Ionic Mechanisms Underlying Depolarizing Responses of an Identified Insect Motor Neuron to Short Periods of Hypoxia

1999 ◽  
Vol 81 (1) ◽  
pp. 307-318 ◽  
Author(s):  
Hervé Le Corronc ◽  
Bernard Hue ◽  
Robert M. Pitman
Keyword(s):  
Motor Neuron ◽  
Periplaneta Americana ◽  
Membrane Properties ◽  
Resting Potential ◽  
Induced Response ◽  
Long Term Effects ◽  
Sodium Influx ◽  
Hypoxia Response ◽  
Initial Transient ◽  
Ionic Mechanisms

Le Corronc, Hervé, Bernard Hue, and Robert M. Pitman. Ionic mechanisms underlying depolarizing responses of an identified insect motor neuron to short periods of hypoxia. J. Neurophysiol. 81: 307–318, 1999. Hypoxia can dramatically disrupt neural processing because energy-dependent homeostatic mechanisms are necessary to support normal neuronal function. In a human context, the long-term effects of such disruption may become all too apparent after a “stroke,” in which blood-flow to part of the brain is compromised. We used an insect preparation to investigate the effects of hypoxia on neuron membrane properties. The preparation is particularly suitable for such studies because insects respond rapidly to hypoxia, but can recover when they are restored to normoxic conditions, whereas many of their neurons are large, identifiable, and robust. Experiments were performed on the “fast” coxal depressor motoneuron (Df) of cockroach ( Periplaneta americana). Five-minute periods of hypoxia caused reversible multiphasic depolarizations (10–25 mV; n = 88), consisting of an initial transient depolarization followed by a partial repolarization and then a slower phase of further depolarization. During the initial depolarizing phase, spontaneous plateau potentials normally occurred, and inhibitory postsynaptic potential frequency increased considerably; 2–3 min after the onset of hypoxia all electrical activity ceased and membrane resistance was depressed. On reoxygenation, the membrane potential began to repolarize almost immediately, becoming briefly more negative than the normal resting potential. All phases of the hypoxia response declined with repeated periods of hypoxia. Blockade of ATP-dependent Na/K pump by 30 μM ouabain suppressed only the initial transient depolarization and the reoxygenation-induced hyperpolarization. Reduction of aerobic metabolism between hypoxic periods (produced by bubbling air through the chamber instead of oxygen) had a similar effect to that of ouabain. Although the depolarization seen during hypoxia was not reduced by tetrodotoxin (TTX; 2 μM), lowering extracellular Na+ concentration or addition of 500 μM Cd2+ greatly reduced all phases of the hypoxia-induced response, suggesting that Na influx occurs through a TTX-insensitive Cd2+-sensitive channel. Exposure to 20 mM tetraethylammonium and 1 mM 3,4-diaminopyridine increased the amplitude of the hypoxia-induced depolarization, suggesting that activation of K channels may normally limit the amplitude of the hypoxia response. In conclusion we suggest that the slow hypoxia-induced depolarization on motoneuron Df is mainly carried by a TTX-resistant, Cd2+-sensitive sodium influx. Ca2+ entry may also make a direct or indirect contribution to the hypoxia response. The fast transient depolarization appears to result from block of the Na/K pump, whereas the reoxygenation-induced hyperpolarization is largely caused by its subsequent reactivation.

Subthreshold frequency selectivity in avian auditory thalamus

1994 ◽  
Vol 71 (4) ◽  
pp. 1361-1372 ◽  
Author(s):  
B. Strohmann ◽  
D. W. Schwarz ◽  
E. Puil
Keyword(s):  
Frequency Selectivity ◽  
Membrane Properties ◽  
Resting Potential ◽  
Resonant Peak ◽  
Auditory Signal ◽  
Voltage Response ◽  
Potential Range ◽  
Na Current ◽  
Frequency Responses ◽  
Low Threshold

