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Coordination of the cardio-respiratory rhythms recorded from lobsters Homarus americanus to an externally-imposed, dorsoventral motion
I lo
Camp. Biochrm. Pkwid.. Vol. 66A. pp. 61 617 0 Pergamon Press Ltd 1980. Printed in Great Brttain
0300.9629/80!0801-061
ISO2.C0/0
COORDINATION OF THE CARDIO-RESPIRATORY RHYTHMS RECORDED FROM LOBSTERS HOMARUS AMERICANUS TO AN EXTERNALLY-IMPOSED, DORSOVENTRAL MOTION P. E. COYER’,R. E. YOUNG’and G. A. WYSE Department of Zoology, University of Massachusetts, Amherst, MA 01003, U.S.A. and Department of Zoology, University of the West Indies, Kingston, Jamaica’ (Receioed 18 October 1979) Abstract-l. In unrestrained lobsters, coupling of the left and right scaphognathite (SG) beating motions at frequencies centering around 2 Hz was recorded from fine, platinum-iridium electrodes implanted in identifiable depressor muscles of the respiratory appendages. 2. The SG/heart systems were entrained by an imposed, dorsoventral movement applied on to the blade of one scaphognathite from which electromyograms (emg’s) were recorded over frequencies ranging from 0.9 to 1.19 Hz. 3. The timing sequence of individual heart contractions recorded with respect to bursts of muscle activity from the entrained SG motor system revealed periods of close heart and SG coordination to the lever motion as indicated by a computer compilation of the phase relationships existing among the impedance measurements of heart beat, SG emg’s, and the imposed movements.
INTRODUCI’ION
For several species of decapod crustaceans, it is known that the basic rhythms underlying ventilatory movements of the scaphognathites (SG’s) and beating motions of the heart (HB) result from endogenous activity of neurons. During alternating phases of membrane polarization, a pair of single-cell, nonspiking neurons initiate cyclic, respiratory motions of the SG’s or gill-bailers (Pasztor, 1968; Mendelson, 1971). Presumably, this occurs either through direct
interaction of the oscillator neurons on to the levator and depressor motor pools or more likely through indirect pathways and synapses on to the motor pool from pre-motor neurons located in the thoracic ganglion of crabs and the subesophageal ganglion of lobsters (Wilkens, 1976). Excitation of motor-type cells resulting in muscular heart contraction is accomplished by driver-potentials emanating from the smaller, pacemaker neurons of the cardiac ganglion (Hagiwara & Bullock, 19.57; Hartline, 1967; Anderson, 1973). Cardio-regulation may also occur by conduction of excitatory and inhibitory signals to the cardiac ganglion via the dorsal nerve from cells lying in the same central ganglion containing the neural network controlling ventilation (Florey, 1960). Central control of heart rate is mediated through the neural effects of the cardio-accelerators and inhibitors (Maynard, 1953; Field & Larimer, 1975a,b) and the neurosecretory effects of the pericardial organ (Cooke & Goldstone, 1970) although bursting activity has been recorded from the second segmental nerve 1 Present address and address for correspondence: Dr Philip E. Coyer, Department of Neurology and the Neurosciences Program, University of Alabama in Birmingham 35294. Alabama Birmingham, Center, Medical (205)934-5284.
(SN II), which contains the cardio-inhibitor axon as well as SG motor axons in the macruran Nephrops noruegicus (Young, 1978). This may indicate a type of phasic control emanating from the SG system and communicating with the cardiac ganglion. Maynard (1960) reported spontaneous inhibitor activity of l-16Hz recorded in the dorsal nerve of Homarus americanus, but Field & Larimer (1975a,b) found only sporadic tonic units within SN II which showed a fixed latency of impulses presumably in the cardioinhibitory axon of the dorsal nerve in crayfish. In brachyurans, Coyer (1977a) was unable to record bursts from the pericardial organ at the point where the cardio-inhibitor enters the dorsal nerve and thus provide a mechanism of phasic input coordinating the heart/SG systems, which is described below. For the two brachyuran decapod species (Cancer irroratus and Cancer borealis) which were studied, it is known that centrally-generated respiratory rhythms of heart beat and one SG movement tend to occur within distinct portions of each other’s normalized cycle length (Coyer, 1977b; Coyer, 1979). Despite covarying rate changes of the cardio-respiratory movements, an invariant phase relationship existed between one SG rhythm and the heart beat. On certain occasions when the heart rate changed, the SG and heart rhythms displayed lock and drift behavior characteristic of relative coordination (see Wendler, 1966 for a discussion of relative coordination). This type of coordination has also been found in the lobster Homarus americanus (Young & Coyer, 1979) although tight coupling between the heart and one SG rhythm may be more commonly expressed in the two cancrid species (Coyer, 1979) since there is probably a stronger “magnet effect” (von Hoist, 1939). To demonstrate the existence of entrainable SG/ heart systems outside the absolute coupling frequencies known for the lobster SG system (Wilkens &
611
P. E.
612
COYER,
R. E.
YOUNG
Young, 1973, gill-bailer electromyograms (emg’s) were first recorded in unrestrained animals. After the heart and ventilatory rhythms were established for lobsters, an experiment which tested the role of sensory afference in modulating their cardio-respiratory systems was conducted. This design follows Wendler’s analysis ~endler, 1974) of the proprio~ptive influence of a central motor program on wing-beat movements in locusts. An external, sinusoidal movement was imposed on one SC from which muscle bursts were recorded to identify the nature of entrainment that might exist within lobsters’ SG systems. It is known that entrainment of the gill-bailer motor system can be effected by applying alternating current to the thoracic ganglion of the green crab Carcinus ~~u~~us (Pilkington, 1976). In addition to obtaining SG emg’s, we monitored the heart beat and contralateral (freely-moving) SG movements and observed the extent to which elements within the subesophageal ganglion controlling the cardio-respiratory system can be coordinated. Usually, the freely-moving SG beats at a faster rate similar to that recorded during bilateral SG coordination. MATERIALS Lobsters
Nomarus
AND METHODS
umericarrus
were
purchased from local
seafood markets in Northampton.
