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R L Calabrese

Publications and source records attributed to R L Calabrese.

66 records · Page 4Linked to original sources
PubMed1980

Control of multiple impulse-initiation sites in a leech interneuron.

1. Several heart interneurons (HN cells) of the leech nerve cord have impulse-initiation sites in every segmental ganglion through which their single axons pass. All these initiation sites are capable of producing rhythmic impulse bursts. However, under normal conditions a dominant primary initiation site in the ganglion where the cell body is located suppresses the activity of the other secondary sites. 2. Hyperpolarization of the primary initiation site by injected current permits immediate expression of rhythmic activity by a secondary site, usually the one located in the next posterior ganglion. 3. The free-running impulse burst rhythm of the primary site is stronger than that of the secondary site, having a greater burst duration and a tendency toward a higher burst frequency. 4. Bursts of primary-site impulses intercalated into the secondary-site impulse burst rhythm have a twofold effect. First, early to midway through the secondary-site's burst cycle, they phase delay its impulse burst rhythm. Second, early in the secondary-site's burst cycle, they tend to suppress ongoing impulse bursts, and late in the secondary-site's burst cycle, they tend to suppress the next expected impulse burst. The amount of burst suppression seen early and late in the secondary-site burst cycle depends on the burst duration and intraburst impulse frequency of the intercalated burst. 5. The ability of a train of primary-site impulse bursts to completely suppress secondary-site activity depends on burst duration, intraburst impulse frequency, and burst period. 6. Primary-site impulse trains with burst parameters close to those of naturally occurring primary-site bursts completely suppress secondary-site activity. 7. These results are consistent with the notion that the primary-site impulse burst rhythm of an HN cell suppresses the activity of its secondary site because, cycle by cycle, it delays and/or suppresses the next secondary-site burst so that no secondary-site bursts are produced. Dominance of the primary site over the secondary site is ensured by virtue of the primary-site's stronger impulse burst rhythm.

Animals↗
PubMed1979

Neural control of heartbeat in the leech and in some other invertebrates.

The heartbeat of the leech Hirudo consists of the contractile rhythm of the circular muscles in the wall of a bilateral pair of celomic sinuses, the heart tubes, that run the length of the leech body. The constriction cycles of the segmental heart-tube sections are coordinated so that on one body side they constrict in a rear-to-front progression (peristalsis), while on the other side they constrict nearly in concert (nonperistalsis). Spontaneous right-left reciprocal transitions between peristaltic and nonperistaltic coordination modes occur every few dozen heartbeat cycles. The constriction of each segmental heart-tube section is controlled via excitatory synapses by a rhythmically active heart motor neuron, or HE cell, of which 17 bilateral pairs are iterated in segmental ganglia of the ventral nerve cord. The activity rhythm of the HE cell ensemble is in turn controlled via inhibitory synapses by a rhythmically active heart interneuron, the HN cell, of which seven bilateral pairs are iterated in the rostral segmental ganglia. The HN heart interneuron owes its activity rhythm to an endogenous polarization cycle, and the cycles of all members of the HN cell ensemble are locked into an appropriate phase relation thanks to their mutual interconnection via excitatory and inhibitory synaptic connections. The observed activity pattern and identified synaptic connections of HE cells and HN cells can account not only for the generation of the two bilaterally asymmetric heartbeat coordination modes but also for the right-left coordination mode transitions. In contrast to the heartbeat of Hirudo, the beat of the single-chambered heart of the lobsters Panulirus and Homarus is controlled by a set of nine rhythmically active neurons that make up the cardiac ganglion. Of these, five larger cells are heart motor neurons that innervate the heart muscle fibers via excitatory synapses. The remaining four smaller neurons of the cardiac ganglion are interneurons that provide excitatory input to each other and to the heart motor neurons. Although all the neurons of the cardiac ganglion appear capable of producing their own endogenous polarization rhythm, it is currently believed that one of the interneurons acts as a pacemaker for the whole ensemble of interneurons and motor neurons. The beat of the two-chambered heart of the marine snail Aplysia is generated by yet an entirely different mechanism. Here, the basic contractile rhythm of the heart is due to an endogenous polarization cycle of the heart muscle fibers. That myogenic rhythm is controlled and modulated by a set of cardiovascular motor neurons located in the abdominal ganglion, some of which make excitatory and others of which make inhibitory connections with the heart muscle fibers. The activity of these cardiovascular motor neurons is controlled by three types of heart interneurons via both inhibitory and excitatory connections. The interneurons are in turn interconnected in a manner that prevents the simultaneous activation of antagonistic cardiac motor acts...

Action Potentials↗
PubMed1979

The roles of endogenous membrane properties and synaptic interaction in generating the heartbeat rhythm of the leech, Hirudo medicinalis.

1. Inhibitory synapses among the central neurones involved in the generation of the heartbeat rhythm of the leech were blocked by either low Cl- physiological saline or presynaptic hyperpolarizing current. 2. Low Cl- saline reversibly blocked inhibitory postsynaptic potentials (IPSPs) from the HN cells onto both other HN cells and HE cells but did not block electrical coupling among HN cells. 3. The rhythmic bursts of impulses in HE cells were abolished when IPSPs were blocked by either low Cl- saline or hyperpolarization of HN cells. 4. The rhythmic bursts of impulses in HN cells were not abolished (except in cell HN(5)) when IPSPs were blocked by low Cl- saline, but phase relations became unfixed (unless the cells were electrically coupled). 5. Both brief depolarizing and hyperpolarizing current pulses reset the rhythm of HN cells whose IPSPs were blocked by low Cl- saline. 6. The results indicate that the motor neurones to the heart (HE cells) produce rhythmic impulse bursts because their steady discharge is periodically inhibited by the HN interneurones. The pattern generated by the HN cells originates from an endogenous rhythm co-ordinated by the inhibitory interactions and electrical coupling between these cells.

