Biomedical subjects

F Clarac

Publications and source records attributed to F Clarac.

At least 55 records · Page 3Linked to original sources

PubMed1994

Inhibitory effects of L-glutamate on central processes of crustacean leg motoneurons.

In crustaceans, glutamatergic excitation at the neuromuscular synapse has been extensively studied. Fewer reports exist of the central and possibly inhibitory actions of glutamate on neurons. The present study analyses the response of intracellularly identified motoneurons, which innervate the proximal leg muscles, to local glutamate pressure applications in the neuropil, in an in vitro thoracic preparation of the crayfish Procambarus clarkii. L-Glutamate application always inhibited motoneuron activity, with a decrease in input resistance. The resulting depolarization or hyperpolarization could usually be reversed within 10 mV of the resting potential. The response persisted in neurons pharmacologically isolated with Cd2+ or tetrodotoxin. The reversal potential of the response to glutamate was displaced in a low-chloride solution. Similar responses were obtained with GABA. Application of GABA blocked the glutamate response in a competitive manner. Both responses were suppressed by beta-guanidino-propionic acid, a competitive antagonist for GABA receptors. This indicates that glutamate activates a chloride-GABA receptor-channel. Micromolar concentrations of picrotoxin reduced both the L-glutamate and the GABA inhibitory responses, thereby unmasking a smaller, picrotoxin-resistant effect of glutamate (but not of GABA), which was excitatory and sensitive to 6,7-dinitroquinoxaline-2,3-dione (DNQX). These results suggest dual and opposite roles for motoneuron glutamatergic connections--a peripheral (well known) net excitatory one and a central net inhibitory one. Direct inhibition of motoneurons by L-glutamatergic neurons is to be expected.

Animals↗

PubMed1994

P-type Ca2+ channels mediate excitatory and inhibitory synaptic transmitter release in crayfish muscle.

The toxin fraction (FTX) and peptide omega-Aga-IVA from the venom of the funnel-web spider Agelenopsis aperta, as well as a synthetic analogue of FTX, specifically block the P-type voltage-dependent Ca2+ channel (VDCC). The effects of these toxins on synaptic transmission were studied in the neuromuscular synapses of the crayfish opener muscle, which has a single excitatory and a single inhibitory motoneuron. FTX selectively and reversibly blocked excitatory and inhibitory postsynaptic currents and potentials in a dose-dependent manner. FTX had no effect on (i) resting and postsynaptic membrane conductance, (ii) postsynaptic L-type VDCC, and (iii) both glutamate- and gamma-aminobutyric acid-induced postsynaptic responses. Mean amplitude and frequency of miniature postsynaptic potentials were unchanged by FTX. The postsynaptic VDCC was inhibited by nifedipine, a selective dihydropyridine antagonist of L-type VDCC, whereas synaptic transmission was unaffected. Transmission was also undisturbed by omega-conotoxin, suggesting that N-type VDCCs are not involved. The peptide omega-Aga-IVA blocked excitatory and inhibitory transmission without affecting postsynaptic VDCC. Synaptic transmission was also blocked by synthetic FTX. We conclude that presynaptic P-type VDCCs are involved in both evoked excitatory and inhibitory transmitter release in crayfish neuromuscular synapses.

Animals↗

PubMed1994

GABAergic inactivation of the central pattern generators for locomotion in isolated neonatal rat spinal cord.

1. Experiments were performed using an isolated brainstem-spinal cord preparation from newborn rats, in order to study the GABAergic control of the spinal neuronal networks that generate locomotor rhythms in mammals. Locomotor-like activities were recorded in the ventral roots, and the various neurochemical compounds were added to the superfusion saline. 2. Bath application of GABA suppressed in a dose-dependent manner the motor activity induced by an excitatory amino acid N-methyl-D,L-aspartate (NMA). Both the GABAA agonist muscimol and the GABAB agonist baclofen mimicked the effects of GABA, since they either slowed down or stopped the rhythmic activity. 3. Experiments were performed in which the lumbar compartment was superfused separately from the brainstem. Chemical activation of the brainstem by NMA alone failed to induce locomotor-like activity. When GABAA (bicuculline) and GABAB (phaclofen) antagonists were simultaneously bath applied to the lumbar spinal cord, however, locomotor-like activity was induced. 4. The GABA uptake inhibitors nipecotic acid and guvacine suppressed the rhythmic motor pattern induced by NMA in a dose-dependent manner. The effects of nipecotic acid were reversed by bicuculline and phaclofen. 5. Bicuculline added during NMA-induced locomotor-like activity greatly increased both the frequency and amplitude of motor bursts, while phaclofen modified only the frequency. 6. The motor pattern depended on the balance between activatory and inactivatory influences, since the rhythmic patterns recorded with low doses of NMA associated with high doses of bicuculline were similar to those elicited by higher doses of NMA associated with low doses of bicuculline.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Presynaptic inhibition is mediated by histamine and GABA in the crustacean escape reaction.