Massachusetts, and in Birmingham, Alabama, in August 1976 and 1979. These animals were kept in well-aerated and filtered seawater aquaria (instant Ocean; salinity. 30.3f,,,) held at 1%18’C. Experiments were conducted in a lucite chamber containing seawater of the same salinity (30.3”,,,), temperature (15 + I”C), and PO2 (12&-130torr) as the laboratory aquaria. Therefore. the free-running heart and gill-bailer rates of four animals could be established under wellaerated, undisturbed situations. To test the degree of heart and SC coordination which exists in crabs (Coyer, 1977a; 1979). a computer-aided analysis of data accumulated from long-term monitoring of a fifth animal was performed during imposed SG movement. Movement of the gill-bailer has been described by Wilkens & McMahon (1972) for Homarus amrricarlus using cinematographic techniques, Young (1973) for Carcims mnenas by monitoring the activity of gill-bailers with a photocell, and by Cochran (1935) and Young (1975) for Cailirtecres sapidus and Carcirtus rnu~t~as relating known muscle movements to levation or depression within the complete cycle. The beating motion observed by these investigators consists of both trapezoidai dorsoventral and anterior-posterior rotations around the point of main skeletal articutation with some pronation-supination of the blade’s anterior edge. Riruromuscufar
recording
qf gibbaikr
In iobsters electromyograms
and heart heafirrg
of muscle activity corresponding to the ventilatory movement of both freelymoving scaphognathites were made by implanting 25 pm platinum-iridium wires into identifiable depressor muscles (Dla or Dlb, according to Young’s terminology, Young, 1975) on the gill-bailers’ ventral surfaces. Muscle potentials were recorded differentially from these implanted electrodes, amplified by Grass P51 I or 7P5B AC preamplifiers, displayed on a Tektronix 7623A oscilloscope, and recorded on a Phillips or Precision Instruments FM tape recorder. Pumping motions of the heart and contralateral gill-bailer were monitored with a suction electrode system and implanted wires respectively (Fig. IA & B). In previous experiments in which gill-bailer movement in crabs was monitored by this method (Fig. IQ deflections in the impedance trace were correlated with the muscle
and G. A. Wusr:
potentials recorded during levation of depression of the SC cycle (See Coyer, 1977a: 1979). The relationship between tissue conductance changes across the carapace during heart beating, which results in muscular contraction. has been established (Coyer. 1976).
Once rhythmic gill-bailer and heart beating occurred without interruptions such as hyperventilation and bradycardia, we stopped the experiment and cemented a wire “splint” (about I mm in diameter) across the SG’s B’B axis (Young, 1975; a plane perpendicular to the axis of dorsoventral movement and parallel to the leading edge of the axis of pronation-supination) with a small quantity of fastdrying methyl cyanoacrylate glue. Therefore. with the “splint” fastened to the blade and attached to a Harvard Apparatus pen-motor via two moveable fulcrum points. one at the level of the gill-bailer and one at the level of the right angle of the inverted L-shaped attachment arm, the gill-bailer could be moved mechanically. It was felt that this would allow the gill-bailer to behave nearly normally. A sine wave generated by a Wave-tek signal generator drove the pen-motor which created an imposed levatordepressor cycle whose frequency could be varied at will (See Fig. 2). The rate of this movement was monitored by a photocell output creating voltage changes corresponding to the arm’s movement (see Fig. 3. second trace). The imposed movement was varied from 0.9 to i.i9 Hz and in most cases was centered around I Hz. about one-half that of the beating rates observed during bilateral SC coordination (Fig. I).
Data from one animal that was ventilated by imposed scaphognathite movement were systematically analyzed for phase preference. These results may not then be typical for the species but at least show the degree of coordination possible between the central nervous elements controlling the heart and SG rhythms relative to an imposed scaphognathite movement at frequencies below the range reported for bilateral SG coordination (Wilkens & Young. 1975). The outputs resulting from a reference square-wave. the photocell monitoring sinusoidal arm motion, the interburst intervals of electromyograms from the right SC Dla muscle, and impedance records of the left scaphognathite and heart movements were recorded on a Phillips FM tape recorder. Data from these tape-recorded signals were photographed with a Grass camera at 2.5 cmjsec (see enl&gement Fig. _ 3). The mean period lengths of the SG em& showing motor control of the beating motions during imposed movements and heart beats are represented in Fig. 4 over the pre-determined frequencies. The phase relationships (4 = 0.1-1.0) existing between the SG emg’s and the applied motor movements were compiled into histograms showing the incidence of each one (s-y axes, vertical orientation in Fig. 68 and horizontal orientation in Fig. 7C). In a similar fashion the latency to the HB could be compared to either the motor (Figs SB & 7A) or the inter-burst intervals of the SG’s (Fig. 78) used as references. As compared with Fig. 7, Figs 5 & 6 were constructed over shorter time periods including a change of frequency from I-0.Y HE (Fig. 6). A statistical analysis of phase relationships existing over 390 cycles (Fig. 7) was devised in the same manner coupling percentages of the heart and gill-bailer rhythms were analyzed earlier (see Coyer. iY79) according to
Hughes’ center of moments (Hughes, 1972). RESULTS
In unrestrained lobsters, bilateral SG coordination occurred when each appendage was beating at a frequency around 2 Hz (Fig. 1A). This is evident from
Heart
and gill-bailer
coordination
613
in lobsters
Reference Squore Wave Photocell output emgs
Impedance Waves
Fig. 3. An enlarged, redrawn portion of the 5-trace oscilloscope camera record shows the reference square wave, the sinusoidal, arm-like motion, SG emg’s and impedance waves associated with HB and contralateral SG movement. The phase relationship (c#J)for a SC emg inter-burst interval (Tr,) over the duration of each imposed movement (TA) is expressed by LAB/T,. L,, represents the latency from the onset of the arm motion to the next emg burst recorded from the SG (see text).
Fig. 1. Coupling of the left and right SG movements demonstrated by electromyogram (ems) recordings from identifiable depressor muscles (see text) in an unrestrained Nomarus americarrus (A), combined heart beat (HB) and bilateral SG emg recording using a suction electrode to monitor HB (middle trace) and implanted SC muscle electrodes (top and bottom) in another Homarus americanus (B), and impedance changes resulting from the muscular contractions of the heart (middle trace) and bilateral SC motions (top and bottom) in a Cancer borealis (C). Calibration mark; 500 ms in A & C, 50 ms in B.
the temporal agreement of emg’s recorded from the depressor muscles on the ventral surfaces of both SG blades. In Fig. lB, which was photographed at a faster sweep speed (50 ms; calibration marker), bursts of junction potentials recorded from one SG depressor
muscle preceded the HB with some regularity. Therefore, it was hypothesized that the heart and scaphognathite beating motions might show some degree of relative coordination. The results of further experiments (see below) support this idea. Frequency modulation of the scaphognathite and heart rates during the imposed movement is graphically represented in Fig. 4 showing the means (x’s) and standard deviations (SD) for the pre-set motor interval, the SG emg’s, and the heart-beat periods (solid, open, and shaded bars respectively). When the driver motor was set at about 1 Hz, neither the SG nor the heart beat speeded up accordingly. They each maintained their rates of beating at slower frequencies corresponding to periods with means ?c = 1.13
Imposed Motor Frequencies Fig. 2. Experimental arrangement for imposing movement on an SC while recording emg’s from one of its depressor muscles and impedance waves associated with the heart beat and the contralateral SG motion. A sine wave input to the Harvard Apparatus pen-motor imposed a dorsoventral movement on the SC, and a corresponding reference square wave provided an accurate time measurement. The dorsoventral motion resulted in a sine-wave output arising from a photocell monitor of the lever’s motion. These traces appear in Fig. 3.
