Tissue engineering of stratified articular cartilage from chondrocyte subpopulations

OBJECTIVE

To test if subpopulations of chondrocytes from different cartilage zones could be used to engineer cartilage constructs with features of normal stratification. ESIGN: Chondrocytes from the superficial and middle zones of immature bovine cartilage were cultured in alginate, released, and seeded either separately or sequentially to form cartilage constructs. Constructs were cultured for 1 or 2 weeks and were assessed for growth, compressive properties, and deposition, and localization of matrix molecules and superficial zone protein (SZP).

RESULTS

The cartilaginous constructs formed from superficial zone chondrocytes exhibited less matrix growth and lower compressive properties than constructs from middle zone chondrocytes, with the stratified superficial-middle constructs exhibiting intermediate properties. Expression of SZP was highest at the construct surfaces, with the localization of SZP in superficial-middle constructs being concentrated at the superficial surface.

CONCLUSIONS

Manipulation of subpopulations of chondrocytes can be useful in engineering cartilage tissue with a biomimetic approach, and in fabricating constructs that exhibit stratified features of normal articular cartilage.

Protein synthesis in synaptosomes: a proteomics analysis

A proteomics approach was used to identify the translation products of a unique synaptic model system, squid optic lobe synaptosomes. Unlike its vertebrate counterparts, this preparation is largely free of perikaryal cell fragments and consists predominantly of pre-synaptic terminals derived from retinal photoreceptor neurones. We metabolically labelled synaptosomes with [(35)S] methionine and applied two-dimensional gel electrophoresis to resolve newly synthesized proteins at high resolution. Autoradiographs of blotted two-dimensional gels revealed de novo synthesis of about 80 different proteins, 18 of which could be matched to silver-stained gels that were run in parallel. In-gel digestion of the matched spots and mass spectrometric analyses revealed the identities of various cytosolic enzymes, cytoskeletal proteins, molecular chaperones and nuclear-encoded mitochondrial proteins. A number of novel proteins (i.e. not matching with database sequences) were also detected. In situ hybridization was employed to confirm the presence of mRNA and rRNA in synaptosomes. Together, our data show that pre-synaptic endings of squid photoreceptor neurones actively synthesize a wide variety of proteins involved in synaptic functioning, such as transmitter recycling, energy supply and synaptic architecture.

Pigment villonodular synovitis of the spine. Case report and review of the literature

Pigmented villonodular synovitis (PVNS) is a disease of the joints which uncommonly involves the spine. We present a 70-year-old woman with radicular symptoms who was found to have a mass arising from a lumbar zygapophyseal joint with extension into the spinal canal. Following gross-total excision of the mass, histology revealed PVNS. One month after surgery, the patient had no symptoms and there was no evidence of residual or recurrent disease.

Growth responses of cartilage to static and dynamic compression

During skeletal development, growth, and maturation, gradual changes in the material properties and physical dimensions of cartilage occur under the influence of mechanical loading. The objective of the current study was to compare glycosaminoglyean biosynthesis and cell proliferation in fetal, calf, and adult bovine cartilage explants, isolated from defined depths from the articular surface, in response to controlled compressive loads. Mechanical testing confirmed that for all cartilage samples subjected to load, there was a marked time-averaged (static) compression, whereas the addition of dynamic load at a frequency of 0.01 Hz induced dynamic strain with amplitude and phase shift characteristics typical of stimuli that previously were found to be associated with stimulation of glycosaminoglycan synthesis. In metabolic studies, the application of static loading (84 kPa) for 24 hours inhibited glycosaminoglycan and deoxyribonucleic acid synthesis in all cultured cartilage samples. The superposition of dynamic loading (200 kPa, 0.01 Hz) induced a 20% stimulation of glycosaminoglycan biosynthesis in calf cartilage from the middle-deep zones over statically-loaded samples and an additional approximate 50% suppression of deoxyribonucleic acid synthesis in fetal and calf cartilage from the articular surface. These results indicate that synthesis of glycosaminoglycan and deoxyribonucleic acid, two distinct indices of cartilage growth, are regulated independently by mechanical loading and that cartilage responds differently to static and dynamic loading at different stages of maturation.

