On the 50th anniversary of Dale's law: multiple neurotransmitter neurons

Desiderata for Normative Models of Synaptic Plasticity

Normative models of synaptic plasticity use computational rationales to arrive at predictions of behavioral and network-level adaptive phenomena. In recent years, there has been an explosion of theoretical work in this realm, but experimental confirmation remains limited. In this review, we organize work on normative plasticity models in terms of a set of desiderata that, when satisfied, are designed to ensure that a given model demonstrates a clear link between plasticity and adaptive behavior, is consistent with known biological evidence about neural plasticity and yields specific testable predictions. As a prototype, we include a detailed analysis of the REINFORCE algorithm. We also discuss how new models have begun to improve on the identified criteria and suggest avenues for further development. Overall, we provide a conceptual guide to help develop neural learning theories that are precise, powerful, and experimentally testable.

Inhibitory signaling in collective social insect networks, is it indeed uncommon?

Individual entities across levels of biological organization interact to reach collective decisions. In centralized neuronal networks, competing neural populations commonly accumulate information over time while increasing their own activity, and cross-inhibiting other populations until one group passes a given threshold. In social insects, there is good evidence for decisions mediated by positive feedbacks, but we found evidence for similar inhibitory signals only in honey bee (Apis mellifera) stop signals, and Pharaoh's ant- (Monomorium pharaonic) repellent pheromones, with only the former occasionally being used as cross-inhibition. We discuss whether these differences stem from insufficient research effort or represent genuine differences across levels of biological organization.

Positive and biphasic extracellular waveforms correspond to return currents and axonal spikes

Multiple biophysical mechanisms may generate non-negative extracellular waveforms during action potentials, but the origin and prevalence of positive spikes and biphasic spikes in the intact brain are unknown. Using extracellular recordings from densely-connected cortical networks in freely-moving mice, we find that a tenth of the waveforms are non-negative. Positive phases of non-negative spikes occur in synchrony or just before wider same-unit negative spikes. Narrow positive spikes occur in isolation in the white matter. Isolated biphasic spikes are narrower than negative spikes, occurring right after spikes of verified inhibitory units. In CA1, units with dominant non-negative spikes exhibit place fields, phase precession, and phase-locking to ripples. Thus, near-somatic narrow positive extracellular potentials correspond to return currents, and isolated non-negative spikes correspond to axonal potentials. Identifying non-negative extracellular waveforms that correspond to non-somatic compartments during spikes can enhance the understanding of physiological and pathological neural mechanisms in intact animals.

Neural Information Processing and Computations of Two-Input Synapses

Information processing in artificial neural networks is largely dependent on the nature of neuron models. While commonly used models are designed for linear integration of synaptic inputs, accumulating experimental evidence suggests that biological neurons are capable of nonlinear computations for many converging synaptic inputs via homo- and heterosynaptic mechanisms. This nonlinear neuronal computation may play an important role in complex information processing at the neural circuit level. Here we characterize the dynamics and coding properties of neuron models on synaptic transmissions delivered from two hidden states. The neuronal information processing is influenced by the cooperative and competitive interactions among synapses and the coherence of the hidden states. Furthermore, we demonstrate that neuronal information processing under two-input synaptic transmission can be mapped to linearly nonseparable XOR as well as basic AND/OR operations. In particular, the mixtures of linear and nonlinear neuron models outperform the fashion-MNIST test compared to the neural networks consisting of only one type. This study provides a computational framework for assessing information processing of neuron and synapse models that may be beneficial for the design of brain-inspired artificial intelligence algorithms and neuromorphic systems.

A Modeling Study of the Emergence of Eye Position Gain Fields Modulating the Responses of Visual Neurons in the Brain

The responses of many cortical neurons to visual stimuli are modulated by the position of the eye. This form of gain modulation by eye position does not change the retinotopic selectivity of the responses, but only changes the amplitude of the responses. Particularly in the case of cortical responses, this form of eye position gain modulation has been observed to be multiplicative. Multiplicative gain modulated responses are crucial to encode information that is relevant to high-level visual functions, such as stable spatial awareness, eye movement planning, visual-motor behaviors, and coordinate transformation. Here we first present a hardwired model of different functional forms of gain modulation, including peaked and monotonic modulation by eye position. We use a biologically realistic Gaussian function to model the influence of the position of the eye on the internal activation of visual neurons. Next we show how different functional forms of gain modulation by eye position may develop in a self-organizing neural network model of visual neurons. A further contribution of our work is the investigation of the influence of the width of the eye position tuning curve on the development of a variety of forms of eye position gain modulation. Our simulation results show how the width of the eye position tuning curve affects the development of different forms of gain modulation of visual responses by the position of the eye.