Fig. 4. Bar graphs of means (_U)and standard deviations (SD’s) for pre-set pen-motor (solid bars), SC (open bars), and HB (shaded bars) periods over several frequencies of imposed movement applied to the SG. The amount of variation about the mean is expressed by the error bars representing k 1 SD. No SD was computed for the last set, which represents the data tabulated not by hand as appears in Figs 5 & 6 but by a computer program using data recorded during 390 cycles of SG inter-burst intervals and HB cycles.
P.
614 ”
216
A
Sequential
E.
COYER,
R.
E. YOUNGand G. A. WYSE
Heart Beat Intervals ot an Imposed Motor Permd of I, I Set
Fig. 5. Instantaneous periods (A) and phase plots (B) of the heart beat intervals relative to the imposed movement at a period length of 1.I set corresponding to a pre-set motor frequency of 0.9 Hz. Solid line in (A) represents the motor period. The phase histogram is oriented vertically along the right margin of B. The longer bar at 4 - 0.4 indicates some coordination but not to the extent shown at 4 = 0.9 for SG/motor coordination (Fig. 6B).
(s = 0.17) and 1.03 (s = 0.07) set respectively. When
the motor frequency was decreased to 0.9 Hz, the SG beat interval became widely scattered reflected by the increase in the SD (second set of bar graphs Fig. 4). As evident by the resetting phase relationships and corresponding flat histogram shown in Fig. 5B, the heart beat did not show a high degree of phase coupling to the sinusoidal arm movement although the rates of both were almost equal (overlapping SD’s, second set of bar graphs Fig. 4). An interesting rate dependency is also seen in Fig. 4 in which moving the gill-bailer at a higher rate of 1.19 Hz depressed both the heart and gill-bailer rates so that they were not overlapping with the rate of the motor’s movement. This inversely-related phenomenon observed at frequencies above that for heart and SG coordination
.
indicates that there is a restricted range of coupling frequencies (1 Hz, Fig. 7). Phase plots of the intended scaphognathite movement with respect to the motor and the gill-bailer’s instantaneous intervals (Fig. 6) were constructed over the first 110 cycles of the experiment during which the frequency of imposed movement on the gill-bailer was changed from 1 to 0.9 Hz at cycle No. 80. As indicated by the instantaneous plots in Fig. 6A (and the large standard deviation in the second set of bar graphs in Fig. 4) observed SG intervals were highly variable and fluctuated widely around the motor period of 1.1 sec. This highly variable rate with respect to the motor movement is shown in the erratic phase drift of the SG beat with respect to the motor movement (Fig. 6B). There were times when the SG
Sequentlol Interburst Intervals of s_Cemg’s ot Imposed Motor Percds of IO and . . . * .
Phase Plot /S_G emg’s
Fig. 6. Instantaneous periods (A) and imposed movement at period lengths and 0.9 Hz. Solid line in (A) represents phase histogram
i Interburst
I I set
Interval) ond Motor Period
phase plots (B) of interburst intervals of SC emg’s relative to the of 1 and 1.1 set corresponding to pre-set motor frequencies of 1 the motor frequency including the transition at cycle No. 80. The is oriented vertically along the margin of B.
Heart A
hb I” motor
and gill-bailer
interval
coordination
615
in lobsters
13 hb
I”
r.sg.emg
record
4or
Phase
C r sa ema’s
Phase I” motor
int
Phase
Fig. 7. Frequency distributions of phase relationships among heart beat and the pre-set motor interval (A), heart beat relative to SG emg’s (B), and SG emg’s and the pre-set motor interval (C) at 1 Hz from data represented in the last set of bar graphs in Fig. 4. The ordinate corresponds to the number of events
falling within a preferred phase (4 0.0 -+ 1.0) and is positioned horizontally unlike the histograms appearing in Figs 5 & 6. Coupling percentages (R) expressed in the histograms of HB/SG and SG/motor coordination are significant (P 5 0.05).
dropped out; i.e. skipped beats and consequently these times could not be recorded as intervals on the phase plots, accounting for the gaps between cycles 9&1OO (Fig. 6B). However, there is a phase preference evident (4 at -0.9) on the ordinate (Fig. 6B) to the motor rhythm over cycles SO-90 and l&1 10 as expressed by the large peak in the histogram lying along the right margin. Although maintenance of a preferred phase is of short duration, it supports a lock and drift model. It is important to recognize that locking of the gill-bailer’s rhythm to the movement of the arm was not coincident with bringing the frequency of the pen lever into a range overlapping that of the gill-bailer beat since the gill-bailer dropped out at times. When it began beating again, it resumed its previous phase 4 of -0.9. Phase histograms of the relative positions of the heart beat in the right scaphognathite interval during imposed movement are shown in Fig. 7. The histograms for coordination of the heart to the scaphognathite (Fig. 7B) and the scaphognathite to the motor movement (Fig. 7C) contain peaks associated with one or more phase preferences. The histogram relating the coordination of the heart beat to the motor movement does not (Fig. 7A). As a result the coupling percentage (R) for the heart beat in the motor interval is low (R = 1.7%; P > 0.05) for the heart beat in the right SG interval (R = 17.4%) and for the right gill-bailer in the motor interval
(R = 14.5”/,); the latter coupling nificant (P d 0.05).