1. We studied the frequency responses of neurons in the nucleus ovoidalis (OV), the principal thalamic auditory relay nucleus of the chicken, in the subthreshold range of membrane potentials. The frequency response is the impedance amplitude profile evident in the voltage response to a broadband stimulus. The stimulus was a deterministic periodic current input of small amplitude, sweeping through a specified frequency range. We used whole-cell, tight-seal recording techniques in slices to study the voltage responses and membrane properties in current and voltage clamp. 2. Generally, low-frequency resonant humps with peak impedances of approximately 6 Hz characterized the frequency responses of OV neurons. This resonance was the principal determinant for frequency selectivity in the majority of OV neurons expressing only a tonic mode of firing. 3. The 6-Hz resonance was voltage dependent and most distinct where the activation ranges of a hyperpolarization activated inward current (IH) and a persistent Na+ current tend to overlap. The potential range for optimal resonance often included the resting potential. 4. Application of the Na+ current antagonist, tetrodotoxin, blocked the persistent Na+ current and most of the resonant hump at depolarized levels but did not affect the resonant peak along the frequency axis. Thus the persistent Na+ current may serve to amplify the resonance. 5. Extracellular application of Cs+, but not Ba2+, blocked a voltage sag during pulsed hyperpolarization as well as the IH current. Application of Cs+ also eliminated the 6-Hz resonance. An IH seems, therefore, instrumental for the resonance. 6. A minority of neurons that expressed low-threshold Ca2+ spikes and burst firing at hyperpolarized states displayed voltage oscillations at 2-4 Hz, spontaneously or in response to pulsatile stimuli. Application of Ni2+ blocked the oscillations and the low-threshold spikes, presumably produced by a T-type Ca2+ current. The resonance at 6 Hz, however, was only slightly affected by Ni2+. A T-type current, therefore, is critical for the 2- to 4-Hz oscillations. 7. Membrane resonance may dominate the power spectrum of subthreshold potential fluctuations. The resonance demonstrated in vitro may be stabilized by experimental procedures; its frequency may be different and more variable in vivo. Resonances in thalamic neurons may play a role in auditory signal processing in birds.

Properties of visceral primary afferent neurons in the nodose ganglion of the rabbit

1985 ◽  
Vol 54 (2) ◽  
pp. 245-260 ◽  
Author(s):  
C. E. Stansfeld ◽  
D. I. Wallis
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Nodose Ganglion ◽  
Time Dependent ◽  
Membrane Properties ◽  
Resting Potential ◽  
Inward Rectification ◽  
C Cells ◽  
Axonal Conduction ◽  
A Cells

The active and passive membrane properties of rabbit nodose ganglion cells and their responsiveness to depolarizing agents have been examined in vitro. Neurons with an axonal conduction velocity of less than 3 m/s were classified as C-cells and the remainder as A-cells. Mean axonal conduction velocities of A- and C-cells were 16.4 m/s and 0.99 m/s, respectively. A-cells had action potentials of brief duration (1.16 ms), high rate of rise (385 V/s), an overshoot of 23 mV, and relatively high spike following frequency (SFF). C-cells typically had action potentials with a "humped" configuration (duration 2.51 ms), lower rate of rise (255 V/s), an overshoot of 28.6 mV, an after potential of longer duration than A-cells, and relatively low SFF. Eight of 15 A-cells whose axons conducted at less than 10 m/s had action potentials of longer duration with a humped configuration; these were termed Ah-cells. They formed about 10% of cells whose axons conducted above 2.5 m/s. The soma action potential of A-cells was blocked by tetrodotoxin (TTX), but that of 6/11 C-cells was unaffected by TTX. Typically, A-cells showed strong delayed (outward) rectification on passage of depolarizing current through the soma membrane and time-dependent (inward) rectification on inward current passage. Input resistance was thus highly sensitive to membrane potential close to rest. In C-cells, delayed rectification was not marked, and slight time-dependent rectification occurred in only 3 of 25 cells; I/V curves were normally linear over the range: resting potential to 40 mV more negative. Data on Ah-cells were incomplete, but in our sample of eight cells time-dependent rectification was absent or mild. C-cells had a higher input resistance and a higher neuronal capacitance than A-cells. In a proportion of A-cells, RN was low at resting potential (5 M omega) but increased as the membrane was hyperpolarized by a few millivolts. A-cells were depolarized by GABA but were normally unaffected by 5-HT or DMPP. C-cells were depolarized by GABA in a similar manner to A-cells but also responded strongly to 5-HT; 53/66 gave a depolarizing response, and 3/66, a hyperpolarizing response. Of C-cells, 75% gave a depolarizing response to DMPP.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of ouabain on background and voltage-dependent currents in canine colonic myocytes

1990 ◽  
Vol 259 (3) ◽  
pp. C402-C408 ◽  
Author(s):  
E. P. Burke ◽  
K. M. Sanders
Keyword(s):  
Membrane Potential ◽  
Potential Gradient ◽  
Circular Muscle ◽  
Input Resistance ◽  
Pump Current ◽  
Muscle Layer ◽  
Membrane Properties ◽  
Resting Potential ◽  
Voltage Dependent ◽  
In Cells