Functional implications of neurotransmitter expression during axonal regeneration: serotonin, but not peptides, auto-regulate axon growth of an identified central neuron

We studied the regenerative properties of one of two electrically coupled molluscan neurons, the serotonergic cerebral giant cells (CGCs) of Lymnaea stagnalis, after axotomy. The CGCs play a crucial role in feeding behavior, and when both cells are disconnected from their target neurons, animals no longer feed. When one CGC was permanently disconnected from its targets and the other was reversibly damaged by a nerve crush, the latter one regenerated over a period of 2 weeks to reform functional synapses with specific target neurons. At the same time, recovery of the feeding behavior was observed. After the crush, neuropeptide gene expression in the CGC was downregulated to approximately 50%. Serotonin synthesis, on the other hand, remained unaffected, suggesting that serotonin might have an active role in regeneration. In primary neuron culture, CGCs failed to extend neurites in the presence of serotonin; in cells that extended neurites in the absence of serotonin, focally applied serotonin, but not neuropeptides, induced growth cone collapse. Using serotonin-sensitive sniffer cells, we show that CGC neurites and growth cones release serotonin in culture. Finally, both the spontaneous and stimulation-induced release of serotonin from CGCs in culture resulted in growth cone collapse responses that could be blocked by the serotonin receptor antagonist methysergide. Our data suggest that auto-released serotonin is inhibitory to CGC neurite outgrowth in vitro. During regeneration in vivo, serotonin release might fine-tune axon guidance and branching by inducing local collapse responses in extending neurites.

Superficial siderosis associated with multiple cavernous malformations: report of three cases

OBJECTIVE AND IMPORTANCE

Superficial siderosis is a rare but potentially devastating syndrome caused by recurrent subarachnoid hemorrhage. We present three cases of superficial siderosis associated with multiple cavernous malformations, and we review previous reports of superficial siderosis attributable to vascular malformations.

CLINICAL PRESENTATION

Patients most commonly present with progressive sensorineural hearing loss, cerebellar ataxia, and pyramidal signs. Magnetic resonance imaging diagnosis may precede symptom development, however. In two of our cases, superficial siderosis was identified on magnetic resonance imaging scans in the absence of clinical symptoms.

INTERVENTION

Magnetic resonance imaging studies revealed hemosiderin deposition, characteristic of superficial siderosis, and multiple cavernous malformations in all three cases. Surgical intervention was not pursued.

CONCLUSION

We conclude that patients with multiple cavernous malformations and those with perisubarachnoid lesions are at risk for the development of superficial siderosis. Clinicians should recognize the radiographic appearance of superficial siderosis and its clinical presentation in patients with vascular malformations.

Structure, localization and potential role of a novel molluscan trypsin inhibitor in Lymnaea

Eggs and egg masses of the freshwater gastropod mollusc Lymnaea provide a microenvironment for developing embryos. Secretions of the exocrine albumen gland of Lymnaea are packaged in the eggs of an egg mass before the eggs are laid externally. The perivitelline fluid that directly surrounds individual oocytes is the main source of nutrition for developing embryos. During early stages of development, the perivitelline fluid is initially internalized by pinocytosis and degraded by lysosomes; in later stages, the embryo ingests the fluid. We previously found that the albumen gland produces large amounts of Lymnaea epidermal growth factor. The albumen gland also appears to produce significant amounts of a novel Lymnaea trypsin inhibitor (LTI), a second peptide that was purified and characterized from Lymnaea albumen gland extracts. The primary structure was determined by microsequence analysis, mass spectrometry, and C-terminal sequence analysis, and showed that LTI is a 57-residue glycosylated peptide. Comparison of the LTI sequence with other known serine protease inhibitors indicates that LTI is a member of the bovine pancreatic trypsin inhibitor family. Reverse phase-high performance liquid chromatography, microsequence analysis, mass spectrometry, and immunocytochemistry demonstrated that abundant amounts of intact LTI are packaged in egg masses. The presence of a trypsin inhibitor in the perivitelline fluid compartment of the egg mass may minimize digestion of peptides and proteins in the perivitelline fluid that are important for the development of the embryo, for example, Lymnaea epidermal growth factor.

L-buthionine sulfoximine potentiates the antitumor effect of 4-hydroperoxycyclophosphamide when administered locally in a rat glioma model

OBJECTIVE

L-buthionine sulfoximine (BSO) inhibits glutathione synthesis and may modulate tumor resistance to some alkylating agents, but it has not been proven effective in the treatment of intracranial neoplasms. To evaluate this drug for the treatment of brain tumors, we studied the use of BSO for potentiating the antineoplastic effect of 4-hydroxyperoxycyclophosphamide (4-HC) in the rat 9L glioma model.