percentages
are sig-
DISCUSSION
The results may indicate that the scaphognathite can be loosely entrained by external scaphognathite movement showing lock and drift behavior characteristic of relative coordination (Wendler, 1966). This is consistent with Pilkington’s observation (Pilkington, 1976) for Curcinus maenas in which he applied alternating current to the thoracic ganglion and recorded phase locking and drift of identifiable levator and depressor muscles of the scaphognathite. The results also show only a slight degree of coordination between the heart beat and imposed motor movement even when they approached the same frequency (Figs 4 and 5B). However, during relative coordination of one gill-bailer to the motor, the heart displayed lock and drift behavior with respect to the imposed SG beating motion (Fig. 7B) and no coordination to the motor movement (Fig. 7A). The observed locking and drifting (showing some phase preference but drifting in and out of phase) behavior found in the crustacean cardio-respiratory system is characteristic of relative coordination. Wilkens & Young (1975) described variations in the degree of tight coupling versus relative coordination
616
P. E. COYER,R. E. YOUX
(lock and drift behavior) of both the gill-bailer rhythms in lobster under changing temperature conditions. In the lobster there is locking of the phase relationship between the cycles over certain ranges, and an overall preference for certain relative phase positions persists although the cycle frequencies may differ. During bilateral scaphognathite coordination, phase locking occurs at neither absolute synchrony where 4 = 1 nor one-half cycle out of phase 4 = 0.5 (Wilkens & Young, 1975). Similarly observed SG and heart coordination in crabs occurs at an average phase angle (4) of 277” having a range of 4 = 060.9 (Coyer, 1979). Furthermore, according to the relative coordination model proposed by Wendler (1966), at specific frequencies a pacemaker rhythm can draw an oscillator into a range of incomplete entrainment so that one or possibly more preferred phase relationships of one rhythm result with respect to the other. Usually, this occurs when the natural frequency of the dependent rhythm approaches that of the pacemaker, or in this case when the rate of heart contraction was attracted to that of SG movement. In the experiments in which movement was imposed on the gill-bailer beating motion, the heart beat cycle coupled with the entrained SG movement over the depressed SG frequency of 1 Hz. However, when the imposed scaphognathite was slowed to 0.9 Hz, the heart beat was attracted to the same frequency range and showed only a slight degree of phase preference (Figs 4 and 5B). The SG beat frequency was erratic compared to the pre-set driver motor’s rate (large SD; Fig. 4), but its rhythm showed some lock and drift behavior (Fig. 6). It is interesting that there is a fine tuning of the heart and gill-bailer rhythms around 1 Hz (motor period of 0.97 set) into the coordinated patterns indicated by the histograms in Fig. 7 showing the phase relationships among heart and scaphognathite beating relative to imposed motor intervals. Pilkington (1976) plotted imposed frequencies of stimulation versus entrained frequencies for the thoracic ganglion of Carcinus maenas describing a region of relative entrainment for scaphognathite muscle bursts near the rate of the observed free-running rhythm. It appears that a neural oscillator system can be brought into a range of frequency-dependency by an external source, and furthermore, during this attraction, there may be phase coupling of the dependent (heart) to the SG rhythm. The range of frequencies for entrainment lies below that reported during bilateral SG coordination (Wilkens & Young, 1975). Thus, this finding of a restricted range of frequencies for coupling is consistent with the relative coordination model (Wendler, 1966). Since these results were taken from data on only five specimens of Homarus americanus, the existence of a centrally-patterned rhythm coordinating the heart and gill-bailer pumping motions is not definitive. While the neuronal basis for heart and SG control in terms of the nature of impulse patterning from the thoracic ganglion has not been elucidated in crabs and lobsters (Coyer, 1979; Young, 1978) there is behavioral and physiological evidence for both relative and absolute coordination of the cardio-respiratory rhythms. However, there are several models one might adopt in devising an internal coordinating sys-
and G. A. WYSE
tern for the heart and scaphognathites. One may consider that there is shared common input acting on both systems, but this probably would not account for maintenance of heart coordination with only one gill-bailer. Reciprocal inhibitory interactions may also account for coordination, but it is doubtful that the observation of unidirectional coordination from the entrainable scaphognathite system to the heart beat follows from this model. The role of tonic or phasic sensory feedback is also unclear. Phasic activity arising from the mechanoreceptive oval organ (Pasztor, 1969) neither initiates the SG rhythm nor coordinates its activity to an imposed movement through reafference (Young & Coyer, 1979). Tonic input seems to frequencies in modulate the cardio-respiratory parallel but does not provide the temporal patterning that one might expect to underlie scaphognathite and heart coordination (Coyer, 1976). Acknowledgements-This fulfillment
of the requirements
work was submitted in partial for the degree of Doctor of
Philosophy at the University of Massachusetts, Amherst, Massachusetts, by the first author (P.E.C.). The authors are grateful to Dr Winsor Watson for writing the computer program used in the analysis. This work was supported by P.H.S. grant NS 08869 to G.A.W. During the initial oeriod of this work, R. E. Young was support:d by a Study and Travel Grant from the University of the West Indies. The authors would also like to thank the Department of Neurology, University of Alabama Medical Center, Birmingham, Alabama, for the use of its facilities and MS Ellen Autery for her typing services rendered in preparation of this manuscript. REFERENCES
ANDERSON M. 0. (1973) Neuromuscular systems in neurogenie arthropod hearts. Am. Zoo/. 13 (2). 291-298. COCHRAN D. M. (1935) The skeletal musculature of the blue crab Callinectrs sapidus. Rathhun. Smithson. Misc. Collect. 92 (9), 76 pp. C%KE I. M. & GOLDSTONE M. (1970) Fluorescence localization of monoamines in crab neurosecretory structures. J. exp. Biol. 53, 651-688. COYER P. E. (1976) Heart and gill-bailer coupling in crabs--evidence for unilateral coordination. Physiologist 19 (3), 243 (abstract). COYERP. E. (1977a) Responses of heart and scaphognathite rates in Cancer horeulis and Cancer irrorutus to hypoxia. Camp. Biochem. Physiol. XiA, 165-l 67. COYERP. E. (1977b) Neuronal mechanisms underlying the coordination of heart and gill-bailer rhythms in decapod crustacea. Ph.D. thesis, University of Massachusetts, Amherst. COYERP. E. (1979) Heart and one gill-bailer rhythm phase couple in Cancer borealis and Cancer irroratus. Camp. Biochem. Physiol. 62, 677-683. FIELD L. H. & LARIMER J. L. (1975a) The cardioregulatory system of crayfish: neuroanatomy and physiology. J. exp. Biol. 62, 519-530. FIELD L. H. & LARIMER J. L. (1975b) The cardioregulatory system of crayfish: the role of the circumesophageal interneurons. J. exp. Biol. 62, 531-543. FLOREY E. (1960) Studies on the nervous regulation of heart beat in decapod crustacea. J. gm. Physiol. 43, 1061-1081. HAGIWARA S. & BULLOCK T. H. (1957) Intracellular potentials in pacemaker and integrative neurons of the lobster cardiac ganglia. J. cell. comp. Physiol. 50, 2547. HARTLINE D. K. (1967) Impulse identification and axon mapping of the nine neurons in the cardiac ganglion of
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the lobster Homarus americanus. J. e.up. Biol. 47, 327-340. HOLST E. VON (1939) Die relative Koordination als Phanomen und als Methode zentralnervtiser Funktionsanalyse. Eraeben. Phvsiol. 42. 228-306. HUG&~ G. G. (1972) The relationship between cardiac and respiratory rhythms in the dogfish Scyliorhinus canicula (L.) J. cup. Biol. 57, 415-434. MAYNARD D. M. (1953) Activity in a crustacean ganglion. I. cardioinhibition and acceleration in Pam&us aryus. Biol. Bull. 104, 156-170. MAYNARD D. M. (1960) Circulation and heart function. In The Physiology qf Crustacea I, (Edited by WATERMAN T. H.). pp. 161-214. Academic Press, New York. MI:NDELSON M. (1971) Oscillator neurons in crustacea ganglia. Scieplce, N. Y. 171, I1 7&l 173. PASZ~OR V. M. (1968) The neurophysiology of respiration in decapod crustacea. I. The motor system. Can. J. Zoo/. 46. 585-596. PASZTOR V. M. (1969) The neurophysiology of respiration in decapod crustacea. II. The sensory system. Can. J. Zool. 47, 435441. PILKINGTON J. B. (1976) Experimental coupling of crab (Carcinus maenas) second maxilla neural motor to an alternating current. Experienfia 32, 1435- 1437. WENDLER G. (1966) The coordination of walking move-
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ments in arthropods. In Symp. Sot. Exp. Biol. 20: Nert10u.sartd Hormonal Mechanisms of integration (Edited by HUGHES G.) Cambridge University Press, Cambridge. WENDLER G. (1974) The influence of proprioceptive feedback on locust flight coordination. J. camp. Physiol. 88, 173-200. WILKENS J. L. (1976) Neuronal control of respiration in decapod crustacea. Fed. Proc.. Fed. Am. Sot. e.up. Biol. 35, 200&2006. WILKENS J. L. & MCMAHON B. R. (1972) Aspects of branchial Irrigation in the lobster Homarus americanus. J. e_yp. Blol. 56, 469-479. WILKENS J. L. & YOUNG R. E. (1975) Bilateral scaphognathite coordination in lobster. J. e\-p. Biol 63, 219-232. YOUNC; R. E. (1973) Nervous control of ventilation in the shore crab Carcinus maenas. Ph.D. thesis, University of St. Andrews. Fife. YOUNG; R. E. (1975) Neuromuscular control of ventilation in the crab Carcinus maenus. J. camp. Physiol. 101, 1-37. YOUXG R. E. (I 978) Correlated activities in the cardioregulater nerves and ventilatory system in the Norwegian lobster, Nephrops norwgicus (L.) Camp. Biochem. Physiol. 61A, 387-395. YOUNG;R. E. & COYER P. E. (1979) Phase coordination in the cardiac and ventilatory rhythms of the lobster Homtnw amrrictmus. J. exp. Biol. 82, 53-74.
