Biomedical subjects

M P Nusbaum

Publications and source records attributed to M P Nusbaum.

34 records · Page 2Linked to original sources

PubMed1994

Neuropeptide degradation produces functional inactivation in the crustacean nervous system.

The pentapeptide proctolin (Proct.; Arg-Tyr-Leu-Pro-Thr) is a modulatory transmitter found throughout the crustacean nervous system. No information is available in this system, however, as to how the actions of this peptide are terminated. To study this issue in the crab Cancer borealis, we incubated exogenous proctolin (10(-5) M) with either the thoracic ganglion (TG) or with conditioned saline (CS) that had been preincubated with the TG. We removed aliquots at standard time points for analysis by reverse-phase high-performance liquid chromatography (HPLC). We found that over time the proctolin peak became progressively smaller, while three novel peaks appeared and increased in size. Comigration experiments using HPLC indicated that the major novel peak was Proct. (Tyr-Leu-Pro-Thr), while one of the two minor peaks was Proct. (Leu-Pro-Thr). The other minor peak appeared to be Proct. (Arg-Tyr), based on similar HPLC retention time to synthetic Proct. The reduction in the proctolin peak and the increase in the Proct. peak was prevented by co-incubation of proctolin with any one of several aminopeptidase inhibitors (10(-4) M). Proct. and Proct. appeared to result from a diaminopeptidase-mediated cleavage of proctolin. We tested whether N-terminal cleavage functionally inactivated proctolin by coapplying proctolin (10(-8) M) and individual aminopeptidase inhibitors (10(-5) M) to the isolated stomatogastric ganglion (STG). We found that these inhibitors significantly enhanced the proctolin excitation of the pyloric rhythm. Furthermore, application of synthetic Proct. to the STG had no effect unless high concentrations (> 10(-6) M) were used, and neither Proct. nor Proct. (10(-4) M) influenced the pyloric rhythm. Our results indicate that proctolin is enzymatically degraded and thereby biologically inactivated in the crab nervous system, primarily by extracellularly located aminopeptidase activity.

Aminopeptidases↗

PubMed1994

Functional consequences of compartmentalization of synaptic input.

Intra-axonal recordings of stomatogastric nerve axon 1 (SNAX1) indicate that there are synaptic inputs onto the SNAX1 terminals in the stomatogastric ganglion (STG) of the crab Cancer borealis (Nusbaum et al., 1992b). To determine whether this synaptic input only influenced SNAX1 activity within the STG, we identified the SNAX1 soma in the commissural ganglion (CoG). We found that this neuron has a neuropilar arborization in the CoG and also receives synaptic inputs in this ganglion. Based on its soma location, we have renamed this neuron modulatory commissural neuron 1 (MCN1). While intracellular stimulation of MCN1soma and MCN1SNAX has the same excitatory effects on the STG motor patterns, MCN1 receives distinct synaptic inputs in the STG and CoG. Moreover, the synaptic input that MCN1 receives within the STG compartmentalizes its activity. Specifically, the lateral gastric (LG) neuron synaptically inhibits MCN1SNAX-initiated activity within the STG (Nusbaum et al., 1992b), and while LG did not inhibit MCN1soma-initiated activity in the CoG, it did inhibit these MCN1 impulses when they arrived in the STG. As a result, during MCN1soma-elicited gastric mill rhythms, MCN1soma is continually active in the CoG but its effects are rhythmically inhibited in the STG by LG neuron impulse bursts. One functional consequence of this local control of MCN1 within the STG is that the LG neuron thereby controls the timing of the impulse bursts in other gastric mill neurons. Thus, local synaptic input can functionally compartmentalize the activity of a neuron with arbors in distinct regions of the nervous system.

Animals↗

PubMed1992

Distribution of modulatory inputs to the stomatogastric ganglion of the crab, Cancer borealis.