Self-organising coordinate transformation with peaked and monotonic gain modulation in the primate dorsal visual pathway

We study a self-organising neural network model of how visual representations in the primate dorsal visual pathway are transformed from an eye-centred to head-centred frame of reference. The model has previously been shown to robustly develop head-centred output neurons with a standard trace learning rule, but only under limited conditions. Specifically it fails when incorporating visual input neurons with monotonic gain modulation by eye-position. Since eye-centred neurons with monotonic gain modulation are so common in the dorsal visual pathway, it is an important challenge to show how efferent synaptic connections from these neurons may self-organise to produce head-centred responses in a subpopulation of postsynaptic neurons. We show for the first time how a variety of modified, yet still biologically plausible, versions of the standard trace learning rule enable the model to perform a coordinate transformation from eye-centred to head-centred reference frames when the visual input neurons have monotonic gain modulation by eye-position.

A self-organizing model of perisaccadic visual receptive field dynamics in primate visual and oculomotor system

We propose and examine a model for how perisaccadic visual receptive field dynamics, observed in a range of primate brain areas such as LIP, FEF, SC, V3, V3A, V2, and V1, may develop through a biologically plausible process of unsupervised visually guided learning. These dynamics are associated with remapping, which is the phenomenon where receptive fields anticipate the consequences of saccadic eye movements. We find that a neural network model using a local associative synaptic learning rule, when exposed to visual scenes in conjunction with saccades, can account for a range of associated phenomena. In particular, our model demonstrates predictive and pre-saccadic remapping, responsiveness shifts around the time of saccades, and remapping from multiple directions.

Influence of neuropeptides on the processes of higher nervous activity in primates. The action of cyclic analogs of enkephalins on the behavior of the lower monkeys

The effect of two cyclic enkephalin analogs (IVS-43 and IVS-46) on the group and individual behavior of rhesus macaques and hamadryas baboons has been studied. A pronounced influence of IVS-46 on competitive and operant goal-directed behavior of the monkeys was identified.

Evolutionary aspects of transmitter molecules, their receptors and channels

Classical transmitters are present in all phyla that have been studied; however, our detailed understanding of the process of neurotransmission in these phyla is patchy and has centred on those neurotransmitter receptor mechanisms which are amenable to study with the tools available at the time, for example, high-affinity ligands, tissues with high density of receptor protein, suitable electrophysiological recording systems. Studies also clearly show that many neurones exhibit co-localization of classical transmitters and neuropeptides. However, the physiological implications of this co-localization have yet to be elucidated in the vast majority of examples. The application of molecular biological techniques to the study of neurotransmitter receptors (to date mainly in vertebrates) is contributing to our understanding of the evolution of these proteins. Striking similarities in the structure of ligand-gated receptors have been revealed. Thus, although ligand-gated receptors differ markedly in terms of the endogenous ligands they recognize and the ion channels that they gate, the structural similarities suggest a strong evolutionary relationship. Pharmacological differences also exist between receptors that recognize the same neurotransmitter but in different phyla, and this may also be exploited to further the understanding of structure-function relationships for receptors. Thus, for instance, some invertebrate GABA receptors are similar to mammalian GABAA receptors but lack a modulatory site operated by benzodiazepines. Knowledge of the structure and subunit composition of these receptors and comparison with those that have already been elucidated for the mammalian nervous system might indicate the functional importance of certain amino acid residues or receptor subunits. These differences could also be exploited in the development of new agents to control agrochemical pests and parasites of medical importance. The study of the pharmacology of receptor proteins for neurotransmitters in invertebrates, together with the application of biochemical and molecular biological techniques to elucidate the structure of these molecules, is now gathering momentum. For certain receptors, e.g. the nicotinic receptor, we can expect to have fundamental information on the function of this receptor at the molecular level in both invertebrates and vertebrates in the near future.

