scholarly journals Degenerate circuits use distinct mechanisms to respond similarly to the same perturbation

2020 ◽  
Author(s):  
D.J. Powell ◽  
E. Marder ◽  
M.P. Nusbaum
Keyword(s):  
Neural Circuit ◽  
Activity Patterns ◽  
Peptide Hormone ◽  
Projection Neuron ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Cancer Borealis ◽  
Hormone Modulation ◽  
Underlying Mechanisms ◽  
Alternate Scenario

AbstractThere is considerable flexibility embedded within neural circuits. For example, separate modulatory inputs can differently configure the same underlying circuit but these different configurations generate comparable, or degenerate, activity patterns. However, little is known about whether these mechanistically different circuits in turn exhibit degenerate responses to the same inputs. We examined this issue using the crab (Cancer borealis) stomatogastric nervous system, in which stimulating the modulatory projection neuron MCN1 and bath applying the neuropeptide CabPK II elicit similar gastric mill (chewing) rhythms in the stomatogastric ganglion, despite differentially configuring the same neural circuit. We showed previously that bath applying the peptide hormone CCAP or stimulating the muscle stretch-sensitive sensory neuron GPR during the MCN1-elicited gastric mill rhythm selectively prolongs the protraction or retraction phase, respectively. Here, we found that these two influences on the CabPK-rhythm elicited some unique and unexpected consequences compared to their actions on the MCN1-rhythm. For example, in contrast to its effect on the MCN1-rhythm, CCAP selectively decreased the CabPK-rhythm retraction phase and thus increased the rhythm speed, whereas the CabPK-rhythm response to stimulating GPR during the retraction phase was similar its effect on the MCN1-rhythm (i.e. prolonging retraction). Interestingly, despite the comparable GPR actions on these degenerate rhythms, the underlying synaptic mechanism was distinct. Thus, degenerate circuits do not necessarily exhibit degenerate responses to the same influence, but when they do, it can occur via different underlying mechanisms.Significance StatementCircuits generating seemingly identical behaviors are often thought to arise from identical circuit states, as that is the most parsimonious explanation. Here we take advantage of an alternate scenario wherein a well-defined circuit with known connectivity generates similar activity patterns using distinct circuit states, via known mechanisms. The same peptide hormone modulation of these distinct circuit states produced divergent activity patterns, whereas the same sensory feedback altered these circuit outputs similarly but via different synaptic pathways. The latter observation limits the insights available from comparable studies in systems lacking detailed access to the underlying circuit.

scholarly journals Similarities and differences in circuit responses to applied Gly1-SIFamide and peptidergic (Gly1-SIFamide) neuron stimulation

2019 ◽  
Vol 121 (3) ◽  
pp. 950-972 ◽  
Author(s):  
Dawn M. Blitz ◽  
Andrew E. Christie ◽  
Aaron P. Cook ◽  
Patsy S. Dickinson ◽  
Michael P. Nusbaum
Keyword(s):  
Activity Patterns ◽  
Projection Neuron ◽  
Projection Neurons ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Cancer Borealis ◽  
Axon Terminals ◽  
Motor Circuits ◽  
Commissural Neuron ◽  
Functional Context

