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

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.

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Different microcircuit responses to comparable input from one versus both copies of an identified projection neuron

Journal of Experimental Biology ◽

10.1242/jeb.228114 ◽

2020 ◽

Vol 223 (20) ◽

pp. jeb228114

Author(s):

Gabriel F. Colton ◽

Aaron P. Cook ◽

Michael P. Nusbaum

Keyword(s):

Firing Rate ◽

Projection Neuron ◽

Projection Neurons ◽

Gastric Mill ◽

Cancer Borealis ◽

Axon Terminals ◽

Commissural Neuron ◽

Co Activation ◽

Multiple Copies ◽

Protraction Phase

ABSTRACTNeuronal inputs to microcircuits are often present as multiple copies of apparently equivalent neurons. Thus far, however, little is known regarding the relative influence on microcircuit output of activating all or only some copies of such an input. We examine this issue in the crab (Cancer borealis) stomatogastric ganglion, where the gastric mill (chewing) microcircuit is activated by modulatory commissural neuron 1 (MCN1), a bilaterally paired modulatory projection neuron. Both MCN1s contain the same co-transmitters, influence the same gastric mill microcircuit neurons, can drive the biphasic gastric mill rhythm, and are co-activated by all identified MCN1-activating pathways. Here, we determine whether the gastric mill microcircuit response is equivalent when stimulating one or both MCN1s under conditions where the pair are matched to collectively fire at the same overall rate and pattern as single MCN1 stimulation. The dual MCN1 stimulations elicited more consistently coordinated rhythms, and these rhythms exhibited longer phases and cycle periods. These different outcomes from single and dual MCN1 stimulation may have resulted from the relatively modest, and equivalent, firing rate of the gastric mill neuron LG (lateral gastric) during each matched set of stimulations. The LG neuron-mediated, ionotropic inhibition of the MCN1 axon terminals is the trigger for the transition from the retraction to protraction phase. This LG neuron influence on MCN1 was more effective during the dual stimulations, where each MCN1 firing rate was half that occurring during the matched single stimulations. Thus, equivalent individual- and co-activation of a class of modulatory projection neurons does not necessarily drive equivalent microcircuit output.

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State-dependent sensorimotor gating in a rhythmic motor system

Journal of Neurophysiology ◽

10.1152/jn.00420.2017 ◽

2017 ◽

Vol 118 (5) ◽

pp. 2806-2818 ◽

Cited By ~ 7

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.

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Differential Activation of Projection Neurons by Two Sensory Pathways Contributes to Motor Pattern Selection

Journal of Neurophysiology ◽

10.1152/jn.00618.2009 ◽

2009 ◽

Vol 102 (5) ◽

pp. 2866-2879 ◽

Cited By ~ 20

Author(s):

Ulrike B. S. Hedrich ◽

Carmen R. Smarandache ◽

Wolfgang Stein

Keyword(s):

Motor Pattern ◽

Projection Neuron ◽

Projection Neurons ◽

Gastric Mill ◽

Stomatogastric Nervous System ◽

Motor Patterns ◽

Commissural Neurons ◽

Sensory Pathways ◽

Motor Circuits ◽

Selection Of

Sensorimotor integration is known to occur at the level of motor circuits as well as in upstream interneurons that regulate motor activity. Here we show, using the crab stomatogastric nervous system (STNS) as a model, that different sensory systems affect the same set of projection neurons. However, they have qualitatively different effects on their activities (excitation vs. inhibition), and these differences contribute to the selection of motor patterns from multifunctional circuits. We compare the actions of the proprioceptive anterior gastric receptor (AGR) and the inferior ventricular (IV) neurons, which relay chemosensory information from the brain to the STNS, on modulatory commissural neurons 1 and 5 (MCN1 and MCN5) and commissural projection neuron 2 (CPN2) and their resulting actions on the gastric mill central pattern generating circuit in the stomatogastric ganglion. When stimulated, AGR and the IV neurons affect all three projection neurons but elicit distinct gastric mill rhythms. The effects of both sensory pathways on the projection neurons differ in the type of excitation provided to CPN2 and MCN5 (electrical vs. chemical) and the effect on MCN1 (direct inhibition by AGR vs. polysynaptic excitation by the IV neurons). The latter is functionally important because a restoration of MCN1 activity during the AGR rhythm made it more similar to that elicited by IV neuron stimulation. Our results thus support the hypothesis that sensory pathways activate different combinations of projection neurons to select distinct outputs from the same neuronal circuit.

