Dietary enrichment with omega-3 polyunsaturated fatty acids reverses age-related decreases in the GluR2 and NR2B glutamate receptor subunits in rat forebrain.

Ageing is associated with a decrease in the brain content of omega-3 polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and with decreased neuroplasticity. The glutamate receptor subunits GluR2 and NR2B play a significant role in forebrain synaptic plasticity. We investigated GluR2 and NR2B in the aged prefrontal cortex, hippocampus and striatum, and tested if treatment with a preparation containing EPA and DHA can reverse age-related changes. The study compared adult and old (3-4 and 24-26 month) rats, and the latter were fed a standard diet or a diet supplemented for 12 weeks with omega-3 PUFA at 270mg/kg/day (ratio EPA to DHA 1.5:1). Ageing was associated with decreases in the GluR2 and NR2B subunits in all structures. These decreases were fully reversed by omega-3 PUFA supplementation. Age-related changes in the phospholipid PUFA content were also seen. Decreases in DHA were mostly corrected by supplementation. This study supports the neuroprotective effect of omega-3 fatty acids in brain ageing, and illustrates specific mechanisms underlying this effect.

Causes of elevated troponin I with a normal coronary angiogram.

BACKGROUND: The new definition of myocardial infarction (MI) emphasizes the pre-eminent role of troponin for diagnosis. Troponin rise indicates myocardial injury, but is not synonymous with infarction or ischaemia. AIMS: To review the precipitating event for troponin elevation in patients with angiographically normal coronary arteries, in a district general hospital. METHODS: Consecutive patients with elevated troponin I (TnI) who underwent angiography for suspected coronary disease were included in the present study if they had normal or mild disease (<50% diameter loss without complex features or thrombus). Precipitating event for TnI elevation was assigned on the totality of clinical evidence. RESULTS: Twenty-one patients qualified, with an average age of 50 years (range 33-73). Sixty-two per cent of participants were female. Troponin release was attributed to tachycardia in six patients, only two of whom had haemodynamic compromise. Physical exertion was the precipitating factor in two patients; pericarditis in two patients; and severe congestive heart failure in one patient. Ten of 21 patients had no identifiable cause for a rise in TnI concentration. Five of 21 patients had left-ventricular wall motion abnormalities. There were no deaths or MI at 41 +/- 24 weeks follow up. CONCLUSION: Troponin is a sensitive marker of myocardial injury and may rise following apparently minor insults. A rise in TnI concentration may have a cause other than acute coronary syndrome and may occur without significant angiographic coronary artery disease.

Trypanosoma brucei: lack of cross-resistance to melarsoprol in vitro by cymelarsan-resistant parasites.

We have examined cross-resistance between trypanocidal drugs using a well-characterised drug-sensitive line, 247, and its cymelarsan-resistant derivative, 247melCyR. The cymelarsan-resistant line was cross-resistant to trimelarsen and melarsen oxide, and partially cross-resistant to two diamidines, pentamidine and berenil (diminazene aceturate). It was cross-resistant to lipid-soluble melarsoprol in vivo but to only a trivial degree in two in vitro assays. The potential role of adenosine transport in arsenical-induced killing of parasites was investigated. Adenosine, adenine, and the diamidines, but not inosine, were able to inhibit killing of drug-sensitive STIB 247 trypanosomes by cymelarsan and melarsen oxide in a concentration-dependent manner. These results are consistent with the view that these arsenical compounds enter trypanosomes via an adenosine-specific transporter. Melarsoprol-induced killing of trypanosomes was unaffected, however, by either purine and to only a slight degree by the diamidines. These data suggest that melarsoprol can enter trypanosomes by a route other than through an adenosine transporter and that there may be two mechanisms contributing to arsenical resistance in this drug-resistant line of trypanosomes.

Identification, tissue localisation and physiological effect in vitro of a neuroendocrine peptide identical to a dipteran Leu-callatostatin in the codling moth Cydia pomonella (Tortricidae: Lepidoptera).

