Structure of cDNA clones and genomic DNA FMRFamide-related peptides (FaRPs) in Helix

A complementary DNA (cDNA) library was prepared from poly(A)(+) RNA isolated from the central ganglia of Helix aspersa from which two classes of FaRP-encoding cDNA clones were identified by hybridization with the Aplysia FMRF-1 clone and oligonucleotides based on known Helix peptides. One type of cDNA (exemplified by HF-1) encodes only the tetrapeptides (FMRFamide and FLRFamide) and is very similar to the tetrapeptide-encoding precursors of other molluscan species. The other type of cDNA (represented by HF-4) encodes no tetrapeptides, but only N-terminally extended peptides, including all of the heptapeptides previously detected in the nervous system as well as some novel predicted peptides, which may be processed into free bio-active peptides. The overall structure of the precursor polypeptide encoded by HF-4 is markedly different from that encoded by HF-1 and more closely resembles the Drosophila FaRP precursor. Restriction digestion and hybridization analysis of genomic DNA indicates that each class of cDNA comes from a single genomic locus and that the two genomic loci span about 14 kbp. Parts of the genomic DNA sequence homologous to HF-1 were determined by PCR of Helix pomatia DNA. All of the coding sequence contained in HF-1 appears to be on one exon since it is contiguous in the genomic PCR products. In the coding region, the sequences from H. aspersa and H. pomatia are about 95% identical, but they are only about 80% identical in the noncoding region.

Synaptic connexions of two symmetrically placed giant serotonin-containing neurones

1. Each giant serotonin cell in Helix pomatia makes synaptic connexions with three non-amine-containing neurones: the anterior, middle and posterior buccal cells.2. Individual e.p.s.p.s, of 500-600 msec duration, were observed in both left and right middle cells following each evoked giant serotonin cell action potential. They were facilitated with repetitive stimulation of the giant serotonin cells and summed to give rise to an action potential. The membrane resistance of the middle cells was reduced when the giant serotonin cells were stimulated to fire rapidly. Evidence is presented which suggests that the link between each giant serotonin cell and each middle cell is monosynaptic.3. Iontophoretically applied serotonin produced a depolarizing potential change in the middle cell perikaryon; the response rapidly desensitized on repetitive application.4. Morphine abolished reversibly the middle cell serotonin potential and antagonized transmission from the giant serotonin cells to the middle cells. Lowering the Na concentration of the medium reversibly diminished the size of the serotonin potential and the giant serotonin cell elicited e.p.s.p.s in the middle cells.5. Reserpine, which depletes serotonin in the giant serotonin cell, impaired transmission from these cells to the middle cells.6. The results suggest that serotonin is the synaptic transmitter released from the giant serotonin cells on to the middle cells and that this system is a suitable model for further analysis of the neuronal role of serotonin.

Histochemical localisation of FMRFamide-gated Na+ channels in Helisoma trivolvis and Helix aspersa neurones

FMRFamide-gated Na+ channels of molluscan neurones belong to the ENa/Deg family of channels which have diverse functions. FMRFamide (Phe-Met-Arg-Phe-NH2) Na+ channels were detected electrophysiologically in specified neurones of Helix (Helix aspersa) and Helisoma (Helisoma trivolvis), and clones (FaNaCs) subsequently identified. We have now made a study to determine the distribution of mRNA for the clones HaFaNaC (Helix) and HtFaNaC (Helisoma) in the nervous systems of these species using standard in situ hybridization techniques. Immunohistochemical experiments were also made using an HtFaNaC antibody to detect the channel protein in Helisoma neurones. Many neurones in the central ganglia, including those which exhibit the FMRFamide Na+ current, stained for FaNaC-mRNA, suggesting a much wider distribution of the channel than was indicated by the earlier work. An immunoreactive response to the channel antibody was also observed in some Helisoma neurones, such as the giant dopamine neurone of the left pedal ganglion, also shown to possess HtFaNaC-mRNA and to exhibit the FMRFamide Na+ current. Taken together, these experiments suggest that the clones HaFaNaC and HtFaNaC are major, if not the only, subunits of the FMRFamide-gated Na+ channel detected electrophysiologically in the identified neurones of these species. However, fewer neurones in Helisoma reacted with the HtFaNaC-antibody than those which exhibited message for the channel. This discrepancy may be due to a difference in sensitivity of the two techniques, or because not all of the channel mRNA is normally expressed as a membrane protein.

Location of a ligand recognition site of FMRFamide-gated Na(+) channels

The second FMRFamide-gated Na(+) channel (HtFaNaC), from Helisoma trivolvis, has been cloned. HtFaNaC has some different pharmacological properties to HaFaNaC, from Helix aspersa, which has enabled a rational approach to be made to start to identify the FMRFamide recognition site. Several chimeras were made by switching sections between the channels. The differences in sensitivity to FMRFamide, and amiloride, were assessed after expression in Xenopus oocytes. The data suggest that a recognition site for FMRFamide, and the potentiating action of amiloride, resides in a sequence of about 120 amino acids in the extracellular loop proximal to the first transmembrane segment.

Cloning and expression of a FMRFamide-gated Na(+) channel from Helisoma trivolvis and comparison with the native neuronal channel

We have cloned a cDNA encoding a Phe-Met-Arg-Phe-NH(2) (FMRFamide)-gated Na(+) channel from nervous tissue of the pond snail Helisoma trivolvis (HtFaNaC) and expressed the channel in Xenopus oocytes. The deduced amino acid sequence of the protein expressed by HtFaNaC is 65 % identical to that of the FMRFamide-gated channel cloned from Helix aspersa (HaFaNaC). HtFaNaC expressed in oocytes was less sensitive to FMRFamide (EC(50) = 70 microM) than HaFaNaC (EC(50) = 2 microM). The two had a similar selectivity for Na+. The amplitude of the FMRFamide response of HtFaNaC was increased by reducing the extracellular concentration of divalent cations. The conductance of the two channels was similar, but the mean open time of unitary events was shorter for expressed HtFaNaC compared to expressed HaFaNaC. Each channel was susceptible to peptide block by high agonist concentrations. In marked contrast to HaFaNaC and other amiloride-sensitive Na(+) channels, amiloride, and the related drugs benzamil and 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), enhanced the FMRFamide response in oocytes expressing HtFaNaC cRNA. The potentiating effects of EIPA and benzamil were greater than those of amiloride. Unitary current analysis showed that with such drugs, there was channel blockade as well as an increased probability of channel opening. The similar permeability of the oocyte-expressed HtFaNaC and the Helisoma neuronal channel, and the susceptibility of both to agonist blockade and blockade by divalent cations, suggest that the channels are the same. However, neuronal channels were less susceptible to enhancement by amiloride analogues and in some patches were more sensitive to FMRFamide than expressed HtFaNaC.