Microcircuit modulation by peptides is well established, but the cellular/synaptic mechanisms whereby identified neurons with identified peptide transmitters modulate microcircuits remain unknown for most systems. Here, we describe the distribution of GYRKPPFNGSIFamide (Gly1-SIFamide) immunoreactivity (Gly1-SIFamide-IR) in the stomatogastric nervous system (STNS) of the crab Cancer borealis and the Gly1-SIFamide actions on the two feeding-related circuits in the stomatogastric ganglion (STG). Gly1-SIFamide-IR localized to somata in the paired commissural ganglia (CoGs), two axons in the nerves connecting each CoG with the STG, and the CoG and STG neuropil. We identified one Gly1-SIFamide-IR projection neuron innervating the STG as the previously identified modulatory commissural neuron 5 (MCN5). Brief (~10 s) MCN5 stimulation excites some pyloric circuit neurons. We now find that bath applying Gly1-SIFamide to the isolated STG also enhanced pyloric rhythm activity and activated an imperfectly coordinated gastric mill rhythm that included unusually prolonged bursts in two circuit neurons [inferior cardiac (IC), lateral posterior gastric (LPG)]. Furthermore, longer duration (>30 s) MCN5 stimulation activated a Gly1-SIFamide-like gastric mill rhythm, including prolonged IC and LPG bursting. The prolonged LPG bursting decreased the coincidence of its activity with neurons to which it is electrically coupled. We also identified local circuit feedback onto the MCN5 axon terminals, which may contribute to some distinctions between the responses to MCN5 stimulation and Gly1-SIFamide application. Thus, MCN5 adds to the few identified projection neurons that modulate a well-defined circuit at least partly via an identified neuropeptide transmitter and provides an opportunity to study peptide regulation of electrical coupled neurons in a functional context. NEW & NOTEWORTHY Limited insight exists regarding how identified peptidergic neurons modulate microcircuits. We show that the modulatory projection neuron modulatory commissural neuron 5 (MCN5) is peptidergic, containing Gly1-SIFamide. MCN5 and Gly1-SIFamide elicit similar output from two well-defined motor circuits. Their distinct actions may result partly from circuit feedback onto the MCN5 axon terminals. Their similar actions include eliciting divergent activity patterns in normally coactive, electrically coupled neurons, providing an opportunity to examine peptide modulation of electrically coupled neurons in a functional context.

Feeding State-Dependent Modulation of Feeding-Related Motor Patterns

2021 ◽  
Author(s):  
Aaron P. Cook ◽  
Michael P. Nusbaum
Keyword(s):  
Neural Circuit ◽  
Projection Neuron ◽  
Neuron Activity ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Cancer Borealis ◽  
Motor Patterns ◽  
State Dependent ◽  
Reduced Activity ◽  
Time Point

Studies elucidating modulation of microcircuit activity in isolated nervous systems have revealed numerous insights regarding neural circuit flexibility, but this approach limits the link between experimental results and behavioral context. To bridge this gap, we studied feeding behavior-linked modulation of microcircuit activity in the isolated stomatogastric nervous system (STNS) of male Cancer borealis crabs. Specifically, we removed hemolymph from a crab that was unfed for ≥24 h ('unfed' hemolymph) or fed 15 min - 2 h before hemolymph removal ('fed' hemolymph). After feeding, the first significant foregut emptying occurred >1 h later and complete emptying required ≥6 h. We applied the unfed or fed hemolymph to the stomatogastric ganglion (STG) in an isolated STNS preparation from a separate, unfed crab to determine its influence on the VCN (ventral cardiac neuron)-triggered gastric mill (chewing)- and pyloric (filtering of chewed food) rhythms. Unfed hemolymph had little influence on these rhythms, but fed hemolymph from each examined time-point (15 min, 1- or 2 h post-feeding) slowed one or both rhythms without weakening circuit neuron activity. There were also distinct parameter changes associated with each time-point. One change unique to the 1 h time-point (i.e. reduced activity of one circuit neuron during the transition from the gastric mill retraction to protraction phase) suggested the fed hemolymph also enhanced the influence of a projection neuron which innervates the STG from a ganglion isolated from the applied hemolymph. Hemolymph thus provides a feeding state-dependent modulation of the two feeding-related motor patterns in the C. borealis STG.

Peptide Hormone Modulation of a Neuronally Modulated Motor Circuit

2007 ◽  
Vol 98 (6) ◽  
pp. 3206-3220 ◽  
Author(s):  
Matthew S. Kirby ◽  
Michael P. Nusbaum
Keyword(s):  
Peptide Hormone ◽  
Firing Frequency ◽  
Projection Neurons ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Motor Circuit ◽  
Motor Circuits ◽  
Hormone Modulation ◽  
Hormonal Modulation ◽  
Active Motor