A neuroendocrine peptide of the Leu-callatostatin family, LPVYNFGL-NH2, has been isolated from tissue extracts of 5th instar larvae of the codling moth, Cydia pomonella (Lepidoptera). It is identical to a peptide previously isolated from the blowfly, Calliphora vomitoria (Diptera). The distribution of this peptide within the tissues of C. pomonella has been mapped by immunocytochemistry using antisera raised against LPVYNFGL-NH2. Midgut endocrine cells contain Leu-callatostatin immunoreactivity, as do several paired Leu-callatostatin neurones in the brain and ventral nerve cord. Within the visceral nervous system, the frontal ganglion contains four Leu-callatostatin neurones. Axons from these cells combine with others originating from neurones in the brain and project within the nervi cardiostomatogastrici to innervate the tissues of the foregut. In particular, the oesophageal valve has a prominent ring of Leu-callatostatin-immunoreactive fibres. The synthetic peptide, LPVYNFGL-NH2, has a potent reversible inhibitory effect in vitro on all visible forms of spontaneous contractile activity of the foregut, including closure of the oesophageal valve. Complete myoinhibition is observed at peptide concentrations from 10(-10 )to 10(-16) M. These results, in conjunction with the results of similar studies on cockroaches, crickets and flies, suggest that the Leu-callatostatins are a ubiquitous family of insect neuroendocrine peptides with an important role in the control of gut motility.

Lepidopteran peptides of the allatostatin superfamily.

Peptides of the allatostatin superfamily with the C-terminal amino acid sequence -YXFGL-NH2 have been isolated and identified from the lepidopterans, the codling moth, Cydia pomonella (Tortricidae) and the bollworm, Helicoverpa armigera (Noctuidae). The peptides, designated cydiastatins and helicostatins respectively, were monitored during purification with radioimmunoassays based on the callatostatins of the blowfly Calliphora vomitoria. The eight peptides from each of the two species appear to form an homologous series with four identical and three that differ by a single amino acid. This study demonstrates the ubiquitous nature of this family of peptides in insects.

Isolation and identification of multiple neuropeptides of the allatostatin superfamily in the shore crab Carcinus maenas.

20 neuropeptides belonging to the allatostatin superfamily were isolated from extracts of cerebral and thoracic ganglia of the shore crab Carcinus maenas. They were purified by HPLC, monitored by radioimmunoassay and identified by mass spectrometry and amino acid sequencing. The allatostatins are characterised by a common C-terminal pentapeptide sequence -YXFGL-NH2. Previously such peptides have only been reported from insects. In insects the variable post-tyrosyl residue is restricted to Ala, Asn, Asp, Gly or Ser. In C. maenas, however, there are only two types; thirteen of the peptides having a post-tyrosyl Ala and the other seven, a post-tyrosyl Ser. The crab peptides include the shortest allatostatins so far identified (YAFGL-NH2 and YSFGL-NH2) as well as the longest, a 27-residue peptide. The total of 20 peptides exceeds the highest number of allatostatins found in any of the insects investigated so far (14 in Periplaneta americana). It is of interest that, despite their clear homology, none of the peptides of C. maenas is identical to any of the more than 50 known insect allatostatins. The crab allatostatins show evidence of gene duplication and mutation that has resulted in several sub-groups with close structural similarities. For example, there are four heptapeptides with the common C-terminus -PYAFGL-NH2 that differ only at the N-terminal residue, which is either Glu, Asp, Asn or Ser. Other motifs, variously extended at the N-terminus, include -GPY(A/S)FGL-NH2 (three peptides), -DMY(A/S)FGL-NH2 (three peptides), and -GQY(A/S)FGL-NH2 (two peptides). Unique among the allatostatin superfamily, one of the crab peptides has a Tyr for Phe substitution at position three from the C-terminus (GGPYSYGL-NH2). Immunocytochemistry has provided clues to the functions of the allatostatins in crustaceans by showing their widespread presence in the central and stomatogastric nervous systems.

Identification of the dipteran Leu-callatostatin peptide family: the pattern of precursor processing revealed by isolation studies in Calliphora vomitoria.

