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J Koester

Publications and source records attributed to J Koester.

At least 37 records · Page 2Linked to original sources
PubMed1989

Chemically and electrically coupled interneurons mediate respiratory pumping in Aplysia.

1. Respiratory pumping in Aplysia consists of synchronous, brief contractions of the mantle organs that can occur spontaneously and also can be triggered by tactile or noxious stimulation. It has been shown previously to be driven in part by a cluster of electrically coupled interneurons, called the L25 cells, located in the left hemiabdominal ganglion. This paper describes a second class of interneurons, the R25 cells, that also plays an important role in the control of respiratory pumping. 2. The R25 cells are a cluster of approximately 14 interneurons located in the right hemiabdominal ganglion, roughly symmetrical to the L25 cells. The R25 cells are electrically coupled to each other and to the L25 cells. Some R25 and L25 cells also produce chemically mediated fast excitation and slow inhibition of other neurons in the R25/L25 network. 3. Three lines of evidence demonstrate that the R25 cells play a role in mediating respiratory pumping: 1) They fire in a synchronous burst each time the behavior occurs. 2) They make direct chemical synaptic connections to motoneurons that mediate the behavior; and 3) Firing a single R25 cell can trigger the entire behavior, by recruiting synchronous bursts of activity in all of the other R25 and L25 neurons. Individual R25 and L25 cells can act both as trigger cells (exciting the other interneurons) and as relay cells (projecting directly to motoneurons). 4. Burst initiation within the R25/L25 network appears to have two phases: 1) There is an initial phase when the R25 and L25 cells fire at a relatively low frequency. This phase can be driven either by endogenous pacemaker activity of the R25/L25 cells or by afferent synaptic input from sensory pathways; and 2) The late, high-frequency phase of the burst results largely from reverberation within the network, as activity in each cell contributes positive feedback via the excitatory chemical and electrical connections between R25 and L25 cells. 5. Synchronization of the different motor outputs that make up the pumping behavior is achieved by three mechanisms: 1) When pumping occurs spontaneously, the electrical coupling between the cells of the R25/L25 network ensures that these cells will all be near spike threshold at the end of each interburst period.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

SCP-containing R20 neurons modulate respiratory pumping in Aplysia.

Respiratory pumping in Aplysia consists of transient, synchronous pumping actions of the gill, siphon, mantle shelf, and parapodia. This behavior has previously been shown to be driven by a network of coupled interneurons in the abdominal ganglion, the R25 and the L25 cells. We describe here a pair of electrically coupled cells, the R20 cells, which when active can initiate respiratory pumping or increase its spontaneous rate of occurrence. This action is mediated by a slow, long-lasting excitation of the endogenous burst mechanism of the cells in the R25/L25 network. The R20 cells, which are located in the abdominal ganglion, also make slow inhibitory connections to the RB cells and to the RG cells in that ganglion, and to the gill motoneurons in the branchial ganglion. The R20 cells are immunoreactive to SCPB, a molluscan neuropeptide. Biochemical purification studies demonstrate that each of the R20 cells synthesizes not only SCPB, but also SCPA, a closely related molecule known to be encoded by the same gene as SCPB. The R20 cells also synthesize in abundance several other low-molecular-weight, methionine-containing peptides. The excitatory actions of the R20 cells on the R25/L25 network are mimicked by SCPA and SCPB. However, the inhibitory actions of the R20 cells on the RB cells, the RG cells, and on the cells of the branchial ganglion are not mimicked by the SCPs. Thus, the data support the hypothesis that the R20 cells release SCPA and SCPB and at least one other unidentified transmitter.

Animals↗
PubMed1989

Innervation of the kidney of Aplysia by L10, the LUQ cells, and an identified peripheral motoneuron.

The purpose of this study was to begin to describe the neural circuit within the abdominal ganglion that modulates renal functioning in Aplysia. We found that the previously described cholinergic neuron L10 and peptidergic left upper quadrant (LUQ) neurons have important roles in the control of the kidney. Cell L10 and a subset of the LUQ cells branch extensively within the kidney and send major processes to the renal pore, a sphincter that controls the efflux of urine. The renal pore has circular (closer) and radial (opener) muscle fibers that act as antagonists. Embedded within the wall of the renal pore is a newly identified peripheral neuron, RPO, which is a renal pore opener motoneuron. L10 activity causes opening of the renal pore by directly exciting pore opener muscle, inhibiting closer muscle, and exciting RPO. When RPO is active, it generates synchronous, discrete twitches in the opener muscle fibers. The action potentials recorded in RPO exhibit pronounced broadening at physiological rates of firing. LUQ cells that project to the renal pore cause it to close, and they antagonize the opening generated by an L10 burst. The pore closing caused by the LUQ cells is mediated in part by heterosynaptic inhibition of the L10 to RPO excitatory connection. The previously described central inhibitory connections from L10 to the LUQ cells ensure that these 2 classes of antagonists fire out of phase with each other. Our data, along with those from earlier studies demonstrating that L10 plays an important role in controlling the circulatory system, suggest that L10 and the LUQ cells modulate various aspects of renal function in Aplysia, including filtration and micturition.

