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V F Castellucci

Publications and source records attributed to V F Castellucci.

At least 19 recordsLinked to original sources
PubMed1992

Contribution of polysynaptic pathways in the mediation and plasticity of Aplysia gill and siphon withdrawal reflex: evidence for differential modulation.

The gill and siphon withdrawal (GSW) reflex of Aplysia is centrally mediated by a monosynaptic and a polysynaptic pathway between sensory and motor neurons. The first objective of this article was to evaluate quantitatively the relative importance of these two components in the mediation of the GSW reflex. We have used an artificial sea water (ASW) solution containing a high concentration of divalent cations to raise the action potential threshold of the interneurons without affecting the monosynaptic component of the reflex (2:1 ASW). Compound EPSPs induced in gill or siphon motor neurons by direct stimulation of the siphon nerve or by tactile stimulation of the siphon skin were reduced by more than 75% in 2:1 ASW. These results indicate that interneurons intercalated between sensory and motor neurons are responsible for a considerable proportion of the afferent input to the motor neurons of the reflex. The second objective of this article was to compare the modulation of the monosynaptic and polysynaptic pathways. We have evaluated their respective contribution in sensitization of the GSW reflex by testing the effects of two neuromodulators of the reflex, 5-HT and small cardioactive peptide B (SCPB). We found that these two neuromodulators have a differential action on the two components of the GSW neuronal network. The polysynaptic pathway was more facilitated than the monosynaptic pathway by the neuropeptide SCPB. By contrast, 5-HT displayed an opposite selectivity. These results suggest that the polysynaptic component of the neuronal network underlying the GSW reflex is very important for its mediation. The data also indicate that the monosynaptic and polysynaptic components of the reflex can be differentially modulated. The diversity of modulatory actions at various sites of the GSW network should be relevant for learning-associated modifications in the intact animal.

Action Potentials↗
PubMed1991

Expression of endothelin-like peptide in the nervous system of the marine mollusk Aplysia.

The distribution of endothelin (ET)-like peptide immunoreactivity and mRNA in the nervous system of Aplysia californica was investigated by means of immunocytochemistry and in situ hybridization. Using specific antisera to human endothelin-1 (ET-1) and to the c-terminal peptide of human big endothelin-1 (22-38) (big ET-1), ET-like immunoreactivity was localized to various types of neurons. Immunoreactive nerve fibers for both antisera were prominent throughout the nervous system. Hybridization of radiolabeled complementary RNA probes for human ET-1 or rat endothelin (endothelin-3, ET-3) to paraformaldehyde-fixed, paraffin-embedded sections of various ganglia revealed the presence of a large number of labeled neurons. The number of labeled neurons was higher than those that were immunoreactive for the ET antisera. Preabsorption of the ET antisera with their respective synthetic peptide or hybridization of sections with the sense probes confirmed the specificity of the data. The present study shows that members of the endothelin family may be found in very distant phylogenetic organisms. This conservation suggests a possible role for this peptide as a neurotransmitter and/or neuromodulator in the central nervous systems of diverse species.

Animals↗
PubMed1991

Receptive fields and properties of a new cluster of mechanoreceptor neurons innervating the mantle region and the branchial cavity of the marine mollusk Aplysia californica.

The rostral LE cluster (rLE) is a new set of mechanoreceptor neurons of the abdominal ganglion innervating the mantle area, the branchial cavity, the gill and the siphon of the marine mollusk Aplysia californica Cooper. We have compared the organization of rLE cell receptive fields with that of three other clusters of sensory neurons in the abdominal ganglion (LE, RE and RF) that we have reanalysed. There is extensive overlap of receptive fields from the four populations of sensory cells, and the most exposed areas of the mantle are the most densely innervated. The sensory threshold is similar for all groups. The action potentials of the LE, rLE and RE neurons are broadened by serotonin and the peptide SCPB and narrowed by dopamine and FMRFamide. The RF group does not show the same kind of sensitivity to these neuromodulators. The synaptic outputs of the LE and rLE neurons undergo similar synaptic depression and homosynaptic and heterosynaptic facilitation. We estimate that 100 mechanoreceptor neurons innervate the entire mantle and siphon skin, gill and branchial cavity of Aplysia. The degree of their convergence onto various interneurons and motor neurons mediating the gill- and siphon-withdrawal reflex and other reflexes is under investigation.