Information from the Leu-callatostatin gene sequences of the blowflies Calliphora vomitoria and Lucilia cuprina was used to develop antisera specific for the variable post-tyrosyl amino-acid residues Ser, Ala and Asn of the common Leu-callatostatin C-terminal pentapeptide sequence -YXFGL-NH2. Radioimmunoassays based on these antisera were used to purify peptides from an extract of 40000 blowfly heads. Five neuropeptides of the Leu-callatostatin family were identified. Three have a seryl residue in the post-tyrosyl position. Two of these are octapeptides that differ only at the N-terminal residue; NRPYSFGL-NH2 and ARPYSFGL-NH2, whilst the third is the heptapeptide derived by N-terminal trimming; RPYSFGL-NH2. Two octapeptides in which X is Ala and Asn were also identified; VERYAFGL-NH2 and LPVYNFGL-NH2. The latter peptide is derived by processing at the internal dibasic site of a putative heneicosapeptide encoded by the DNA. These findings stress the necessity to have putative structures verified at the peptide level. Potent, reversible inhibitory effects on the spontaneous contractile activity of the blowfly rectum were recorded for ARPYSFGL-NH2 (monophasic dose-response curve with an IC50 = 10 fM) and for LPVYNFGL-NH2 (biphasic dose-response curve with IC50 values of approximately 1 fM and 1 nM). It is suggested that regulation of gut motility in insects, rather than an allatostatic function, may represent an ancestral and universal function of the allatostatins. One of the reasons for the large number of members of the Leu-callatostatin family appears to be in the provision of an integrated form of gut motility control, with different peptides controlling specific regions of the gut.

Characterisation of cloned lines of Trypanosoma brucei expressing stable resistance to MelCy and suramin.

Two cloned drug-sensitive stocks of Trypanosoma brucei (STIB 247 and STIB 386) were each used to generate cloned lines expressing resistance to the melaminophenyl arsenical drug cymelarsan (247MelCyR and 386MelCyR) and to suramin (247SurR and 386SurR). The drug-resistance phenotypes were stable after passaging in mice in the absence of drug pressure and three of the lines were transmitted through tsetse flies with no alteration of drug-resistance. There was no evidence of cross-resistance between melCy and suramin in vivo. Twenty-four hour growth inhibition assays were conducted on bloodstream and procyclic forms in axenic in vitro cultures. Suramin-resistance was expressed in bloodstream forms but not in the procyclic stage, while the melCy-resistant lines expressed melCy-resistance in both stages. No cross-resistance between melCy and suramin was observed. Cross-resistance between melCy and another arsenical drug, melB (melarsoprol), was observed in vivo, but to only a very limited extent in vitro. We propose that this difference between the in vivo and in vitro results for melB may indicate that an alteration in a surface adenosine transporter responsible for reduced melCy uptake was bypassed by melB over 24 hours in vitro.

Analysis of the murine ecotropic leukemia virus receptor reveals a common biochemical determinant on diverse cell surface receptors that is essential to retrovirus entry.

Two residues, tyrosine 235 and glutamic acid 237, of the ecotropic murine leukemia virus receptor (ATRC1) have been shown to be essential for receptor-mediated virus envelope binding and entry. We performed genetic analyses to examine the biochemical contribution of these residues in a productive virus-receptor interaction. Altered ATRC1 receptors bearing either a phenylalanine, a tryptophan, a histidine, or a methionine at position 235 mediated ecotropic virus entry comparable to that mediated by ATRC1. In contrast, altered ATRC1 receptors bearing alanine, threonine, serine, or proline at position 235 exhibited a 300- to 10,000-fold decrease in receptor capability. Furthermore, substitution of tyrosine or phenylalanine into the corresponding position (242) of the homologous human protein that lacks ecotropic virus receptor capability resulted in acquisition of ecotropic virus receptor function comparable to that of ATRC1. Substitution of a tryptophan or a histidine at that position of the human protein, however, resulted in a much-reduced receptor capability, suggesting a preference for a benzene ring in the hydrophobic side chain. A similar analysis of proteins substituted at position 237 revealed that aspartic acid, but not arginine or lysine, can functionally substitute for glutamic acid 237 in ATRC1 or at the corresponding position in the human protein. These results suggest a requirement for an acidic and a nearby hydrophobic amino acid for efficient ecotropic virus entry. Similar motifs have been identified in the virus binding sites of other retrovirus receptors, suggesting that the initial step of retrovirus entry may be governed by a common mechanism.

The sulfakinins of the blowfly Calliphora vomitoria. Peptide isolation, gene cloning and expression studies.

