The lamprey (a lower vertebrate, cyclostome), in addition to ordinary swimming, is also capable of crawling. Here we describe crawling forward in a narrow U-shaped tunnel. A rapid movement along the tunnel was evoked by stimulating the tail. The muscle activity responsible for propulsion was confined to the area around the body bend. Muscles on the inner (concave) side were activated when approaching the turn, and inactivated on the top of the arc. Muscles on the outer (convex) side were co-active with their antagonists, but also active in the area of straightening of the body bend. This pattern of muscle activity propagated along the body. The role of central and reflex mechanisms in the generation of locomotor movements is discussed.
(1) Neurons of different groups (for group classification, see Arshavsky et al. 1988a) have been polarized through an intracellular recording microelectrode in Planorbis corneus buccal ganglia during feeding rhythm generation. Group 1 neurons, active in the quiescence (Q) and in the protractor (P) phases of the cycle, and also group 2 and 4 neurons, active in the retractor (R) phase, have proved to be "influential", i.e., altering the rhythm generator operation. (2) Injection of a depolarizing current into group 1 neurons caused an increase of the rate of depolarization that neurons of this group exhibit in the Q- and P-phases of the feeding cycle. As a result, Q-phase shortened, the P-phase became longer, and the feeding rhythm accelerated. Opposite effects occurred when a hyperpolarizing current was injected into group 1 neurons. In some of the experiments, the hyperpolarization of group 1 neurons resulted in cessation of both their activity and the activity of all other protractor neurons. As a result, the P-phase of the cycle disappeared, i.e., the rhythm generator transited from A mode of operation to B mode. (3) With hyperpolarization of individual group 2 or 4 neurons, excitation of the R-phase neurons was delayed and the feeding rhythm phase shifted. This delay was accompanied by the enhanced activity of protractor neurons. (4) A generator model is considered in which two groups (1 and 2) of endogeneously active neurons are coordinated by the excitatory effect of group 1 on group 2 and the inhibitory action of group 2 on group 1. (5) Evidence is given that the different modes of rhythm generator operation (A, B and C, see Arshavsky et al. 1988a) are determined by different tonic inflow to group 1 neurons.
(1) The buccal mass of the freshwater snail Planorbis corneus, dissected together with the buccal ganglia, performs rhythmic feeding movements. Radula movements and the electrical activity in various nerves of buccal ganglia were recorded in such a preparation. The cycle of radula movements consisted of three phases: quiescence (Q), protraction (P) and retraction (R). The activity in the radular nerve was observed mainly in the P-phase and that in the dorsobuccal nerve, largely in the R-phase. (2) Isolated buccal ganglia were capable of generating a feeding rhythm, the activity in buccal nerves being similar to that observed in the buccal mass-buccal ganglion preparation, i.e., a burst in the radular nerve preceded a burst in the dorsobuccal nerve. The activity of neurons in isolated buccal ganglia during generation of the feeding rhythm has been studied with intracellular microelectrodes. About 10% of ganglion neurons exhibited periodic activity related to the feeding rhythm ("rhythmic" neurons). (3) Rhythmic neurons have been divided into 7 groups according to the phase of their activity and to the characteristics of slow oscillations of the membrane potential during the feeding cycle. Group 1 neurons revealed a gradual increase of depolarization during the Q- and P-phases. In subgroup 1e neurons, spike discharges began in the Q-phase, while in subgroup 1d neurons activity started in the P-phase. During the R-phase, group 1 neurons were strongly hyperpolarized, and their discharges terminated. In group 2 neurons, small depolarization gradually increased during the Q- and P-phases. Then, in the R-phase, a large (20-50 mV) rectangular wave of depolarization arose with superimposed high-frequency oscillations. Group 3 neurons exhibited an excitatory postsynaptic potential (EPSP) in the P-phase and inhibitory postsynaptic potential (IPSP) in the R-phase. The neurons of group 4 revealed two EPSPs: a small one in the P-phase and a larger one in the R-phase. Group 5 neurons exhibited an EPSP in the P-phase, those of group 7 - an IPSP in the R-phase, and those of group 9 - IPSPs in the P- and R-phases. Neurons within each of the groups 1, 2 and 4 were electrically coupled, and in addition, there were also electrical connections between neurons of groups 2 and 4. (4) Data are presented showing that neurons of groups 1 and 2 are the main source of postsynaptic potentials in rhythmic neurons in the P-phase and in the R-phase of the cycle, respectively.
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