Previous studies have suggested that the membrane potential gradient across the circular muscle layer of the canine proximal colon is due to a gradient in the contribution of the Na(+)-K(+)-ATPase. Cells at the submucosal border generate approximately 35 mV of pump potential, whereas at the myenteric border the pump contributes very little to resting potential. Results from experiments in intact muscles in which the pump is blocked are somewhat difficult to interpret because of possible effects of pump inhibitors on membrane conductances. Therefore, we studied isolated colonic myocytes to test the effects of ouabain on passive membrane properties and voltage-dependent currents. Ouabain (10(-5) M) depolarized cells and decreased input resistance from 0.487 +/- 0.060 to 0.292 +/- 0.040 G omega. The decrease in resistance was attributed to an increase in K+ conductance. Studies were also performed to measure the ouabain-dependent current. At 37 degrees C, in cells dialyzed with 19 mM intracellular Na+ concentration [( Na+]i), ouabain caused an inward current averaging 71.06 +/- 7.49 pA, which was attributed to blockade of pump current. At 24 degrees C or in cells dialyzed with low [Na+]i (11 mM), ouabain caused little change in holding current. With the input resistance of colonic cells, pump current appears capable of generating at least 35 mV. Thus an electrogenic Na+ pump could contribute significantly to membrane potential.

scholarly journals Ionic mechanisms of two types of on-center bipolar cells in the carp retina. I. The responses to central illumination.

1979 ◽  
Vol 73 (1) ◽  
pp. 73-90 ◽  
Author(s):  
T Saito ◽  
H Kondo ◽  
J I Toyoda
Keyword(s):  
Reversal Potential ◽  
Maximum Amplitude ◽  
Bipolar Cells ◽  
Light Spot ◽  
Membrane Properties ◽  
Resistance Increase ◽  
Membrane Conductances ◽  
Electric Interaction ◽  
Ionic Mechanisms ◽  
Resistance Decrease

Properties of the depolarizing response of on-center bipolar cells to a light spot stimulus were studied in the carp retina. On-center bipolar cells were classified into two types, cone-dominant and rod-dominant, according to their major input from cones and rods. Cone-dominant bipolar cells responded to spectral light with the maximum amplitude near 625 nm, suggesting major input from red cones. The response was accompanied by a resistance increase and showed a reversal potential at -63 +/- 21 mV when the membrane was hyperpolarized by current. The results suggest that the photoresponse of cone-dominant cells is due to a decrease of gK and/or gCl, membrane conductances to potassium and chloride, respectively. Rod-dominant bipolar cells responded to spectral light with the maximum amplitude near 525 nm under scotopic conditions and near 625 nm under photopic conditions, providing evidence that they receive input from rods and red cones. In the scoptopic condition their response was accompanied by a resistance decrease and showed a reversal potential at 29 +/- 13 mV, whereas in the photopic condition the response in most of them was accompanied by a resistance increase, at least in their part and showed a reversal at -53 +/- 11 mV. The results suggest that the photoresponse activated by rod input is due to an increase in gNa. In the mesopic condition rod-dominant cells showed complex electrical membrane properties as the result of electric interaction between the above two differnt ionic mechanisms activated by rod and cone inputs.

scholarly journals A genetic manipulation of motor neuron excitability does not alter locomotor output in Drosophila larvae

2014 ◽  
Author(s):  
Erin C. McKiernan
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Motor Behavior ◽  
Genetic Manipulation ◽  
Motor Output ◽  
Membrane Properties ◽  
Neuron Excitability ◽  
Motor Neuron Excitability ◽  
The Face

Motor activity, like that producing locomotion, is generated by networks of neurons. At the last output level of these networks are the motor neurons, which send signals to the muscles, causing them to contract. Current research in motor control is focused on finding out how motor neurons contribute to shaping the timing of motor behaviors. Are motor neurons just passive relayers of the signals they receive? Or, do motor neurons shape the signals before passing them on to the muscles, thereby influencing the timing of the behavior? It is now well accepted that motor neurons have active, intrinsic membrane properties - there are ion channels in the cell membrane that allow motor neurons to respond to input in non-linear and diverse ways. However, few direct tests of the role of motor neuron intrinsic properties in shaping motor behavior have been carried out, and many questions remain about the role of specific ion channel genes in motor neuron function. In this study, two potassium channel transgenes were expressed in Drosophila larvae, causing motor neurons to fire at lower levels of current stimulation and at higher frequencies, thereby increasing excitability. Mosaic animals were created in which some identified motor neurons expressed the transgenes while others did not. Motor output underlying crawling was compared in muscles innervated by control and experimental neurons in the same animals. Counterintuitively, no effect of the transgenic manipulation on motor output was seen. Future experiments are outlined to determine how the larval nervous system produces normal motor output in the face of altered motor neuron excitability.

