immunocytochemical distribution in the rat spinal cord and dorsal root ganglia was studied at both light microscope and ultrastructural levels. The widespread distribution of Rxt1 in spinal cord and ganglia cannot be correlated with any known classical or peptidergic transmitter. Rxt1 is expressed in a subpopulation of glutamatergic primary afferent fibers, in large and medium-sized ganglion cells, while small glutamate cells exhibit generally no Rxt1-like immunoreactivity. In the spinal cord, Rxt1-immunoreactive cell body distribution is quite ubiquitous since Rxt1 is expressed in all laminae in various neuronal types like interneurons, some projection neurons and motoneurons. Some of these neurons are cholinergic. At the electron microscope level, the peroxidase labeling was never localized to the plasma membrane, but rather associated with different organelles including the outer membrane of small synaptic vesicles and large granular vesicles. This localization resembles that of vesicular transporters detected with the same method and suggests that Rxt1, in contrast to other Na +/Cl − transporters, is expressed on vesicles. This was confirmed using a pre-embedding silver-intensified colloidal gold method. Indeed, most gold particles appeared to be localized into the axoplasm on synaptic vesicle accumulations; only few gold particles were observed close to the plasma membrane. These results suggest that Rxt1, despite its molecular characteristics predicting a plasma membrane localization, might be a vesicular transporter.

Future developments.

Neuronal signalling cannot always be reduced to classical synaptic transmission resulting in a binary inhibition or excitation. Many types of molecules that are bioactive do not fit readily into the profile of a classical neurotransmitter. Release of bioactive substances can occur beyond the familiar axonal synapse. The actions of bioactive substances, including classical transmitters, can be modulatory, global and long term. It is erroneous to extrapolate from events at the level of the neuron or gene to wholescale functions and dysfunctions. The actions of bioactive substances have to be appreciated within the context of neuronal populations, and in turn within the holistic anatomical context of the brain. Molecular biology will contribute to this more precise understanding of the relationship between individual genes, gene mutations, molecular and cellular phenotypes, and corresponding functions and dysfunctions.

Do all of human midbrain tyrosine hydroxylase neurons synthesize dopamine?

We examined whether all of human midbrain tyrosine hydroxylase (TH) neurons substantially synthesize dopamine (DA) using dual labeling immunohistochemical technique of TH and aromatic l-amino acid decarboxylase (AADC). In the substantia nigra, besides many neurons doubly stained for TH and AADC, neurons stained only for TH and only for AADC (D-neurons [C.B. Jaeger, D.A. Ruggiero, V.R. Albert, T.H. Joh, D.J. Reis, Immunocytochemical localization of aromatic l-amino acid decarboxylase, in: A. Björklund, T. Hökfelt (Eds.), Handbook of Chemical Neuroanatomy, Classical Transmitters in the CNS, Vol. 2, Part 1, Elsevier, Amsterdam, 1984, pp. 387–408.]) were identified. In the ventral tegmental area, dually labeled neurons and TH-only-positive neurons were found. It is indicated that the number of midbrain TH neurons does not reflect the exact number of DA neurons.

Analysis of binary diffraction gratings: Comparison of different approaches

Diffraction characteristics of periodic binary diffractive structures are studied using three different theoretical approaches. Namely rigorous coupled-wave analysis (RCWA), Kogelnik's two-wave method, and the scalar method of transmittance have been applied to study diffraction characteristics and have been compared, and their applicability has been determined. For comparison purposes, a binary surface-relief grating made from an isotropic non-absorbing substrate in the planar diffraction regime, and a transverse electric polarized incident wave, are considered in this paper. Additionally, by calculating the diffraction efficiency of such gratings using the RCWA method, with special respect to grating profile depth and period, it was possible to describe and explain the complex behaviour of diffraction efficiency, that is to find regions with typical diffraction regimes, of all gratings of a chosen kind, in this case given by the binary grating profile. Moreover, it has been shown how the classical scalar transmittance method for analysis of thin diffraction gratings can be modified by an estimation of the propagation process through the grating depth in order to describe the volume phase synchronism dependence on the relative grating period.