Rhythmically active motor circuits are influenced by neuronally released and circulating hormone modulators, but there are few systems in which the influence of a peptide hormone modulator on a neuronally modulated motor circuit has been determined. We performed such an analysis in the isolated crab stomatogastric nervous system by assessing the influence of the hormone crustacean cardioactive peptide (CCAP) on the gastric mill (chewing) rhythm elicited by identified modulatory projection neurons. The gastric mill circuit is located in the stomatogastric ganglion. In situ, this ganglion is located within the ophthalmic artery and thus is in the path of circulating hormones such as CCAP. Focally-applied CCAP directly excited some gastric mill neurons, including the gastric mill central pattern generator neurons LG and Int1, but it did not elicit a sustained gastric mill rhythm. At concentrations as low as 10−10 M, however, CCAP did influence gastric mill rhythms elicited by coactivating the projection neurons MCN1 and CPN2 and by selectively stimulating MCN1. In both cases, CCAP slowed this rhythm by selectively prolonging the protraction phase, although its influence on the MCN1-elicited rhythm was limited to those with relatively brief cycle periods. Interestingly, CCAP also reduced the threshold MCN1 firing frequency for activating the gastric mill rhythm. Last, the gastric mill neurons that exhibited altered activity during these CCAP-influenced rhythms did not correspond completely to the set of CCAP-responsive neurons. These results highlight the ability of hormonal modulation to enhance the flexibility provided by the neuronal modulation of rhythmically active motor circuits.

Recruitment of a projection neuron determines gastric mill motor pattern selection in the stomatogastric nervous system of the crab, Cancer borealis

1994 ◽  
Vol 72 (4) ◽  
pp. 1451-1463 ◽  
Author(s):  
B. J. Norris ◽  
M. J. Coleman ◽  
M. P. Nusbaum
Keyword(s):  
Nervous System ◽  
Synaptic Input ◽  
Motor Pattern ◽  
Rhythmic Activity ◽  
Projection Neuron ◽  
Projection Neurons ◽  
Muscarinic Agonist ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Cancer Borealis

1. In the isolated stomatogastric nervous system of the crab Cancer borealis (Fig. 1), the muscarinic agonist oxotremorine elicits several distinct gastric mill motor patterns from neurons in the stomatogastric ganglion (STG; Fig. 2). Selection of a particular gastric mill rhythm is determined by activation of distinct projection neurons that influence gastric mill neurons within the STG. In this paper we identify one such neuron, called commissural projection neuron 2 (CPN2), whose rhythmic activity is integral in producing one form of the gastric mill rhythm. 2. There is a CPN2 soma and neuropilar arborization in each commissural ganglion (CoG). The CPN2 axon projects through the superior esophageal nerve (son) and the stomatogastric nerve (stn) to influence neurons in the STG (Figs. 3 and 4A). 3. CPN2 activity influences most of the gastric mill neurons in the STG. Specifically, CPN2 excites gastric mill neurons GM and LG (gastric mill and lateral gastric, respectively) and inhibits the dorsal gastric (DG), anterior median (AM), medial gastric (MG), and inferior cardiac (IC) neurons (Figs. 5 and 6). CPN2 also indirectly inhibits gastric mill neurons Int1 and VD (interneuron 1 and ventricular dilator neuron, respectively) through its activation of LG. The CPN2 excitatory effects are mediated at least partly via discrete excitatory postsynaptic potentials (EPSPs; Fig. 4B), whereas its inhibitory effects are produced via smooth hyperpolarizations. 4. Within the CoG, CPN2 receives excitatory synaptic input from the anterior gastric receptor neuron (AGR), a gastric mill proprioceptive sensory neuron (Fig. 7) and inhibitory synaptic input from the gastric mill interneuron, Int1 (Fig. 8). 5. During one form of the gastric mill rhythm, CPN2 fires rhythmically in time with the gastric mill motor pattern, whereas it is silent or fires weakly during other gastric mill rhythms (Fig. 9). 6. When CPN2 rhythmic activity is suppressed during a CPN2-influenced gastric mill rhythm, the gastric mill rhythm continues, but the pattern is altered (Fig. 10). Moreover, transiently stimulating CPN2 during any ongoing gastric mill motor pattern can reset the timing of that rhythm (Fig. 11). 7. Tonic activity in CPN2 is insufficient to elicit a gastric mill rhythm (Fig. 12). Phasic activity in CPN2 can elicit a gastric mill rhythm only in preparations in which gastric mill neurons are already in an excited state (Figs. 12 and 13). 8. CPN2 recruitment plays a pivotal role in determining the final form of the gastric mill rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals State-dependent sensorimotor gating in a rhythmic motor system