METHODS

The survival of male Fischer 344 rats with intracranial 9L gliomas was measured after implantation of controlled-release polymers containing one of the following: no drug, BSO, 4-HC, or both BSO and 4-HC. The efficacy of intracranial 4-HC treatment was assessed with and without serial systemic intraperitoneal BSO injections. Tissue glutathione levels were measured in the brains, tumors, and livers of animals treated with intraperitoneal injections or local delivery of BSO.

RESULTS

The median survival of animals treated with intracranial polymers containing 4-HC was 2.3 times greater than that of controls. This survival benefit was doubled by local delivery of BSO. In contrast, systemic BSO therapy did not improve survival time. In animals that were treated systemically, both liver and tumor glutathione levels were significantly lower than they were in control animals. In the locally treated animals, glutathione levels were reduced in the brain tumor but not in the liver.

CONCLUSION

These results demonstrate that local but not systemic delivery of BSO enhances the antineoplastic effect of 4-HC in this rat 9L glioma model. In addition, because local delivery of BSO within the brain did not deplete glutathione levels systemically, this method of treatment may be safer than systemic administration of BSO.

Synovitis, acne, pustulosis, hyperostosis, and osteitis syndrome presenting as a primary calvarial lesion. Case report and review of the literature

The synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome is a recently described, currently evolving clinical entity that groups together several idiopathic disorders of bone and skin formerly described under a variety of names. Among the spectrum of possible locations for the bone lesions, there is no previous report in the literature of primary involvement of the skull vault. A patient with primary involvement of the calvaria in the setting of SAPHO syndrome is described here, which, to the authors' knowledge, is the first report of such localization. The clinically and radiologically benign evolution of the different stages of the bone lesions is presented. The authors suggest that the SAPHO syndrome should be considered in the differential diagnosis of lytic, sclerotic, or hyperostotic lesions of the skull, particularly before considering invasive diagnostic procedures.

Surgical resection of a cerebral arteriovenous malformation for treatment of superficial siderosis: case report

BACKGROUND

To our knowledge, there are only two reported cases of cerebral arteriovenous malformation associated with superficial siderosis. In both cases, the patients were asymptomatic and were discovered on retrospective review of magnetic resonance imaging.

CASE DESCRIPTION

We describe a case of superficial siderosis in a 47-year-old male with a remote history of closed head injury that presented with progressive hearing loss, cerebellar ataxia, and urinary incontinence. Lumbar puncture was indicative of active subarachnoid bleeding. Cerebral angiography revealed a small vascular malformation that was resected.

RESULTS

Pathological examination confirmed the diagnosis of the arteriovenous malformation. Six months after surgery the patient is neurologically stable with no further progression of clinical signs or symptoms.

CONCLUSIONS

We report the first case of surgical resection of an intracranial arteriovenous malformation for the treatment of superficial siderosis. We emphasize the necessity of a detailed evaluation when superficial siderosis is suspected to localize and resect potential bleeding sources, because the disease is progressive and often irreversible.

Mechanical compression modulates proliferation of transplanted chondrocytes

The presence of an appropriate number of reparative cells in an articular cartilage defect is probably necessary for consistent and successful repair. Following the transplantation of chondrocytes into a defect, cell proliferation may modulate local defect cellularity. Transplanted cells can be compressed during cartilage repair as a result of joint-loading or press-fitting a graft into a cartilage defect. The objective of this study was to characterize the proliferative response of chondrocytes after attachment to cartilage and application of static compressive stress between cartilaginous surfaces in an ex vivo model. The chondrocytes were isolated from adult bovine cartilage, cultured in high-density monolayer, resuspended, and then transplanted onto the surface of devitalized cartilage at a density of 250,000 cells/cm2. The total DNA content of transplanted cell layers increased steadily to a plateau by 5 days and represented a 4-fold increase in cell number during incubation in medium including serum and ascorbate. Over the culture period, the level of DNA synthesis ([3H]thymidine incorporation), on a per cell basis, decreased steadily (88% between days 0 and 6). The application of 24 hours of static compressive stress (0.06-0.4 MPa) to the adherent cells at 1 and 4 days after transplantation inhibited overall DNA synthesis by 70-approximately 87% compared with unloaded controls. After release from load, cell proliferation generally remained at low levels. The marked proliferation of chondrocytes when attached to cartilage without applied load and the inhibition of this proliferation by relatively low-amplitude static compressive stress may be relevant to the occasional overgrowth of tissue in some chondrocyte transplantation procedures. The dosimetry of these effects suggests that the in vivo mechanical environment may have a marked effect on proliferation of transplanted chondrocytes.