1. Presynaptic inhibition of sensory transmission during the escape reaction in Crustacea has been studied using an in vitro preparation of the crayfish thoracic ganglia. Electrical stimulation of the medial giant fiber mediating the escape reaction induced depolarization in sensory afferent terminals of the coxo-basal chordotonal organ (CBCO). This depolarization was associated with an increase of the membrane conductance and was partially blocked by a gamma-aminobutyric acid (GABA) antagonist, picrotoxin, and by a histamine antagonist, cimetidine. 2. Pressure ejection of histamine on CBCO sensory terminals (CBT) recorded intracellularly, induced a depolarization of the membrane potential accompanied by a large increase of the conductance. Histamine-induced depolarization persisted after blockade of synaptic transmission mediated by Na+ spikes by tetrodotoxin. The amplitude of histamine-induced depolarization increased when negative current was injected into the sensory terminal through the recording electrode. Moreover, injection of chloride into the CBT, which shifts the reversal potential of chloride to a more positive value, resulted in an increase of the amplitude of the histamine-induced depolarization. 3. The existence of separate receptors for GABA and histamine on the CB sensory terminals was demonstrated using two complementary sets of experiments. The first one consisted of using specific blockers of GABA and histamine. Picrotoxin blocked selectively the GABA-induced depolarization of the CB sensory terminals, while it was ineffective in blocking the histamine-induced depolarization. Conversely, cimetidine blocked the histamine-induced depolarization totally, but did not affect the GABA response. The second set of experiments tested for of cross-desensitization between GABA and histamine responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗

PubMed1994

Nicotinic and muscarinic activation of motoneurons in the crayfish locomotor network.

1. We investigated the effects of acetylcholine (Ach) on identified motoneurons (MNs) using an in vitro preparation of the crayfish thoracic nervous system. Discontinuous current-clamp and single electrode voltage-clamp recordings from 50 MNs were performed along with micropipette pressure ejection of Ach (or agonists) close to the recording electrode. 2. Localized ejections of relatively large volumes (500-2,500 pl) of Ach (10(-2) M) or of the muscarinic agonist oxotremorine (Oxo, 10(-2)M) onto the MN neuropile region, usually (90% of the cases) induced a slow, alternating rhythmic activity in antagonistic MNs. In other cases (4 experiments), with similar deliveries of Ach or Oxo, MNs developed the ability to fire rhythmically but only when depolarized by sustained current injection. Pressure ejections of smaller volumes (50-200 pl) of Ach (10(-2)M) close to the recorded MN could give rise to a fast (1-2 s) large amplitude (< or = 20 mV) membrane depolarization (12%), a long-lasting (10 s to several minutes) and small (2-5 mV) depolarization (14%), and a combination of the two (74%). These responses appeared to involve different regions of the neurite because they changed when the drug-ejection pipette was displaced in the neuropile. Moreover, fast and long-lasting depolarizing components resulted from a direct effect of Ach onto the MNs because they persisted under tetrodotoxin (TTX, 10(-6)M) and cobalt (Co2+, 5 x 10(-3) M) superfusion. 3. Whereas the membrane resistance decreased during the fast Ach-induced depolarization, it increased during the long-lasting depolarization. The increase in membrane resistance was more pronounced at depolarized potentials more than -55 mV and involve a reduction in K+ conductance. 4. Superfusion with nicotinic and muscarinic antagonists revealed that the fast Ach-induced depolarization involved nicotinic receptors, muscarinic receptors, or both, whereas the slow depolarization was exclusively muscarinic. 5. The Ach-evoked inward currents were studied under voltage clamp. The fast nicotinic component (Inic) increased with hyperpolarizing holding potentials and decreased with depolarizing potentials, reversing at between 10 and 30 mV. The fast muscarinic current (Ifmus) displayed similar characteristics and reversed at about -10 mV. Whereas both fast components were voltage independent, the long-lasting muscarinic component (Ismus) was voltage dependent. The response grew with membrane depolarization, but when the holding potential was hyperpolarized below resting level, the response declined to disappear at about -60 mV and beyond.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗

