Jerrel L. Wilkens

Peptidergic Modulation of Cardiac Performance in Isolated Hearts from the Shore Crab Carcinus maenas

The present study examined the effects of two peptide hormones on rate, pressures, and flow generated by isolated in situ crustacean hearts. Saline, pumped by spontaneous contractions, was collected through a cannula attached to the sternal artery. Cardiac flow was measured directly with an electromagnetic low probe, while arterial and ventricular pressures were recorded with pressure transducers. Crustacean cardioactive peptide (CCAP), known to be present in the pericardial organs of Carcinus, increased cardiac output mainly by increasing heart rate. On average, CCAP caused a modest increase in stroke volume. Proctolin, another peptide found in the pericardial organs, also increased cardiac output, but generally elicited large changes in the stroke volume. Proctolin also increased heart rate, but to a lesser extent than did CCAP. Both peptides increased ventricular pressure, stroke work, and cardiac power. Mean effective dose (ED50) values associated with the effects on heart rate were approximately 4 X 10⁻⁹ for proctolin and 1 × 10⁻⁷ nmol · L⁻¹ for CCAP. Responses to the peptides did not indicate receptor desensitization. The results support the hypothesis that hormones from the pericardial organs play a physiological role in modulating cardiac output in crustaceans.

Respiratory and Circulatory Coordination in Decapod Crustaceans

Two components of the crustacean respiratory system — gill ventilation and perfusion — are required to meet the metabolic requirements for gas exchange. All crustaceans possess some means of moving the external medium past their gas exchange surfaces. In primitive forms such as Hutchinsoniella (Cephalocarida) and Branchionecta (Brachiopoda) the paired thoracic appendages are serially similar and by their paired phase-locked movements these appendages facilitate respiration, locomotion and feeding. In some smaller crustaceans an internal circulatory system to transport oxygen may not be necessary because sufficient gas exchange can occur by diffusion. Decapods and other large crustaceans, on the other hand, depend on a dual hydraulic pumping system to effect gas exchange between the external medium and the blood. In decapods the gills are enclosed within branchial chambers, and scaphognathites, modified portions of the 2nd maxillae located anterior to the gills, pump water or air through the gill chambers. The heart with possible assistance from accessory contractile structures, pumps blood throughout the body and internally perfuses the gills. In this paper I will focus on the scaphognathites and heart as pumps and discuss how these two systems are integrated to meet the range of demands placed on them. Other aspects of this topic are soon to be reviewed (McMahon and Wilkens, in press).

Evolutionary derivation of the American lobster cardiovascular system: an hypothesis based on morphological and physiological evidence

The cardiovascular system of the American lobster includes a large muscular heart that pumps blood into seven arteries, each of which ramifies extensively. Portions of the system may be viewed as relatively primitive, while others are highly derived. We have confirmed earlier findings that the sternal artery is not a single vessel, but a paired structure. The sternal artery and its partner closely resemble the medial branches of the segmental lateral vessels from the dorsal abdominal artery in anterior segments of the abdomen, and they may be homologous. We report that the walls of the dorsal abdominal artery contain blocks of striated muscle cells and that the artery can be induced to contract in response to electrical stimulation or perfusion with proctolin. These observations provide the basis for an attempt to trace the evolution of the heart and arteries from that of primitive malacostracans to its state of development in lobsters. Additional key words: Crustacea, Homarus americanus, evolution, heart, dorsal abdominal artery, sternal artery We present here anatomical and physiological evidence supporting the hypothesis that the cardiovascular system in adult decapod crustaceans, as illustrated for Homarus americanus (e.g., McLaughlin 1983), is derived, by migration and regional specialization, from the evolutionarily primitive plan of a dorsal, longitudinal, tubular, muscular heart with a pair of ostia in each segment running from the head to the telson (Siewing 1963; Hessler et al. 1982). It has been postulated, based on the Cephalocarida, that crustacean ancestors displayed strong serial homology in body plan (Sanders 1955), possibly arising from annelid ancestral antecedants such as an extended nauplius-like larva (Hessler et al. 1982). The Cephalocarida and Branchiopoda (Anostraca, fairy shrimps) are closest to this prototype. This primitive plan is still the general plan in stomatopods (Siewing 1963; McLaughlin 1980). In the ancestral plan, the heart tube lies immediately dorsal to the gut and extends the entire length of the body. The heart tube supplies hemolymph to a short non-muscular anterior median artery to the brain, to some form of serially homologous segmental lateral arterial supply in each body segment, and to an unpaired posterior artery to the telson. The segmental a Author with whom to correspond. lateral arteries are short and do not branch extensively. Paired ostia admit returning hemolymph to the heart tube in each segment. In adults of H. americanus, the single-chambered heart is suspended in the pericardial sinus in the dorsal thorax by several pairs of alary ligaments (Lochhead 1950, pp. 428-431; McLaughlin 1980, pp. 138-141). These elastic ligaments are stretched during systole, and they expand the heart during diastole. During diastole, the heart passively fills with hemolymph from the pericardial sinus through three pairs of muscular,

