Invertebrate Neurons

The fact that most serotonergic dorsal raphe neurons are dependent on extrinsic excitatory or facilitatory inputs to express their characteristic spontaneous activity may seem to contradict previous studies suggesting that these neurons may function as autonomous pacemakers (42) with an endogenous rhythm (31) attributable to the presence of pacemaker potentials (8). Such a contradiction exists only if one insists that endogenous rhythms and pacemaker potentials must, by definition, be totally autonomous, i.e., completely independent of all extrinsic synaptic or neurohumoral influences. Such a definition would seem too restrictive in view of the fact that some invertebrate neurons display pacemaker potentials only when certain afferent fibers are stimulated (38) or when exposed to certain neurohumoral substances (18,28). 

PC12) cells. Inhibition of L-type Ca2+ currents by phenothiazine drug was also found in invertebrate neurons. Investigations performed by Cruzblanca et al. [266] revealed that TFP (5) caused reversible and dose-dependent reduction of L-type Ca2+ currents in Helix aspersa (brown snail) neurons. The efficacy of inactivation of this current was enhanced by this drug. The possibility that calcium currents were altered by the influence of TFP (5) on the protein kinase C (PKC) activity was excluded in this paper. 

Spafford JD, Munno DW, Van Nierop P, Feng ZP, Jarvis SE, Gallin WJ, Smit AB, Zamponi GW, Syed NI (2003) Calcium channel structural determinants of synaptic transmission between identified invertebrate neurons. J Biol Chem 278 4258-67 Spafford JD, Zamponi GW (2003) Functional interactions between presynaptic calcium channels and the neurotransmitter release machinery. Curr Opin Neurobiol 13 308-14 Splawski I, Timothy KW, Decher N, Kumar P, Sachse FB, Beggs AH, Sanguinetti MC, Keating MT (2005) Severe arrhythmia disorder caused by cardiac L-type calcium channel mutations. Proc Natl Acad Sci U S A 102 8089-96 discussion 8086-8... 

In particular, neurochemistry has found CE especially useful for quantifying neurotransmitter concentrations in single cells. Since important cellular processes such as neurotransmitter synthesis, storage and release are affected by the cytoplasmic concentrations of neurotransmitters, methods to sample and quantify cytoplasmic concentrations of neurotransmitters from single invertebrate cells have been developed. Invertebrate neurons are particularly amenable for sampling because they can be quite large, for example, the giant dopamine neuron of pond snails is 200 p,m... 

For extracellular signal recordings from electrically active cells in culture, two main concepts have been developed in the past microelectrode arrays (MEAs) (see Fig. 2a) with metalized contacts on silicon or glass substrates have been used to monitor cardiac impulse propagation from dissociated embryonic myocytes [1-3], dissociated invertebrate neurons [4, 5] and mammalian neurons [6] spinal cord [7], and mouse dorsal root... 

Mozzachiodi, R, et al. (2001) Caulerpenyne, a toxin from the seaweed Caulerpa taxifolia, depresses after polarization in invertebrate neurons. Neuroscience. 107, 519-526... 

Nature has created a diverse array of plant and animal toxins that act at mammalian muscle and ganglionic nAChRs or invertebrate nAChRs because the critical physiological functions of these receptors make them prime targets for defensive or predatory strategies. More recently, the perceived validity of neuronal nAChR as therapeutic targets has prompted the generation of new synthetic ligands. Examples are listed in Table 1. 

Neurones without impulses their significance for vertebrate and invertebrate systems. Edited by... 

Tyramine is produced by decarboxylation of tyrosine and is present in the CNS in higher (threefold) concentrations than m-tyramine, the hydroxylated derivative of phenylethylamine. In the periphery / -tyramine is easily hydroxylated to octopamine, which has some direct effects on ai adrenoceptors, unlike tyramine which functions by releasing NA. When tested on central neurons tyramine always produces the same effects as NA but they are slower and less marked, implying an indirect action. By contrast octopamine often produces the opposite effect to NA and it is probable that octopamine may have a functional role in the invertebrate CNS where it is found in higher concentrations (5pg/g) than in the mammalian brain (0.5ng/g). Neither tyramine nor octopamine have distinct behavioural effects, unlike phenylethylamine,... 

It is most probable that sleep and waking stem from an inherent cycle of neuronal activity that can be influenced dramatically by changes in sensory stimulation. This is demonstrable not only in humans and laboratory animals, but also in invertebrates. Thus, while we cannot be sure that other animals sleep in the same way that we do, they do show a circadian cycle of motor activity. In some (nocturnal) species, such as the rat, this activity is actually highest during darkness. Even aplysia, the sea hare, has such a rhythm but this is more like that of humans in being maximally active during daylight (diurnal). 

In addition to the diversity of action of a single transmitter released from a neuron, it has become weU established that among invertebrates up to... 

Octopamine (4.41), which carries a p-hydroxyl group, is taken up even more readily into storage vesicles and is, in turn, released when the neuron fires. As an adrenergic agonist, octopamine is, however, only about one-tenth as active as NE therefore, it acts as a very weak neurotransmitter. Compounds such as this behave like neurotransmitters of low potency, and are called false transmitters. On the other hand, octopamine may be a true transmitter in some invertebrates, with receptors that cannot be occupied either by other catecholamines or by serotonin. 

Hormones of insects and crustaceans. Peptide neurohormones of insect brains348 include the pentapeptide proctolin (Table 30-5), which was first iso-lated from the cockroach and has since been found in crustaceans and in mammalian brain. It has been traced to specific insect neurons.349 A nonapeptide neurohormone from the shore crab does not resemble any other known vertebrate or invertebrate hormone.350... 

The nervous system, a network of neurons in active communication, reaches its ultimate development in the 1.5 kg human brain.149 393 396 Many invertebrates, such as leeches,3963 crayfish, insects, and snails, have brains containing no more than 104 to 105 neurons,396b/397 398 but the human brain contains 10n. Each of these neurons interconnects through synapses with hundreds or thousands of other neurons. The number of connections is estimated to be as many as 60,000 with each Purkinje cell of the human cerebellum. There may be many more than 1014 synapses in the human brain.399 400... 

Serotonin and melatonin. The indolealkyl amine serotonin (5-hydroxytryptamine, 5-HT Fig. 30-28), is found in all mammalian brains and in invertebrates as well. Its distribution in the brain is limited, serotonin-containing neurons being found in the raphe nuclei of the brainstem from which they ascend into the brain and down the spinal cord. Serotonin-containing neurons have been traced within brains of snails using 3H-labeled serotonin.777 Studies with these simpler brains have revealed both inhibitory and excitatory responses to these neurons. Serotonin-accumulating neurons are also found in the retina778 and are widely distributed in the peripheral nervous... 

Effects of pollutants on aquatic organisms. Edited by A. P.M. Lockwood 6. Neurones without impulses their significance for vertebrate and invertebrate systems. Edited by... 

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