Peptidic regulation of heart rate and interactions with the autonomic nervous system.

Autonomic influences on the heart rate have been the subject of intense research for many decades and are classically devoted to the sympathetic and parasympathetic systems. However, developments over the past few years in our knowledge of the organization of the autonomic nervous system have led to the conclusion that in addition to the classical transmitters, peptidic transmitters are clearly present and have direct or indirect actions on cardiac conduction. Neuropeptides have been found to collocate with each other or with classical transmitters, thereby increasing the variety of chemical signals that a neuron can utilize to communicate with other cells. Neuropeptides can act as neurotransmitters, neuromodulators or neurohormones. Some are produced in endocrine glands and circulate as hormones, while others are contained in cardiac myocytes, neurons, or endothelial cells in proximity to the sinoatrial node and can therefore act in a paracrine or autocrine way on the pacemaker cells to modulate heart frequency. There is evidence supporting such a role, especially for locally situated neuropeptide Y, vasoactive intestinal peptide, calcitonin gene-related peptide, substance P, angiotensin II, natriuretic peptides, endothelins and possibly many others. The role of the peptidic neurotransmitters in the conduction system should not be exaggerated. Nevertheless, neuropeptides certainly represent a new category of neurotransmitters forming a third component of the autonomic nervous system and may have complex actions with potential therapeutic implications in man.

Menek Goldstein (1926–1997)

Professor Goldstein was born in 1926 in Kolomea, Poland. As a 15-year-old boy he escaped from a line-up in the Ghetto by running away under gun fire. He was then hidden by a Catholic family for a long period. He studied at the University in Berne, Switzerland, and from 1953 to 1956 worked as Research Assistant in their Department of Chemistry and received his PhD in Biochemistry in 1955. In 1956 he moved to the United States, initially the Worcester Foundation for Experimental Biology in Shrewsbury, Massachusetts and the following year the New York University Medical Center, where he played an active role for the rest of his life. He became Assistant Professor in Biochemistry in 1960, Associate Pro- fessor in 1963 and was appointed to Professor in Neurochemistry in 1969. In fact, this was one of the first Professorships in neurochemistry in the United States. Menek Goldstein received several honours, including the Robert and Adele Blank Lectureship Award (1986) and the Sarah L. Poiley Memorial Award (1989) at the New York Academy of Sciences; he was also elected Honorary Doctor of the Karolinska Institute in 1982, where he also held the additional title of Foreign Adjunct Professor from 1992. He was a member of several Editorial and Advisory Boards including the American Parkinson Disease Foundation and National Parkinson Foundation.Menek Goldstein's first publications, together with I. Abelin, were entitled `Specific dynamic action of proteins' (1954) and `Determination of catecholamines and brenzcat- echines in urine' (1956). In fact, these were to be the main themes of his research throughout his life, his work being focused on catecholamines and their enzymes. During his career he published more than 350 original articles, numerous abstracts and co-authored more than 70 articles for books. One of his most important scientific contributions was to purify all four enzymes in the catecholamine synthetic pathway, that is tyrosine hydroxylase, aromatic l-amino acid decarboxylase, dopamine β-hydroxylase and phenylethanolamine N-methyl transferase, three of which he achieved as the first. This pioneering work was rapidly followed by the production of powerful antisera which allowed central and peripheral catecholamine systems to be mapped. This work was the foundation of our collaboration with Menek, which resulted in the first mapping of the central adrenaline systems. His antisera also made possible the description of co-existence between classical transmitters and neuropeptides. Other important contributions include discoveries relating to the activation and regulation of the catecholamine biosynthesis and the role of cyclic nucleotides in dopamine synthesis control, which led to an extensive analysis of central dopamine receptors and their role in Parkinson's disease. He and his collaborators developed a monkey model with experimentally induced lesions mimicking the symptoms seen in Parkinson's disease, i.e. tremor and hypokinesia. In this way it was possible to test and develop new drugs for treatment of this disease. In the dopamine receptor field he is, among other things, well known for his analysis of the so- called receptor reserve for dopamine agonists, which are important for our understanding of how autoreceptors regulate dopamine synthesis and release. Finally, he also made important contributions in the Lesch–Nyhan syndrome, a biochemical abnormality involving dopamine D1 receptor dysfunction.We met Menek, together, for the first time in Basel in 1969, at the International Pharmacology Congress. This meeting turned out to have considerable consequences, not only for our professional, but also our personal, lives, and would result in a warm and life-long friendship and, eventually, in more than 200 publications together and inspiring encounters at many scientific and more personal meetings. Menek often visited Sweden where he was a dear guest and had many friends. Although he never married and had no children, Menek was surrounded by people who loved him, especially Mirra who was his loving companion for many years. We enjoyed spending time with him at the NYU Medical Center where he worked, or in the apartment house where he lived. It was a pleasure to see how he called a friendly `how are you?' to everyone and how their faces lit up when they returned Menek's greetings. The same happened at conferences – Menek knew so many, and so many knew and liked Menek. Visits to New York will not be the same without him: no planning of experiments, no steaks and Delicatessen, and no strolling around on the east side of Manhattan. Science without Menek will be much less fun but the warm memories of a wonderful friend will comfort us for years to come.