Animals↗
PubMed1986

Serotonin enhances the excitatory acetylcholine response in the RB cell cluster of Aplysia californica.

The RB cells, an identified cluster of serotonergic neurons in the abdominal ganglion of Aplysia californica, are excited by ACh. We have found that serotonin (5-HT) enhances the ACh responses recorded from the RB cells. The locus and specificity of the serotonergic interaction with the ACh response were analyzed using the conventional two-electrode voltage-clamp technique. We compared the current responses evoked in RB cells by constant-current iontophoretic pulses of ACh in control solutions and in solutions containing various concentrations of 5-HT. Serotonin consistently enhances the ACh evoked response in a dose-dependent manner while simultaneously directly activating the RB cells by turning on a small steady-state inward current. The dose-response characteristics for the 5-HT-mediated steady-state current differ, however, from those of the 5-HT-induced ACh response facilitation. The ACh response enhancement appears to be an effect of 5-HT upon RB cell ACh receptors since the enhancement is present under conditions that eliminate presynaptic input, and 5-HT is still capable of enhancing the iontophoretically evoked response when the AChE-resistant agonist carbachol is substituted for ACh. We tested other neurons in the Aplysia CNS exhibiting ACh evoked responses qualitatively similar to the RB cell ACh responses; 5-HT does not enhance the iontophoretically evoked ACh responses of these cells. Also, although the RB cells are responsive to dopamine and histamine, these putative neurotransmitters do not enhance the ACh response.

Acetylcholine↗
PubMed1985

Distribution of serotonin-immunoreactive cell bodies and processes in the abdominal ganglion of mature Aplysia.

Sensitization of the gill withdrawal reflex in Aplysia californica is an elementary form of learning, in part resulting from presynaptic facilitation of the LE mechanoreceptor neurons of the abdominal ganglion. It has previously been established that either application of serotonin or direct stimulation of a group of facilitatory neurons, the L29 cells of the abdominal ganglion, can simulate the effect of physiological stimulation in producing presynaptic facilitation. Because the evidence that serotonin serves as a facilitatory transmitter was indirect, we examined the distribution of serotonin-immunoreactive fibers and cell bodies in the abdominal ganglion in order to answer two questions: (1) do the sensory neurons receive serotonergic innervation and (2) are the L29 cells serotonergic? We observed two distinctive patterns of serotonergic innervation within the ganglion, sparse and dense. The sparse pattern is correlated with a serotonin-stimulated increase in cAMP in identified target cells, while the dense innervation is not. We found a sparse distribution of serotonin-immunoreactive fibers with varicosities close to both cell bodies and processes of identified LE sensory cells. It therefore is likely that the sensory neurons do receive serotonergic innervation. We also mapped the population of serotonergic neuronal cell bodies in the ganglion, and found five clusters of neurons. Cells in one of these clusters, the identified RB neurons, had previously been shown to synthesize serotonin from tryptophan and to contain the neurotransmitter in high concentration. Identified L29 facilitator cells marked by injection with Lucifer Yellow do not contain serotonin immunoreactivity and therefore evidently are not a source of serotonergic input onto sensory cells.

Animals↗
PubMed1984

Malonyl-coenzyme A:isoflavone 7-O-glucoside-6"-O-malonyltransferase from roots of chick pea (Cicer arietinum L.).

A malonyltransferase which catalyzes the malonylation of isoflavone 7-O-glucosides in position 6 of the glucose moiety using malonyl-coenzyme A as acyl donor has been purified 157-fold from 4-day-old roots of chick pea (Cicer arietinum L.). The enzyme showed a pH optimum of 8.0 and a molecular weight of 112,000. The Km for malonylcoenzyme A was 48 microM and, for the chick pea isoflavones biochanin A and formononetin, 36 and 24 microM, respectively. Various other isoflavone, flavone, and flavonol 7-O-glucosides and chalcone 4'-O-glucosides were much poorer substrates. Flavonol 3-O-glucosides and isoflavone 4'-O-glucosides were not malonylated by the malonyltransferase.

Acyl Coenzyme A↗
PubMed1984

Neuronal mediation of cardiovascular effects of food arousal in aplysia.