Tension sensitivity of the heart pacemaker neurons in the isopod crustacean Ligia pallasii

SUMMARY In the crustacean neurogenic heart, the cardiac ganglion (CG) acts as a peripherally located central pattern generator (CPG) by producing rhythmic motor output that initiates the heartbeat. In the isopod Ligia, the CG consists of six electrically coupled neurons that all function both as endogenous oscillators and as glutamatergic motoneurons innervating heart muscle. In the present study, we present several lines of evidence to suggest that the CG neurons are sensitive to passive stretch and active tension of the heart muscle. Stretching the heart wall caused a sustained decrease in the burst frequency of the CG neuron. Releasing from the stretch caused a rebound increase in burst frequency above the control rate. A brief stretch (200-300 ms duration) caused either phase advance or phase delay of the following CG bursts, depending on the timing at which the stretch was applied. Repeated brief stretches could entrain the CG bursts to either higher or lower frequencies than the free-run burst frequency. Intracellular recording from one of the CG neurons revealed that it exhibited hyperpolarization during the stretch. The stretch-induced hyperpolarization was followed by a burst discharge upon release from the stretch. With increased stretch amplitude, the amplitude of hyperpolarizing response increased and the timing of the following burst was advanced. When the myogenic activity of the heart muscle was pharmacologically isolated from the ganglionic drive by applying a glutamatergic antagonist, Joro spider toxin (JSTX), the spontaneous muscle contraction caused a hyperpolarizing deflection in the CG neuron. Under specific conditions made by JSTX and tetrodotoxin, the CG burst became entrained to the myogenic rhythm. These results suggest that the Ligia CG neurons have tension sensitivity in addition to their pacemaker and motoneuronal functions. Such multifunctional neurons may form a single neuron reflex arc inside the heart.

The effects of six pericardial hormones and hypoxia on the semi-isolated heart and sternal arterial valve of the lobster Homarus americanus☆

Abstract Each of three amine and three peptide hormones of the pericardial organs exerts a unique effect on heart rate and ventricular pressure, and on outflow through the sternal arterial valve in Homarus americanus. At the concentrations of 0.1-0.25 μM, all of the six hormones except crustacean cardioactive peptide (CCAP) increased heart rate while only two (proctolin and F2) significantly increased ventricular pressure. Octopamine by itself had almost no effect, but augmented ventricular pressure when combined with proctolin. Whenever a hormone caused an increase in ventricular pressure, there was also an increase in dorsal abdominal artery pressure or flow. All hormones except dopamine caused a reduction in sternal artery flow. Dopamine by relaxing the sternal arterial valve increased the sternal flow, but it had no effect on ventricular pressure or dorsal abdominal artery flow. CCAP and serotonin did not significantly change the magnitudes of ventricular pressure or dorsal abdominal flow, but both reduced flow in the sternal artery. Hypoxia depressed heart rate and to a lesser extent contractility, but did not alter the responsiveness of the heart or sternal arterial valve to hormones.

Neural Control of Cardiac Outflow through the Sternal Valve in the Lobster Homarus americanus

In the American lobster, the sternal artery and the dorsal abdominal artery arise from the bulbus arteriosus, which is located immediately behind the heart. A nonmuscular flap valve is located at the entrance to the bulbus, and a muscular bicuspid flap valve is located at the origin of the sternal artery. The sternal valve muscles receive inhibitory innervation. Stimulation of these nerves causes the muscles to relax and, in actively pumping hearts, to increase outflow to the sternal artery. The neurohormone proctolin causes contracture of these muscles, and outflow is reduced. Stimulation of the valve nerve overrides the effects of proctolin.

Responses of the isolated crab ventilatory central pattern generators to variations in oxygen tension

Summary1.The response of the isolated crab ventilatory central pattern generator (CPG) to changes in oxygen tension was examined. The ventilatory rate increased and motor neuron burst durations decreased as oxygen tension (

Sites and modes of action of proctolin and the FLP F2 on lobster cardiac muscle.

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