Excitation and inhibition of the heart of the snail, Lymnaea, by non-FMRFamidergic motoneurons

Abstract

1. The present paper extends the model of neuronal control of the Lymnaea heart by the use of intracellular recording techniques to identify further types of cardioactive neurons in the CNS that, like the previously described E heart excitor (Ehe) cells, influence the myogenic heartbeat. 2. Four new types of neuron that act on the heart are described. These are excitatory Hhe and She cells (H and S heart excitors) and the inhibitory Khi cell (K heart inhibitor). The fourth class, tonus pericardium excitor (Tpe), modulates the heart by action on pericardial tissue. 3. Pharmacologic, electrophysiological, and anatomic evidence is presented that shows that these cells are motoneurons, innervating heart muscle fibers directly: blocking central chemical synapses failed to prevent the actions of the neurons on the heart; simultaneous intracellular recordings showed unitary EJPs in heart muscle after 1:1 and with constant delay from evoked neuronal action potentials; intracellular injection of the dye Lucifer yellow showed all cells had axonal branches entering the intestinal nerve (which innervates the heart). 4. The use of selective antagonists to 5-hydroxytryptamine (5-HT) (cinanserin), dopamine (ergonovine), and acetylcholine (alpha-bungarotoxin) provided evidence that the actions of She and Hhe cells are mediated by 5-HT, whereas those of the Khi cell are mediated by acetylcholine. 5. A cyclically active network of three interneuronal inputs acting on the heart motoneurons is described. 6. One of these, input 3, is responsible for periodic excitation of the heart via its effects on the Hhe cells.

Histamine Immunoreactive Elements in the Central and Peripheral Nervous Systems of the Snail, Biomphalaria spp., Intermediate Host for Schistosoma mansoni

“…stagnalis , with axons projecting toward the pedal nerves, are consistent with involvement of HA in the locomotory activity of these snails (see below). HA in the several neurons and neuropilar regions of the visceral-parietal ganglion complex suggests a role for this amine in regulating respiratory and circulatory systems controlled by these ganglia, e.g., heart activity as reported in other pulmonates [56][57][58]. Finally, the present study supports the function of HA as a primary neurotransmitter of the statocyst hair cells in gastropod molluscs.…”

Transmitter contents of cells and fibers in the cephalic sensory organs of the gastropod mollusc Phestilla sibogae

“…The absence of 5-HT-lir peripheral somata is consistent with reports of only efferent fibers in selected peripheral tissues, such as the heart and buccal mass, of other gastropods (Weiss et al 1978;Buckett et al 1990;Skelton et al 1992). More recently, Moroz et al (1997) conducted a more comprehensive study of various peripheral tissues in two other opisthobranchs, Pleurobranchaea and Tritonia, and they also reported what appeared to be exclusively efferent fibers with no peripheral somata.…”

The neuronal control of cardiac functions in Molluscs

“…2). The myocardial, pericardial, and the whole heart functions in diverse Mollusca are widely studied (Kobayashi and Irisawa, 1961; S.-Rozsa and Zhuravlev, 1981; Buckett et al, 1990a; Weatherill and Chase, 2005; Bini et al, 2006a; Malyshev et al, 2008). Similar to vertebrates, each cardiac compartment is constituted of myocytes that contract simultaneously, thereby resulting in functional hemolymph pumping heart-beats.…”

“…Neurons may possess inhibitory and excitatory effects on each other, and thereby they can either directly or indirectly modulate the heart. Neurons are identified by their neurotransmitters: cholin-, seroton-, peptid- and catecholaminergic (Cottrell et al, 1981; Boyd et al, 1984; Croll, 1988; Buckett et al, 1990a, 1990b; Brezden et al, 1991; Bright et al, 1993; Kuwasawa and Hill, 1997; Croll et al, 1999; Dyakonova et al, 2009). The role of some peptides for cardiac and neuronal functions overlaps between Molluscs and mammals (Walker et al, 2009).…”