Storage and fast transport of noradrenaline, dopamine beta-hydroxylase and neuropeptide Y in dog sciatic nerve axons

The axonal transport and subcellular distribution of noradrenaline (NA), dopamine beta-hydroxylase (DBH) and neuropeptide Y (NPY) were determined in dog sciatic nerve using an accumulation technique. The results were compared with those obtained by application of the same procedures and methods on the splenic nerve in the same animal species. Evidence was found for the coexistence of NA and NPY in large dense-cored vesicles in dog sciatic nerve axons. After differential centrifugation and isopyenic sucrose density gradient centrifugation of 24 h ligated sciatic nerve pieces NA and NPY equilibrated around 1M sucrose. The DBH activity was dispersed broadly on the gradient. Subsequently, the accumulation of NA, DBH and NPY was studied in proximal and sital segments of 8, 12 and 24 h dog ligated sciatic nerve and inferences were made concerning the axonal transport of these compounds. NA, DBH and NPY displayed a divergent accumulation proximal to the ligation. After 12 h of ligation a transport rate was calculated of 4.8 +/- 1.8 mm/h for NA, of 5.9 +/- 1.5 mm/h for DBH and of 4.9 +/- 2.0 mm/h for NPY. With a correction for the stationary fractions, a similar fast transport rate of approximately 10 to 12 mm/h was proposed for NA, DBH and NPY. The occurrence was shown of a limited retrograde transport of DBH and possibly NPY, but not of NA.

Effects of guinea pig vasoactive intestinal peptide on the isolated perfused guinea pig heart

The pharmacological effects of guinea pig vasoactive intestinal peptide (VIP) were studied in isolated perfused guinea pig hearts. Bolus injections of VIP produced a dose-dependent tachycardia that was not affected by atenolol. A decrease in amplitude of ventricular contractions occurred in response to all doses of VIP. This response was preceded by a small increase in amplitude in 3 of 6 hearts at the highest dose. VIP produced a decrease in perfusion pressure which was prominent after coronary tone was elevated with [Arg8]-vasopressin. The present findings support speculation that VIP may have a role in the regulation of heart rate and coronary blood flow.

Activities of octopamine and synephrine stereoisomers on alpha-adrenoceptors

1. The activities of the (-)- and (+)-forms of m- and p-octopamine and m- and p-synephrine on alpha 1-adrenoceptors from rat aorta and anococcygeus and alpha 2-adrenoceptors from rabbit saphenous vein were compared with those of noradrenaline (NA). 2. The rank order of potency of the (-)-forms on alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors was NA greater than m-octopamine = m-synephrine greater than p-octopamine = p-synephrine. The two m-compounds were 6 fold less active than NA on alpha 1-adrenoceptors from rat aorta and 150 fold less active on alpha 2-adrenoceptors. The two p- compounds were 1,000 fold less active than NA on both alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors. The rank order of potency of the (-)- forms on alpha 1-adrenoceptors from rat anococcygeus was NA = m-synephrine greater than m-octopamine greater than p-octopamine = p-synephrine. m-Octopamine was 4 fold less active than NA and (-)-m-synephrine. The two p- compounds were 30 fold less active than NA. 3. The rank order of potency of the (+)- forms was NA greater than m-octopamine greater than m-synephrine greater than p-octopamine greater than p-synephrine on both alpha 1- and alpha 2-adrenoceptors. The potency of each (+)- form was 1-2 orders of magnitude less than that of the (-) counterpart, the differences being greater for the stereoisomers of synephrine than for those of octopamine on both alpha 1- and alpha 2-adrenoceptors. 4. The yohimbine diastereoisomer antagonists, rauwolscine and corynanthine, were tested against (-)-NA and (-)-m-octopamine-induced contractions in both preparations. Based upon the known selectivities of these isomers for alpha-adrenoceptor subtypes, it is concluded that the rat aorta contains only alpha 1-adrenoceptors while the rabbit saphenous vein possesses predominantly alpha 2-adrenoceptors. 5. Ligand binding data for the octopamine and synephrine stereoisomers at alpha 1- and alpha 2-binding sites from rat cerebral cortex was also obtained. (-)-Forms were more active than (+)-forms. The rank order of affinity of the (-)-forms for both alpha 1- and alpha 2-binding sites was NA greater than m-octopamine = m-synephrine greater than p-synephrine greater than p-octopamine. The relative affinities of the members of the series against alpha 1-binding sites were very similar to their relative functional activities on rat aorta. However, the affinities of both m- and p-compounds relative to that of ( -)-NA were much greater at the x2-binding sites than were the relative activities in rabbit saphenous vein, possibly suggesting low intrinsic efficacy. Functional antagonist responses to NA by the (-)-octopamine and synephrines could not, however, be demonstrated on rat aorta or rabbit saphenous vein. 6. The activities of m-octopamine and m-synephrine were not significantly different from each other on either a,-adrenoceptors from rat aorta or x2-adrenoceptors; however, m-synephrine is more active than m-octopamine on a,-adrenoceptors from rat anococcygeus. Both m-octopamine and msynephrine can be considered to be naturally occurring x,-selective amines. However, if m- and poctopamine are co-released with NA in amounts proportional to their concentration, it is concluded that their activities on m,- and x2-adrenoceptors are too low to be physiologically significant.