Effects of norepinephrine upon superficial layer neurons in the superior colliculus of the hamster: In vitro studies

1999 ◽  
Vol 16 (3) ◽  
pp. 557-570 ◽  
Author(s):  
HONGJING TAN ◽  
RICHARD D. MOONEY ◽  
ROBERT W. RHOADES
Keyword(s):  
Superior Colliculus ◽  
Optic Tract ◽  
Reversal Potential ◽  
Outward Current ◽  
Input Resistance ◽  
Superficial Layer ◽  
Membrane Properties ◽  
Induced Response

Intracellular recording techniques were used to evaluate the effects of norepinephrine (NE) on the membrane properties of superficial layer (stratum griseum superficiale and stratum opticum) superior colliculus (SC) cells. Of the 207 cells tested, 44.4% (N = 92) were hyperpolarized by ≥3 mV and 8.7% (N = 18) were depolarized by ≥3 mV by application of NE. Hyperpolarization induced by NE was dose dependent (EC50 = 8.1 μM) and was associated with decreased input resistance and outward current which had a reversal potential of −94.0 mV. Depolarization was associated with a very slight rise in input resistance and had a reversal potential of −93.1 mV for the single cell tested. Pharmacologic experiments demonstrated that isoproterenol, dobutamine, and p-aminoclonidine all hyperpolarized SC cells. These results are consistent with the conclusion that NE-induced hyperpolarization of SC cells is mediated by both α2 and β1 adrenoceptors. The α1 adrenoceptor agonists, methoxamine and phenylephrine, depolarized 35% (6 of 17) of the SC cells tested by ≥3 mV. Most of the SC cells tested exhibited responses indicative of expression of more than one adrenoceptor. Application of p-aminoclonidine or dobutamine inhibited transsynaptic responses in SC cells evoked by electrical stimulation of optic tract axons. Inhibition of evoked responses by these agents was usually, but not invariably, associated with a hyperpolarization of the cell membrane and a reduction in depolarizing potentials evoked by application of glutamate. The present in vitro results are consistent with those of the companion in vivo study which suggested that NE-induced response suppression in superficial layer SC neurons was primarily postsynaptic and chiefly mediated by both α2 and β1 adrenoceptors.

Morphological and Membrane Properties of Rat Magnocellular Basal Forebrain Neurons Maintained in Culture

1998 ◽  
Vol 80 (4) ◽  
pp. 1653-1669 ◽  
Author(s):  
J. A. Sim ◽  
T.G.J. Allen
Keyword(s):  
Basal Forebrain ◽  
Cell Types ◽  
Membrane Properties ◽  
Resting Potential ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Magnocellular Neurons ◽  
Membrane Hyperpolarization ◽  
Cell Excitability ◽  
Forebrain Neurons