Partial characterization of a novel cardioinhibitory peptide from the brain of the snail Helix aspersa

1. We report the isolation of a peptide from the brain of the snail Helix aspersa by radioimmunoassay using an antisomatostatin. 2. The sequencing of an immunopositive fraction showed the presence of a new tridecapeptide, termed Helix cardioinhibitory peptide (HCIP), with the following primary structure: H-Val-Phe-Gln-Asn-Gln-Phe-Lys-Gly-Ile-Gln-Gly-Arg-Phe-NH2. It is structurally related to the Achatina cardioexcitatory peptide (ACEP-1) and the terminal-amino acid sequence of HCIP is identical to that of FMRFamide family peptides. 3. The synthetic HCIP was tested on heart and neuronal activities and it was found to have inhibitory actions not only on the ventricle but also on visceral neurons of the central nervous system of Helix. Immunocytochemical investigation indicates its presence in visceral and parietal ganglia, in which cells taking part in the regulation of the heartbeat have been previously identified.

Separation and identification of peptides in single neurons by microcolumn liquid chromatography-matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and postsource decay analysis

Microcolumn liquid chromatography (LC) was interfaced with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for separation and identification of peptides present in single neurons from the brain of the snail Lymnaea stagnalis. The nanoliter microcolumn LC effluent, mixed off-line with nanoliter matrix solution, was deposited onto the sample target every 60 s, producing fractions of approximately 145 nL in volume, which, upon drying, produced spots of approximately 1 mm in size. At the end of the chromatographic separation, fractions from the sample target were scanned by MALDI-TOF-MS. Identification of peptide peaks was achieved on the basis of LC elution order and mass information. Further identification based on sequence information was carried out for a native peptide fractionated by microcolumn LC from a single neuron with the postsource decay technique.

Direct mass spectrometric peptide profiling and sequencing of single neurons reveals differential peptide patterns in a small neuronal network

Mass spectrometry (MS) was employed to detect and structurally characterize peptides in two functionally related neurons, named VD1 and RPD2, which form a network involved in the modulation of heartbeat in Lymnaea. Matrix-assisted laser desorption/ionization MS, directly applied to single neurons VD1 and RPD2, showed overlapping yet distinct mass profiles, with a subset of putative peptides specifically present in neuron VD1. Direct tandem MS of a single VD1 neuron revealed the primary structures of the VD1-specific peptides, which were identified as members of the family of small cardioactive peptides. Based on the tandem MS data, a degenerate oligonucleotide was made for use in a polymerase chain reaction strategy to isolate the cDNA encoding the precursor to the small cardioactive peptides from a brain-specific cDNA library. The calculated masses of the mature, posttranslationally modified peptides, as predicted from the corresponding cDNA, agreed with the measured masses of the actual peptides, as detected in single-cell MS analysis. In situ hybridization studies showed that the transcript encoding the precursor is present in VD1, but not in RPD2, thus corroborating the single-cell MS analysis. Finally, the small cardioactive peptides were shown to enhance the contractions of the auricle in vitro.

Towards understanding the role of insulin in the brain: lessons from insulin-related signaling systems in the invertebrate brain

Insulin is a molecule that has played a key role in several of the most important landmarks in medical and biological research. It is one of the most extensively studied protein hormones, and its structure and function have been elucidated in many vertebrate species, ranging from man to hagfish and turkey. The structure, function as well as tissue of synthesis of vertebrate insulins are strictly conserved. The structural identification of insulin-related peptides from invertebrates has disrupted the picture of an evolutionary stable peptide hormone. Insulin-related peptides in molluscs and insects turned out to be a structurally diverse group encoded by large multi-gene families that are uniquely expressed in the brain and serve functions different from vertebrate insulin. In this review, we discuss invertebrate insulins in detail. We examine how these peptides relate to the model role that vertebrate insulin has played over the years; however, more importantly, we discuss several unique principles that can be learned from them. We show how diversity of these peptides is generated at the genetic level and how the structural diversity of the peptides is linked to the exclusive presence of a single type of neuronal insulin receptor-related receptor. We also discuss the fact that the invertebrate peptides, in addition to a hormonal role, may also act in a synaptic and/or nonsynaptic fashion as transmitters/neuromodulators on neurons in the brain. It can be expected that the use of well-defined neuronal preparations in invertebrates may lead to a further understanding of these novel functions and may act as guide preparations for a possible role of insulin and its relatives in the vertebrate brain.