Receptor-stimulated system mediated interactions of neuropeptides in GH3 cells

The interaction between two neuropeptides, VIP and TRH, was studied. The TRH receptor binding ability was examined using intact GH3 cells and its membrane fraction. The TRH binding ability decreased when intact cells were preincubated with VIP, forskolin or db-cAMP, but not when the membrane fraction was treated with these agents. The binding was reduced only when the membrane fraction was treated with catalytic subunit of cAMP dependent protein kinase (A-kinase). These results indicate that the binding ability of TRH receptors, which are linked to inositol phospholipid metabolism, is suppressed when A-kinase increases due to activation of the adenylate cyclase or its dependent system. This, in turn, suggests the presence of a communication via a cytoplasmic factor (probably A-kinase) between the two principal second messenger systems in the cell.

Clonidine and morphine increase [3H]-noradrenaline overflow in mouse vas deferens

1. Field stimulation of mouse isolated vas deferens produced a biphasic contraction that consisted of an initial brief non-adrenergic, non-cholinergic (NANC) twitch, followed by a more prolonged noradrenergic component. 2. Field stimulation of vasa, previously loaded with [3H]-noradrenaline ([3H]-NA), increased the amount of radioactivity in the Krebs bathing solution; 77% of this radioactivity was derived from [3H]-NA. 3. Tetrodotoxin (3 x 10(-6) M) abolished the biphasic motor response to field stimulation and the accompanying increased overflow of [3H]-NA. 4. Morphine (10(-7)-10(-5) M) inhibited the initial NANC component but potentiated the secondary noradrenergic component of the motor response to field stimulation. Morphine also increased the field stimulation-induced overflow of radioactivity. Naloxone (10(-6) M) antagonized the effects of morphine on the motor response and also on the overflow of radioactivity. 5. Clonidine (10(-9)-10(-7) M) inhibited the initial NANC component but potentiated the secondary noradrenergic component of the motor response to field stimulation. Clonidine also increased the field stimulation-induced overflow of radioactivity. 6. The ability of morphine (10(-7) M) and of clonidine (10(-9) M) to potentiate the field stimulation-induced overflow of radioactivity persisted in the presence of a combination of tranylcypromine (10(-5) M), desmethylimipramine (10(-5) M) and 17-beta-oestradiol (10(-5) M). 7. The inhibition of the initial NANC component of the motor response to field stimulation produced by morphine and clonidine may be related to the ability of these drugs to potentiate both the secondary noradrenergic component and the overflow of radioactivity, if the NANC transmitter is involved in regulating NA release.

Beta-adrenergic activities of octopamine and synephrine stereoisomers on guinea-pig atria and trachea

The activities of the (-)- and (+)-forms of m- and p-octopamine and m- and p-synephrine on beta 1- and beta 2-adrenoceptors in guinea-pig atria and trachea have been compared with that of noradrenaline. The rank order of potency of the (-)-forms on beta 1-adrenoceptors was noradrenaline greater than m-synephrine greater than m-octopamine = p-octopamine greater than p-synephrine. m-Synephrine was 100-fold, m- and p-octopamine about 6000-fold, and p-synephrine about 40,000-fold less active than noradrenaline. The (+)-forms were 1-2 orders of magnitude less active than their (-)-counterparts. The four (-)-compounds were more than four orders of magnitude less active than noradrenaline on beta 2-adrenoceptors, and the (+)-forms had no detectable activity in concentrations as high as 10(-4) M. If m- and p-octopamine are co-released with noradrenaline in amounts proportional to their concentration, their activities at these structures are too low to be physiologically significant.