Camp. Biochrm. Pkwid.. Vol. 66A. pp. 61 617 0 Pergamon Press Ltd 1980. Printed in Great Brttain
0300.9629/80!0801-061
ISO2.C0/0
COORDINATION OF THE CARDIO-RESPIRATORY RHYTHMS RECORDED FROM LOBSTERS HOMARUS AMERICANUS TO AN EXTERNALLY-IMPOSED, DORSOVENTRAL MOTION P. E. COYER’,R. E. YOUNG’and G. A. WYSE Department of Zoology, University of Massachusetts, Amherst, MA 01003, U.S.A. and Department of Zoology, University of the West Indies, Kingston, Jamaica’ (Receioed 18 October 1979) Abstract-l. In unrestrained lobsters, coupling of the left and right scaphognathite (SG) beating motions at frequencies centering around 2 Hz was recorded from fine, platinum-iridium electrodes implanted in identifiable depressor muscles of the respiratory appendages. 2. The SG/heart systems were entrained by an imposed, dorsoventral movement applied on to the blade of one scaphognathite from which electromyograms (emg’s) were recorded over frequencies ranging from 0.9 to 1.19 Hz. 3. The timing sequence of individual heart contractions recorded with respect to bursts of muscle activity from the entrained SG motor system revealed periods of close heart and SG coordination to the lever motion as indicated by a computer compilation of the phase relationships existing among the impedance measurements of heart beat, SG emg’s, and the imposed movements.
INTRODUCI’ION
For several species of decapod crustaceans, it is known that the basic rhythms underlying ventilatory movements of the scaphognathites (SG’s) and beating motions of the heart (HB) result from endogenous activity of neurons. During alternating phases of membrane polarization, a pair of single-cell, nonspiking neurons initiate cyclic, respiratory motions of the SG’s or gill-bailers (Pasztor, 1968; Mendelson, 1971). Presumably, this occurs either through direct
interaction of the oscillator neurons on to the levator and depressor motor pools or more likely through indirect pathways and synapses on to the motor pool from pre-motor neurons located in the thoracic ganglion of crabs and the subesophageal ganglion of lobsters (Wilkens, 1976). Excitation of motor-type cells resulting in muscular heart contraction is accomplished by driver-potentials emanating from the smaller, pacemaker neurons of the cardiac ganglion (Hagiwara & Bullock, 19.57; Hartline, 1967; Anderson, 1973). Cardio-regulation may also occur by conduction of excitatory and inhibitory signals to the cardiac ganglion via the dorsal nerve from cells lying in the same central ganglion containing the neural network controlling ventilation (Florey, 1960). Central control of heart rate is mediated through the neural effects of the cardio-accelerators and inhibitors (Maynard, 1953; Field & Larimer, 1975a,b) and the neurosecretory effects of the pericardial organ (Cooke & Goldstone, 1970) although bursting activity has been recorded from the second segmental nerve 1 Present address and address for correspondence: Dr Philip E. Coyer, Department of Neurology and the Neurosciences Program, University of Alabama in Birmingham 35294. Alabama Birmingham, Center, Medical (205)934-5284.
(SN II), which contains the cardio-inhibitor axon as well as SG motor axons in the macruran Nephrops noruegicus (Young, 1978). This may indicate a type of phasic control emanating from the SG system and communicating with the cardiac ganglion. Maynard (1960) reported spontaneous inhibitor activity of l-16Hz recorded in the dorsal nerve of Homarus americanus, but Field & Larimer (1975a,b) found only sporadic tonic units within SN II which showed a fixed latency of impulses presumably in the cardioinhibitory axon of the dorsal nerve in crayfish. In brachyurans, Coyer (1977a) was unable to record bursts from the pericardial organ at the point where the cardio-inhibitor enters the dorsal nerve and thus provide a mechanism of phasic input coordinating the heart/SG systems, which is described below. For the two brachyuran decapod species (Cancer irroratus and Cancer borealis) which were studied, it is known that centrally-generated respiratory rhythms of heart beat and one SG movement tend to occur within distinct portions of each other’s normalized cycle length (Coyer, 1977b; Coyer, 1979). Despite covarying rate changes of the cardio-respiratory movements, an invariant phase relationship existed between one SG rhythm and the heart beat. On certain occasions when the heart rate changed, the SG and heart rhythms displayed lock and drift behavior characteristic of relative coordination (see Wendler, 1966 for a discussion of relative coordination). This type of coordination has also been found in the lobster Homarus americanus (Young & Coyer, 1979) although tight coupling between the heart and one SG rhythm may be more commonly expressed in the two cancrid species (Coyer, 1979) since there is probably a stronger “magnet effect” (von Hoist, 1939). To demonstrate the existence of entrainable SG/ heart systems outside the absolute coupling frequencies known for the lobster SG system (Wilkens &
611
P. E.
612
COYER,
R. E.
YOUNG
Young, 1973, gill-bailer electromyograms (emg’s) were first recorded in unrestrained animals. After the heart and ventilatory rhythms were established for lobsters, an experiment which tested the role of sensory afference in modulating their cardio-respiratory systems was conducted. This design follows Wendler’s analysis ~endler, 1974) of the proprio~ptive influence of a central motor program on wing-beat movements in locusts. An external, sinusoidal movement was imposed on one SC from which muscle bursts were recorded to identify the nature of entrainment that might exist within lobsters’ SG systems. It is known that entrainment of the gill-bailer motor system can be effected by applying alternating current to the thoracic ganglion of the green crab Carcinus ~~u~~us (Pilkington, 1976). In addition to obtaining SG emg’s, we monitored the heart beat and contralateral (freely-moving) SG movements and observed the extent to which elements within the subesophageal ganglion controlling the cardio-respiratory system can be coordinated. Usually, the freely-moving SG beats at a faster rate similar to that recorded during bilateral SG coordination. MATERIALS Lobsters
Nomarus
AND METHODS
umericarrus
were
purchased from local
seafood markets in Northampton.