Pattern changes of pituitary peptides in rat after salt-loading as detected by means of direct, semiquantitative mass spectrometric profiling

We have established a differential peptide display method, based on a mass spectrometric technique, to detect peptides that show semiquantitative changes in the neurointermediate lobe (NIL) of individual rats subjected to salt-loading. We employed matrix-assisted laser desorption/ionization mass spectrometry, using a single-reference peptide in combination with careful scanning of the whole crystal rim of the matrix-analyte preparation, to detect in a semiquantitative manner the molecular ions present in the unfractionated NIL homogenate. Comparison of the mass spectra generated from NIL homogenates of salt-loaded and control rats revealed a selective and significant decrease in the intensities of several molecular ion species of the NIL homogenates from salt-loaded rats. These ion species, which have masses that correspond to the masses of oxytocin, vasopressin, neurophysins, and an unidentified putative peptide, were subsequently chemically characterized. We confirmed that the decreased molecular ion species are peptides derived exclusively from propressophysin and prooxyphysin (i.e., oxytocin, vasopressin, and various neurophysins). The putative peptide is carboxyl-terminal glycopeptide. The carbohydrate moiety of the latter peptide was determined by electrospray tandem MS as bisected biantennary Hex3HexNAc5Fuc. This posttranslational modification accounts for the mass difference between the predicted mass of the peptide based on cDNA studies and the measured mass of the mature peptide.

Cloning, characterization, and expression of a G-protein-coupled receptor from Lymnaea stagnalis and identification of a leucokinin-like peptide, PSFHSWSamide, as its endogenous ligand

Neuropeptides are known to be important signaling molecules in several neural systems of the pond snail Lymnaea stagnalis. Although the functions of these peptides have been studied in many neurons, the nature of the postsynaptic signal transduction is mainly unknown. The cloning and characterization of neuropeptide receptors in Lymnaea thus would be very valuable in further elucidating peptidergic pathways. Indirect evidence suggests that these neuropeptides operate via G-protein-coupled mechanisms indicating the presence of G-protein-coupled receptors as the initial postsynaptic targets. Here we describe the cloning of a neuropeptide receptor from Lymnaea and the isolation of an endogenous ligand. This peptide, PSFHSWSamide, belongs to the leucokinin family of peptides, and, thus, this Lymnaea receptor is the first example of a leucokinin-like neuropeptide receptor, representing a new subfamily of G-protein-coupled neuropeptide receptors.

Intracellular degradation of C-peptides in molluscan neurons producing insulin-related hormones

Single Light Green Cells (LGC) of Lymnaea stagnalis, expressing four genes encoding insulin-related peptides (MIPs) and C-peptides, and sections from the median lip nerve (MLN) were subjected to MALDI-MS. Mass spectra of LGCs and MLNs were almost identical. Masses corresponding to those of the MIPs and some C alpha-peptides could be distinguished. ProMIP III C alpha-peptide and C beta-peptides were not found. The spectra showed additional masses matching those of carboxyterminally truncated C alpha-peptides. Peptides with similar masses were isolated from MLN extracts by HPLC, using electrospray-MS screening. Amino acid sequence analysis revealed intact proMIP I, II and V C alpha-peptides and I, II C alpha-peptide 1-24, 1-22 and 1-15.

Stabilization of unstable and unintuitive plants by fuzzy control

A heuristically derived stabilization strategy for an unstable and unintuitive plant by fuzzy control is described. It is shown that the often used classical fuzzy controller, which is both static and time invariant, is incapable of stabilizing such types of plants. However, a simple modification to the classical fuzzy controller architecture that separates the measurement and control phases, together with a hierarchical control strategy, enable the unstable and unintuitive plant to be stabilized. The fuzzy control strategy, as well as the new fuzzy controller architecture, are based on the consideration of "what a human subject would do when dealing with a physical plant which is both unstable and unintuitive". The stabilization strategy is then generalized to other mathematically similar systems. While the rules for the stabilization of the plant are heuristically defined, the membership functions associated with the rules are tuned by a simulated annealing procedure.

CRNF, a molluscan neurotrophic factor that interacts with the p75 neurotrophin receptor

A 13.1-kilodalton protein, cysteine-rich neurotrophic factor (CRNF), was purified from the mollusk Lymnaea stagnalis by use of a binding assay on the p75 neurotrophin receptor. CRNF bound to p75 with nanomolar affinity but was not similar in sequence to neurotrophins or any other known gene product. CRNF messenger RNA expression was highest in adult foot subepithelial cells; in the central nervous system, expression was regulated by lesion. The factor evoked neurite outgrowth and modulated calcium currents in pedal motor neurons. Thus, CRNF may be involved in target-derived trophic support for motor neurons and could represent the prototype of another family of p75 ligands.

