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R P Croll

Publications and source records attributed to R P Croll.

53 records · Page 3Linked to original sources
PubMed1990

Axonal regeneration and sprouting following injury to the cerebral-buccal connective in the snail Achatina fulica.

Axonal sprouting and regeneration were studied in the land snail Achatina fulica following a unilateral crush to the cerebral-buccal connective. Both normal projection patterns and changes induced by injury were examined with axonal filling techniques. As expected, most staining was lost shortly after the crush when filling across the lesion site. Much of this decrease is attributable to the direct disruption of fiber pathways, but evidence also indicates that a limited amount of retraction of some neurites occurred during the first week. A subsequent, gradual increase in the numbers of stained elements culminated in supernumerary counts of fibers in many pathways and in some novel labeling of cell bodies. Maximum numbers of supernumerary fibers usually occurred 21-28 days after the lesion. Most of these extra neurites and cell bodies subsequently disappeared, and by day 35 the appearance of projections generally returned to within the ranges observed in normal, unlesioned animals. Together the results demonstrate the extent of neuritic regeneration, sprouting, and retraction that occurs in vivo within the gastropod nervous system following injury. The study also indicates the usefulness of such in vivo approaches to understand the long-term processes that contribute to the restoration of morphological and functional integrity.

Animals↗
PubMed1990

Distribution of catecholamines and of immunoreactivity to substances like vertebrate enzymes for the synthesis of catecholamines within the central nervous system of the snail, Lymnaea stagnalis.

Catecholamines (CAs) were detected histochemically within over 185 cell bodies in the central nervous system (CNS) of juvenile and young adult Lymnaea. This distribution of CA-containing cells in all central ganglia except the pleural ganglia is more widespread than previously described but is consistent with other reports suggesting numerous roles for CAs within the nervous system. This study also describes the distribution of substances which are antigenically similar to four bovine enzymes for catecholamine synthesis, but the distribution patterns showed little or no overlap with each other or with CA. These results suggest the need for caution in the interpretation of such immunohistochemical studies.

Aldehydes↗
PubMed1989

Postembryonic development of serotoninlike immunoreactivity in the central nervous system of the snail, Lymnaea stagnalis.

Posthatching growth in the pond snail Lymnaea stagnalis involves approximately a 20-fold increase in the linear dimensions of the ganglia composing the central nervous system. Developmental change within the population of neurons exhibiting serotoninlike immunoreactivity (SLIR) was examined in order to explain this growth in cellular terms. The study indicates that at least two factors contribute to the growth of the nervous system. First, SLIR cells approximately double in number from the 200-250 cells in hatchlings to the complement found in animals approaching sexual maturity. Much of this increase in cell number occurred within identifiable discrete clusters of neurons with different clusters adding cells at different rates and at different times. The number of SLIR cells also increased in more diffuse populations, particularly along the medial aspects of the paired pedal and the right parietal ganglion. No identified cells were added postembryonically. In addition to the increases in neuron numbers, posthatching development in Lymnaea also involves the growth of individual cells. All cells examined showed continuous somatic growth during posthatching development, but different identified cells and different cell clusters were characterized by different rates of relative growth. Together, the results highlight the complexity of postembryonic development in the snail by indicating the temporal and spatial specificity for both cell addition and cell growth within the nervous system.

Age Factors↗
PubMed1988

Distribution of monoamines within the central nervous system of the juvenile pulmonate snail, Achatina fulica.

The distributions of serotonin and catecholamines were examined within the central ganglia of juvenile Achatina through the histological localization of serotonin-like immunoreactivity and of glyoxylic acid-induced fluorescence. Somata containing these amines were widely distributed throughout all central ganglia except the two pleural ganglia and the left parietal ganglion. Most catecholaminergic neurons were very small (5-10 microns in diameter) and located in clusters in the cerebral and pedal ganglia, although a few, somewhat larger catecholaminergic neurons were also scattered throughout other locations. Catecholamines also appeared to be heavily concentrated in certain neuropilar regions of the central ganglia. Serotonergic neurons were generally much larger than the catecholaminergic neurons, and some of these somata reached relatively large sizes (up to 50-70 microns in diameter). The majority of serotonergic cells were located in the pedal ganglia but major populations were also located in the paired cerebral, the right parietal and the visceral ganglia. Several of the serotonergic cells could be reliably recognized as distinct individuals which appear to be identical to those described in previous studies. Among the previously identified cells which appear to contain serotonin are v-RCDN ad v-LCDN (the right and left metacerebral giant cells) of the cerebral ganglia, d-LPeLN of the left pedal ganglion, and TAN, TAN-2, and TAN-3 of the right parietal ganglion. Comparisons are drawn with general distribution patterns of monoamines and with identified monoaminergic cells and cell populations found in other gastropod species.

