Control of feeding movements in the freshwater snail Planorbis corneus

Abstract

(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.

A Pair of Identified Interneurons inAplysiathat Are Involved in Multiple Behaviors Are Necessary and Sufficient for the Arterial-Shortening Component of a Local Withdrawal Reflex

“…Others may find that such classification helps organize possibly confusing functional analyses and adds an intuitive dimension that can supplement more abstract computational or mathematical ac-counts of the functional operation of circuits. An important recent notion related to that of command neuron, but lacking the behavioral and philosophical implications of command, is that of the "influential" neuron (Arshavsky et al, 1988). Although originally defined as a neuron that has some effect on a rhythmic motor Figure 11.…”

“…Key words: command; withdrawal reflex; Aplysia; mechanosensory; feeding; head turning A major task in neuroscience is to understand the functioning of the nervous system in terms of the activity of individual neurons or aggregates of neurons. Studies of invertebrates and vertebrates have shown that certain interneurons appear to be extraordinarily focused in their function (Kupfermann and Weiss, 1978;Nolen and Hoy, 1984;Arshavsky et al, 1988;McCrohan and Kyriakides, 1989;Delaney and Gelperin, 1990;Young and Yamane, 1992;Celebrini and Newsome, 1994;Frost and Katz, 1996) and that there are a small number of cells that appear to act as so-called command neurons, i.e., individual cells that meet the criteria of necessity and sufficiency for a particular behavior (Kupfermann and Weiss, 1986). One problem with the concept of command neurons is that there are good theoretical reasons (Getting, 1989;Churchland and Sejnowski, 1992) as well as growing empirical evidence that neurons can be involved in more than one behavior, and that their role in different behaviors may not be invariant (Hooper and Moulins, 1989;Lockery and Kristan, 1990;Fetz, 1992;Meyrand et al, 1994;Wu et al, 1994).…”

C-PR Neuron ofAplysiaHas Differential Effects on “Feeding” Cerebral Interneurons, Including Myomodulin-Positive CBI-12

“…The behavioral sequences that provide the components of each behavioral act are generated by systems of interconnected neurons termed pattern generators (PGs) or central pattern generators (CPGs). Studies in several invertebrates suggest that the activity of pattern generating circuits often is initiated or modulated by the firing of a small number of higher-order interneurons (Arshavsky et al 1988(Arshavsky et al , 1989Bartos and Nusbaum 1997;Delaney and Gelperin 1990;Frost and Katz 1996;Kupfermann and Weiss 1978;Rosen et al 1991;Wiersma and Ikeda 1964). Those higher-order neurons that exert relatively large effects have been termed command neurons (Kupfermann and Weiss 1978;Wiersma and Ikeda 1964), command-like neurons (Deodhar et al 1994), or influential neurons (Arshavsky et al 1988).…”

“…Studies in several invertebrates suggest that the activity of pattern generating circuits often is initiated or modulated by the firing of a small number of higher-order interneurons (Arshavsky et al 1988(Arshavsky et al , 1989Bartos and Nusbaum 1997;Delaney and Gelperin 1990;Frost and Katz 1996;Kupfermann and Weiss 1978;Rosen et al 1991;Wiersma and Ikeda 1964). Those higher-order neurons that exert relatively large effects have been termed command neurons (Kupfermann and Weiss 1978;Wiersma and Ikeda 1964), command-like neurons (Deodhar et al 1994), or influential neurons (Arshavsky et al 1988). Analogous higher-order neurons, rather than directly participating in the generation of behaviors, contribute to the generation of motivational states, which function to coordinate and optimize the functioning of the various somatic and visceral behaviors that comprise complex behavioral acts (Teyke et al 1990).…”

Multifunctional Neuron CC6 inAplysiaExerts Actions Opposite to Those of Multifunctional Neuron CC5

“…Research in a number of invertebrate species as well is in some verterbrates has shown that behavior and the activity of pattern-generating circuits can be initiated or modulated by the firing of single or relatively few higher order interneurons (Arshavsky et al 1988(Arshavsky et al , 1989; Bartos and Nusbaum 1997;Delaney and Gelperin 1990;Didomenico et al 1988;Frost and Katz 1996;Kupfermann and Weiss 1978;Rosen et al 1991;Wiersma and Ikeda 1964). Some of these higher order neurons exert relatively large effects and have been called various names, including command neurons (Kupfermann and Weiss 1978;Wiersma and Ikeda 1964), commandlike neurons (Deodhar et al 1994), or influential neurons (Arshavsky et al 1988). In Aplysia a commandlike neuron (CC5) has been recently described, which is of special interest because it is active in many different behaviors (Xin et al 1996a,b).…”