Identification of minority ion-cyclotron emission during radio frequency heating in the JET tokamak

First measurements and identification of minority ion-cyclotron emission (MICE) during ICRF (H)D minority heating in the JET tokamak are presented. An inner wall radiofrequency (rf) probe shows the new single MICE spectral line, down-shifted from the heating frequency and appearing approximately 400 ms after the ICRH switch-on. The line is narrow (Deltaomega/omega approximately 0.04), characterized by the ion-cyclotron frequency of minority protons in the outer-edge midplane plasma and is observed irrespective of whether single or multifrequency ICRH is applied. The observations are consistent with the classical evolution and population of the plasma edge with approximately 3 MeV ICRH protons on orbits near the outboard limiters. Particle loss and energy filtering contribute to a local non-Maxwellian energetic ion distribution, which is susceptible to ion-cyclotron instability.

Ketamine and phenobarbital do not reduce the evoked-potential enhancement induced by electroconvulsive shock seizures in the rat

Electroconvulsive shock (ECS) seizures provide an animal analog of electroconvulsive therapy (ECT). Repeated ECS seizures cause a long-lasting, and perhaps permanent, enhancement of entorhinal-dentate evoked potentials (EPs) in the rat. Recently it has been reported that ketamine protects against ECS-induced EP enhancement. The present study was designed to replicate these findings and to extend them by incorporating a phenobarbital group (to control for ketamine's partial diminution of seizures) and an animal test of antidepressant activity (the Porsolt test). Unexpectedly, we found that neither ketamine nor phenobarbital protected against ECS-induced enhancement of EPs. Both, however, diminished the 'therapeutic' effects of ECS, as modeled by the Porsolt test. These data suggest that the use of ketamine would not eliminate the unwanted effects of ECT and that it might diminish ECT's therapeutic benefits.

Mossy fiber sprouting induced by repeated electroconvulsive shock seizures

The elicitation of repeated focal seizures (kindling) induces mossy fiber sprouting in the hippocampus of the rat. The present study investigated whether repeated generalized seizures also induce mossy fiber sprouting. Human psychiatric patients receive repeated generalized seizures during electroconvulsive therapy (ECT). Male Long-Evans rats received a course of eight electroconvulsive shock (ECS) seizures administered on a 48-h schedule over a course of 2 1/2 weeks. Control subjects received matched handling, but no stimulation. Fourteen days after the last ECS trial, all subjects were sacrificed and their brains subjected to Timm staining. Cell counts and area measures were also taken in the hilus. Significant sprouting, but not significant cell loss, was seen in the fascia dentata of the subjects that had received ECS.

Block of the helix FMRFamide-gated Na+ channel by FMRFamide and its analogues

1. In Helix neurones high doses of Phe-Met-Arg-Phe-NH2 (FMRFamide) often evoke biphasic inward whole-cell currents with brief application, and suppression of the current with prolonged application. With outside-out patches, a transient early suppression of the unitary current amplitude was seen following application of high doses of FMRFamide. 2. Continuous application of a concentration of FMRFamide from 30 microM to 1 mM resulted in a reduction in the amplitude of the unitary currents and an increase in open state noise. There was also an increase in the occurrence of smaller, 'subconductance' currents with the higher concentrations of FMRFamide. Similar effects were seen with FMRFamide on FaNaC expressed in oocytes. The FMRFamide analogues FLRFamide and WnLRFamide were more effective in evoking the lower conductance state. These effects of agonist at high concentrations were voltage dependent suggesting channel block. 3. A similar effect was seen when one of the related peptides FKRFamide, FM(D)RFamide, nLRFamide or N-AcFnLRFamide was co-applied with a low FMRFamide concentration. However, the non-amidated peptides FKRF, FLRF and nLRF and also WMDFamide did not have this effect. 4. The inhibition of unitary currents induced by amiloride was qualitatively different from that produced by FMRFamide analogues with no obvious occurrence of subconductance levels. FMRFamide-gated channels were also blocked by guanidinium, but only at very high concentrations. 5. The results strongly suggest a partial inhibition of current flow through the FMRFamide- gated channel by some part of the agonist or the related antagonist peptide molecules.

Single-channel currents of a peptide-gated sodium channel expressed in Xenopus oocytes

1. Single-channel recordings were made from outside-out membrane patches of Xenopus oocytes injected with the cDNA clone FaNaCh, which encodes a peptide-gated Na+ channel from Helix aspersa. 2. The natural peptides FMRFamide and FLRFamide only activated unitary currents in oocytes injected with FaNaCh; the EC50 values were 1.8 and 11.7 microM, respectively. 3. The slope conductance of the channel was 9.2 pS for both peptides. 4. With FMRFamide, the open probability (Po) of the channel was 0.06 at 0.3 microM and 0.76 at 30 microM, whereas for FLRFamide the open probability increased from 0.04 at 1.8 microM to 0.49 at 50 microM. The Hill coefficient was greater than 1 for both peptides. 5. High concentrations of each peptide evoked very fast flickering between open and closed states which led to decreased unitary current amplitude. 6. At low doses, brief single openings and bursts of longer openings occurred. With higher doses, the occurrence of the brief openings declined and the number of longer openings increased; the duration of the longer openings was shorter with FLRFamide than with FMRFamide. 7. For each peptide, frequency distribution histograms of open events were best fitted by the sum of two exponential components, suggesting the existence of two open states of the channel. Closed events were fitted by the sum of three components, suggesting the existence of three closed states. 8. The data were analysed according to a five-state model in which the brief openings correspond to a single liganded open form of the channel and the longer openings to a doubly liganded open form. According to this interpretation, the greater whole-cell response observed with FMRFamide than with FLRFamide results mostly from a slower closing rate constant for the longer (doubly liganded) channel openings.