2017 ◽  
Vol 118 (5) ◽  
pp. 2806-2818 ◽  
Author(s):  
Rachel S. White ◽  
Robert M. Spencer ◽  
Michael P. Nusbaum ◽  
Dawn M. Blitz
Keyword(s):  
Motor Activity ◽  
Motor System ◽  
Sensory Feedback ◽  
Activity Patterns ◽  
Motor Pattern ◽  
Projection Neuron ◽  
Projection Neurons ◽  
Gastric Mill ◽  
Sensory Regulation ◽  
Motor Circuits

Sensory feedback influences motor circuits and/or their projection neuron inputs to adjust ongoing motor activity, but its efficacy varies. Currently, less is known about regulation of sensory feedback onto projection neurons that control downstream motor circuits than about sensory regulation of the motor circuit neurons themselves. In this study, we tested whether sensory feedback onto projection neurons is sensitive only to activation of a motor system, or also to the modulatory state underlying that activation, using the crab Cancer borealis stomatogastric nervous system. We examined how proprioceptor neurons (gastropyloric receptors, GPRs) influence the gastric mill (chewing) circuit neurons and the projection neurons (MCN1, CPN2) that drive the gastric mill rhythm. During gastric mill rhythms triggered by the mechanosensory ventral cardiac neurons (VCNs), GPR was shown previously to influence gastric mill circuit neurons, but its excitation of MCN1/CPN2 was absent. In this study, we tested whether GPR effects on MCN1/CPN2 are also absent during gastric mill rhythms triggered by the peptidergic postoesophageal commissure (POC) neurons. The VCN and POC pathways both trigger lasting MCN1/CPN2 activation, but their distinct influence on circuit feedback to these neurons produces different gastric mill motor patterns. We show that GPR excites MCN1 and CPN2 during the POC-gastric mill rhythm, altering their firing rates and activity patterns. This action changes both phases of the POC-gastric mill rhythm, whereas GPR only alters one phase of the VCN-gastric mill rhythm. Thus sensory feedback to projection neurons can be gated as a function of the modulatory state of an active motor system, not simply switched on/off with the onset of motor activity. NEW & NOTEWORTHY Sensory feedback influences motor systems (i.e., motor circuits and their projection neuron inputs). However, whether regulation of sensory feedback to these projection neurons is consistent across different versions of the same motor pattern driven by the same motor system was not known. We found that gating of sensory feedback to projection neurons is determined by the modulatory state of the motor system, and not simply by whether the system is active or inactive.

Stomatogastric Nervous System

2017 ◽  
Author(s):  
Wolfgang Stein
Keyword(s):  
Nervous System ◽  
Neural Circuit ◽  
Activity Patterns ◽  
Cellular Level ◽  
Target Cells ◽  
Descending Pathways ◽  
Stomatogastric Nervous System ◽  
Motor Circuits ◽  
Insight Into

The crustacean stomatogastric nervous system contains a set of distinct but interacting rhythmic motor circuits that control movements of the foregut. When isolated, these circuits produce activity patterns that are almost perfect replicas of their behavior in vivo. The ease with which distinct circuit neurons are identified, recorded, and manipulated has provided considerable insight into the general principles of how motor circuits operate and are controlled at the cellular level. The small number of relatively large neurons has facilitated several technical advances in neuroscience research and allowed the identification of one of the earliest circuit connectomes. This enabled, for the first time, studies of circuit dynamics using the relationships between all component neurons of a nervous center. A major discovery was that circuits are not dedicated to producing a single neuronal activity pattern, and that the involved neurons are not committed to particular circuits. This flexibility results predominantly from the ability of neuromodulators to change the cellular and synaptic properties of circuit neurons. The relatively unique access to, and detailed documentation of, identified circuit, sensory, and descending pathways has also started new avenues into examining how individual modulatory neurons and transmitters affect their target cells. Groundbreaking experimental and modeling work has further demonstrated that the intrinsic properties of neurons depend on their recent history of activation and that neurons and circuits counterbalance destabilizing influences by compensatory homeostatic regulation of ionic conductances. The stomatogastric microcircuits continue to provide key insight into neural circuit operation in numerically larger and less accessible systems.