Massachusetts, and in Birmingham, Alabama, in August 1976 and 1979. These animals were kept in well-aerated and filtered seawater aquaria (instant Ocean; salinity. 30.3f,,,) held at 1%18’C. Experiments were conducted in a lucite chamber containing seawater of the same salinity (30.3”,,,), temperature (15 + I”C), and PO2 (12&-130torr) as the laboratory aquaria. Therefore. the free-running heart and gill-bailer rates of four animals could be established under wellaerated, undisturbed situations. To test the degree of heart and SC coordination which exists in crabs (Coyer, 1977a; 1979). a computer-aided analysis of data accumulated from long-term monitoring of a fifth animal was performed during imposed SG movement. Movement of the gill-bailer has been described by Wilkens & McMahon (1972) for Homarus amrricarlus using cinematographic techniques, Young (1973) for Carcims mnenas by monitoring the activity of gill-bailers with a photocell, and by Cochran (1935) and Young (1975) for Cailirtecres sapidus and Carcirtus rnu~t~as relating known muscle movements to levation or depression within the complete cycle. The beating motion observed by these investigators consists of both trapezoidai dorsoventral and anterior-posterior rotations around the point of main skeletal articutation with some pronation-supination of the blade’s anterior edge. Riruromuscufar
recording
qf gibbaikr
In iobsters electromyograms
and heart heafirrg
of muscle activity corresponding to the ventilatory movement of both freelymoving scaphognathites were made by implanting 25 pm platinum-iridium wires into identifiable depressor muscles (Dla or Dlb, according to Young’s terminology, Young, 1975) on the gill-bailers’ ventral surfaces. Muscle potentials were recorded differentially from these implanted electrodes, amplified by Grass P51 I or 7P5B AC preamplifiers, displayed on a Tektronix 7623A oscilloscope, and recorded on a Phillips or Precision Instruments FM tape recorder. Pumping motions of the heart and contralateral gill-bailer were monitored with a suction electrode system and implanted wires respectively (Fig. IA & B). In previous experiments in which gill-bailer movement in crabs was monitored by this method (Fig. IQ deflections in the impedance trace were correlated with the muscle
and G. A. Wusr:
potentials recorded during levation of depression of the SC cycle (See Coyer, 1977a: 1979). The relationship between tissue conductance changes across the carapace during heart beating, which results in muscular contraction. has been established (Coyer. 1976).
Once rhythmic gill-bailer and heart beating occurred without interruptions such as hyperventilation and bradycardia, we stopped the experiment and cemented a wire “splint” (about I mm in diameter) across the SG’s B’B axis (Young, 1975; a plane perpendicular to the axis of dorsoventral movement and parallel to the leading edge of the axis of pronation-supination) with a small quantity of fastdrying methyl cyanoacrylate glue. Therefore. with the “splint” fastened to the blade and attached to a Harvard Apparatus pen-motor via two moveable fulcrum points. one at the level of the gill-bailer and one at the level of the right angle of the inverted L-shaped attachment arm, the gill-bailer could be moved mechanically. It was felt that this would allow the gill-bailer to behave nearly normally. A sine wave generated by a Wave-tek signal generator drove the pen-motor which created an imposed levatordepressor cycle whose frequency could be varied at will (See Fig. 2). The rate of this movement was monitored by a photocell output creating voltage changes corresponding to the arm’s movement (see Fig. 3. second trace). The imposed movement was varied from 0.9 to i.i9 Hz and in most cases was centered around I Hz. about one-half that of the beating rates observed during bilateral SC coordination (Fig. I).
Data from one animal that was ventilated by imposed scaphognathite movement were systematically analyzed for phase preference. These results may not then be typical for the species but at least show the degree of coordination possible between the central nervous elements controlling the heart and SG rhythms relative to an imposed scaphognathite movement at frequencies below the range reported for bilateral SG coordination (Wilkens & Young. 1975). The outputs resulting from a reference square-wave. the photocell monitoring sinusoidal arm motion, the interburst intervals of electromyograms from the right SC Dla muscle, and impedance records of the left scaphognathite and heart movements were recorded on a Phillips FM tape recorder. Data from these tape-recorded signals were photographed with a Grass camera at 2.5 cmjsec (see enl&gement Fig. _ 3). The mean period lengths of the SG em& showing motor control of the beating motions during imposed movements and heart beats are represented in Fig. 4 over the pre-determined frequencies. The phase relationships (4 = 0.1-1.0) existing between the SG emg’s and the applied motor movements were compiled into histograms showing the incidence of each one (s-y axes, vertical orientation in Fig. 68 and horizontal orientation in Fig. 7C). In a similar fashion the latency to the HB could be compared to either the motor (Figs SB & 7A) or the inter-burst intervals of the SG’s (Fig. 78) used as references. As compared with Fig. 7, Figs 5 & 6 were constructed over shorter time periods including a change of frequency from I-0.Y HE (Fig. 6). A statistical analysis of phase relationships existing over 390 cycles (Fig. 7) was devised in the same manner coupling percentages of the heart and gill-bailer rhythms were analyzed earlier (see Coyer. iY79) according to
Hughes’ center of moments (Hughes, 1972). RESULTS
In unrestrained lobsters, bilateral SG coordination occurred when each appendage was beating at a frequency around 2 Hz (Fig. 1A). This is evident from
Heart
and gill-bailer
coordination
613
in lobsters
Reference Squore Wave Photocell output emgs
Impedance Waves
Fig. 3. An enlarged, redrawn portion of the 5-trace oscilloscope camera record shows the reference square wave, the sinusoidal, arm-like motion, SG emg’s and impedance waves associated with HB and contralateral SG movement. The phase relationship (c#J)for a SC emg inter-burst interval (Tr,) over the duration of each imposed movement (TA) is expressed by LAB/T,. L,, represents the latency from the onset of the arm motion to the next emg burst recorded from the SG (see text).