PubMed1994

MOTOR NEURONES OF THE CRAYFISH WALKING SYSTEM POSSESS TEA+-REVEALED REGENERATIVE ELECTRICAL PROPERTIES

In crustaceans, some motor neurones (MNs) have been shown to be part of the central pattern generator in the stomatogastric system (Harris-Warrick et al. 1992; Moulins, 1990), the swimmeret system (Heitler, 1978) or the walking system (Chrachri and Clarac, 1990). These MNs induce changes in the central rhythm when depolarized and are conditional oscillators in the stomatogastric ganglion. Moreover, in the walking system, rhythmic activity can be triggered by muscarinic cholinergic agonists (Chrachri and Clarac, 1987). We have recently analyzed the role of muscarinic receptors in crayfish walking leg MNs (D. Cattaert and A. Araque, in preparation) and demonstrated that oxotremorine, a muscarinic agonist, evoked long-lasting depolarizing responses associated with an increased input resistance. The outward current blocked by oxotremorine is likely to be carried by K+, as is the case for the M current (IM) in vertebrates (Brown and Adams, 1980). In most neurones, K+ conductances play a principal role in maintaining the membrane potential at rest: for example, IM is active at the resting membrane potential, thus contributing to its maintenance, and the 'delayed-rectifier' (IK) assists the fast repolarization after an action potential. Some K+ conductances are Ca2+-dependent (IK,Ca) and are activated by an increase in internal Ca2+ concentration. In such cases, Ca2+ currents may result in hyperpolarization of the neurone through activation of IK,Ca. In opposition to these K+ currents, the direct effect of Na+ and Ca2+ conductances is to depolarize the neurone. For example, the persistant Na+ current (INap) that is responsible for the slow subthreshold depolarization termed slow pre-potentials (Gestrelius et al. 1983; Leung and Yim, 1991) participates in the formation of pacemaker depolarization (Barrio et al. 1991) and generates plateau-type responses in control conditions (Barrio et al. 1991; Llinas and Sugimori, 1980). Similarly Ca2+ or non-specific (Na+/Ca2+) conductances generate such events in Aplysia californica burster neurones (Adams and Benson, 1985), crustacean cardiac ganglion (Tazaki and Cooke, 1990), insect neurones (Hancox and Pitman, 1991) and crustacean stomatogastric ganglion (Kiehn and Harris-Warrick, 1992). Since crustacean MNs can participate in rhythm production, such depolarizing conductances may exist in most of them and may contribute to the long-lasting MN depolarizations and spike bursts present during locomotion.

Journal Article↗

PubMed1993

In vitro, proctolin and serotonin induced modulations of the abdominal motor system activities in crayfish.

An in vitro thoraco-abdominal preparation of the crayfish (Procambarus clarkii) ventral nerve cord was used to study the sites of action and the effects of proctolin and serotonin on the nervous activities of the two abdominal motor systems, namely the swimmeret and the abdominal positioning systems. In this preparation spontaneous motor activity was recorded corresponding to continuous rhythmic bursts in the swimmeret motor nerves and tonic discharge of motoneurons in both abdominal extensor and flexor motor nerves. Proctolin applied on the abdominal ganglia elicited bursts of spikes in the flexor motor nerve which were able to disturb and even stop the swimmeret activity. Increasing concentrations of serotonin applied on the thoracic ganglia were able, first, to increase the period durations of the swimmeret bursting activity and, second, to stop it. In this last condition, continuous swimmeret activity resumed by application of proctolin on the abdominal ganglia although period durations stayed slightly longer than in control. The actions of serotonin and proctolin on the two abdominal motor systems were discussed in terms of modulations and interactions between central neuronal networks and behaviors.