Hormonal Modulation of Two Coordinated Rhythmic Motor Patterns

2010 ◽  
Vol 104 (2) ◽  
pp. 654-664
Author(s):  
Debra E. Wood ◽  
Melissa Varrecchia ◽  
Michael Papernov ◽  
Denise Cook ◽  
Devon C. Crawford
Keyword(s):  
Motor Pattern ◽  
Projection Neuron ◽  
Frequency Regulation ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Motor Patterns ◽  
Rhythmic Motor ◽  
Hormonal Modulation ◽  
Frequency Relationship ◽  
Pyloric Rhythm

Neuromodulation is well known to provide plasticity in pattern generating circuits, but few details are available concerning modulation of motor pattern coordination. We are using the crustacean stomatogastric nervous system to examine how co-expressed rhythms are modulated to regulate frequency and maintain coordination. The system produces two related motor patterns, the gastric mill rhythm that regulates protraction and retraction of the teeth and the pyloric rhythm that filters food. These rhythms have different frequencies and are controlled by distinct mechanisms, but each circuit influences the rhythm frequency of the other via identified synaptic pathways. A projection neuron, MCN1, activates distinct versions of the rhythms, and we show that hormonal dopamine concentrations modulate the MCN1 elicited rhythm frequencies. Gastric mill circuit interactions with the pyloric circuit lead to changes in pyloric rhythm frequency that depend on gastric mill rhythm phase. Dopamine increases pyloric frequency during the gastric mill rhythm retraction phase. Higher gastric mill rhythm frequencies are associated with higher pyloric rhythm frequencies during retraction. However, dopamine slows the gastric mill rhythm frequency despite the increase in pyloric frequency. Dopamine reduces pyloric circuit influences on the gastric mill rhythm and upregulates activity in a gastric mill neuron, DG. Strengthened DG activity slows the gastric mill rhythm frequency and effectively reduces pyloric circuit influences, thus changing the frequency relationship between the rhythms. Overall dopamine shifts dependence of frequency regulation from intercircuit interactions to increased reliance on intracircuit mechanisms.

Dual modulatory effects on feedback from a proprioceptor in the crustacean stomatogastric nervous system

2021 ◽  
Author(s):  
Davis Grininger ◽  
John T. Birmingham
Keyword(s):  
Nervous System ◽  
Inhibitory Action ◽  
Muscle Contractions ◽  
Proprioceptive Feedback ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Cancer Borealis ◽  
Muscle Stretch ◽  
Excitatory Action ◽  
Central Network

Neuromodulatory actions that change the properties of proprioceptors or the muscle movements to which they respond necessarily affect the feedback provided to the central network. Here we further characterize the responses of the gastropyloric receptor 1 (GPR1) and gastropyloric receptor 2 (GPR2) neurons in the stomatogastric nervous system of the crab Cancer borealis to movements and contractions of muscles, and we report how neuromodulation modifies those responses. We observed that the GPR1 response to contractions of the gastric mill 4 (gm4) muscle was absent, or nearly so, when the neuron was quiescent but robust when it was spontaneously active. We also found that the effects of four neuromodulatory substances (GABA, serotonin, proctolin and TNRNFLRFamide) on the GPR1 response to muscle stretch were similar to those previously reported for GPR2. Finally, we showed that an excitatory action on gm4 due to proctolin combined with an inhibitory action on GPR2 due to GABA can allow for larger muscle contractions without increased proprioceptive feedback.

Serotonergic/cholinergic muscle receptor cells in the crab stomatogastric nervous system. II. Rapid nicotinic and prolonged modulatory effects on neurons in the stomatogastric ganglion

1989 ◽  
Vol 62 (2) ◽  
pp. 571-581 ◽  
Author(s):  
P. S. Katz ◽  
R. M. Harris-Warrick
Keyword(s):  
Motor Neurons ◽  
Preceding Paper ◽  
Stomatogastric Ganglion ◽  
Cell Group ◽  
Muscarinic Antagonists ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Cancer Borealis ◽  
Mechanical Coupling ◽  
Plateau Potential