Fig. 1. Coupling of the left and right SG movements demonstrated by electromyogram (ems) recordings from identifiable depressor muscles (see text) in an unrestrained Nomarus americarrus (A), combined heart beat (HB) and bilateral SG emg recording using a suction electrode to monitor HB (middle trace) and implanted SC muscle electrodes (top and bottom) in another Homarus americanus (B), and impedance changes resulting from the muscular contractions of the heart (middle trace) and bilateral SC motions (top and bottom) in a Cancer borealis (C). Calibration mark; 500 ms in A & C, 50 ms in B.
the temporal agreement of emg’s recorded from the depressor muscles on the ventral surfaces of both SG blades. In Fig. lB, which was photographed at a faster sweep speed (50 ms; calibration marker), bursts of junction potentials recorded from one SG depressor
muscle preceded the HB with some regularity. Therefore, it was hypothesized that the heart and scaphognathite beating motions might show some degree of relative coordination. The results of further experiments (see below) support this idea. Frequency modulation of the scaphognathite and heart rates during the imposed movement is graphically represented in Fig. 4 showing the means (x’s) and standard deviations (SD) for the pre-set motor interval, the SG emg’s, and the heart-beat periods (solid, open, and shaded bars respectively). When the driver motor was set at about 1 Hz, neither the SG nor the heart beat speeded up accordingly. They each maintained their rates of beating at slower frequencies corresponding to periods with means ?c = 1.13
Imposed Motor Frequencies Fig. 2. Experimental arrangement for imposing movement on an SC while recording emg’s from one of its depressor muscles and impedance waves associated with the heart beat and the contralateral SG motion. A sine wave input to the Harvard Apparatus pen-motor imposed a dorsoventral movement on the SC, and a corresponding reference square wave provided an accurate time measurement. The dorsoventral motion resulted in a sine-wave output arising from a photocell monitor of the lever’s motion. These traces appear in Fig. 3.
Fig. 4. Bar graphs of means (_U)and standard deviations (SD’s) for pre-set pen-motor (solid bars), SC (open bars), and HB (shaded bars) periods over several frequencies of imposed movement applied to the SG. The amount of variation about the mean is expressed by the error bars representing k 1 SD. No SD was computed for the last set, which represents the data tabulated not by hand as appears in Figs 5 & 6 but by a computer program using data recorded during 390 cycles of SG inter-burst intervals and HB cycles.
P.
614 ”
216
A
Sequential
E.
COYER,
R.
E. YOUNGand G. A. WYSE
Heart Beat Intervals ot an Imposed Motor Permd of I, I Set
Fig. 5. Instantaneous periods (A) and phase plots (B) of the heart beat intervals relative to the imposed movement at a period length of 1.I set corresponding to a pre-set motor frequency of 0.9 Hz. Solid line in (A) represents the motor period. The phase histogram is oriented vertically along the right margin of B. The longer bar at 4 - 0.4 indicates some coordination but not to the extent shown at 4 = 0.9 for SG/motor coordination (Fig. 6B).
(s = 0.17) and 1.03 (s = 0.07) set respectively. When
the motor frequency was decreased to 0.9 Hz, the SG beat interval became widely scattered reflected by the increase in the SD (second set of bar graphs Fig. 4). As evident by the resetting phase relationships and corresponding flat histogram shown in Fig. 5B, the heart beat did not show a high degree of phase coupling to the sinusoidal arm movement although the rates of both were almost equal (overlapping SD’s, second set of bar graphs Fig. 4). An interesting rate dependency is also seen in Fig. 4 in which moving the gill-bailer at a higher rate of 1.19 Hz depressed both the heart and gill-bailer rates so that they were not overlapping with the rate of the motor’s movement. This inversely-related phenomenon observed at frequencies above that for heart and SG coordination
.
indicates that there is a restricted range of coupling frequencies (1 Hz, Fig. 7). Phase plots of the intended scaphognathite movement with respect to the motor and the gill-bailer’s instantaneous intervals (Fig. 6) were constructed over the first 110 cycles of the experiment during which the frequency of imposed movement on the gill-bailer was changed from 1 to 0.9 Hz at cycle No. 80. As indicated by the instantaneous plots in Fig. 6A (and the large standard deviation in the second set of bar graphs in Fig. 4) observed SG intervals were highly variable and fluctuated widely around the motor period of 1.1 sec. This highly variable rate with respect to the motor movement is shown in the erratic phase drift of the SG beat with respect to the motor movement (Fig. 6B). There were times when the SG
Sequentlol Interburst Intervals of s_Cemg’s ot Imposed Motor Percds of IO and . . . * .
Phase Plot /S_G emg’s
Fig. 6. Instantaneous periods (A) and imposed movement at period lengths and 0.9 Hz. Solid line in (A) represents phase histogram
i Interburst
I I set
Interval) ond Motor Period
phase plots (B) of interburst intervals of SC emg’s relative to the of 1 and 1.1 set corresponding to pre-set motor frequencies of 1 the motor frequency including the transition at cycle No. 80. The is oriented vertically along the margin of B.
Heart A
hb I” motor
and gill-bailer
interval
coordination
615
in lobsters
13 hb
I”
r.sg.emg
record
4or
Phase
C r sa ema’s
Phase I” motor
int
Phase
Fig. 7. Frequency distributions of phase relationships among heart beat and the pre-set motor interval (A), heart beat relative to SG emg’s (B), and SG emg’s and the pre-set motor interval (C) at 1 Hz from data represented in the last set of bar graphs in Fig. 4. The ordinate corresponds to the number of events
falling within a preferred phase (4 0.0 -+ 1.0) and is positioned horizontally unlike the histograms appearing in Figs 5 & 6. Coupling percentages (R) expressed in the histograms of HB/SG and SG/motor coordination are significant (P 5 0.05).
dropped out; i.e. skipped beats and consequently these times could not be recorded as intervals on the phase plots, accounting for the gaps between cycles 9&1OO (Fig. 6B). However, there is a phase preference evident (4 at -0.9) on the ordinate (Fig. 6B) to the motor rhythm over cycles SO-90 and l&1 10 as expressed by the large peak in the histogram lying along the right margin. Although maintenance of a preferred phase is of short duration, it supports a lock and drift model. It is important to recognize that locking of the gill-bailer’s rhythm to the movement of the arm was not coincident with bringing the frequency of the pen lever into a range overlapping that of the gill-bailer beat since the gill-bailer dropped out at times. When it began beating again, it resumed its previous phase 4 of -0.9. Phase histograms of the relative positions of the heart beat in the right scaphognathite interval during imposed movement are shown in Fig. 7. The histograms for coordination of the heart to the scaphognathite (Fig. 7B) and the scaphognathite to the motor movement (Fig. 7C) contain peaks associated with one or more phase preferences. The histogram relating the coordination of the heart beat to the motor movement does not (Fig. 7A). As a result the coupling percentage (R) for the heart beat in the motor interval is low (R = 1.7%; P > 0.05) for the heart beat in the right SG interval (R = 17.4%) and for the right gill-bailer in the motor interval
(R = 14.5”/,); the latter coupling nificant (P d 0.05).