Amygdala-kindled and electroconvulsive seizures alter hippocampal expression of the m1 and m3 muscarinic cholinergic receptor genes

Expression of m1 and m3 muscarinic cholinergic receptors mRNAs was examined in rat hippocampus following either: (1) kindling to five Stage 5 amygdala-kindled seizures; or (2) eight electroconvulsive shock (ECS) seizures. Twenty-four hours after the last seizure of either type, there was a significant decrease in both m1 and m3 mRNAs in CA1, CA3 and the dentate gyrus subfields of the hippocampus. Twenty-eight days after the last seizure of either type, there was a significant increase in m1 mRNAs in CA1, CA3, and the dentate gyrus; for m3 mRNAs, there was a significant increase in CA3 28 days after the last ECS seizure, and in CA1 and CA3 28 days after the last kindled seizure. These results suggest that seizures alter the cholinergic system in the hippocampus, and that some of the alterations are very long-lasting.

The first peptide-gated ion channel

Patch-clamp experiments on the C2 neurone of Helix aspersa have shown that the neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) directly gates a Na+ channel. The channel is amiloride-sensitive. Activation of this channel is responsible for the fast excitatory action of the peptide. Using primers based on amiloride-sensitive epithelial Na+ channels, a complete cDNA sequence (FaNaCh) was cloned and sequenced from a Helix library. The sequence is predicted to have just two membrane-spanning regions and a large extracellular loop. When expressed in Xenopus laevis oocytes, the channel responded to FMRFamide. Taken together, these data provide the first evidence for a peptide-gated ion channel. Comparison of the properties of the expressed FaNaCh with the native neuronal channel show small differences in the sensitivities to some drugs and in channel conductance. It is not yet clear whether the native channel is a homo-oligomer or comprises other subunits. The peptide FKRFamide is an effective antagonist of FMRFamide on the expressed and neuronal channels. Nucleotide sequences encoding similar channel proteins occur in neurones of species as dissimilar as man and Caenorhabditis elegans. Some channels are thought to be associated with mechano-sensation, at least one is a proton-gated channel and others may also be ligand-gated channels.

Long-term enhancement of entorhinal-dentate evoked potentials following 'modified' ECS in the rat

Electroconvulsive therapy (ECT) is widely used as a treatment for drug-resistant depression. The animal analogue of ECT is electroconvulsive shock (ECS) seizures. We have recently shown that repeated ECS seizures cause a long-lasting, perhaps permanent, enhancement in entorhinal-dentate evoked potentials in the rat. Our study, however, involved 'unmodified' ECS, whereas in clinical practice ECT is now usually given in its 'modified' form (with near-threshold currents, a short-acting barbiturate, muscle relaxant and oxygen). We have therefore repeated our experiments using modified ECS. Entorhinal-dentate evoked potentials were measured in Long-Evans rats before and after: (1) eight modified ECS seizures; or (2) eight sham modified ECS trials. Despite the use of the modified procedure, a significant and long-lasting enhancement in population spike amplitude was seen in the ECS group. We conclude that the modified procedure does not protect rats against the long-lasting enhancement of evoked potentials. Similar changes may be occurring in the brains of patients subjected to modified ECT.

Modulation of ligand-gated dopamine channels in Helix neurones

Dopamine gates a fast excitatory response in Helix C2 neurones. Whole cell, and multiple unitary dopamine-gated currents showed variable decay rates and desensitization properties, suggesting the presence of more than one channel type. Manipulation of internal free [Ca2+] by various procedures (external zero Ca2+ or 1 mM Co2+, prolonged depolarization, A23187, or flufenamic acid), affected both the amplitude and decay time for the response, and also suggested the presence of separate fast and slowly decaying components. Responses were prolonged by intracellular fluoride a non specific phosphatase inhibitor, and attenuated and shortened by the protein kinase inhibitors H7 and staurosporine, and the calmodulin inhibitor W7. Phorbol ester potentiated and prolonged the response and this effect was reversibly antagonized by the specific protein kinase C inhibitor chelerythrine. Different dopamine-activated unitary currents were distinguished in outside-out patches by conductance (5, 8, 12 and 15pS), rate of recovery from desensitization, and pattern of openings. Discrimination of slow and fast components of the response was possible with apomorphine, ADTN, and caffeine. Paradoxically the dopamine antagonists chlorpromazine and spiperone, but not dopamine itself, stimulated sustained activity of 5pS unitary currents which did not desensitize in outside-out patches. Modulation of different channels underlying the fast dopamine response by protein kinase C, and possibly other mechanisms, provides a potent means of controlling excitatory dopaminergic synaptic transmission.

Actions of FMRFamide-related peptides on the gCa2+ of the C1 neuron in Helix aspersa

The endogenous neuropeptides FMRFamide and FLRFamide (tetrapeptides) reversibly reduced a voltage-activated calcium current in the C1 neuron of Helix aspersa by an average of 20%. Two structurally related heptapeptides, pQDPFLRFamide and pQDPFLRIamide, both derived from another precursor protein in this species, did not reduce the current at all.