The pyloric and gastric mill neural networks in the crustacean stomatogastric ganglion receive modulatory inputs from more anteriorly located ganglia via the stomatogastric nerve. In this study we employed biocytin backfilling and immunostaining, as well as electron microscopy, to determine the origin of these inputs in the crab, Cancer borealis. Fiber counts from electron micrographs of sections through the stomatogastric nerve showed that this nerve contains 55-60 medium to large diameter fibers (1-13 microns). These fibers were individually wrapped by several layers of membrane, presumably glial in origin. There was also a single cluster of jointly wrapped, small diameter (< 1 micron) fibers that may originate from peripheral sensory somata. Biocytin backfills revealed that approximately two thirds of the individually wrapped fibers in this nerve originate from somata in the other three ganglia of the stomatogastric nervous system, including the paired commissural ganglia and the single oesophageal ganglion. There were approximately 20 biocytin-labeled somata in each commissural ganglion and 3 somata in the oesophageal ganglion. An additional ten somata were localized to the stomatogastric ganglion itself. This accounts for nearly all of the medium to large diameter fibers in the stomatogastric nerve. We used double-labeling with backfills and immunocytochemistry to determine that there are two proctolin-immunoreactive neurons and four FMRFamide-like immunoreactive neurons among the biocytin-labeled neurons in each commissural ganglion. Both peptides modulate neural network activity in the stomatogastric ganglion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Presynaptic control of modulatory fibers by their neural network targets.

Numerous modulatory fibers control the output of the pyloric and gastric mill neural networks in the crustacean stomatogastric ganglion (STG). We now describe the first results of intracellular recordings from the axon of one of these input neurons, stomatogastric nerve axon 1 (SNAX 1), close to where it enters the STG. SNAX 1 excites both the pyloric and gastric mill rhythms and is identified on the basis of its synaptic interactions with identified STG neurons. SNAX 1 receives synaptic input from several sources within the STG. As a result of these synaptic inputs, SNAX 1 fires bursts of action potentials that are time-locked to both the pyloric and gastric mill rhythms. The synaptic connections made onto the SNAX axon terminals are likely to play important roles in shaping the impulse activity patterns in these modulatory inputs. Thus, the fibers that modulate the pattern-generating networks in the STG are themselves influenced by elements in these networks, and modulation is a dynamic interaction between input fibers and STG neurons.

Action Potentials↗

PubMed1989

A modulatory proctolin-containing neuron (MPN). I. Identification and characterization.

The pentapeptide proctolin has been localized previously to the crustacean stomatogastric nervous system and shown to modulate the rhythmic activity of the pyloric network in the stomatogastric ganglion (STG) (Marder et al., 1986; Hooper and Marder, 1987). We have now identified a pair of modulatory proctolin-containing neurons (MPNs) that cause proctolin-like modulation of the pyloric rhythm. Individual MPNs were identified by combining intracellular Lucifer yellow dye injection with rhodamine-visualized proctolin immunolabeling. Both MPNs are located in the esophageal nerve and send processes to the STG. Current injection into one MPN influences the second MPN, suggesting that they are electrically coupled. The 2 MPNs have similar effects on the pyloric rhythm of the STG. Intracellular stimulation of a single MPN was sufficient to enhance already active pyloric rhythms and initiated the pyloric rhythm in quiescent preparations.

Animals↗

PubMed1989

A modulatory proctolin-containing neuron (MPN). II. State-dependent modulation of rhythmic motor activity.

The effects of stimulating the modulatory proctolin-containing neurons (MPNs) on the pyloric rhythm of the stomatogastric ganglion of the crab, Cancer borealis, were compared with those produced by exogenously applied proctolin. The effects of both MPN stimulation and proctolin applications depend on the preceding physiological state of the preparation. Both treatments increase the pyloric cycle frequency dramatically in preparations that are slowly cycling, but they have little or no effect on pyloric cycle frequency in preparations that are already rapidly cycling. MPN and proctolin produce maximal pyloric cycle frequencies of about 1.2 Hz, although much faster pyloric frequencies are possible. MPN stimulation and proctolin applications affect the number of impulses fired in each burst by pyloric network neurons. MPN's excitatory actions are longer lasting when a preparation is active than when it is quiescent before stimulation. These data suggest that many of MPN's physiological actions result from its release of proctolin. Small unitary postsynaptic potentials evoked by MPN stimulation in the lateral pyloric neuron may indicate the presence of a second neurotransmitter in MPN.