percentages
are sig-
DISCUSSION
The results may indicate that the scaphognathite can be loosely entrained by external scaphognathite movement showing lock and drift behavior characteristic of relative coordination (Wendler, 1966). This is consistent with Pilkington’s observation (Pilkington, 1976) for Curcinus maenas in which he applied alternating current to the thoracic ganglion and recorded phase locking and drift of identifiable levator and depressor muscles of the scaphognathite. The results also show only a slight degree of coordination between the heart beat and imposed motor movement even when they approached the same frequency (Figs 4 and 5B). However, during relative coordination of one gill-bailer to the motor, the heart displayed lock and drift behavior with respect to the imposed SG beating motion (Fig. 7B) and no coordination to the motor movement (Fig. 7A). The observed locking and drifting (showing some phase preference but drifting in and out of phase) behavior found in the crustacean cardio-respiratory system is characteristic of relative coordination. Wilkens & Young (1975) described variations in the degree of tight coupling versus relative coordination
616
P. E. COYER,R. E. YOUX
(lock and drift behavior) of both the gill-bailer rhythms in lobster under changing temperature conditions. In the lobster there is locking of the phase relationship between the cycles over certain ranges, and an overall preference for certain relative phase positions persists although the cycle frequencies may differ. During bilateral scaphognathite coordination, phase locking occurs at neither absolute synchrony where 4 = 1 nor one-half cycle out of phase 4 = 0.5 (Wilkens & Young, 1975). Similarly observed SG and heart coordination in crabs occurs at an average phase angle (4) of 277” having a range of 4 = 060.9 (Coyer, 1979). Furthermore, according to the relative coordination model proposed by Wendler (1966), at specific frequencies a pacemaker rhythm can draw an oscillator into a range of incomplete entrainment so that one or possibly more preferred phase relationships of one rhythm result with respect to the other. Usually, this occurs when the natural frequency of the dependent rhythm approaches that of the pacemaker, or in this case when the rate of heart contraction was attracted to that of SG movement. In the experiments in which movement was imposed on the gill-bailer beating motion, the heart beat cycle coupled with the entrained SG movement over the depressed SG frequency of 1 Hz. However, when the imposed scaphognathite was slowed to 0.9 Hz, the heart beat was attracted to the same frequency range and showed only a slight degree of phase preference (Figs 4 and 5B). The SG beat frequency was erratic compared to the pre-set driver motor’s rate (large SD; Fig. 4), but its rhythm showed some lock and drift behavior (Fig. 6). It is interesting that there is a fine tuning of the heart and gill-bailer rhythms around 1 Hz (motor period of 0.97 set) into the coordinated patterns indicated by the histograms in Fig. 7 showing the phase relationships among heart and scaphognathite beating relative to imposed motor intervals. Pilkington (1976) plotted imposed frequencies of stimulation versus entrained frequencies for the thoracic ganglion of Carcinus maenas describing a region of relative entrainment for scaphognathite muscle bursts near the rate of the observed free-running rhythm. It appears that a neural oscillator system can be brought into a range of frequency-dependency by an external source, and furthermore, during this attraction, there may be phase coupling of the dependent (heart) to the SG rhythm. The range of frequencies for entrainment lies below that reported during bilateral SG coordination (Wilkens & Young, 1975). Thus, this finding of a restricted range of frequencies for coupling is consistent with the relative coordination model (Wendler, 1966). Since these results were taken from data on only five specimens of Homarus americanus, the existence of a centrally-patterned rhythm coordinating the heart and gill-bailer pumping motions is not definitive. While the neuronal basis for heart and SG control in terms of the nature of impulse patterning from the thoracic ganglion has not been elucidated in crabs and lobsters (Coyer, 1979; Young, 1978) there is behavioral and physiological evidence for both relative and absolute coordination of the cardio-respiratory rhythms. However, there are several models one might adopt in devising an internal coordinating sys-
and G. A. WYSE
tern for the heart and scaphognathites. One may consider that there is shared common input acting on both systems, but this probably would not account for maintenance of heart coordination with only one gill-bailer. Reciprocal inhibitory interactions may also account for coordination, but it is doubtful that the observation of unidirectional coordination from the entrainable scaphognathite system to the heart beat follows from this model. The role of tonic or phasic sensory feedback is also unclear. Phasic activity arising from the mechanoreceptive oval organ (Pasztor, 1969) neither initiates the SG rhythm nor coordinates its activity to an imposed movement through reafference (Young & Coyer, 1979). Tonic input seems to frequencies in modulate the cardio-respiratory parallel but does not provide the temporal patterning that one might expect to underlie scaphognathite and heart coordination (Coyer, 1976). Acknowledgements-This fulfillment
of the requirements
work was submitted in partial for the degree of Doctor of
Philosophy at the University of Massachusetts, Amherst, Massachusetts, by the first author (P.E.C.). The authors are grateful to Dr Winsor Watson for writing the computer program used in the analysis. This work was supported by P.H.S. grant NS 08869 to G.A.W. During the initial oeriod of this work, R. E. Young was support:d by a Study and Travel Grant from the University of the West Indies. The authors would also like to thank the Department of Neurology, University of Alabama Medical Center, Birmingham, Alabama, for the use of its facilities and MS Ellen Autery for her typing services rendered in preparation of this manuscript. REFERENCES
ANDERSON M. 0. (1973) Neuromuscular systems in neurogenie arthropod hearts. Am. Zoo/. 13 (2). 291-298. COCHRAN D. M. (1935) The skeletal musculature of the blue crab Callinectrs sapidus. Rathhun. Smithson. Misc. Collect. 92 (9), 76 pp. C%KE I. M. & GOLDSTONE M. (1970) Fluorescence localization of monoamines in crab neurosecretory structures. J. exp. Biol. 53, 651-688. COYER P. E. (1976) Heart and gill-bailer coupling in crabs--evidence for unilateral coordination. Physiologist 19 (3), 243 (abstract). COYERP. E. (1977a) Responses of heart and scaphognathite rates in Cancer horeulis and Cancer irrorutus to hypoxia. Camp. Biochem. Physiol. XiA, 165-l 67. COYERP. E. (1977b) Neuronal mechanisms underlying the coordination of heart and gill-bailer rhythms in decapod crustacea. Ph.D. thesis, University of Massachusetts, Amherst. COYERP. E. (1979) Heart and one gill-bailer rhythm phase couple in Cancer borealis and Cancer irroratus. Camp. Biochem. Physiol. 62, 677-683. FIELD L. H. & LARIMER J. L. (1975a) The cardioregulatory system of crayfish: neuroanatomy and physiology. J. exp. Biol. 62, 519-530. FIELD L. H. & LARIMER J. L. (1975b) The cardioregulatory system of crayfish: the role of the circumesophageal interneurons. J. exp. Biol. 62, 531-543. FLOREY E. (1960) Studies on the nervous regulation of heart beat in decapod crustacea. J. gm. Physiol. 43, 1061-1081. HAGIWARA S. & BULLOCK T. H. (1957) Intracellular potentials in pacemaker and integrative neurons of the lobster cardiac ganglia. J. cell. comp. Physiol. 50, 2547. HARTLINE D. K. (1967) Impulse identification and axon mapping of the nine neurons in the cardiac ganglion of
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