The peptide pQFYRFamide is encoded on the FMRFamide precursor of the snail Helix aspersa but does not activate the FMRFamide-gated sodium current

The complete sequence of the FMRFamide precursor cDNA from Helix aspersa is reported here. Since the 5' end of this cDNA is identical to that of the precursor that encodes the heptapeptide analogs of FLRFamide, the two transcripts are probably derived by alternative RNA splicing. A novel pentapeptide, Glp-Phe-Tyr-Arg-Phe-NH2 (pQFYRFamide), predicted from the cDNA sequence, was purified from extracts of H. aspersa ganglia and identified by mass spectroscopy. Partial gene sequences for the FMRFamide precursors of two closely related pulmonate species-Cepaea nemoralis and Polydontes acutangula-were also determined and compared with the cDNA sequence of H. aspersa and a partial gene sequence previously determined from H. pomatia. Not only are the FMRFamide-related sequences and proteolytic processing sites conserved, but the linear arrangement of these landmarks is also retained. Synthetic pQFYRFamide has some effects on the isolated heart and on neuronal potassium currents in H. aspersa that are similar to those of FMRFamide, but it does not activate the neuronal FMRFamide-gated sodium channel.

Ligand-gated ion channels opened by 5-HT in molluscan neurones

1. 5-Hydroxytryptamine (5-HT) activated a fast (70 ms to half maximum) and desensitizing inward current through non-selective channels conducting predominantly monovalent cations in neurons of Helix aspersa. 2. alpha-Methyl-5-HT was equipotent with 5-HT in activating this current, but the known selective agonists at vertebrate 5-HT3 receptors, 2-methyl-5-HT and arylbiguanides were ineffective (< 100 microM). 5-Methoxytryptamine which is inactive on vertebrate 5-HT3 receptors was a very weak agonist. 3. The responses were antagonized by the specific vertebrate 5-HT3 receptor blocker MDL-72222 (IC50 = 1 microM), but were only weakly affected by ondansetron (10 microM). The 5-HT2-type antagonist, ketanserin (< 5 microM) had no effect. The responses were also antagonized by the non-specific antagonists (+)-tubocurarine and strychnine. 4. Unitary currents through channels non-selective for monovalent cations, and with a conductance of 2pS, could be activated repeatedly by 5-HT or alpha-methyl-5-HT in outside-out patches from neurones exhibiting the fast 5-HT-activated current (I[5-HT]fast), even in the presence of 500 microM GDP-[beta S] in the recording pipette. This strongly supports direct-gating of these channels by 5-HT. The properties of these unitary currents resembled those of I[5-HT]fast. 5. The pharmacological properties of this molluscan 5-HT-operated, ligand-gated channel differed sufficiently from known vertebrate 5-HT3-type receptors to suggest that it represents a new class of 5-HT receptor.

Amygdala-kindled convulsions in suspended rats

Amygdala-kindled Long-Evans rats were suspended in a harness--with all four feet off the ground--and their convulsions were triggered, videotaped, and scored. In the suspended subjects, it was found that kindled convulsions involve the hindlimbs as well as the forelimbs and that they involve tonus as well as clonus. These data contradict the commonly held view that kindled convulsions consist only of face and forelimb clonus. They suggest that kindled convulsions resemble the generalized, whole-body convulsions observed in the maximal electroshock model and other "maximal" seizure models.

Dopamine directly activates a ligand-gated channel in snail neurones

Synaptically released dopamine is known to evoke fast as well as slow synaptic potentials in neurones of gastropod molluscs. Here evidence is presented that the fast excitatory response to dopamine is mediated by the direct activation of a ligand-gated channel: unitary currents were observed in outside-out patches of neurones exposed to dopamine, and the response persisted in the presence of intracellular guanosine 5'-o-(2-thiobiphosphate), GDP[beta-S], a condition known to block G-protein-coupled responses to dopamine and other agents. In whole-cell recordings, the fast response desensitized very rapidly; it was less desensitized in outside-out patches, suggesting dependence of desensitization on an intracellular factor. The response to dopamine was blocked by D-tubocurarine and strychnine (both probably by channel blockade), by apomorphine, chlorpromazine and relatively high doses of (+/-)-sulpiride and spiperone. The channel conducts predominantly monovalent cations. Unexpectedly, the fast response to dopamine was also observed in an identified dopaminergic neurone when maintained in isolation in culture. The receptors on the dopaminergic neurone were unevenly distributed, being more abundant on the axon-hillock, axon and neurite terminals.

Long-term changes in entorhinal-dentate evoked potentials induced by electroconvulsive shock seizures in rats

Entorhinal-dentate evoked potentials were measured in rats before and after: (1) eight electroconvulsive shock (ECS) seizures, or (2) matched handling. In animals that received ECS, evoked potentials were significantly enhanced, as evidenced by a long-lasting increase in the amplitude of the population spike. This increase in population-spike amplitude lasted for at least 3 months after the last ECS trial. No evoked-potential changes were observed in the subjects that received matched handling. These data suggest that ECS seizures produce long-lasting, perhaps permanent, changes in the brain.

Properties of an identified dopamine-containing neurone in culture from the snail Helisoma

The giant neurone in the left pedal ganglion of the snail Helisoma trivolvis is homologous with the giant dopaminergic neurone of Planorbis corneus, because the neurones have a very similar location and morphology, and react similarly with glyoxylic acid to produce an intense blue fluorescence, indicating the presence of dopamine. Each of these neurones is therefore referred to as a giant dopaminergic neurone, or GDN. Conditions for the extension of neurites and formation of chemical junctions in culture have been determined for the H. trivolvis GDN, and compared with other neurones from this species. The pattern of neurites that extended from the neurone was indistinguishable from that of another identified aminergic neurone, the large serotonergic neurone (LSN), but differed markedly from many other central neurones. However, the type of substrate also greatly affected the pattern of the neurites observed. Some of the electrical properties of the GDN in culture differed from those recorded in situ: peak spike amplitude was increased, spike half-width reduced and the firing pattern of the neurone was altered. However, the resting membrane potential was very similar. The GDN formed chemical and electrical junctions in culture. The chemical junctions formed were of the same type as those found in situ. They formed rapidly, within 18 h after plating, but were not stable and were lost within 48 h, to be replaced by a non-rectifying electrical junction. A chemical junction may form in either direction between the GDN and the LSN, but only rarely did such junctions allow transmission in both directions, as observed in situ. Experiments in which neurones were plated out at different times suggested that the direction of formation of the chemical junction was not dependent on the degree or state of neurite extension.