Animals↗
PubMed1989

Inhibitor of protein synthesis blocks long-term behavioral sensitization in the isolated gill-withdrawal reflex of Aplysia.

To study the effects of protein synthesis inhibition on long-term sensitization of the gill- and siphon-withdrawal reflex of Aplysia, we have developed an isolated reflex preparation in which we could expose the inhibitor to only that part of the central nervous system involved in mediating the reflex and not to the other parts of the animal's central nervous system, thus minimizing the possible systemic side effects. We have found that long-term sensitization can be obtained in the isolated gill reflex, and that this long-term process, but not the short-term process, is blocked selectively by anisomycin, a reversible inhibitor of protein synthesis. Moreover, to obtain this blockade of long-term sensitization, this drug need only be applied during the training procedure.

Animals↗
PubMed1988

cAMP evokes long-term facilitation in Aplysia sensory neurons that requires new protein synthesis.

Behavioral sensitization leads to both short- and long-term enhancement of synaptic transmission between the sensory and motor neurons of the gill-withdrawal reflex in Aplysia. Serotonin (5-HT), a transmitter important for short-term sensitization, can evoke long-term enhancement of synaptic strength detected 1 day later. Because 5-HT mediates short-term facilitation through adenosine 3',5'-monophosphate (cAMP)-dependent protein phosphorylation, the role of cAMP in the long-term modulation of this identified synapse was examined. Like 5-HT, cAMP can also evoke long-term facilitation lasting 24 hours. Unlike the short-term change, the long-lasting change is blocked by anisomycin, a reversible inhibitor of protein synthesis, and therefore must involve the synthesis of gene products not required for the short-term change.

1-Methyl-3-isobutylxanthine↗
PubMed1988

A quantitative analysis of 2-D gels identifies proteins in which labeling is increased following long-term sensitization in Aplysia.

Long-term memory for sensitization of the gill- and siphon-withdrawal reflex in Aplysia, produced by 4 days of training, is associated with increased synaptic efficacy of the connection between the sensory and motor neurons. This training is also accompanied by neuronal growth; there is an increase in the number of synaptic varicosities per sensory neuron and in the number of active zones. Such structural changes may be due to changes in the rates of synthesis of certain proteins. We have searched for proteins in which the rates of [35S]methionine labeling are altered during the maintenance phase of long-term memory for sensitization by using computer-assisted quantitative 2-D gel analysis. This method has allowed us to detect 4 proteins in which labeling is altered after 4 days of sensitization training.

Animals↗
PubMed1987

Ultrastructure of the osphradium of Aplysia californica.

The osphradium of Aplysia californica, a sensory organ, is a small yellow-brown epithelial patch located in the mantle cavity immediately anterior to the rostral attachment of the gill. Scanning electron microscopy reveals a round ellipsoid structure of 0.6-1 mm in diameter with a central, occasionally folded, sensory epithelium. The central area is covered with microvilli and surrounded by a densely ciliated epithelium. Transmission electron micrographs show that the columnar supporting cells in the sensory epithelium contain an abundance of apical pigment granules and microvilli. Between the epithelial-supporting cells, the putative sensory elements consist of thin neurites (0.4-1.5 micron in diameter) that reach the sea-water side of the osphradium. The neurites contain many neurotubules, mitochondria, vesicles and cilia in their apices. The nerve endings originate from cell bodies up to 40 microns below the epithelium or in the osphradial ganglion itself, as revealed by electron microscopy and retrograde labeling with Lucifer yellow. There appear to be two populations of putative sensory cells, a large population of heavily stained cell bodies 4-10 microns in diameter and a few scattered cells of large diameter (25-60 microns). Following lanthanum impregnation, septate junctions can be seen between all types of cells in the epithelium, 3-5 microns below the sea-water surface. This study provides new information for further investigation of osmo- and mechanosensation in Aplysia californica.