The effect of reserpine on sympathetic, purinergic neurotransmission in the isolated mesenteric artery of the dog: a pharmacological study

Electrical transmural stimulation evoked a transient contraction in the isolated mesenteric artery of the dog. This contraction was abolished by guanethidine or tetrodotoxin and was partially inhibited by prazosin. Noradrenaline was competitively antagonized by prazosin. Similarly, in the reserpine-treated artery, electrical transmural stimulation produced a transient contraction which was abolished by guanethidine or tetrodotoxin. However, prazosin failed to inhibit this contraction. The contraction to noradrenaline was not significantly different from the response it produced in control vessels. Tyramine (10(-5) M), which acts on sympathetic nerves to release noradrenaline, evoked a tonic contraction in the untreated artery. This contraction was abolished or markedly attenuated by prazosin or guanethidine. The response was not observed in the reserpine-treated artery, indicating that reserpine had depleted the nerves of noradrenaline. In the control vessel alpha,beta-methylene-ATP produced a transient contraction which was followed by a complete relaxation to the basal level. This contractile response was not significantly different in the presence of guanethidine or prazosin or in the reserpine-treated artery. After desensitization of the vessel to alpha,beta-methylene ATP (5 X 10(-6) M) the prazosin-resistant contractions induced by electrical transmural stimulation were abolished both in reserpine-treated and untreated arteries. Also the contractile responses to ATP and alpha-beta-methylene-ATP were abolished but the responses to tyramine (control vessels), noradrenaline and KCl were not affected. 8-Phenyltheophylline (10(-5) M) showed no inhibitory effect on the contractile responses to electrical transmural stimulation, tyramine, ATP or alpha,beta-methylene-ATP. 7. Neuropeptide Y, peptide YY, vasoactive intestinal polypeptide, bombesin and substance P (10-7 and 10-6 M for each peptide) caused no contractile response in the dog mesenteric artery. 8. These experiments provide further evidence that the sympathetic contraction of the isolated mesenteric artery of the dog induced by electrical transmural stimulation consists ofan adrenergic and a purinergic component and that the latter component is mediated through postsynaptic P2- purinoceptors.

Comparison of the responses to the sensory neuropeptides, substance P, neurokinin A, neurokinin B and calcitonin gene-related peptide and to trigeminal nerve stimulation in the iris sphincter muscle of the rabbit

Three mammalian tachykinins (substance P, neurokinin A and B) and two non-mammalian ones (eledoisin and physalaemin) produced potent contractions of the isolated rabbit iris sphincter muscle. The rank order of potencies was eledoisin greater than neurokinin B = physalaemin greater than substance P greater than neurokinin A. The maximum efficacy was much the same. The contractile responses to neurokinin A and eledoisin developed more rapidly than did those to the other tachykinins used and were selectively attenuated by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Electrical transmural stimulation produced a contraction consisting of cholinergic and tachykininergic components. The tachykininergic component was abolished by pretreatment with capsaicin or by trigeminal denervation (Fujiwara et al., 1984). [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP attenuated the tachykininergic component, but not the cholinergic one. KCl and capsaicin also produced a tachykininergic contraction which was inhibited by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Calcitonin gene-related peptide affected neither the iris sphincter muscle nor the response to electrical transmural stimulation. These results suggest that the tachykininergic responses induced by electrical transmural stimulation, KCl and capsaicin are predominantly mediated by neurokinin A, probably released from the peripheral endings of trigeminal nerves.

Colocalization of (3H)-adenosine accumulation and GABA immunoreactivity in the chicken and rabbit retinas

Using combined autoradiography and immunohistochemistry, we have compared (3H)-adenosine accumulation and GABA immunoreactivity in the chicken and rabbit retinas. Colocalization of the two markers was observed in a subset of amacrine cells and in certain cell bodies in the ganglion cell layer in both species and in a few horizontal cells in the chicken retina. Cells that contained only (3H)-adenosine or GABA were also seen. The degree of colocalization differed greatly between the two species. The results demonstrate a morphological relationship between the adenosine and GABA systems and provides information on the possible anatomical substrates underlying at least some types of functional interactions.