N-terminally extended FMRFamide-related peptides of Helix aspersa: processing of the precursor protein and distribution of the released peptides

Sequencing of cDNA clones reveals a precursor protein that can be processed into 10 different hepta-FaRPs. Two of the peptides are previously undescribed and are N-terminally extended forms of-YMRFamide, making them the only methionine-containing peptides in the precursor. They are separated from the main cluster of hepta-FaRPs by a recognition site (RQKR) for the Golgi-resident proteolytic enzyme furin. Antisera raised against the synthetic peptide KQDPFLRFGK specifically stain the clusters of neurons in the parietal ganglia that have been shown to contain hepta-FaRP mRNA. These antisera recognize two major protein bands of 35 and 23 kDa on immunoblots. Evidence is presented to identify the larger band as the precursor protein and the smaller band as the fragment containing the main cluster of hepta-FaRPs produced after furin cleavage. A series of immunostaining bands of 22-13 kDa suggests sequential and non-preferential N- or C-terminal cleavage at the mainly monobasic (K and R) sites that link all of the peptide sequences throughout the 23-kDa fragment, to yield the preamidated hepta-FaRPs. Immunostaining of sections shows punctate staining in the perikarya of the parietal cluster neurons commensurate with label within the endoplasmic reticulum and Golgi apparatus. Staining is followed through the axons to many fibers in the nerve trunks and is picked up as fine processes within the skin. These observations indicate that the antiserum used here recognizes one or more of the processed hepta-FaRPs, a view confirmed by radioimmunoassay. The abundance of immunoreactive fibers within the skin suggests a major role for the peptides in this tissue.

The neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) directly gates two ion channels in an identified Helix neurone

FMRFamide (i.e. Phe-Met-Arg-Phe-NH2) application to the C2 neurone of Helix caused a depolarizing response which consisted of a large, rapidly developing, and rapidly desensitizing inward current, underlain by a smaller, slower inward current which did not desensitize. Both currents were carried through sodium-selective channels which were insensitive to D-tubocurarine, and the to the fast sodium channel blockers tetrodotoxin (TTX) and lignocaine. Only the faster, desensitizing current could be blocked by amiloride. FMRFamide also activated two types of unitary inward currents with slightly differing amplitudes in outside-out patches taken from the C2 neurone, both through sodium-selective ion channels. Only the smaller unitary currents readily desensitized and were susceptible to block by amiloride, and they also activated more rapidly. Unitary currents of both types were recorded in outside-out patches in the absence of freely diffusible intracellular mediators, and were also activated when guanosine 5'-O-(2-thiodiphosphate) (GDP [beta-S]) was included in the recording pipette solution. This supports a tight receptor/channel coupling for both responses, with no involvement of GTP-binding proteins. Further, the very fast rate of activation of the smaller channels, which generally carry the major part of the FMRFamide-induced current, strongly indicates that these channels are ligand gated.

Expression of mRNA encoding FMRFamide-related peptides (FaRPs) in the nervous system of Helix aspersa

The FMRFamide-related peptides (FaRPs) of Helix fall into two groups with often different pharmacological effects: the tetrapeptides FMRFamide and FLRFamide (tetraFaRPs) and the heptapeptides, which have the general structure XDP(F or Y)LRFamide (heptaFaRPs). Previously, we have shown that each group of FaRPs is encoded within a separate type of cDNA clone, a situation which corresponds to two distinct mRNA species existing in the CNS of Helix. Here, we report on the expression patterns of the two FaRP mRNAs both through embryo-genesis and in the fully differentiated regions of the adult nervous system. The levels and locations of FaRP mRNAs were studied by molecular and in situ hybridization using antisense riboprobes. The onset of expression of FaRP mRNAs occurs in Helix embryos about half-way between egg laying and hatching. First detection of the FaRPs themselves occurs about 2 days later. In embryos, as in the adult CNS, the heptaFaRP mRNA is at least five times more abundant than the tetraFaRP mRNA. In adults, the tetraFaRP mRNA is located primarily in the cerebral ganglia, most obviously in the C3 neuron, but also in a crescent-shaped cluster of small neurons lying anterior to C3. Occasional neurons expressing the tetraFaRP mRNA are detected in the parietal ganglia, but these have not yet been mapped. In contrast, the heptaFaRP mRNA is expressed almost exclusively in the parietal ganglia: in large clusters of about 100 neurons lying near to the anterior surface. The most interesting aspect of FaRP mRNAs is that their expression is not only exclusive to a relatively small number of specified neurons, but that expression appears to be mutually exclusive, that is, a particular neuron expresses only the mRNA for tetra-FaRPs or heptaFaRPs, never both. These results are discussed in relation to what we now know about the structure of the individual mRNA molecules.

Biological activity and receptor binding properties of some C-terminally modified analogues of FMRFamide

The functional role of the C-terminal amide group (-CONH2) of the molluscan regulatory peptide FMRFamide has been examined in two sets of analogues based on FnLKFamide and FnLRFamide (nL = norleucine). In each series the amide group was replaced by -CONHCH3, -CON(CH3)2, -CONHNH2, -COOCH3, -CH2OH, and -COOH. The analogues were tested for their ability to bind to receptors in membranes from Helix aspersa circumoesophageal ganglia and for their biological effects on the isolated Helix heart. The results indicate i) that agonist activity, but not binding to the receptor, requires the presence of the amide carbonyl group; ii) the hydrogen atoms of the amide group are not essential either for binding or for agonist activity (the mono- and dimethylamides were more effective than the parent compounds on both counts); iii) the is more effective an agonist than is the amide in stimulating Helix heart.