Presynaptic Modulation of Cholecystokinin Release by Protein Kinase C in the Rat Hippocampus

The role of protein kinase C (PKC) in modulating the release of the octapeptide cholecystokinin (CCK-8) was investigated in rat hippocampal nerve terminals (synaptosomes). The PKC-activating phorbol ester 4beta-phorbol 12,13-dibutyrate (beta-PDBu) dose dependently (5-5,000 nM) increased CCK-8 release in a strictly Ca2+dependent way. This effect was observed only when synaptosomes were stimulated with the K+(A) channel blocker 4-aminopyridine (4-AP; 1 mM) but not with KCl (10-30 mM). The PDBu-induced exocytosis of CCK-8 was completely blocked by the two selective PKC inhibitors chelerythrine and calphostin-C and was not mimicked by alpha-PDBu, an inactive phorbol ester. In addition, an analogue of the endogenous PKC activator diacylglycerol, oleoylacetylglycerol, dose dependently increased CCK-8 exocytosis. Beta-PDBu (50-100 nM) also stimulated the 4-AP-evoked Ca2+-dependent release of the classic transmitter GABA, which co-localizes with CCK-8 in hippocampal interneurons. As a possible physiological trigger for PKC activation, the role of the metabotropic glutamate receptor was investigated. However, the broad receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid did not stimulate, but instead inhibited, both the CCK-8 and the GABA exocytosis. In conclusion, presynaptic PKC may stimulate exocytosis of distinct types of co-localizing neurotransmitters via modulation of presynaptic K+ channels in rat hippocampus.

Identification and characterization of the vesicular GABA transporter.

Synaptic transmission involves the regulated exocytosis of vesicles filled with neurotransmitter. Classical transmitters are synthesized in the cytoplasm, and so must be transported into synaptic vesicles. Although the vesicular transporters for monoamines and acetylcholine have been identified, the proteins responsible for packaging the primary inhibitory and excitatory transmitters, gamma-aminobutyric acid (GABA) and glutamate remain unknown. Studies in the nematode Caenorhabditis elegans have implicated the gene unc-47 in the release of GABA. Here we show that the sequence of unc-47 predicts a protein with ten transmembrane domains, that the gene is expressed by GABA neurons, and that the protein colocalizes with synaptic vesicles. Further, a rat homologue of unc-47 is expressed by central GABA neurons and confers vesicular GABA transport in transfected cells with kinetics and substrate specificity similar to those previously reported for synaptic vesicles from the brain. Comparison of this vesicular GABA transporter (VGAT) with a vesicular transporter for monoamines shows that there are differences in the bioenergetic dependence of transport, and these presumably account for the differences in structure. Thus VGAT is the first of a new family of neurotransmitter transporters.