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

Journal of Neurophysiology ◽

10.1152/jn.1994.72.4.1451 ◽

1994 ◽

Vol 72 (4) ◽

pp. 1451-1463 ◽

Cited By ~ 39

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)

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Distinct Microcircuit Response to Comparable Input from a Full and Partial Projection Neuron Population

10.1101/2020.05.01.072629 ◽

2020 ◽

Author(s):

Gabriel F. Colton ◽

Aaron P. Cook ◽

Michael P. Nusbaum

Keyword(s):

Firing Rate ◽

Single Copy ◽

Projection Neuron ◽

Projection Neurons ◽

Gastric Mill ◽

Cancer Borealis ◽

Axon Terminals ◽

Co Activation ◽

Multiple Copies ◽

Summary Statement

ABSTRACTNeuronal inputs to microcircuits are often present as multiple copies of apparently equivalent neurons. Thus far, however, little is known regarding the relative influence on microcircuit output of activating all or only some copies of such an input. We are examining this issue in the crab (Cancer borealis) stomatogastric ganglion, where the gastric mill (chewing) microcircuit is activated by MCN1, a paired modulatory projection neuron. Both MCN1s contain the same cotransmitters, influence the same gastric mill circuit neurons, can drive the biphasic gastric mill rhythm, and are co-activated by all identified MCN1-activating pathways. Here, we determine whether the gastric mill circuit response is equivalent when stimulating one or both MCN1s under conditions where the pair are matched to collectively fire at the same overall rate and pattern as single MCN1 stimulation. The dual MCN1 stimulations elicited more consistently coordinated rhythms, and these rhythms exhibited longer phases and cycle periods. These different outcomes from single and dual MCN1 stimulation may have resulted from the relatively modest, and equivalent, firing rate of the gastric mill neuron LG during each matched set of stimulations. The LG neuron-mediated, ionotropic inhibition of the MCN1 axon terminals is the trigger for the transition from the retraction to protraction phase. This LG neuron influence on MCN1 was more effective during the dual stimulations, where each MCN1 firing rate was half that occurring during the matched single stimulations. Thus, equivalent individual- and co-activation of a class of modulatory projection neurons will not necessarily drive equivalent microcircuit output.Summary StatementCo-stimulating both copies of an identified modulatory projection neuron at the same collective firing rate used for single copy stimulation results in distinct microcircuit output.

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

10.1101/2020.07.24.220442 ◽

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.

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Feeding State-Dependent Modulation of Feeding-Related Motor Patterns

Journal of Neurophysiology ◽

10.1152/jn.00387.2021 ◽

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.

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GABA and responses to GABA in the stomatogastric ganglion of the crab Cancer borealis

Journal of Experimental Biology ◽

10.1242/jeb.203.14.2075 ◽

2000 ◽

Vol 203 (14) ◽

pp. 2075-2092 ◽

Cited By ~ 1

Author(s):

A.M. Swensen ◽

J. Golowasch ◽

A.E. Christie ◽

M.J. Coleman ◽

M.P. Nusbaum ◽

...

Keyword(s):

Nervous System ◽

Gaba Receptors ◽

Reversal Potential ◽

Stomatogastric Ganglion ◽

Projection Neurons ◽

Gamma Aminobutyric Acid ◽

Stomatogastric Nervous System ◽

Cancer Borealis ◽

Excitatory Response ◽

Commissural Neuron

The multifunctional neural circuits in the crustacean stomatogastric ganglion (STG) are influenced by many small-molecule transmitters and neuropeptides that are co-localized in identified projection neurons to the STG. We describe the pattern of gamma-aminobutyric acid (GABA) immunoreactivity in the stomatogastric nervous system of the crab Cancer borealis and demonstrate biochemically the presence of authentic GABA in C. borealis. No STG somata show GABA immunoreactivity but, within the stomatogastric nervous system, GABA immunoreactivity co-localizes with several neuropeptides in two identified projection neurons, the modulatory proctolin neuron (MPN) and modulatory commissural neuron 1 (MCN1). To determine which actions of these neurons are evoked by GABA, it is necessary to determine the physiological actions of GABA on STG neurons. We therefore characterized the response of each type of STG neuron to focally applied GABA. All STG neurons responded to GABA. In some neurons, GABA evoked a picrotoxin-sensitive depolarizing, excitatory response with a reversal potential of approximately −40 mV. This response was also activated by muscimol. In many STG neurons, GABA evoked inhibitory responses with both K(+)- and Cl(−)-dependent components. Muscimol and beta-guanidinopropionic acid weakly activated the inhibitory responses, but many other drugs, including bicuculline and phaclofen, that act on vertebrate GABA receptors were not effective. In summary, GABA is found in projection neurons to the crab STG and can evoke both excitatory and inhibitory actions on STG neurons.

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Peptide Hormone Modulation of a Neuronally Modulated Motor Circuit

Journal of Neurophysiology ◽

10.1152/jn.00795.2006 ◽

2007 ◽

Vol 98 (6) ◽

pp. 3206-3220 ◽

Cited By ~ 15

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.

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

Journal of Neurophysiology ◽

10.1152/jn.00741.2003 ◽

2004 ◽

Vol 91 (1) ◽

pp. 78-91 ◽

Cited By ~ 39

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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