The nonapeptide, Phe-Asp-Asp-Tyr(SO3)-Gly-His-Met-Arg-Phe-NH2 was isolated from heads of the blowfly Calliphora vomitoria. Designated callisulfakinin I, the peptide is identical to the earlier known drosulfakinin I of Drosophila melanogaster and to neosulfakinin I of Neobellieria bullata. It belongs to the sulfakinin family, all known members of which (from flies, cockroaches and locusts) have the C-terminal heptapeptide sequence Asp-Tyr(SO3)-Gly-His-Met-Arg-Phe-NH2. The callisulfakinin gene of C. vomitoria was cloned and sequenced. In addition to callisulfakinin I, the DNA revealed a coding sequence for the putative tetradecapeptide. Gly-Gly-Glu-Glu-Gln-Phe-Asp-Asp-Tyr-Gly-His- Met-Arg-Phe-NH2, callisulfakinin II. However, this peptide was not identified in the fly head extracts. Confocal laser scanning immunocytochemical studies with antisera raised against the synthetic undecapeptide C-terminal fragment of drosulfakinin II from D. melanogaster, Asp-Gln-Phe-Asp-Asp-Tyr(SO3)- Gly-His-Met-Arg-Phe-NH2, revealed only four pairs of sulfakinin neurones in the brain of C. vomitoria and no others anywhere else in the neural, endocrine or gut tissues. In situ hybridisation studies with a digoxigenin-labelled sulfakinin gene probe (from the blowfly Lucilia cuprina) also revealed only four pairs of neurones in the brain. The perikarya of two pairs of cells are situated medially in the caudo-dorsal region, close to the roots of the ocellar nerve. The other perikarya are slightly more posterior and lateral. Although it has been suggested by several authors that the insect sulfakinins are homologous to the vertebrate peptides gastrin and cholecystokinin, such arguments (based essentially on C-terminal structural similarities) do not take account of important differences in the C-terminal tetrapeptide. His-Met-Arg-Phe-NH2 in the sulfakinins, compared with Trp-Met-Asp-Phe-NH2 in gastrin and cholecystokinin. Furthermore, whereas the sulfakinin neurons of C. vomitoria are small in number and have a very specialised location, a greater number of cells throughout the nervous system react positively to gastrin/cholecystokinin antisera. Chromatographic profiles of the present study also revealed peaks of gastrin/cholecystokinin-immunoreactive material separate from the sulfakinin peptides. This evidence suggests that the insect and vertebrate peptides may not necessarily be homologous.

Isolation, identification and functional significance of [Hyp2]Met-callatostatin and des Gly-Pro Met-callatostatin, two further post-translational modifications of the blowfly neuropeptide Met-callatostatin.

Two post-translationally modified neuropeptides of the Met-callatostatin (Gly-Pro-Pro-Tyr-Asp-Phe-Gly-Met-NH2) family have been identified from head extracts of the blowfly Calliphora vomitoria. They are the octapeptide, [Hyp2]Met-callatostatin, (Gly-Hyp-Pro-Tyr-Asp-Phe-Gly-Met-NH2) and the truncated hexapeptide, des Gly-Pro Met-callatostatin (Pro-Tyr-Asp-Phe-Gly-Met-NH2). The existence of the [Hyp2]Met-callatostatin variant, in addition to the previously identified [Hyp3]Met-callatostatin peptide, suggests that the motif for prolyl hydroxylation in C. vomitoria is more variable than those known from mammalian and other invertebrate studies where, in those regulatory peptides containing a pair of adjacent prolyl residues so far studied, e.g., bradykinin, and the mosquito peptide Aea HP-I, only one of the pair (the second) is known to undergo hydroxylation. The truncated hexapeptide, des Gly-Pro Met-callatostatin could be produced as a result of the action of a dipeptidyl peptidase II type of enzyme which is known from mammalian studies to be unique in its ability to cleave between the two prolyl residues of an Xaa-Pro-Pro- sequence, where Xaa is any unprotected NH2-terminal amino acid. This enzyme is, however, considered unlikely to be able to cleave the Gly-Hyp-Pro-sequence, which would suggest a functional significance for such a post-translational modification. For this reason, it is of interest that [Hyp2]Met-callatostatin (and earlier, [Hyp3]Met-callatostatin) have been shown to be potent inhibitors of the spontaneous contractions of the hindgut of C. vomitoria (biphasic dose-response curve with IC50 values of 10(-14) M and 10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

[Hyp3]Met-callatostatin. Identification and biological properties of a novel neuropeptide from the blowfly Calliphora vomitoria.