Animals↗
PubMed1987

Distribution of monoamines in the central nervous system of the nudibranch gastropod, Hermissenda crassicornis.

The distribution of monoamines in the central ganglia of the nudibranch gastropod Hermissenda crassicornis was examined through the histological localization of both glyoxylic acid-induced fluorescence and serotonin-like immunoreactivity. Glyoxylic acid histochemistry revealed several clusters of catecholamine-containing cells which were located principally in the cerebropleural ganglia. One large unpaired catecholamine-containing cell was also located in the right pedal ganglion. Glyoxylic acid histochemistry and immunohistochemistry together revealed several serotonin-containing cells. The most prominent of these was a bilateral pair of cells (the metacerebral giants or MCG's) with somata located in the anterior lobes of the cerebropleural ganglia and each with a single large axon running through the ipsilateral cerebrobuccal connective to the buccal ganglia. Apart from the MCG's and a few smaller ones in the cerebropleural ganglia, most other serotonergic cells were located in the pedal ganglia. Among the serotonergic cells identified in the pedal ganglia was a single unpaired giant cell (LP1) located only on the left side. The neurites of LP1 projected through the cerebropleural ganglia to the contralateral pedal ganglion. Similarities in the distribution of monoamines in different gastropod species are discussed.

Animals↗
PubMed1987

Hyperphagia resulting from gut denervation in the sea slug, Pleurobranchaea.

Previous research suggests that gut distension by ingested bulk plays an important role in the regulation of food intake in gastropod molluscs. The present study tested whether the bilateral stomatogastric nerves which innervate the esophagus and crop in Pleurobranchaea form a neural pathway carrying information about gut distension to the central nervous system. The posterior branches of the paired stomatogastric nerves were surgically exposed and sectioned in seven experimental animals while the nerves were simply exposed and not sectioned in seven sham-operated control animals. In three, subsequent, daily feeding sessions, the experimental subjects consumed a greater amount of food in terms of percentage of body weight than the control subjects. The experimental animals also gained a greater percentage of body weight and later were found to contain much more food within their guts. The results support the hypothesis that stretch receptors which innervate the gut and which have axons in the stomatogastric nerves form an important negative feedback pathway for the control of feeding in the sea slug.

Animals↗
PubMed1986

Modified cobalt staining and silver intensification techniques for use with whole-mount gastropod ganglion preparations.

While silver intensification of cobalt-filled cells is a common procedure for use with many arthropod preparations, it has not been routinely applied to gastropods. Several modifications in cobalt-staining techniques currently used with gastropods along with adaptations of silver intensification techniques used in insects are described. Cobalt was introduced into cells through axonal filling of cut nerve trunks or by either pressure injection or iontophoresis from intracellular, micropipette electrodes that had previously had their tips etched in dilute hydrofluoric acid. Etching produced consistent, sharp tips with large lumina. Further procedural modifications allowed complete, even intensification of neurons in large gastropod ganglia. These techniques have proved to be reliable and apparently broadly applicable, having been successfully used on three diverse gastropod species.

Animals↗
PubMed1985

Learning: neural analysis in the isolated brain of a previously trained mollusc, Pleurobranchaea californica.

The neural manifestations of food avoidance learning in the mollusc, Pleurobranchaea, survive the surgical reduction of the preparation to the nearly isolated brain. These manifestations include increased synaptic inhibition and reduced synaptic excitation of the phasic paracerebral feeding command interneurons (PCps) in the brain in response to food stimulation of chemosensory structures left attached to the brain. The same changes are not evident, however, in brains removed from naive, control or satiated specimens. Therefore the nearly isolated brain preparation permits analysis of the cellular substrates of learning in relative isolation from non-associative motivational variables. The isolated brain preparation is here used to show that the increased synaptic inhibition consequent to associative training is distributed not only to the PCps but also to their identified central presynaptic inputs, including other identified feeding command interneurons (PSEs and ETIIs; ref. 21). The decrease in PCp excitation is explained in part by a training-induced inhibition of excitatory inputs to the PCps, and in part by a training-induced reduction in the efficacy of an identified polysynaptic excitatory pathway presynaptic to the PCps.

Animals↗
PubMed1985

Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. I. Central motor programs underlying ingestion, egestion, and the "neutral" rhythm(s).