1. The gastropyloric receptor (GPR) cells, which are described in the preceding paper, are a set of proprioceptive cells in the crabs Cancer borealis and Cancer irroratus that contain serotonin (5-hydroxytryptamine, 5-HT) and choline acetyltransferase. These cells have a variety of synaptic effects on cells in the stomatogastric ganglion (STG). We used pharmacologic methods to distinguish the effects that were due to acetylcholine (ACh) from those that could be due to serotonin. 2. The GPR cells evoke excitatory postsynaptic potentials (EPSPs) in two gastric mill motor neurons [lateral and dorsal gastric (LG and DG)] in the stomatogastric ganglion. The EPSPs exhibit nicotinic pharmacology, indicating that they may be due to the release of ACh from the GPR cells. 3. A train of GPR action potentials induces plateau potential properties in the DG motor neuron. This plateau potential induction is not blocked by nicotinic or muscarinic antagonists, suggesting it might be due to serotonin released from the GPR cells. Bath-applied serotonin induces a tonic depolarization of DG with high-intensity spiking. 4. In the accompanying paper, it is shown that DG-evoked muscle contraction leads to the excitation of GPR2 through mechanical coupling of the muscles. Because GPR2 also excites DG, a positive feedback loop exists between GPR2 and DG. This reflex loop may be involved in the control of the medial tooth of the gastric mill. 5. GPR stimulation initiates or enhances rhythmic pyloric cycling. This is due at least in part to a direct enhancement of bursting in the pyloric dilator/anterior burster (PD/AB) pacemaker cell group and can outlast the period of GPR stimulation by up to 1 min. GPR-induced PD burst enhancement continues in the presence of nicotinic and muscarinic antagonists, indicating that the effect is probably not due to the release of ACh. Bath application of serotonin mimicks the neuromodulatory effect of GPR stimulation on the PD/AB group by inducing or enhancing bursting. 6. Thus the GPR cells elicit at least three different synaptic actions in the stomatogastric ganglion: 1) classical, fast nicotinic cholinergic EPSPs that may be important for reflex functions in the gastric mill; 2) noncholinergic, cycle-by-cycle plateau potential induction that might be critical for the timing and operation of the gastric mill, and 3) prolonged, noncholinergic burst enhancement in pyloric neurons that is mimicked by serotonin, lasts many cycles, and may act to assure that the pyloric central pattern generator (CPG) is activated and cycling strongly.

scholarly journals Long-Lasting Activation of Rhythmic Neuronal Activity by a Novel Mechanosensory System in the Crustacean Stomatogastric Nervous System

2004 ◽  
Vol 91 (1) ◽  
pp. 78-91 ◽  
Author(s):  
Mark P. Beenhakker ◽  
Dawn M. Blitz ◽  
Michael P. Nusbaum
Keyword(s):  
Nervous System ◽  
Neural Circuits ◽  
Motor Pattern ◽  
Projection Neurons ◽  
Gastric Mill ◽  
Stomatogastric Nervous System ◽  
Cancer Borealis ◽  
Pressure Application ◽  
Mechanosensory System ◽  
Pyloric Rhythm

Sensory neurons enable neural circuits to generate behaviors appropriate for the current environmental situation. Here, we characterize the actions of a population (about 60) of bilaterally symmetric bipolar neurons identified within the inner wall of the cardiac gutter, a foregut structure in the crab Cancer borealis. These neurons, called the ventral cardiac neurons (VCNs), project their axons through the crab stomatogastric nervous system to influence neural circuits associated with feeding. Brief pressure application to the cardiac gutter transiently modulated the filtering motor pattern (pyloric rhythm) generated by the pyloric circuit within the stomatogastric ganglion (STG). This modulation included an increased speed of the pyloric rhythm and a concomitant decrease in the activity of the lateral pyloric neuron. Furthermore, 2 min of rhythmic pressure application to the cardiac gutter elicited a chewing motor pattern (gastric mill rhythm) generated by the gastric mill circuit in the STG that persisted for ≤30 min. These sensory actions on the pyloric and gastric mill circuits were mimicked by either ventral cardiac nerve or dorsal posterior esophageal nerve stimulation. VCN actions on the STG circuits required the activation of projection neurons in the commissural ganglia. A subset of the VCN actions on these projection neurons appeared to be direct and cholinergic. We propose that the VCN neurons are mechanoreceptors that are activated when food stored in the foregut applies an outward force, leading to the long-lasting activation of projection neurons required to initiate chewing and modify the filtering of chewed food.

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