Action Potentials↗

PubMed1988

Multifunctional interneurons in behavioral circuits of the medicinal leech.

We are using the medicinal leech to study the neuronal basis of behavioral choice. In particular, we are recording from neurons, both extracellularly and intracellularly, in preparations that can express three different behaviors: the shortening reflex, crawling and swimming. We have found that particular mechanosensory neurons can elicit any of the behaviors, and that the movements are produced by just four sets of muscles, each controlled by a small number of motor neurons. Hence, there must be three different pattern-generating neuronal circuits, each of which can be activated by the same set of sensory neurons. We are studying how the choice is made among the three behaviors by recording, while one behavior is being performed, from neurons known to be involved in the initiation of the other two. We have found that an interneuron, cell 204, which is known to initiate and maintain swimming, is also active during shortening and crawling. The activity level in this interneuron can influence whether a mechanosensory stimulus produces shortening or swimming. The neuronal mechanisms by which this choice is normally effected awaits further elucidation of the circuits that elicit and generate shortening and crawling.

Animals↗

PubMed1988

Substance P-like immunoreactivity in the stomatogastric nervous systems of the crab Cancer borealis and the lobsters Panulirus interruptus and Homarus americanus.

The distribution of substance P-like immunoreactivity in the stomatogastric nervous systems of three decapod crustacean species, Cancer borealis, Homarus americanus, and Panulirus interruptus, was studied. The stomatogastric ganglion showed dense staining in the neuropil, but none in the somata. A single neuron stained in the esophageal ganglion. Lucifer yellow backfills and intracellular injections followed by incubation with the substance P antibody showed that the axons of this neuron project into the inferior esophageal nerves towards the paired commissural ganglia. The commissural ganglia showed a pronounced projection from a large bundle of fibers in the anterior medial portion of the circumesophageal connective. Additionally, less dense neuropil and stained somata were seen in the commissural ganglia. Staining was completely blocked by preabsorption with authentic substance P, physalaemin, eledoisin, and substance K. These data suggest that in the nervous system of crustacean species a molecule with C-terminal homology to substance P and other tachykinins is released as a neuroregulator in the stomatogastric ganglion.

Animals↗

PubMed1987

Distribution and partial characterization of FMRFamide-like peptides in the stomatogastric nervous systems of the rock crab, Cancer borealis, and the spiny lobster, Panulirus interruptus.

The distribution of FMRFamide-like peptides was studied in the complete stomatogastric nervous system [the paired commissural ganglia, single oesophageal ganglion, and the single stomatogastric ganglion (STG)] of two decapod crustacean species, the spiny lobster Panulirus interruptus and the rock crab Cancer borealis, by using immunocytochemical techniques. Antiserum 231 from the O'Donohue laboratory and antiserum 671C (described here) gave essentially the same staining patterns. In the commissural ganglia of both species there were ten to 20 stained neurons and dense neuropilar staining. The oesophageal ganglion of the crab had four stained neurons. Lucifer Yellow backfills followed by immunostaining showed that the two larger stained neurons of the oesophageal ganglion sent processes into the inferior ventricular nerve. The two smaller neurons sent processes into the inferior oesophageal nerves. The oesophageal ganglion of the lobster had two stained neurons that sent processes into the inferior ventricular nerve as well. None of the somata of the STG stained in either species, but in both species stained fibers were seen in the stomatogastric nerve that entered the STGs and ramified profusely throughout the neuropil. In some preparations of the crab, a stained fiber was visible in the dorsal ventricular nerve. The amounts of the FMRFamide-like peptides found in all regions of the nervous system of P. interruptus and C. borealis were determined by radioimmune assay (RIA). Column chromatography and high-performance liquid chromatography suggest that, in both species, much if not all of the RIA-assayable material is accountable for by peptides that are larger and more hydrophobic than FMRFamide.

Animals↗

PubMed1987

Neural mechanisms generating the leech swimming rhythm: swim-initiator neurons excite the network of swim oscillator neurons.