Ascorbic acid enhances the release of luteinizing hormone-releasing hormone from the mediobasal hypothalamus in vitro

Ascorbic acid is frequently used in in vitro studies of neurotransmitter-evoked release of luteinizing hormone-releasing hormone (LHRH) from hypothalamic fragments. Although it is assumed that ascorbate merely prevents the oxidative degradation of catecholamines, we have discovered that ascorbic acid itself produces significant increases in the release of LHRH. Our studies showed that ascorbic acid, at concentrations below 1 mM, produced a dose-dependent release of LHRH from incubated rat mediobasal hypothalamus (MBH). The magnitude of the ascorbate-induced release was in the range of 100-200% above controls; significant amounts of LHRH were released only if the MBH were incubated with ascorbate for time periods longer than 30 minutes. We also found that ascorbate-induced increases in LHRH were equivalent to those produced by another LHRH secretagogue, naloxone, and that the combined effects of the two substances were additive in nature. Although the mechanisms underlying this effect are not fully understood, nonspecific chemical reduction is probably not a factor since sodium metabisulfite did not induce the release of LHRH. It seems probable that ascorbate may enhance the activity of endogenous norepinephrine in the MBH and, thereby, lead to increased release of LHRH.

Pharmacologic characterization and autoradiographic distribution of binding sites for iodinated tachykinins in the rat central nervous system

P-type, E-type, and K-type tachykinin binding sites have been identified in the mammalian CNS. These sites may be tachykinin receptors for which the mammalian neuropeptides substance P, neuromedin K, and substance K are the preferred natural agonists, respectively. In the present investigation, we have compared the pharmacology and the autoradiographic distribution of CNS binding sites for the iodinated (125I-Bolton-Hunter reagent) tachykinins substance P, eledoisin, neuromedin K, and substance K. Iodinated eledoisin and neuromedin K exhibited an E-type binding pattern in cortical membranes. Iodinated eledoisin, neuromedin K, and substance K each labeled sites that had a similar distribution but one that was considerably different from that of sites labeled by iodinated substance P. CNS regions where there were detectable densities of binding sites for iodinated eledoisin, neuromedin K, and substance K and few or no sites for iodinated substance P included cortical layers IV-VI, mediolateral septum, supraoptic and paraventricular nuclei, interpeduncular nucleus, ventral tegmental area, and substantia nigra pars compacta. Binding sites for SP were generally more widespread in the CNS. CNS regions where there was a substantial density of binding sites for iodinated substance P and few or no sites for iodinated eledoisin, neuromedin K, and substance K included cortical layers I and II, olfactory tubercle, nucleus accumbens, caudate-putamen, globus pallidus, medial and lateral septum, endopiriform nucleus, rostral thalamus, medial and lateral preoptic nuclei, arcuate nucleus, dorsal raphe nucleus, dorsal parabrachial nucleus, parabigeminal nucleus, cerebellum, inferior olive, nucleus ambiguus, retrofacial and reticular nuclei, and spinal cord autonomic and somatic motor nuclei. In the brainstem, iodinated substance P labeled sites in both sensory and motor nuclei whereas iodinated eledoisin, neuromedin K, and substance K labeled primarily sensory nuclei. Our results are consistent with either of two alternatives: (1) that iodinated eledoisin, neuromedin K, and substance K bind to the same receptor site in the rat CNS, or (2) that they bind to multiple types of receptor sites with very similar distribution.