Animals↗
PubMed1986

A critical period for macromolecular synthesis in long-term heterosynaptic facilitation in Aplysia.

Both long-term and short-term sensitization of the gill and siphon withdrawal reflex in Aplysia involve facilitation of the monosynaptic connections between the sensory and motor neurons. To analyze the relationship between these two forms of synaptic facilitation at the cellular and molecular level, this monosynaptic sensorimotor component of the gill-withdrawal reflex of Aplysia can be reconstituted in dissociated cell culture. Whereas one brief application of 1 microM serotonin produced short-term facilitation in the sensorimotor connection that lasted minutes, five applications over 1.5 hours resulted in long-term facilitation that lasted more than 24 hours. Inhibitors of protein synthesis or RNA synthesis selectively blocked long-term facilitation, but not short-term facilitation, indicating that long-term facilitation requires the expression of gene products not essential for short-term facilitation. Moreover, the inhibitors only blocked long-term facilitation when given during the serotonin applications; the inhibitors did not block the facilitation when given either before or after serotonin application. These results parallel those for behavioral performance in vertebrates and indicate that the critical time window characteristic of the requirement for macromolecular synthesis in long-term heterosynaptic facilitation is not a property of complex circuitry, but an intrinsic characteristic of specific nerve cells and synaptic connections involved in the long-term storage of information.

Amanitins↗
PubMed1986

Cell and molecular analysis of long-term sensitization in Aplysia.

We have found that one cellular locus for the storage of the memory underlying short-term sensitization of the gill and siphon withdrawal reflex in Aplysia is the set of monosynaptic connections between the siphon sensory cells and the gill and siphon motor neurons. These connections also participate in the storage of memory underlying long-term sensitization. In animals that have undergone long-term sensitization, the amplitudes of the monosynaptic connections are significantly larger (2.2x) than the ones in control animals. To study the mechanisms of onset and retention of long-term synaptic facilitation that underly long-term sensitization and the role of protein synthesis in long-term memory, we have developed two types of reduced preparations: the intact reflex isolated from the remainder of the animal, and a dissociated cell culture system in which the monosynaptic component (sensory neurons and motor neurons) of the neuronal circuit mediating the withdrawal reflex is reconstituted. We found that protein synthesis inhibitors, such as anisomycin or emetine, and RNA synthesis inhibitors, such as actinomycin D or alpha-amanitin, blocked long-term facilitation without interfering with short-term facilitation. These results suggest that the acquisition of long-term memory may require the expression of genes and the synthesis of proteins not needed for short-term memory.

Amanitins↗
PubMed1984

Two endogenous neuropeptides modulate the gill and siphon withdrawal reflex in Aplysia by presynaptic facilitation involving cAMP-dependent closure of a serotonin-sensitive potassium channel.

We have found that two endogenous neuropeptides in Aplysia, the small cardioactive peptides SCPA and SCPB, facilitate synaptic transmission from siphon mechano-sensory neurons and enhance the defensive withdrawal reflex that these sensory neurons mediate. Single-channel recording revealed that these peptides close a specific K+ channel, the S channel, which is sensitive to cAMP. Moreover, the peptides increase cAMP levels in these sensory neurons. This reduction in K+ current slows the repolarization of the action potential in these cells, which increases transmitter release. In these actions, the SCPs resemble both noxious sensitizing stimuli, which enhance the reflex, and serotonin. Bioassay of HPLC fractions of abdominal ganglion extracts and immunocytochemistry indicate that both the SCPs and serotonin are present in the ganglion and are found in processes close to the siphon sensory neurons, suggesting that these transmitters may be involved in behavioral sensitization. Recent evidence suggests that one group of identified facilitatory interneurons, the L29 cells, does not appear to contain either the SCPs or serotonin but may use yet another facilitatory transmitter. Thus, it appears that several transmitters can converge to produce presynaptic facilitation in the sensory neurons of the defensive withdrawal reflex. All of the transmitters studied here, the SCPs and serotonin, act via an identical molecular cascade: cAMP-dependent closure of the S-K+ channel, broadening of the presynaptic action potential, and facilitation of transmitter release.