Abdomen↗

PubMed1993

Induction of fictive locomotion by sulphur-containing amino acids in an in vitro newborn rat preparation.

The role of the sulphur-containing amino acids (SAAs) in the initiation of fictive locomotion was tested in an isolated spinal cord preparation from newborn rats. These substances were bath-applied and the fictive locomotion was recorded in the lumbar ventral roots. It emerged from this study that all the compounds tested could trigger an organized pattern (alternating left and right bursts of activity) with a dose-dependent response. However, specific frequency and concentration ranges were observed with each of these SAAs. Moreover, a clear-cut difference between D and L isomers in the ability of the SAAs to induce this activity was observed; the SAAs of the D-forms were found to be generally more potent than those of the L-forms. The effects of the SAAs were found to be mediated by both NMDA and non-NMDA receptors, since they were blocked in a dose-dependent manner by the specific antagonists of these receptors. Moreover, it was observed that beta-p-chlorophenylglutamic acid, an uptake inhibitor of homocysteic acid (HCA), potentiated the effect of exogenously applied HCA, which supports the idea that HCA may act as a transmitter. The sulphuric and non-sulphuric amino acids were also classified in their order of potency. The most potent compound turned out to be D-homocysteine sulphinic acid, while D-cysteine sulphinic acid was the least potent. It also emerged that the maximal frequencies obtained with SAAs and excitatory amino acids were in the same range, which might correspond to the maximal limits of this system.

Amino Acids↗

PubMed1993

Electrical coupling of mechanoreceptor afferents in the crayfish: a possible mechanism for enhancement of sensory signal transmission.

1. Central electrical coupling between primary afferent axons was investigated in an in vitro preparation of the crayfish thoracic locomotor system by using intracellular recordings. 2. Intracellular injection of the dye Lucifer yellow in single afferents resulted in staining of one to three additional afferents through dye-coupling. Three-dimensional confocal imaging of dye-coupled axons revealed a large zone of close apposition that may correspond to the gap junction site. 3. A depolarization preceding the spike in one sensory terminal was shown to facilitate the excitatory postsynaptic potential occurring in postsynaptic motoneurons. Further, a spike in one afferent axon can depolarize other, electrically coupled, axons above spike threshold, resulting in an increased number of active afferents. 4. The electrical coupling occurred between sensory afferents of similar function. It may therefore serve to facilitate sensory signal transmission from functionally homologous afferents onto postsynaptic target neurons.

Action Potentials↗

PubMed1993

Oscillatory properties of the central pattern generator for locomotion in neonatal rats.

1. The oscillatory properties of the lumbar spinal networks that generate locomotor activity in mammals were studied. These experiments were performed on an in vitro isolated spinal cord preparation from newborn rats. Adding to the saline serotonin (5-HT) and N-methyl-D-aspartate (NMDA) excitatory amino acid receptor agonist (N-methyl-D,L-aspartate, NMA) induced rhythmic locomotor-like activity that was recorded in the ventral roots. 2. The period of the rhythmic locomotor-like activity could be set by combining the neurotransmitters at various concentrations. The combined transmitters also acted on the instantaneous variations of the period value. The stability of the period from one cycle to another increased when 5-HT was mixed with NMA compared with the activity induced by bath application of the compound alone. 3. K(+)-induced depolarizations were used to set the neuron membrane potential. These systematic changes in the K+ concentration resulted in a change in the period value. 4. Stimulation of the dorsal roots reset the ongoing rhythm. Phase-response curves were drawn up that showed that the spinal networks exhibit a differential sensitivity to the same stimulus depending on the phase at which the stimulus is applied. The free-running activity could be entrained by the cyclic volleys of sensory discharges. Entrainment occurred, on average, between -28 and 36% of the rest period. Because the lumbar segments were completely isolated by means of a sucrose blockade of all descending neuronal activity, the entrainment of the locomotor activity must take place directly at the lumbar level. 5. In conclusion, our data show that, at birth, the rhythmic activity produced by the spinal networks is based on a neuronal architecture that displays oscillatory properties. At this early age, the peripheral sensory afferents have already established connections with the central pattern generator. These sensory inputs are able to control the cycling activity of the spinal networks step by step.

Animals↗

PubMed1992

Presynaptic control as a mechanism of sensory-motor integration.