A novel, hydroxyproline-containing neuropeptide, Gly-Pro-Hyp-Tyr-Asp-Phe-Gly-Met-NH2, designated [HYP3]Met-callatostatin, has been identified from extracts of heads of the blowfly Calliphora vomitoria. The peptide is a naturally occurring hydroxylate analogue of Met-callatostatin, a previously identified allatostatin-like peptide, and is present to the extent of 20% of the nonhydroxylated form. In bioassays, both forms of the peptide show allatostatic activity by inhibiting juvenile hormone synthesis and release in the cockroaches Periplaneta americana, Diploptera punctata, and Blattella germanica (IC50 = 100 pM-10 nM). They do not, however, influence juvenile hormone bisepoxide synthesis and release in the blowfly. In flies, [Hyp3]Met-callatostatin inhibits the peristaltic movements of the hindgut, showing a biphasic response (IC50 = 0.5 pM and 0.5 microM) compared with the monophasic response of Met-callatostatin (IC50 = 100 nM). Immunocytochemical studies with Met-callatostatin antisera provide the cytological basis for a myoinhibitory role in the gut since the axons of immunoreactive neurons in the abdominal ganglion project to the ileum. There are also endocrine cells in the midgut that, by releasing the peptides into the hemolymph, would allow the Met-callatostatins to fulfill a neurohormonal role on muscles of the gut and heart. In contrast, there are no Met-callatostatin neural pathways from the brain to the corpus allatum, the gland that produces juvenile hormone. NH2-terminal degradation of Met-callatostatins incubated with the hemolymph of P. americana results in cleavage of the Pro-Tyr bond giving the pentapeptide Tyr-Asp-Phe-Gly-Met-NH2 as a degradation product. In contrast, the Hyp-Tyr bond resists cleavage. With hemolymph from C. vomitoria, no immunoassayable degradation product has been observed with either peptide.

Nasogastric feeding in the management of severe dysphagia in motor neurone disease.

This paper reviews the experience of managing 31 patients with severe dysphagia in motor neurone disease. Thirteen patients were fed nasogastrically and the remaining 18 were managed conservatively without a nasogastric tube. The introduction of nasogastric feeding led to the development of new problems in some patients, without any significant differences in survival times or relief of distressing symptoms.

Agrobacterium-mediated transformation of white clover using direct shoot organogenesis.

White clover (Trifolium repens L.) plants from the cultivars Grasslands Huia and Grasslands Tahora have been transformed using Agrobacterium-mediated T-DNA transfer. Transgenic plants regenerated directly from cells of the cotyledonary axil. To transform white clover, shoot tips from 3 day old seedlings were co-cultivated with A. tumefaciens strain LBA4404 carrying the plasmid vector pPE64. This vector contains the neomycin phosphotransferase II gene (nptII) and ß-glucuronidase reporter gene (gus) both under the control of the CaMV 35S promoter. Kanamycin-resistant plants regenerated within 42 days after transfer onto selective media. Integration of the nptII and gus genes into the white clover genome was confirmed using Southern blotting, and histochemical analysis indicated that the gus gene was expressed in a variety of tissues. In reciprocal crosses between a primary transformant and a non-transformed plant the introduced gus gene segregated as a single dominant Mendelian trait.

Callatostatins: neuropeptides from the blowfly Calliphora vomitoria with sequence homology to cockroach allatostatins.

Five neuropeptides with C-terminal amino acid sequence homology to cockroach allatostatins have been identified in the blowfly Calliphora vomitoria. Three have the same pentapeptide C-terminal amino acid sequence as allatostatin 1 of the cockroach Diploptera punctata. A hexadecapeptide designated callatostatin 1, isolated from thoracic ganglia, brains, and heads, has the sequence Asp-Pro-Leu-Asn-Glu-Glu-Arg-Arg-Ala-Asn-Arg-Tyr-Gly-Phe-Gly-Leu-NH2. Callatostatins 2 and 3 have been isolated from heads and thoracic ganglia, respectively; they comprise the last 14 and 8 residues of callatostatin 1. Callatostatin 4, isolated from thoracic ganglia, has the sequence Xaa-Arg-Pro-Tyr-Ser-Phe-Gly-Leu-NH2, where Xaa is either Asp or Asn. This peptide, with a serine substitution for glycine at position 5, has a C-terminal pentapeptide sequence identical to that of allatostatins 3 and 4 of D. punctata. Callatostatin 5, with the sequence Gly-Pro-Pro-Tyr-Asp-Phe-Gly-Met-NH2, was identified from whole flies. All five peptides inhibit juvenile hormone production by the corpora allata of D. punctata in vitro. Callatostatin 5 was the most potent allatostatin so far tested in this species, with maximum inhibition occurring at 1 nM. In contrast, none of the callatostatins or the allatostatins showed allatostatic activity in mature female C. vomitoria when tested at concentrations of 100 to 0.1 microM. In accordance with these results, immunoreactivity to an antiserum directed against the common C terminus of callatostatin 1 and allatostatin 1 was observed in the corpora allata of D. punctata but not in the corpus allatum of C. vomitoria, despite its presence in neurons of the brain. Neurons in the thoracic ganglion of C. vomitoria that are immunoreactive against this antiserum project to the hindgut, rectum, rectal papillae, and oviduct, suggestive of a function different from that of a true allatostatin.