This paper describes newly identified excitatory connections linking the segmentally iterated swim-initiator interneurons with the network of oscillator neurons that generates the leech swimming rhythm. Apparently monosynaptic excitatory chemical connections are made from one class of swim-initiator neurons (cells 204/205) to several members of the swim oscillator network, including cells 28, 115 and, as described by Weeks (1982c), cell 208. A second class of swim-initiator neurons, cells 21 and 61, also excites this subset of the oscillator neurons. The unpaired swim oscillator neuron, cell 208, also chemically excites cells 28 and 115, apparently directly. Thus, in addition to its role as a member of the swim oscillator, the excitatory output from cell 208 to the swim oscillator adds to that provided by the swim-initiator neurons. The results of this paper enlarge the subset of identified swim oscillator neurons synaptically excited by the swim-initiator neurons. These newly described targets of the swim-initiators strengthen the hypotheses that: 1) the swim-initiator neurons supply much of the tonic excitatory drive responsible for activation and maintenance of the swim central motor program, and 2) the two classes of swim-initiators, cells 204/205 and cells 21/61, act synergistically to initiate and maintain swimming.

Animals↗

PubMed1987

Neural control of limb coordination. I. Comparison of hatching and walking motor output patterns in normal and deafferented chicks.

Previous work has shown that the neural circuits underlying the leg movements of walking and hatching coexist in post-hatching chicks (Bekoff and Kauer, 1984). In the present study, quantitative analysis of leg EMGs shows that there are some similarities, but also significant differences, in the motor output patterns of walking and hatching. This study examines the effect of removing sensory feedback from the legs on the production of the distinctive leg motor patterns. The temporal characteristics and interlimb coordination of hatching and walking are little affected. However, major changes in intralimb motor output patterns are seen when compared to records from normal chicks. These changes fall into one of 2 categories. Some parameters show similar changes in both behaviors after deafferentation (e.g., increases in flexor burst durations and cycle period). This suggests that certain features of sensory input from the legs normally modulate the hatching and walking pattern-generating circuitry in similar ways. Other parameters show convergence. That is, these aspects of the 2 intralimb motor patterns become more similar to each other after removal of sensory input. This is consistent with the hypothesis that some feature of sensory input from the legs normally modulates one set of multiuse intralimb circuitry to produce different output patterns. In general, the walking pattern becomes more like hatching after deafferentation, rather than the reverse, which suggests that the hatching pattern is a more basic one. The maintenance of some residual differences in intralimb motor patterns after leg deafferentation suggests that other sources of modulation must also be involved, or that there are some additional elements of circuitry that are called into play during the normal production of walking and hatching.

Animals↗

PubMed1986

A kinematic study of crawling behavior in the leech, Hirudo medicinalis.

The medicinal leech crawls along a solid substrate by repeated alternating extensions and shortenings of the body. Extension occurs with the posterior sucker attached and the head sucker free. The head sucker then attaches, followed by shortening and release of the tail sucker. The tail sucker is then pulled toward the head, where it reattaches to the substrate. The head sucker then releases, and another crawling cycle begins (Figs. 1, 5). There are two crawling variants: inchworm crawling, in which the head and tail suckers are closely apposed at the end of a cycle and the body forms a loop above the substrate, and vermiform crawling, in which the suckers are placed farther apart and the body remains fairly close to the substrate (Fig. 1). The cycle period and the distance traveled during a cycle are greater in inchworm than in vermiform crawling; however, the velocity of travel is the same for both (Fig. 2). For both variants, the interval between head sucker attachment and tail sucker release is similar at all cycle periods and has a value consistent with direct interneuronal conduction of a signal from head sucker sensory neurons to tail sucker motor neurons. The interval between tail sucker attachment and head sucker release, however, is longer and varies with the cycle period, suggesting a more complex interneuronal circuit in the pathway from tail sucker sensory neurons to head sucker motor neurons (Fig. 4). The onsets of the components of the crawling cycle (extension, post-extension pause, shortening, and post-shortening pause) show an anteroposterior lag (Figs. 5, 7). For both variants, the travel time between segments varies directly with the period (Fig. 8). For both crawl types, the durations of the cycle components vary directly with the period, with several exceptions (Figs. 9, 10). A model is presented that summarizes the coordination of the various motor events in a cycle of leech crawling (Figs. 11 and 12).