Biological activity and receptor binding properties of some analogues of pQDPFLRFamide

To investigate the role of the N-terminal region of the heptapeptide FMRFamide-like peptide, pQDPFLRFamide, three analogues were synthesized. The analogues [pQNPFLRFamide, pQDAibFLRFamide (Aib = aminoisobutyric acid) and pQDGFLRFamide] contained modifications at amino acid residues 2 and 3, which we believed might be critical for maintaining the bioactive conformation of the heptapeptide. The analogues were tested for their ability to bind to receptors in membranes from Helix aspersa circumoesophageal ganglia and for their biological effects on the isolated Helix heart, the Helix tentacle retractor muscle, and extensor-tibiae neuromuscular preparation of the locust. Schistocerca gregaria. The substitution of Asn for Asp2 and that of Aib for Pro3 were conservative with respect to retention of heptapeptide-like biological activity, whereas the substitution of Gly for Pro3 significantly improved the binding affinity of the peptide for the FMRFamide receptors and conferred on the peptide some characteristic FMRFamide-like biological activity. Thus, pQDPFLRFamide bioactivity may depend on a bent conformation in solution.

The neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) increases levels of inositol 1,4,5-trisphosphate in the tentacle retractor muscle of Helix aspersa

The C3 neurone, which acts as a motoneurone for the tentacle retractor muscle in Helix aspersa, contains both Phe-Met-Arg-Phe-NH2 (FMRFamide) and acetylcholine (ACh). Each of these transmitter substances evokes contraction of the isolated muscle. FMRFamide induces a delayed rise in tension followed by phasic contractions. Unlike the response to ACh, this response is not associated with a depolarization of the muscle cells. Here we show that FMRFamide stimulates the inositol phosphate second messenger system in the muscle and causes a significant increase in total inositol trisphosphate (InsP3) levels. The isomer which releases intracellular Ca2+ stores, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), is increased in a similar proportion to the total InsP3. The production of Ins(1,4,5)P3 is therefore likely to be involved in the response of the muscle to FMRFamide and may account for the oscillatory nature of the mechanical response. The N-terminally extended heptapeptide pGlu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (pQDPFLRFamide), which relaxes the muscle, had no acute effect on InsP3 levels. Indirect evidence also indicates that intracellular Ca2+ stores are required for the generation of the FMRFamide response.

FMRFamide-related peptides potentiate transmission at the squid giant synapse

The stellate ganglion of the squid Loligo pealli contains the neuropeptides Phe-Met-Arg-Phe-NH2 (FMRFamide), Phe-Leu-Arg-Phe-NH2 (FLRFamide) and at least one N-terminally extended FMRFamide-related peptide that is yet to be fully characterized. Both local application and arterial perfusion of FLRFamide potentiate transmission at the giant synapse. The N-terminally related peptide Ser-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (SDPFLRFamide) produced a similar effect. The threshold for both the tetra- and the hepta-peptides was less than 10 microM. Potentiation could be detected as an increase in rate of rise of the EPSPs, as an increase in amplitude of the EPSP in the absence of spikes, or under voltage clamp as an increase in the EPSC. The effect was most pronounced when the synapse was fatigued by high frequency stimulation. Another molluscan peptide, eledoisin and also leucine enkephalin were without effect. In the absence of any detectable effects of FLRFamide on the resting membrane potential of either pre- or postsynaptic terminals or on the presynaptic spike, it is suggested that the peptide influences transmitter mobilization. However, the peptide could also exert small changes in preterminal calcium currents, which so far we have been unable to detect.

Effects of dopamine D1 antagonists SCH23390 and SK&F83566 on locomotor activities in rats

The effects of the dopamine D1 antagonists R-(+)-7-chloro-8-hydroxy-3-methyl-1phenyl-2,3,4,5-tetrahydro-1-H-3 -benzazapine (SCH23390) and (+-)-7-bromo-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1- H-3-benzazapine (SK&F83566) were tested for 2 h on linear locomotor, rearing, stereotypy, and margin times in an open field. Each of the antagonists attenuated the duration of linear locomotion, rearing, and stereotypy times in a dose- and time-dependent manner. The effectiveness of the antagonists was relatively brief and SCH23390 was more effective than SK&F83566 on each behavior. The two antagonists had differential effects on margin time.

The wide range of actions of the FMRFamide-related peptides and the biological importance of peptidergic messengers

The importance of peptides as intercellular messengers is discussed. The view is put forward that peptides evolved early in evolution as chemical messengers and that they have come to exert a wide range of actions. Using as an example the FMRFamide (Phe-Met-Arg-Phe-NH2) related peptide family of molluscs, the wide range of peptide actions on membrane currents is discussed and considered in relation to co-localization of peptides with low molecular weight (or "classical") intercellular messengers.

Intracerebral haloperidol potentiates the dorsal immobility response in the rat

The effects of intracerebral microinjections of 4-[4-(4-chlorophenyl)-4-hydroxy-1-piperidinyl]-1-(4- fluorophenyl)-1-butanone (haloperidol) (1.0 microgram, 0.5 microliter) in five regions of the brain were tested on the duration of the dorsal immobility response (DIR) and the cling and bar catalepsy in the rat. The duration of the DIR was significantly potentiated (but not the cling and bar catalepsy) following 2-h postinjection of haloperidol in the caudate putamen, nucleus accumbens, and globus pallidus but not in the substantia nigra pars compacta or cortex. These data further expand the previous evidence of regional variations in dopamine to the effects upon inhibitory behaviors.

Rapid visualization of NMDA receptors in the brain: characterization of (+)-3-[125I]-iodo-MK-801 binding to thin sections of rat brain

We have developed and characterized a method for the rapid autoradiographic determination of receptor sites for the non-competitive NMDA receptor antagonist, MK-801, using an iodinated form of the compound, (+)-3-[125I]-iodo-MK-801. The binding site was shown to exhibit those criteria necessary for its definition as a receptor site, i.e., the binding was saturable, of high affinity, easily reversible, and stereospecific. Saturation analysis of binding to thin brain sections revealed a Bmax of 108.1 +/- 10.5 fmol/mg protein and a Kd of 383 +/- 67 pM. The pharmacology of the interaction of the ligand with the binding site yielded good correlation between the potency of various substances to complete for the binding site and their ability to act as antagonists of NMDA. Autoradiographs of thin coronal brain sections using (+)-3-[125I]-iodo-MK-801 yielded high quality images in 24-48 h with a distribution of binding sites paralleling that reported for the tritiated form of the ligand, i.e., with high densities in the hippocampus, cerebral cortex and lateral septum. Other areas with significant binding included parts of the thalamus, the amygdala and the olfactory tubercules. Furthermore, due to its high specific activity, this ligand lends itself to the study of regions not rich in MK-801 binding sites, such as the diencephalon.