Site characterization for radon supply potential: a progress review.

"Radon-resistant" house foundations were developed by 1981, but additional construction costs made it undesirable to require them unless necessary. The survey methods used then were labor-intensive and cost so much that it was impractical to identify "radon-prone" areas by nationwide surveys. A cheaper method was required to show where radon-resistant foundations were needed. Information available in 1981 suggested that unusual soil conditions were needed to produce high radon concentrations in houses. If these conditions could be identified, elevated radon concentration levels could be predicted from soil measurements at a lower cost than a radon-in-housing survey. Recent radon surveys show that near-surface bedrock or clay soils, which cover most of the continent, are radon-prone. The measurement methods cannot be used in these soils. The cost of radon surveys has been greatly reduced over the past 10 y. Radon-prone areas can now be identified by radon surveys at a lower cost than soil measurements, and the cost of radon-resistant foundations has been reduced. These developments have removed most of the financial incentive for developing soil-based site classification methods. The priority task now is to encourage the adoption of radon-resistant foundations in radon-prone areas.

Isolation, structure, and activity of -Phe-Met-Arg-Phe-NH2 neuropeptides (designated calliFMRFamides) from the blowfly Calliphora vomitoria.

Thirteen neuropeptides varying in length from 7 to 11 residues and ending C-terminally in -Phe-Met-Arg-Phe-NH2 (calliFMRFamides 1-13) and one dodecapeptide ending in -Met-Ile-Arg-Phe-NH2 (calliMIRFamide 1) have been isolated from thoracic ganglia of the blowfly Calliphora vomitoria. Different repeating patterns of amino acid sequences enable the peptides to be arranged into distinct groups. One such group of five nonapeptides has the sequence Xaa-Pro-Xaa-Gln-Asp-Phe-Met-Arg-Phe-NH2. Three peptides in this group, with the N-terminal tripeptide sequences Thr-Pro-Gln-, Thr-Pro-Ser-, and Ser-Pro-Ser-, are able to induce fluid secretion from the isolated salivary gland of Calliphora at a concentration of 0.1 to 1 nM. However, two other members of this group with the N-terminal tripeptide sequences Lys-Pro-Asn- and Ala-Pro-Gly-, the latter being the most abundant peptide isolated, were inactive in this assay, as were all the other peptides isolated. This indicates that the N terminus (in addition to the C terminus as previously found for FMRFamides of other organisms) is crucial for at least some biological activities.

Chromatographic characterisation and biological activity of neuropeptides immunoreactive to antisera against Met5-enkephalin-Arg6-Phe7 (YGGFMRF) extracted from the blowfly Calliphora vomitoria (Diptera).

Neuropeptides identified with a radioimmunoassay specific for the C-terminus of Met5-enkephalin-Arg6-Phe7 (YGGFMRF) have been extracted from nervous tissues of the blowfly Calliphora vomitoria and also from whole flies. Chromatographic characterisation, based on criteria of molecular weight, charge and hydrophobicity, reveals a complex multiplicity of immunoreactive peptides. Variations in the amounts and types of peptides found within different nervous tissues is evidence that the cellular precursor processing is selective. Physiological studies on the isolated blowfly salivary gland show that synthetic YGGFMRF is a potent secretagogue with a maximal rate of fluid secretion induced at a concentration of between 10(-13) and 10(-12) M. The tetrapeptide comprising the last four residues of the C-terminus of YGGFMRF, Phe-Met-Arg-Phe, is equally potent. However, the carboxyamidated variants, YGGFMRF-NH2 and the molluscan cardioacceleratory peptide FMRF-NH2, as well as the opioid peptides Met5- and Leu5-enkephalin, have no activity. Partially purified YGGFMRF-immunoreactive peptides from the blowfly have ED50 values in the bioassay approximating to 0.3 thoracic ganglion, 2.1 hypocerebral ganglion and 3.0 brain equivalents.