Action Potentials↗
PubMed1983

Behavioral changes in aging Aplysia: a model system for studying the cellular basis of age-impaired learning, memory, and arousal.

The marine mollusc Aplysia californica was used to examine the effects of age on simple forms of learning, memory, and arousal. We have found that aging impairs the long-term retention of habituation and prevents the acquisition of sensitization in the siphon withdrawal reflex. In addition, aging reduces arousal as evident in the heart rate component of the response to food stimuli. Our results are similar to the age-dependent alterations in the capacity for behavioral plasticity that have been reported in a variety of vertebrates, including man. These similarities suggest that the mechanisms underlying the effects of age on behavior and its modification may share common features across phyla and therefore might be studied to advantage in Aplysia whose central nervous system is especially accessible to cell biological approaches.

Aging↗
PubMed1982

Inhibitor of adenosine 3':5'-monophosphate-dependent protein kinase blocks presynaptic facilitation in Aplysia.

Sensitization of the gill withdrawal reflex results from presynaptic facilitation at the excitatory synapses made by sensory neurons on gill motor neurons. Facilitation is accompanied by an increase in the duration of the action potential in sensory cells because of the depression of a K+ current. This results in an increasd influx of CA2+ and a greater release of transmitter from sensory neurons. There is evidence that serotonin is the facilitating transmitter and that the depression of the K+ current by serotonin mediated by cAMP-dependent protein phosphorylation. To test further the role of the cAMP-dependent protein kinase and of protein phosphorylation in sensitization, we have attempted to prevent or reverse the development of the electrophysiological correlates that accompany sensitization. We have pressure-injected sensory neurons with a specific and a stable protein inhibitor of the cAMP-dependent protein kinase both before and after the application of serotonin or the activation of the facilitator neurons. The increase in spike broadening that accompanies facilitation was prevented or diminished by injection of the inhibitor. Moreover, injection of the inhibitor could reverse fully the developed spike broadening produced by prior application of serotonin. These observations strenthen the evidence for the involvement of protein phosphorylation in presynaptic facilitation. Phosphorylation of the substrate protein evidently is quite labile and does not persist after the kinase is inhibited. Thus, the time course of short term sensitization appears to be determined by an active kinase. We think that it is likely that the mechanism for maintaining the kinase in an active form resides in the slow decay of the cAMP produced by the action of serotonin or the facilitator neurons on the sensory cells.

Animals↗
PubMed1982

Facilitatory transmitter causes a selective and prolonged increase in adenosine 3':5'-monophosphate in sensory neurons mediating the gill and siphon withdrawal reflex in Aplysia.

Sensitization of the gill and siphon withdrawal reflex in the marine mollusc, Aplysia california, is a simple form of learning Underlying this behavioral changes is a cascade of biochemical events. The first step in this cascade is postulated to be an increase in cAMP within the sensory neurons of the abdominal ganglion. We have developed a labeling protocol with 32Pi which permits us to measure the synthesis of cAMP within a single sensory neurons. Application of serotonin for 5 min was found to triple the content of [32P]cAMP in sensory neurons. The response is specific to serotonin: dopamine, a transmitter that does not produce sensitization, did not increase cAMP. Physiological stimulation of facilitator neurons also resulted in a 3.5-fold increase of cAMP in sensory neurons but not in other cells of the ganglion. We studied the time course of the increase of cAMP in sensory cells stimulated with serotonin and found that it parallels closely the time course of the short term form of presynaptic facilitation. We also have determined the effects of transmitters on the synthesis of cAMP in other identified neurons of the ganglion. The bag cells responded specifically to serotonin. R15, which has been shown to be hyperpolarized both the serotonin and by dopamine, responded to both transmitters by increased synthesis synthesis of cAMP. Thus, the dopamine- and serotonin-sensitive cyclase can be localized to both the same and different cells. Other cells did not respond to serotonin or to dopamine, indicating that a transmitter-sensitive adenylate cyclase is a specific property and is not present in all neurons.

Animals↗