Animals↗

PubMed1986

Swim initiation in the leech by serotonin-containing interneurones, cells 21 and 61.

Two pairs of serotonin-containing neurones, designated cells 21 and 61, were characterized physiologically and anatomically in the hirudinid leeches Macrobdella decora and Hirudo medicinalis. Both of these cells are bilaterally paired interneurones and each cell is weakly electrically coupled to the other serotonin-containing cells both intra- and interganglionically. Cells 21 and 61 are excited polysynaptically by individual identified mechano-sensory neurones. Segmental nerve shock sufficient to elicit an episode of swimming strongly excites cells 21 and 61, which then tend to generate bursts of impulses that are phase-locked to the swim motor pattern. Intracellular stimulation of either cell 21 or cell 61 often causes the initiation of swimming, acting in parallel with the nonserotonergic swim-initiator cell 204. Cells 61 and 204 are also weakly electrically coupled. The latency to swim onset by stimulating cell 21 or 61 is similar to that of cell 204 and different from that of the serotonergic Retzius cell. This result, with those in the accompanying paper (Nusbaum, 1986), suggests that unlike the Retzius cell and similar to cell 204, cells 21 and 61 synaptically contact cells of the swim central pattern generator (CPG).

Animals↗

PubMed1986

Synaptic basis of swim initiation in the leech. III. Synaptic effects of serotonin-containing interneurones (cells 21 and 61) on swim CPG neurones (cells 18 and 208).

Serotonin-containing cells 21 and 61 strongly excite a swim central pattern generator (CPG) neurone, cell 208, in nearby segmental ganglia in the leech Macrobdella decora. This excitatory effect is apparently independent of activity in the swim-initiating neurone cell 204, which monosynaptically excites cell 208 (Weeks, 1982b). Cell 208 excites cell 21, apparently directly. This is the first identified direct pathway for feedback from the swim central pattern generator to a swim initiator neurone. Focally applied serotonin has no effect on the soma of cell 208, but causes both excitatory and inhibitory responses in cell 208 when applied to different places within the neuropile. Cell 61 polysynaptically excites distant, posterior cells 208. This excitation is mediated at least in part by the activation of nearby cells 208, which polysynaptically excite posterior cells 208. Cell 208 is dye-coupled intraganglionically to a newly identified pair of neurones, designated cells 18. Cell 208 also excites posterior cells 18, apparently directly. This interaction may be the pathway whereby cell 61 polysynaptically excites posterior cells 208. During swimming, cell 18's membrane potential oscillates in phase with cell 208. Intracellular current injection into cell 18 during swimming perturbs the swim motor pattern. Therefore, cell 18 qualifies as a candidate swim CPG neurone.

Animals↗

PubMed1985

Identified GABAergic inhibitory motor neurons in the leech central nervous system take up GABA.

Physiologically identified inhibitory motor neurons in the leech central nervous system were double-labeled by intracellular injection of the dye Lucifer Yellow and gamma-amino-[3H]butyric acid ([3H]GABA) uptake to demonstrate that these inhibitory neurons are among the approx. 35 neurons per abdominal ganglion previously shown to take up GABA. GABA uptake into the inhibitory motor neurons is stimulated by electrical activity in the neurons.

Action Potentials↗

PubMedDate not supplied

The dual role of serotonin in leech swimming.

The swimming behavior of the leech depends upon the level of serotonin in its blood stream: the higher the level, the more likely the leech is to swim. Serotonin is contained in Retzius cells, segmentally paired neurons, which release enough of this substance to affect its blood level and thus the swimming behavior of the animal. Retzius cells appear not to have synaptic effects on swim-related neurons. Pairs of other serotonin-containing neurons (cells 21 and 61) are also present in each ganglion. Stimulation of these cells can initiate swimming within seconds. In contrast to Retzius cells, neurons 21 and 61 make synaptic connections onto swim-related neurons; for example, cell 61 makes what appears to be a conductance decrease excitatory synapse onto the pattern-generating interneuron cell 208. These results suggest that the two classes of serotonin-containing neurons control the swimming behavior of the leech through two different mechanisms: Retzius cells exert a neurohormonal action whereas cells 21 and 61 act synaptically.

Animals↗