In studies of central nervous system networks, it is synaptic transmission to the postsynaptic soma-dendritic membrane that has received the most attention, in particular in relation to the analysis of sensory-motor integration. Sensory transmission is gated during ongoing movements in both invertebrates and vertebrates, such that it may be depressed in one phase of a cyclic movement and facilitated in another, in order to optimize the execution of the ongoing motor task. This presynaptic modulation is not limited to sensory afferents, but also occurs in synapses of both excitatory and inhibitory premotor interneurons. The modulation can be mediated by the release of different transmitters at axo-axonal synapses, which activate different types of receptors. In addition, presynaptic sensory axons can be coupled via gap junctions, which under certain conditions may mediate a presynaptic facilitation.

Action Potentials↗

PubMed1992

Activation of the central pattern generators for locomotion by serotonin and excitatory amino acids in neonatal rat.

1. The role of serotonin (5-HT) and excitatory amino-acids (EAAs) in the activation of the neural networks (i.e. the central pattern generators) that organize locomotion in mammals was investigated in an isolated brainstem-spinal cord preparation from the newborn rat. 2. The neuroactive substances were bath applied and the activity of fictive locomotion was recorded in the ventral roots. 3. Serotonin initiated an alternating pattern of right and left action potential bursts. The period of this rhythm was dose dependent, i.e. it decreased from around 10 s at 2 x 10(-5) M to 5 s at 10(-4) M. The effects of serotonin were blocked by a 5-HT1 antagonist (propranolol) and by 5-HT2 antagonists (ketanserin, cyproheptadine, mianserin). 5-HT3 antagonists were ineffective. The effects of methoxytryptamine, a non-selective 5-HT agonist, mimicked the 5-HT effects. 4. The endogenous EAAs, glutamate and aspartate, also triggered an alternating rhythmic pattern. Their effects were blocked by 2-amino-5-phosphonovaleric acid (AP-5; a N-methyl-D-aspartate (NMDA) receptor blocker) and 6,7-dinitro-quinoxaline-2,3-dione (a non-NMDA receptor blocker). 5. Several EAA agonists (N-methyl-D,L-aspartate (NMA) and kainate) initiated rhythmic activity. The period of the induced rhythm (from 3 to 1 s) was similar with both of these substances but in a range of concentrations which was ten times lower in the case of kainate (10(-6) to 5 x 10(-6) M) than in that of NMA (10(-5) to 4 x 10(-5) M). alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionate and quisqualate occasionally triggered some episodes of fictive locomotion with a threshold at 6 x 10(-7) and 10(-5) M, respectively.

Action Potentials↗

PubMed1992

Direct evidence for presynaptic inhibitory mechanisms in crayfish sensory afferents.

1. The central control of sensory inputs from a proprioceptor [chordotonal organ (CO)] in the second joint [coxo-basipodite (CB)] of the fifth leg was studied in crayfish in vitro preparations (Fig. 1A). Simultaneous intracellular recordings from CBCO terminals (CBT) and postsynaptic motoneurons (MNs) were performed along with micropipette pressure ejection or bath application of gamma-aminobutyric acid (GABA), to study the presynaptic mechanisms at work in the CBT (Fig. 1B). 2. Two intracellular recordings were used to show that the spikes never overshoot, and that the more central the recording site within the neuropile, the smaller the spikes (Fig. 2). Only electrotonic conduction occurs, therefore, in the sensory afferents within the ganglion. 3. Pressure ejection of GABA close to the recording site of CBTs in the ganglion (Fig. 3A) gave rise to a membrane depolarization, the reversal potential of which was about -25 mV (Fig. 7), as well as to an increase in the membrane conductance (Fig. 3C) and a decrease in the orthodromic spike amplitude; moreover, it did not elicit either hyperpolarization, or any change in the membrane conductance of the postsynaptic MN (Fig. 3B), which indicates that pressure ejection of GABA affected only a restricted area around the CBT and not the postsynaptic MNs. 4. In CBT, spontaneous primary afferent depolarizations (PADs) occurred irregularly when the activity of the preparation was not rhythmic (Fig. 4A), and in bursts when the preparation displayed fictive locomotion (Fig. 4B). In the latter case, antidromic spikes were sometimes superimposed on PADs (Fig. 4D). The amplitude of the PADs was reduced when picrotoxin (PTX), a GABA antagonist, was applied (Fig. 5), which suggests that GABA may be involved in spontaneous PADs. The reversal potential of PADs was about -25 mV (Figs. 6 and 7). 5. During simultaneous recordings from a CBT and a monosynaptically related MN, GABA applied by pressure ejection close to the CBT (Fig. 8A) completely suppressed the excitatory postsynaptic potentials (EPSPs) elicited by CBT spikes in the MN (Fig. 8, B and D). This was due to a presynaptic mechanism because no change in the membrane potential or membrane conductance was observed in the MN (Fig. 8C) and most of the CBTs associated with a given MN were affected (Fig. 9). 6. Simultaneously recording from a CBT and a monosynaptically related MN demonstrated that, during bouts of PADs, the spike amplitude decreased in proportion to the PAD amplitude (Fig. 10A).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Serotonin and proctolin modulate the response of a stretch receptor in crayfish.