The buccal musculature of the carnivorous gastropod Pleurobranchaea is used in three cyclic patterns of coordination underlying, respectively, ingestion, egestion, and a third, unknown behavior(s) (Croll, R. P., and W. J. Davis (1981) J. Comp. Physiol. 145: 277-287; Croll, R. P., and W. J. Davis (1982) J. Comp. Physiol. 147: 143-154). The corresponding three motor programs can be identified and distinguished in the intact animal (Croll, R. P., and W. J. Davis (1981) J. Comp. Physiol. 145: 277-287), the reduced preparation (Croll, R. P., and W. J. Davis (1982) J. Comp. Physiol. 147: 143-154, and the present paper), and the isolated CNS (present paper), on the basis of several qualitative and quantitative criteria. Distinguishing parameters developed here include: the activity of the salivary duct, which bursts in phase with protraction during ingestion, is silent during egestion, and usually bursts biphasically and in antiphase with protraction during the third ("neutral") rhythm(s); and the protractor duty cycle, which is generally 33 to 50% during ingestion, greater than 50% during egestion, and less than 33% during the neutral rhythm(s). Retractor duty cycles did not differ significantly between the three motor programs. The neutral rhythm(s) may be a low-intensity version of the ingestion motor program, with which it shares most features. The three buccal motor programs can be elicited in the reduced preparation (sensory feedback intact) and in the isolated, deafferented CNS. Therefore, multiple motor programs in this metastable motor system are each endogenous to the CNS; i.e., they can each be generated by a central pattern generator(s) in the absence of sensory feedback.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. II. Role of the ventral white cell, anterior ventral, and B3 buccal neurons.

Identified buccal neurons in the mollusc Pleurobranchaea were stimulated and recorded intracellularly while recording the resultant identified motor program from buccal muscles (reduced preparation) or nerves (isolated central nervous system). Neurons studied included the ventral white cell (VWC), members of the anterior ventral (AV) population, and interneuron B3. Each of these neurons elicited the egestion motor program or its characteristic components when stimulated intracellularly. The characteristic prolonged plateau potential of the VWC was frequently associated with the egestion motor program but never with the ingestion motor program or its characteristic components. Intracellular recordings from these same neurons during spontaneous or induced buccal motor programs were consistent with the view that these neurons participate in production of the egestion motor program. The VWC discharged also during the neutral buccal rhythm, although in a different pattern from that seen during the egestion motor program, suggesting that it is multifunctional. Synaptic targets of the VWC are unknown, but synaptic influences of the AV and B3 neurons were found and are appropriate to their proposed role in egestion. This study therefore indicates that an interrelated cluster of buccal neurons is specialized to command the egestion motor program.

Animals↗
PubMed1985

Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. III. Role fo the paracerebral neurons and other identified brain neurons.

Identified neurons in the cerebropleural ganglion (brain) of the mollusc Pleurobranchaea were stimulated and recorded from intracellularly while recording the identified motor program from buccal muscles (reduced preparation) or nerves (isolated central nervous system). Neurons studied included the metacerebral giant neurons (MCGs), phasic paracerebral neurons (PCp's), polysynaptic excitors of the PCp's (PSEs), type II electrotonic neurons (ETII's), type I electrotonic neurons (ETI's) and several other identified neurons or neuronal classes. Intracellular stimulation of the above identified neurons generally elicited the ingestion motor program or its characteristic components, but never the egestion motor program and seldom its characteristic components. Intracellular recordings from these neurons in the isolated central nervous system preparation while eliciting the ingestion and egestion motor program generally showed cyclic membrane potential oscillations in phase with both motor programs, indicating that these neurons receive synaptic feedback from the ingestion and egestion central pattern generator(s). This study is therefore consistent with the view that an interrelated cluster of brain neurons is specialized to command the ingestion motor program. A neural model of motor program switching in the buccal motor system is formulated, comprising separate command pathways for ingestion and egestion that converge on a common central pattern generator(s).

Animals↗
PubMed1984

Brain oscillator(s) underlying rhythmic cerebral and buccal motor output in the mollusc, Pleurobranchaea californica.

Tonic (d.c.) intracellular depolarization of the previously identified phasic paracerebral feeding command interneurones (PCps) in the brain of the carnivorous gastropod Pleurobranchaea causes oscillatory neural activity in the brain, both before and after transecting the cerebrobuccal connectives. Therefore, cycle-by-cycle ascending input from the buccal ganglion is not essential to cyclic brain activity. Instead the brain contains an independent neural oscillator(s), in addition to the oscillator(s) demonstrated previously in the buccal ganglion (Davis et al. 1973). Transection of the cerebrobuccal connectives immediately reduces the previously demonstrated (Kovac, Davis, Matera & Croll, 1983) long-latency polysynaptic excitation of the PCps by the polysynaptic excitors (PSEs) of the PCps. Therefore polysynaptic excitation of the PCps by the PSEs is mediated by an ascending neurone(s) from the buccal ganglion. The capacity of feeding command interneurones to induce neural oscillation in the isolated brain declines to near zero within 1 h after transection of the cerebrobuccal connectives, suggesting that this capacity is normally maintained by ascending information from the buccal ganglion. The results show that this motor system conforms to a widely applicable general model of the neural control of rhythmic behaviour, by which independent neural oscillators distributed widely in the central nervous system are coupled together to produce coordinated movement.