Action Potentials↗
PubMed1978

Neuronal generation of the leech swimming movement.

The swimming movement of the leech is produced by an ensemble of bilaterally symmetric, rhythmically active pairs of motor neurons present in each segmental ganglion of the ventral nerve cord. These motor neurons innervate the longitudinal muscles in dorsal or ventral sectors of the segmental body wall. Their duty cycles are phase-locked in a manner such that the dorsal and ventral body wall sectors of any given segment undergo an antiphasic contractile rhythm and that the contractile rhythms of different segments form a rostrocaudal phase progression. This activity rhythm is imposed on the motor neurons by a central swim oscillator, of which four bilaterally symmetric pairs of interneurons present in each segmental ganglion appear to constitute the major component. These interneurons are linked intra- and intersegmentally via inhibitory connections to form a segmentally iterated and inter-segmentally concatenated cyclic neuronal network. The network appears to owe its oscillatory activity pattern to the mechanism of recurrent cyclic inhibition.

Action Potentials↗
PubMed1976

Integration of directional mechanosensory input by crayfish interneurons.

1. Interneurons activated by mechanosensory hairs on the crayfish telson respond selectively to directional displacements of the medium; the directions of maximum sensitivity lie 180 degrees apart in approximately the rostrocaudal plane, corresponding to the directional sensitivities of the two populations of primary afferent neurons. We have examined the basis for this selectivity by intracellular recording in the interneurons, correlating subthreshold potentials with activity evoked in identified afferents by bending single hairs or by producing nearfield displacements of the medium. 2. Interneurons can usually be caused to discharge by a brief train of impulses in single sensory axons. Unitary EPEPs are associated with arriving affterent spikes in the fourth (sensory) root; each primary interneuron receives convergence from several sensory axons, all sensitive to the same direction of movement. Since each afferent axon is drawn from a pair innervating a single sensory structure, this remarkable specificity of connection is unlikely to depend on an anatomical mode of address. 3. Higher order interneurons receive from directionally sensitive lower order interneurons of the same class, as well as from primary afferents of that class. The responses of such cells may show much more decrement during a train of displacement stimuli than do those of lower order cells. Directionality does not appear to be enhanced. 4. During the "null phase" some interneurons appear to be actively inhibited: bending of single hairs 180 degrees away from the effective direction may produce membrane hyperpolarization and slow spontaneous discharges, and shocks to afferent roots produce mixtures of monosynaptic EPSPs and polysynaptic IPSPs.

Animals↗
PubMed1976

Rhythmic swimming activity in neurones of the isolated nerve cord of the leech.

1. Repeating bursts of motor neurone impulses have been recorded from the nerves of completely isolated nerve cords of the medicinal leech. The salient features of this burst rhythm are similar to those obtained in the semi-intact preparation during swimming. Hence the basic swimming rhythm is generated by a central oscillator. 2. Quantitative comparisons between the impulse patterns obtained from the isolated nerve cord and those obtained from a semi-intact preparation show that the variation in both dorsal to ventral motor neurone phasing and burst duration with swim cycle period differ in these two preparations. 3. The increase of intersegmental delay with period, which is a prominent feature of swimming behaviour of the intact animal, is not seen in either the semi-intact or isolated cord preparations. 4. In the semi-intact preparation, stretching the body wall or depolarizing an inhibitory motor neurone changes the burst duration of excitatory motor neurones in the same segment. In the isolated nerve cord, these manipulations also change the period of the swim cycle in the entire cord. 5. These comparisons suggest that sensory input stabilizes the centrally generated swimming rhythm, determines the phasing of the bursts of impulses from dorsal and ventral motor neurones, and matches the intersegmental delay to the cycle period so as to maintain a constant body shape at all rates of swimming.

Action Potentials↗
PubMed1974

Presynaptic inhibition: primary afferent depolarization in crayfish neurons.

Inhibition of transmission between tactile sensory neurons and interneurons in the crayfish was investigated by intracellular recording int the presynaptic processes. Inhibition is correlated with a depolarization of the presynaptic process, as in the mammalian spinal cord; the depolarization is accompanied by a conductance increase, and is mediated by interneurons that can be excited by a variety of routes.

Animals↗
PubMedDate not supplied

Identification of RFamide neuropeptides in the medicinal leech.

Using a four-step reverse phase HPLC separation and RIA, five RFamide peptides were purified from CNS extracts of the leech Hirudo medicinalis. YMRFamide, FMRFamide, YLRFamide, FLRFamide, and GGKYMRFamide were identified by a combination of antiserum specificity in RIA, Edman degradation, and mass spectrometry. At least three of these five endogenous peptides can modulate neuromuscular interactions in the leech (38). FMRFamide-like immunoreactivity was selectively released from neural processes on isolated heart tubes in the presence of calcium and depolarizing levels of potassium.

Amino Acid Sequence↗
PubMedDate not supplied

A model of a segmental oscillator in the leech heartbeat neuronal network.

We modeled a segmental oscillator of the timing network that paces the heartbeat of the leech. This model represents a network of six heart interneurons that comprise the basic rhythm-generating network within a single ganglion. This model builds on a previous two cell model (Nadim et al., 1995) by incorporating modifications of intrinsic and synaptic currents based on the results of a realistic waveform voltage-clamp study (Olsen and Calabrese, 1996). Due to these modifications, the new model behaves more similarly to the biological system than the previous model. For example, the slow-wave oscillation of membrane potential that underlies bursting is similar in form and amplitude to that of the biological system. Furthermore, the new model with its expanded architecture demonstrates how coordinating interneurons contribute to the oscillations within a single ganglion, in addition to their role of intersegmental coordination.

Animals↗