The Secretion of Classical and Peptide Cotransmitters from a Single Presynaptic Neuron Involves a Synaptobrevin-Like Molecule

It is not yet understood how the molecular mechanisms controlling the release of neuropeptides differ from those controlling the release of classical transmitters, mainly because there are few peptidergic synapses in which the environment at the presynaptic release sites can be manipulated. Using Aplysia californica neuron B2, which synthesizes both peptide and classical transmitters, we have established two synaptic types. When B2 is cocultured with a sensory neuron, a peptidergic synapse is formed. In contrast, when B2 is cocultured with neuron B6, a classical synapse is formed. In contrast to a common assumption, single action potentials can release both types of transmitters. The secretion of peptide and classical transmitters by B2 is inhibited by the presynaptic injection of tetanus toxin, but not by an inactive mutant. Thus a synaptobrevin-like molecule is involved in the secretion of these two types of transmitters.

The role of vesicular transport proteins in synaptic transmission and neural degeneration.

Classical neurotransmitters are synthesized in the cytoplasm, so they require transport into secretory vesicles for regulated exocytotic release. Previous work has identified distinct vesicular transport activities for the different classical transmitters, and all depend on the H+-electrochemical gradient across the vesicle membrane but differ in the extent to which they rely on the chemical and electrical components of this gradient. Drugs that interfere with vesicular amine transport have implicated this activity in psychiatric disease. Selection for a cDNA encoding vesicular amine transport in the neurotoxin MPP+ also implicates the activity in Parkinson's disease. Molecular cloning of vesicular monoamine transporters shows sequence similarity to bacterial antibiotic resistance proteins, supporting a role for transport in detoxification and defining a novel mammalian gene family that now also includes a transporter for acetylcholine. Current work focuses on the mechanism of transport and the role that regulation of activity and its subcellular localization have in transmitter release, behavior, and neural degeneration.

NITRIC OXIDE AND FIBROBLAST GROWTH FACTOR IN AUTONOMIC NERVOUS SYSTEM: SHORT- AND LONG-TERM MESSENGERS IN AUTONOMIC PATHWAY AND TARGET-ORGAN CONTROL

The freely diffusible messenger nitric oxide (NO), generated by NO synthase (NOS)-containing “nitroxergic” (NO-ergic) neurons, is unique among classical synaptic chemical transmitters because of its “non-specificity”, molecular “NO-receptors” (e.g. guanylyl cyclase, iron complexes, nitrosylated proteins or DNA) in target cells, intracellular targeting, regulated biosynthesis, and growth factor/cytokine-dependence. In the nervous system, expression of NOS is particularly intriguing in central and peripheral autonomic pathways and their targets. Here, anatomical and functional links appear to exist between NOS, its associated catalytic NADPH-diaphorase enzyme activity (NOSaD) and fibroblast growth factor-2 (FGF-2), a pleiotropic cytokine with mitogenic actions, suggesting mutual “short- and long-term” actions. Several recent studies performed in the rat sympathoadrenal system, an anatomically and neurochemically well-defined autonomic pathway with target-specific functional units of sympathetic preganglionic neurons (SPNs) in the spinal cord, provide evidence for this hypothesis. The NO and cytokine signals may interact at the level of gene expression, transcription factors, post-transcriptional control or second messenger cross-talk. Thus, unique biological roles of FGF-2 and the NO system are likely to exist in neuroendocrine actions, vasomotory perfusion control as well as in neurotrophic actions in sympathetic innervation of the adrenal gland. In view of their anatomical co-existence, functional interplay and synchronizing effects on neuronal networks, multiple roles are suggested for both “short- and long-term” signalling molecules in neuroendocrine functions and integrated autonomic target organ control. © 1997 Elsevier Science Ltd. All Rights Reserved.