The modulatory effects of proctolin and a biogenic amine (5-hydroxytryptamine; 5-HT) have been investigated on a leg mechanoreceptor in the crayfish. Single afferent sensory units were recorded extra- and intracellularly during imposed sinusoidal movement to the receptor strand; all responses were facilitated by a bath application of proctolin and 5-HT at various concentrations (10(-9)-10(-6) M).

Animals↗

PubMed1991

A cooling/heating system for use with in vitro preparations: study of temperature effects on newborn rat rhythmic activities.

We have developed a universal stage that is particularly suitable for use with vertebrate and invertebrate in vitro preparations. Based on the Peltier effect, the same compact apparatus can be used to cool or heat within a wide temperature range (from 5 to 50 degrees C). Due to the use of interchangeable rings, the stage is compatible with a wide variety of dishes. We used this system to analyze the effects of temperature on the spinal networks that generate fictive locomotion in newborn rats. The results showed that these spinal networks can be active in a wide temperature range, producing an organized pattern (bursts alternating between the right and left sides) even at very low temperatures (15 degrees C). From 15 to 20 degrees C the period decreased before reaching a plateau (between 20 to 30 degrees C).

Action Potentials↗

PubMed1990

Variability as a characteristic of immature motor systems: an electromyographic study of swimming in the newborn rat.

Swimming behaviour was studied in neonate rats by carrying out electromyographic recordings. The study showed that the early swimming pattern was characterized by highly instable temporal parameters. A decrease was found to occur with age in the variability of the instantaneous period in each leg and in that of the antiphase pattern. Moreover, a dissociation occurred during development between the foreleg and the backleg activity. While patterns involving the forelegs always remained extremely instable, a considerable improvement was found to occur with time in the hindlimb activity.

Afferent Pathways↗

PubMed1990

Motoneuronal commands during swimming behaviour in the shore crab.

Neurograms of proximal leg motor nerves were obtained during swimming in the shore crab. Whereas excitor motoneurones fire in bursts, the common inhibitor motoneurone discharges tonically with simultaneous spikes in all the motor nerves. The average firing frequency of the common inhibitor increases as the period of the swimming cycle decreases. Moreover, greater fluctuations of the firing frequency of the common inhibitor occurs within long rather than short swim cycle periods.

Action Potentials↗

PubMed1990

Two types of motor rhythm induced by NMDA and amines in an in vitro spinal cord preparation of neonatal rat.

Rhythmic motor activities were studied in two rat spinal cord preparations; in the first one, the spinal cord was completely isolated and the ventral roots activity was recorded; in the other, spinal cord and hindlimbs were kept in order to record muscle activities. Motor patterns were therefore recorded in ventral roots and/or hindlimb muscles. Two kinds of specific patterns were elicited by neurochemicals. The first which was induced by N-methyl-D,L-aspartate (NMDA) and serotonin (5-HT) was a slow rhythm (0.5-0.2 Hz) of left and right alternating bursts of spikes. The second one which was induced by NMDA, 5-HT and norepinephrine (NE), was a high frequency rhythm (5-10 Hz). One particularity observed was that these two rhythms could occur simultaneously. The relationship between the two in vitro rhythms is discussed and they are compared with those reported in other rhythmic systems.

Action Potentials↗