Sim, J. A. and T.G.J. Allen. Morphological and membrane properties of rat magnocellular basal forebrain neurons maintained in culture. J. Neurophysiol. 80: 1653–1669, 1998. Morphological and electrophysiological characteristics of magnocellular neurons from basal forebrain nuclei of postnatal rats (11–14 days old) were examined in dissociated cell culture. Neurons were maintained in culture for periods of 5–27 days, and 95% of magnocellular (>23 μm diam) neurons stained positive with acetylcholinesterase histochemistry. With the use of phase contrast microscopy, four morphological subtypes of magnocellular neurons could be distinguished according to the shape of their soma and pattern of dendritic branching. Corresponding passive and active membrane properties were investigated with the use of whole cell configuration of the patch-clamp technique. Neurons of all cell types displayed a prominent (6–39 mV; 6.7–50 ms duration) spike afterdepolarization (ADP), which in some cells reached firing threshold. The ADP was voltage dependent, increasing in amplitude and decreasing in duration with membrane hyperpolarization with an apparent reversal potential of −59 ± 2.3 (SE) mV. Elevating [Ca2+]o (2.5–5.0 mM) or prolonging spike repolarization with 10 mM tetraethylammonium (TEA) or 1 mM 4-aminopyridine (4-AP), potentiated the ADP while it was inhibited by reducing [Ca2+]o (2.5–1 mM) or superfusion with Cd2+ (100 μM). The ADP was selectively inhibited by amiloride (0.1–0.3 mM or Ni2+ 10 μM) but unaffected by nifedipine (3 μM), ω-conotoxin GVIA (100 nM) or ω-agatoxin IVA (200 nM), indicating that Ca2+ entry was through T-type Ca2+ channels. After inhibition of the ADP with amiloride (300 μM), depolarization to less than −65 mV revealed a spike afterhyperpolarization (AHP) with both fast and slow components that could be inhibited by 4-AP (1 mM) and Cd2+ (100 μM), respectively. In all cell types, current-voltage relationships exhibited inward rectification at hyperpolarized potentials ≥ E K (approximately −90 mV). Application of Cs+ (0.1–1 mM) or Ba2+ (1–10 μM) selectively inhibited inward rectification but had no effect on resting potential or cell excitability. At higher concentrations, Ba2+ (>10 μM) also inhibited an outward current tonically active at resting potential ( V H −70 mV), which under current-clamp conditions resulted in small membrane depolarization (3–10 mV) and an increase in cell excitability. Depolarizing voltage commands from prepulse potential of −90 mV ( V H −70 mV) in the presence of tetrodotoxin (0.5 μM) and Cd2+ (100 μM) to potentials between −40 and +40 mV cause voltage activation of both transient A-type and sustained delayed rectifier-type outward currents, which could be selectively inhibited by 4-AP (0.3–3 mM) and TEA (1–3 mM), respectively. These results show that, although acetylcholinesterase-positive magnocellular basal forebrain neurons exhibit considerable morphological heterogeneity, they have very similar and characteristic electrophysiological properties.

Distinct Electrophysiological Properties in Subtypes of Nonspiking Olfactory Local Interneurons Correlate With Their Cell Type–Specific Ca2+ Current Profiles

2009 ◽  
Vol 102 (5) ◽  
pp. 2834-2845 ◽  
Author(s):  
Andreas Husch ◽  
Moritz Paehler ◽  
Debora Fusca ◽  
Lars Paeger ◽  
Peter Kloppenburg
Keyword(s):  
Periplaneta Americana ◽  
Membrane Properties ◽  
Type Ii ◽  
Diverse Population ◽  
Cell Type ◽  
Cellular Mechanisms ◽  
Electrophysiological Properties ◽  
Local Interneurons ◽  
Cell Type Specific ◽  
Process Structure

A diverse population of local interneurons (LNs) helps to process, structure, and spatially represent olfactory information in the insect antennal lobe. In Periplaneta americana, we identified two subtypes of nonspiking local interneurons (type II LNs) by their distinct morphological and intrinsic electrophysiological properties. As an important step toward a better understanding of the cellular mechanisms that mediate odor information processing, we present a detailed analysis of their distinct voltage-activated Ca2+ currents, which clearly correlated with their distinct intrinsic electrophysiological properties. Both type II LNs did not posses voltage-activated Na+ currents and apparently innervated all glomeruli including the macroglomerulus. Type IIa LNs had significant longer and thicker low-order neurites and innervated each glomerulus entirely and homogeneously, whereas type IIb LNs innervated only parts of each glomerulus. All type II LNs were broadly tuned and responded to odorants of many chemical classes with graded changes in the membrane potential. Type IIa LNs responded with odor-specific elaborate patterns of excitation that could also include “spikelets” riding on the depolarizations and periods of inhibition. In contrast, type IIb LNs responded mostly with sustained, relatively smooth depolarizations. Consistent with the strong active membrane properties of type IIa LNs versus type IIb LNs, the voltage-activated Ca2+ current of type IIa LNs activated at more hyperpolarized membrane potentials and had a larger transient component.