Modulation of voltage-dependent calcium current in Helix aspersa buccal neurones by serotonin and protein kinase C activators

In Helix aspersa, activation of the cerebral giant serotonin neurones (GSNs) evokes a biphasic, excitatory synaptic response in the M neurones of the buccal ganglia. Local application of serotonin to the current-clamped M neurones also evokes fast and slow depolarizing responses. The slow response is thought to be dependent on calcium ions, whereas sodium ions have been implicated in the fast response. Here we provide further evidence that the slow response results from an increase in conductance to calcium ions, and show that okadaic acid, an antagonist of protein phosphatases 1 and 2A, potentiates the effect of serotonin, suggesting that the response is phosphorylation dependent. Further, agents known to activate protein kinase C, such as 1-oleoyl-2-acetyl-rac-glycerol and active phorbol esters (but not an inactive one) were found to increase the calcium current (actually carried by barium ions) of the M neurones. Such data suggest that the slow synaptic response mediated by serotonin can occur by activation of protein kinase C and phosphorylation of the affected voltage-sensitive calcium channels, or some closely associated protein(s).

Identified Helix Neurons: Mutually Exclusive Expression of the Tetrapeptide and Heptapeptide Members of the FMRFamide Family

Extracts were prepared from selected neurons taken from the central ganglia of the pulmonate snail Helix aspersa, and parallel radioimmunoassay (RIA) and high pressure liquid chromatography (HPLC) were used to analyze for FMRFamide-related peptides (FaRPs). Some neurons (e.g., the cerebral C3 neuron) contained only the tetrapeptides related to FMRFamide (tetra-FaRPs), whereas two clusters of neurons in the parietal ganglia contain a preponderance of the hepta-FaRPs. Using cloned cDNA probes in molecular hybridization studies, we showed that the C3 neuron (and some other large neurons) contain the mRNA species that encodes the tetra-FaRPs. In contrast, the neurons of the parietal clusters predominantly express the mRNA that encodes the hepta-FaRPs. These results were confirmed by in situ hybridization with antisense RNA on whole mount ganglia. Each type of experiment supports the view that FaRP-containing Helix neurons express either the tetra-FaRPs or the hepta-FaRPs, but not both.

Potentiation of the dorsal immobility response following intrastriatal injections of enkephalins

The effects of bilateral intrastriatal injections (1.0 microgram/side) of leucine5- and methionine5-enkephalins and their related nonopiate fragments upon three measures of immobility over a time course were investigated. Both leucine5-enkephalin and des-Tyr1-leucine-enkephalin potentiated the duration of the dorsal immobility response (DIR) 15 min postinjection and over a 1-h time course. On the other hand, methionine5-enkephalin and des-Tyr1-methionine-enkephalin potentiated the duration of the DIR at 5 and 15 min. These enkephalins and their fragments had no effect upon vertical cling and bar catalepsy. In a second study, an SC injection of 4 mg/kg naloxone 15 min prior to the central injections blocked the potentiation of the DIR effects of the enkephalins.

Effects of intracerebral quinpirole on locomotion in rats

The effects of the dopamine D2 receptor agonist quinpirole (LY 171555) on locomotor activity and margin time (thigmotaxis or wall-hugging) were measured for 2 h in rats injected either s.c. (vehicle, 0.02, 2.0 mg/kg) or directly into either the dorsal striatum or nucleus accumbens (vehicle, 0.1, 1.0, 10, 20 or 40 micrograms bilaterally in each site). In all groups, margin time decreased as drug dose increased. As in previous research, quinpirole given s.c. decreased locomotor activity at a low dose and had a biphasic effect on locomotor activity at the high dose. Both of these effects were also elicited by quinpirole injected directly into the dorsal striatum; 10 and 20 micrograms decreased locomotion immediately, while 40 micrograms led to both the immediate decrease and a later increase. In contrast, the lowest doses of quinpirole (0.1 and 1.0 microgram) injected into the nucleus accumbens led to an increase in locomotion from 20 to 60 min, while the higher doses led only to the early decrease. Thus, both the locomotor activating and inhibiting effects of quinpirole are found in both the nucleus accumbens and the dorsal striatum, but the differing dose-response relationships indicate that the mechanisms are not the same in these two brain regions.

Dopamine D1 antagonists potentiate the durations of bar and cling catalepsy and the dorsal immobility response in rats

The effects of dopamine D1 antagonists SCH 23390 or SK&F 83566 (at SC doses of 0.00, 0.01, 0.05, and 0.1 mg/kg) were tested for 2 h on bar and cling catalepsy and the dorsal immobility response. Each of the drugs potentiated the duration of each of the three measures of immobility in a dose- and time-dependent manner. Each of the drugs had rapid but brief effects on all three response measures; the peak effect of SK&F 83566 took place at 20 min and that for SCH 23390 at 40 min for each behavior. At each effective drug dose, SCH 23390 had a greater effect than SK&F 83566 on each behavior. Dopamine D1 antagonists potentiated three different immobility responses, as do dopamine D2 antagonists.

The neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) can activate a ligand-gated ion channel in Helix neurones

This report presents evidence that the molluscan neuropeptide FMRFamide can directly activate a ligand-gated ion channel in Helix neurones. Using the patch-clamp technique we have observed unitary currents activated by the application of FMRFamide onto outside-out patches. As for the whole-cell response, Na+ ions are the main charge carriers. We conclude that FMRFamide may act as a fast depolarizing neurotransmitter in the Helix nervous system.

Effects of cholinergic agonists on the dorsal immobility response

The effects of pilocarpine, arecoline, and physostigmine on the dorsal immobility response in ovariectomized female rats were tested. The effect of pretreatment with the cholinergic antagonist scopolamine was also tested. Pilocarpine, arecoline, and physostigmine all significantly decreased the duration of the dorsal immobility response in a dose-dependent way. Scopolamine significantly blocked the effect of pilocarpine. Thus, cholinergic agonists attenuate the dorsal immobility response via their effect on cholinergic systems in the central nervous system.