Action Potentials↗
PubMed1983

Organization of synaptic inputs to paracerebral feeding command interneurons of Pleurobranchaea californica. I. Excitatory inputs.

Neurons presynaptic to the phasic paracerebral feeding command interneurons (PCP's; Ref. 55) of Pleurobranchaea were located in the isolated central nervous system (CNS) and studied anatomically by lucifer yellow injection and physiologically by current injection and intracellular recording in normal and ion-substituted seawater during quiescence and fictive feeding. The present paper describes excitatory inputs to PCP's, while the accompanying paper (54) reports inhibitory inputs. Monosynaptic excitors (MSEs) are a group of at least three monopolar neurons per hemiganglion. Two have similar dendritic structures and functional effects. Each MSE monosynaptically excites the PCP's and fires action-potential bursts in phase with PCP bursts during fictive feeding. The class I electrotonic neuron (ETI) is a single, identified monopolar neuron per hemiganglion with a sparse dendritic arborization and no descending axon in the cerebrobuccal connective (CBC). The ETI is coupled with PCP's only by means of a non-rectifying electrical synapse. Paradoxically, ETI receives opposite synaptic inputs from PCP's and fires in antiphase with PCP's during fictive feeding. Class II electrotonic neurons (ETII's) are a group of at least two identified multipolar neurons per hemiganglion with indistinguishable dendritic architectures and similar but distinguishable functional effects. Each cell is coupled with PCP's by means of a nonrectifying electrical synapse. One of the ETII's also delivers graded, long-latency poly-synaptic chemical inputs to PCP's. ETII's have descending axons in the CBC, elicit fictive feeding when depolarized, and fire cyclically and in phase with PCP's during fictive feeding. Polysynaptic excitors (PSEs) are a group of at least two identified monopolar neurons per hemiganglion with similar elaborate dendritic fields and functional effects. Each cell excites PCP's by a long-latency, relatively nongraded polysynaptic pathway. PSEs also have descending axons in the ipsilateral CBC, elicit fictive feeding when depolarized, and fire in phase with PCP's during fictive feeding. PSEs and ETII's are here recognized as subclasses of neurons previously identified as paracerebral neurons. They are inhibited by the same neurons that supply recurrent inhibition to PCP's (47), share excitatory inputs with PCP's, and exhibit a similar "command" capacity. This study thus documents redundancy and functional specialization within a command system controlling a relatively complex rhythmic motor behavior.

Afferent Pathways↗
PubMed1983

Organization of synaptic inputs to paracerebral feeding command interneurons of Pleurobranchaea californica. III. Modifications induced by experience.

Phasic paracerebral feeding command interneurons (PCP's) were studied in whole-animal preparations of Pleurobranchaea drawn from four populations with different behavioral histories: food avoidance conditioned, yoked controls, food satiated, and naive. PCP responses to chemosensory food stimuli (liquefied squid) and mechanosensory touch stimuli (tactile stimulation of anterior and posterior structures) were recorded intracellularly, scored blind, and compared quantitatively across the four populations. PCP's from avoidance-conditioned specimens (10, 18, 19) showed decreased excitatory and increased inhibitory responses to food and touch in comparison with naive (untrained) specimens. Control animals did not show these effects. PCP's from satiated specimens showed decreased excitatory and increased inhibitory responses to food and touch in comparison with PCP's from control, naive, and conditioned specimens. Inhibitory postsynaptic potentials (IPSPs) induced in PCP's of conditioned and satiated specimens by food and touch are indistinguishable in amplitude and waveform from IPSPs produced in the same PCP's by the previously described cyclic inhibitory network (CIN; Ref. 13). In addition, tonic paracerebral neurons (PCT's) that lack input from the CIN, are not inhibited but rather are excited in trained and satiated animals. Therefore the inhibitory responses to food and touch by PCP's of conditioned and satiated specimens appear to be mediated by the CIN. This study demonstrates that associative and nonassociative processes (learning and food satiation, respectively) manifest similarly at the level of command interneurons. The findings furnish a neurophysiological explanation for behavioral motivation in Pleurobranchaea, namely, modulation of the balance of excitation/inhibition in command neurons controlling the corresponding behavior. A cellular model of food avoidance learning and food satiation is formulated to account for these data, based on the identified neural circuitry of the paracerebral command system (15, 17).

Animals↗