Altered excitability of goldfish mauthner cell following axotomy. I. Characterization and correlations with somatic and axonal morphological reactions

1986 ◽  
Vol 55 (6) ◽  
pp. 1424-1439 ◽  
Author(s):  
M. J. Titmus ◽  
D. S. Faber ◽  
S. J. Zottoli
Keyword(s):  
Cell Body ◽  
Initial Segment ◽  
Membrane Properties ◽  
Resting Potential ◽  
M Cells ◽  
M Cell ◽  
Spike Amplitude ◽  
Axon Hillock ◽  
The Mean ◽  
Lateral Dendrite

Axonal transection 7-10 mm distal to the cell body of the goldfish Mauthner (M) cell induced alterations in its excitability; namely, the antidromic spike recorded in the soma was converted from a single-component axon-hillock response to a larger amplitude, two-component impulse. The mean spike amplitude of the axotomized cells was approximately 50% greater (59.6 +/- 15.1 mV, n = 94) than that in controls (39.4 +/- 6.3 mV, n = 73). The onset of the induced increase in spike amplitude occurs at approximately 20 days postaxotomy, and the transition to a reactive spike is complete by approximately 30-35 days. Eighty-three percent of the M-cells axotomized for more than 30 days were physiologically reactive as judged by their large spike amplitudes and/or the presence of an additional spike component. Concomitant with the enhanced spike amplitudes, there was a depression of excitability in the initial segment-axon hillock region of the axotomized cells. This depression was suggested by a decrease in the initial segment (IS) spike height (from 39.4 +/- 6.3 mV, n = 73, in controls to 27.5 +/- 5.6 mV, n = 13, in axotomized cells), a decrease in its maximum rate of rise (from 153.6 +/- 24 V/s, n = 15, to 112.5 +/- 30 V/s, n = 29), and frequent failure of antidromic invasion into the initial segment and axon hillock. These changes in excitability could not be attributed to alterations in passive membrane properties, since the mean resting potential (77.8 +/- 5.2 mV, n = 37, control; 76.9 +/- 7.8 mV, n = 87, axotomized) and input resistance (170 +/- 21.3 K omega, n = 13, control; 176 +/- 26.6 K omega, n = 21, axotomized) were not altered significantly by axotomy. Threshold voltage was also unaffected (13.4 +/- 3.2 mV, n = 11, control; 11.9 +/- 2.5 mV, n = 11, axotomized). Sequential recordings of spike amplitudes from the axon hillock, soma, and lateral dendrite suggest that the generator of the axotomy-induced component is localized to the normally passive soma and proximal dendrite. In addition, the presumed soma-dendritic In addition, the presumed soma-dendritic component contributes very little if anything to the action potentials recorded in the axon. The onset and occurrence of alterations in excitability and cell body morphology (chromatolysis and nuclear associated changes) were compared in different M-cell populations and in the same identified M-cells. The comparisons suggested that these two events tend to occur in parallel.(ABSTRACT TRUNCATED AT 400 WORDS)

Endogenous Motor Neuron Properties Contribute to a Program-Specific Phase of Activity in the Multifunctional Feeding Central Pattern Generator of Aplysia

2007 ◽  
Vol 98 (1) ◽  
pp. 29-42 ◽  
Author(s):  
Geidy E. Serrano ◽  
Clarissa Martínez-Rubio ◽  
Mark W. Miller
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Central Pattern Generators ◽  
Ingestive Behavior ◽  
Membrane Properties ◽  
Motor Patterns ◽  
Effector System ◽  
Bilateral Pair ◽  
Pattern Generators ◽  
Specific Phase

Multifunctional central pattern generators (CPGs) are circuits of neurons that can generate manifold actions from a single effector system. This study examined a bilateral pair of pharyngeal motor neurons, designated B67, that participate in the multifunctional feeding network of Aplysia californica. Fictive buccal motor programs (BMPs) were elicited with four distinct stimulus paradigms to assess the activity of B67 during ingestive versus egestive patterns. In both classes of programs, B67 fired during the phase of radula protraction and received a potent inhibitory postsynaptic potential (IPSP) during fictive radula retraction. When programs were ingestive, the retraction phase IPSP exhibited a depolarizing sag and was followed by a postinhibitory rebound (PIR) that could generate a postretraction phase of impulse activity. When programs were egestive, the depolarizing sag potential and PIR were both diminished or were not present. Examination of the membrane properties of B67 disclosed a cesium-sensitive depolarizing sag, a corresponding Ih-like current, and PIR in its responses to hyperpolarizing pulses. Direct IPSPs originating from the influential CPG retraction phase interneuron B64 were also found to activate the sag potential and PIR of B67. Dopamine, a modulator that can promote ingestive behavior in this system, enhanced the sag potential, Ih-like current, and PIR of B67. Finally, a pharyngeal muscle contraction followed the radula retraction phase of ingestive, but not egestive motor patterns. It is proposed that regulation of the intrinsic properties of this motor neuron can contribute to generating a program-specific phase of motor activity.

Sign in / Sign up

Export Citation Format

Share Document