Novel omega-conotoxins block dihydropyridine-insensitive high voltage-activated calcium channels in molluscan neurons

We have identified two novel peptide toxins from molluscivorous Conus species that discriminate subtypes of high voltage-activated (HVA) calcium currents in molluscan neurons. The toxins were purified using assays on HVA calcium currents in the caudodorsal cells (CDCs) of the snail Lymnaea stagnalis. The CDC HVA current consists of a rapidly inactivating, transient current that is relatively insensitive to dihydropyridines (DHPs) and a slowly inactivating, DHP-sensitive L-current. The novel toxins, designated omega-conotoxins PnVIA and PnVIB, completely and selectively block the transient HVA current in CDCs with little (PnVIA) or no (PnVIB) effect on the sustained L-type current. The block is rapid and completely reversible. It is noteworthy that both PnVIA and PnVIB reveal very steep dose dependences of the block, which may imply cooperativity in toxin action. The amino acid sequences of PnVIA (GCLEVDYFCGIPFANNGLCCSGNCVFVCTPQ) and of PnVIB (DDDCEPPGNFCGMIKIGPPCCSGWCFFACA) show very little homology to previously described omega-conotoxins, although both toxins share the typical omega-conotoxin cysteine framework but have an unusual high content of hydrophobic residues and net negative charge. These novel omega-conotoxins will facilitate selective analysis of the functions of HVA calcium channels and may enable the rational design of drugs that are selective for relevant subtypes.

A novel hydrophobic omega-conotoxin blocks molluscan dihydropyridine-sensitive calcium channels

A novel calcium channel blocking peptide designated omega-conotoxin-Tx VII has been characterized from the venom of the molluscivorous snail Conus textile. The amino acid sequence (CKQADEPCDVFSLDCCTGICLGVCMW) reveals the characteristic cysteine framework of omega-conotoxins, but it is extremely hydrophobic for this pharmacological class of peptides and further unusual in its net negative charge (-3). It is further striking that the sequence of TxVII, a calcium current blocker, is 58% identical to that of delta-conotoxin-TxVIA, which targets sodium channels. TxVII effects were examined in the caudodorsal cell (CDC) neurons from the mollusc Lymnaea stagnalis. The toxin has no significant effect on sodium or potassium currents in these cells, but it clearly blocks the calcium currents. TxVII most prominently blocks the slowly inactivating, dihydropyridine- (DHP-) sensitive current in CDCs, while blockade of the rapidly inactivating current is less efficient. This novel omega-conotoxin is apparently targeted to DHP-sensitive calcium channels and thereby provides a lead for future design of selective conopeptide probes for L-type channels.

Post-translational processing of the alternative neuropeptide precursor encoded by the FMRFamide gene in the pulmonate snail Lymnaea stagnalis

The neuropeptide gene encoding FMRFamide-like peptides in the pulmonate mollusc Lymnaea is subject to alternative splicing that generates cell-specific expression of distinct sets of peptides in the CNS. In this paper, we analyse the post-translational processing of the alternative protein precursor encoded by the exon I, III-V transcript (type 2 transcript). We raised anti-peptide antisera specific to distinct segments of the precursor in order to address the pattern of endoproteolytic cleavages, specifically around the tetrabasic site RRKR. We first showed that not all peptides predicted by the precursor structure are generated as final steady-state products. We then identified a novel peptide by biochemical purification, amino acid sequencing and mass spectrometry- the 35 amino acid SDPFFRFGKQQVATDDSGELDDEILSRVSDDDKNI, which we termed the acidic peptide, previously not predicted on the basis of the precursor structure. This novel peptide, abundant in the snail brain (0.7 pmol per central nervous system), includes the N-terminal sequence SDPFFRF, which was previously considered to be a variant of the known heptapeptide SDPFLRFamide, also encoded within the same protein precursor. We showed by in situ hybridization and immunocytochemistry that the acidic peptide is produced in all cells that transcribe type 2 FMRFamide mRNA. We mapped the expression of this novel peptide in the CNS and localized it mainly in three identifiable neuronal clusters - the E, F and B groups of cells - and some additional neurons, all situated in three of the eleven central ganglia. Immunoreactive neurons included the single identifiable visceral white interneuron (VWI or VD4), a key cell of the cardiorespiratory network.