Gonadotropin-releasing hormone (GnRF), molluscan cardioexcitatory peptide (FMRFamide), enkephalin and related neuropeptides affect goldfish retinal ganglion cell activity

Recently gonadotropin-releasing hormone (GnRF)-like and molluscan cardioexcitatory peptide (FMRFamide)-like compounds have been colocalized immunocytochemically to the terminal nerve, a presumed olfactoretinal efferent system in goldfish. In the present study these and related neuropeptides were shown to affect ganglion cell activity, recorded extracellularly, when applied to the isolated superfused goldfish retina. GnRF was usually excitatory. Salmon GnRF (sGnRF) was 10-30x more potent than chicken or mammalian GnRF. FMRFamide and enkephalin also were often excitatory but caused more varied responses than sGnRF. Met5-enkephalin-Arg6-Phe7-NH2 (YGGFMRFamide), which contains both enkephalin and FMRFamide sequences, tended to act like both of these peptides but with mainly enkephalin-like properties. Neuropeptide Y and the C-terminal hexapeptide of pancreatic polypeptides, whose C-terminus (-Arg-Tyr-NH2) is closely related to that of FMRFamide (-Arg-Phe-NH2), gave no consistent responses. Threshold doses were equivalent to: 0.1 microM for sGnRF; 0.5 microM for YGGFMRFamide; 1.5 microM for FMRFamide and enkephalin. Rapid, complete and irreversible desensitization was induced by single, 10-20x threshold doses of sGnRF; but desensitization was infrequent and limited with the other peptides. In general, all peptides tested affected the spatially and chromatically antagonistic receptive field components similarly, but selective actions were seen in a few cases with FMRFamide and with the opioid antagonist, naloxone. Responses, especially to sGnRF and FMRFamide, tended to be most frequently obtained and pronounced in winter and spring, suggesting a correlation with seasonally regulated sexual and reproductive activity. Our observations provide further evidence for transmitter-like roles of neuropeptides related to sGnRF and FMRFamide in the teleostean terminal nerve. The actions of agonists and antagonists, singly and in combination, imply strongly that there are distinctive postsynaptic receptors and/or neural pathways for GnRF-, FMRFamide- and enkephalin-like peptides in the goldfish retina.

Peptide transmitters of primary sensory neurons: similar actions of tachykinins and bombesin-like peptides

Previous studies have demonstrated that two peptides, substance P (SP) and substance K (SK), are contained in a common prohormone--beta-preprotachykinin. Both peptides are cleaved from the prohormone and appear to coexist throughout the brain. This study evaluated the behavioral activity of SK and compared it to the activities of SP, bombesin (BN), and structurally related peptides. After intraspinal injection, all of the peptides induced "bite/scratch" behaviors, which differed in durations of action. The specific rank order of these durations of action were: BN greater than gastrin releasing peptide (GRP) = ranatensin (RT) greater than neuromedin B (NMB) greater than kassinin (KASS) = SK = SP and ranged from dose-dependent maxima of approximately 2 min (SP) to approximately 100 min (BN). To examine the possibility that differences in durations of action are due to differences in rates of proteolytic degradation, each peptide was incubated in spinal cord homogenates at 37 degrees C, and the degradation rates were monitored by radioimmunoassay (RIA) and by bioassay. The lengths of incubation time required to produce approximately 90% degradation of peptide immunoreactivity varied across peptides from less than 5 min (SP) to more than 60 min (BN and RT). Degradation of bioactivity generally paralleled degradation of immunoreactivity. The results of this study suggest that durations of nociceptive effects produced by the peptides tested are due, in part, to their resistance to proteolytic degradation.

Excretion of octopamine metabolites in neuroblastoma

The urinary concentrations of o-hydroxymandelic acid, m-hydroxymandelic acid, p-hydroxymandelic acid, homovanillic acid and vanillylmandelic acid were determined in 57 healthy children and 9 patients with neuroblastoma. The concentrations of o-hydroxymandelic acid and p-hydroxymandelic were not significantly different for both groups whereas the concentrations of m-hydroxymandelic acid, homovanillic acid and vanillylmandelic acid were elevated 20- to 30-fold in the neuroblastoma patients.

Tyramine-induced release of neuropeptide Y (NPY) in isolated rabbit intestine

The effect of tyramine on the contractile activity of rabbit ileal segments was studied. Treatment with tyramine initiated a short-lived, fast contraction followed first by a relaxation then by a subsequent sustained contracture. Although the mechanism of the initial fast contraction remains obscure, the relaxation was abolished by the pretreatment with a combination of phentolamine and propranolol and the sustained contracture was blocked by neuropeptide Y (NPY)-antiserum. The inhibitory effect of the NPY-antiserum was produced in a dose-dependent manner. Thus, it is suggested that tyramine induced the release of NPY to initiate the subsequent sustained contracture.