Actions of steroids and bemegride on the GABAA receptor of mouse spinal neurones in culture

The effects of a synthetic and an endogenous steroid were studied on the GABAA receptors of isolated mouse spinal neurones, maintained in culture. Low doses of alphaxalone reversibly increased GABA-evoked whole-cell currents. Alphaxalone at higher doses (10-50 microM), when pressure ejected onto spinal neurones, also directly evoked a membrane chloride current. Such currents were reversibly suppressed by bicuculline (a GABAA antagonist) and enhanced by phenobarbitone. 5 beta-Pregnan-3 alpha-ol-20-one, a progesterone metabolite, dose-dependently potentiated the amplitude of GABA-evoked whole-cell currents. The mechanism of potentiation was examined at the single-channel level using outside-out patches from spinal neurones. The main action of the steroid on the GABAA receptor appears to be similar to that found for barbiturates, in that they prolonged GABA-activated bursts of channel openings. Bemegride had an antagonistic action on the GABAA receptor, suppressing both GABA- and pentobarbitone-evoked whole-cell currents to similar extents.

Effects of intrastriatal hormones on the dorsal immobility response in male rats

Previous research has shown that estradiol administered either peripherally or directly into the striatum potentiates the dorsal immobility response (DIR) in ovariectomized female rats. Male rats are even more responsive than females to intrastriatal estradiol, and furthermore respond to the effects of catecholestrogens while females do not. In order to determine whether the heightened effects of estrogens in males are due to conversion to catecholestrogens, castrated male rats were given bilateral intrastriatal implants of moxestrol, which cannot be readily converted to a catecholestrogen, and diethylstilbestrol, which can. To determine whether the effects of intrastriatal estradiol in male rats might be related to the effects of androgens on the striatum, castrated male rats were given bilateral intrastriatal implants of testosterone, which can be aromatized to estrogen, and 5 alpha-dihydrotestosterone, which cannot. The effects of each of the hormones tested were measured against those of cholesterol (an inactive control substance) and 17 beta-estradiol. In each case the DIR was measured four hours after the hormone implant. Both synthetic estrogens and 17 beta-estradiol significantly potentiated the DIR, while neither of the androgens had an effect. Thus, the effects of estradiol, synthetic estrogens and catecholestrogens on the male striatum appear to be due to the estrogenic properties of these hormones.

Effects of intrastriatal hormones on the dorsal immobility response in the rat

Previous research has shown that the dorsal immobility response (DIR) changes significantly in duration across the estrous cycle. In order to test whether gonadal steroid hormones act directly on the striatum to modulate this behavior, ovariectomized female Long-Evans hooded rats were given bilateral intrastriatal implants of 17 beta-estradiol, 2-hydroxyestradiol, progesterone, or cholesterol. These implants were made at one-week intervals, each animal receiving each treatment in a Latin square design. Four hours after each hormone implant, the animals were tested for the DIR. Only rats receiving the intrastriatal 17 beta-estradiol implant were significantly different from those receiving cholesterol, and showed greatly potentiated DIR's.

The effects of intrastriatal hormones on the dorsal immobility response in gonadectomized male and female rats

Previous research has shown that intrastriatal estradiol potentiates the dorsal immobility response in ovariectomized female rats. In order to test whether the gonadal steroid hormones act on the male striatum in the same way, gonadectomized male and female Long-Evans hooded rats were given bilateral intrastriatal implants of 17 beta-estradiol (17 beta-E2), 17-alpha-estradiol (17-alpha-E2), 2-hydroxyestradiol (2-OH-E2), 4-hydroxyestradiol (4-OH-E2), or cholesterol. Four hours after the hormone implant the dorsal immobility response (DIR) was measured. In the ovariectomized females, the DIR was significantly potentiated only by 17 beta-E2 and 17-alpha-E2. In the castrated males, the DIR was significantly potentiated by 17 beta-E2, 17-alpha-E2, 2-OH-E2, and 4-OH-E2. While the DIR durations did not differ between males and females after intrastriatal cholesterol, the males had significantly longer DIR durations after each of the other hormones. These results are discussed in terms of estradiol stereospecificity and the properties of catechol estrogens in male and female rats.

An electrophysiological investigation of the characteristics and function of GABAA receptors on bovine adrenomedullary chromaffin cells

The characteristics and function of gamma-aminobutyric acidA (GABAA) receptors expressed on bovine chromaffin cells in culture have been investigated using patch-clamp techniques. In voltage-clamped whole-cells, locally applied GABA (100 microM) evoked a transmembrane chloride current which demonstrated outward rectification. The amplitude of such currents was reversibly suppressed by the GABAA receptor antagonists bicuculline, picrotoxin and RU5135, and enhanced by the general anaesthetic propanidid. Glycine (100 microM) and baclofen (100 microM) were ineffective as agonists. In support of a physiological role for GABA in the adrenal medulla, the co-existence of GABAA and nicotinic acetylcholine (ACh) receptors was demonstrated on whole cells and outside-out membrane patches. Ionophoretically applied GABA reduced the amplitude of depolarization and action potential discharge occurring in response to locally applied ACh (100 microM), but had no effect upon the underlying ACh-induced current. In addition, an excitatory action of GABA was demonstrated by recording action potential waveforms in cell-attached patches. The results are discussed in the context of a GABA-ergic regulation of catecholamine secretion.

Effects of intracerebral estradiol on the dorsal immobility response in the rat

The effects of intracerebral implants of 17 beta estradiol and cholesterol in five brain regions were tested on the duration of the dorsal immobility response in ovariectomized female rats. The dorsal immobility response was significantly prolonged by 4-hr implants of 17 beta estradiol in the dorsal striatum and nucleus accumbens, but not in the cortex, the globus pallidus, or the substantia nigra pars compacta. These data further support previous evidence that estradiol acts directly on the striatum to affect behavior in the rat.