Previous studies have demonstrated that heart rate and blood pressure increase in Aplysia during an arousal state elicited by food stimuli. In addition, during biting, blood flow is routed alternately to the head (during protraction of the buccal mass) and to the digestive system (during retraction). In this study, cutting the pleuroabdominal connectives eliminated 75% of the heart rate response during food arousal, and cutting the pleuroabdominal connectives eliminated 20-50% of the pressor response. Recording in the abdominal ganglion from the RBHE heart excitor and the three LBVC vasoconstrictor motor neurons in a reduced preparation showed that activity in these neurons was increased 50 and 100%, respectively, during food arousal. Activity of the LBVC cells was maximal during the protraction phase of biting. The LBVC vasoconstrictor motor neurons, when fired at the rates recorded during food arousal, can occlude the abdominal aorta completely. We conclude that the RBHE and LBVC neurons mediate, in part, the heart rate and pressor responses recorded during food arousal and that cyclic activity in LBVC contributes significantly to the cyclic alternation of blood flow between the head and the gut during rhythmic biting behavior.

Animals↗
PubMed1983

Behavioral changes in aging Aplysia: a model system for studying the cellular basis of age-impaired learning, memory, and arousal.

The marine mollusc Aplysia californica was used to examine the effects of age on simple forms of learning, memory, and arousal. We have found that aging impairs the long-term retention of habituation and prevents the acquisition of sensitization in the siphon withdrawal reflex. In addition, aging reduces arousal as evident in the heart rate component of the response to food stimuli. Our results are similar to the age-dependent alterations in the capacity for behavioral plasticity that have been reported in a variety of vertebrates, including man. These similarities suggest that the mechanisms underlying the effects of age on behavior and its modification may share common features across phyla and therefore might be studied to advantage in Aplysia whose central nervous system is especially accessible to cell biological approaches.

Aging↗
PubMed1980

Different cholinergic synapses converging onto neurons in Aplysia produce the same synaptic action.

We have investigated neurons that receive inputs from more than one cholinergic interneuron, to see whether one cholinergic input can depolarize and the other hyperpolarize by virtue of activating different ACh receptors. We have examined synapses made in the abdominal ganglion of Aplysia californica by 3 cholinergic interneurons. Two of those interneurons have previously been shown to be cholinergic. Using both biochemical and pharmacological tests we have shown a third interneuron to be cholinergic. For 7 postsynaptic cells, we compared 6 new connections that we have identified from cholinergic interneurons, and 12 previously known connections. In each case we found that different cholinergic inputs onto any given cell produced the same synaptic action. This finding held even for L7, a cell known to have two types of ACh receptors. These data are consistent with the hypothesis that a postsynaptic cell does not segregate different types of ACh receptors. If generally true, this lack of segregation may help explain why a nervous system uses more than one neurotransmitter as well as why certain interneurons are needed in neural networks.

Acetylcholine↗
PubMed1979

Cellular studies of peripheral neurons in siphon skin of Aplysia californica.

1. To account for the similarity in the kinetics of habituation between the central and peripheral components of siphon withdrawal, we have tested the idea (52) that each centrally located mechanoreceptor sensory neuron sends two branches to siphon motor neurons; one to centrally located siphon motor neurons and a collateral branch that remains in the periphery and innervates the peripheral siphon motor neurons. 2. We have found a group of peripheral siphon motor neurons and tested the connection onto these cells by central mechanoreceptors. In addition, we have defined by various electrophysiological and morphological criteria two general classes of peripheral neurons that lie along the course of the siphon nerve. 3. One class (type I) consists of only a single cell in each animal. This peripheral neuron typically has the largest cell body found lying along the siphon nerve and is the only peripheral nerve cell that appears white when viewed under epi-illumination. The type I neuron often has a highly regular firing pattern, which occurs in the absence of spontaneous synaptic input. The three-dimensional morphology of this neuron suggests a paucity of fine processes, most of which do not arborize and may terminate in the connective tissue sheath. Fine structural observations of the peripheral white cell have revealed the presence of large densecore granules. The peripheral type I neuron is similar in most of its electrophysiological and morphological properties to central neurons postulated to be neurosecretory. The peripheral white cell is, at present, the only peripheral neuron we can identify with certainty as a unique individual. 4. The second class (type II) of peripheral neurons are siphon motor neurons for the peripheral component of the siphon-withdrawal reflex. In contrast to the type I neurons, members of the second class of peripheral neurons possess smaller, more spherical cell bodies that have varying amounts of orange pigmentation and which give rise to a relatively well-developed and arborized dendritic tree. Type II neurons feature an irregular spontaneous firing pattern that is occasionally modulated by a rich spontaneous synaptic input. Peripheral siphon motor neurons have restricted motor fields that produce contraction of the mantle floor and the base of the siphon. Most of the type II neurons were found to be electrically coupled to one another. 5. The peripheral siphon motor neurons resemble the central siphon motor neurons in that they receive a collateral synapse from centrally located mechanoreceptor sensory neurons. This peripheral sensory-to-motor synapse exhibits the same kinetics of decrement as its central counterpart, both of which parallel behavioral habituation. 6. The rich mechanoreceptor input onto the relatively isolated dendritic trees of the peripheral siphon motor neurons provide a uniquely restricted neuropil to study the sensory-to-motor synapse. The peripheral motor neurons may, therefore, be a useful simple preparation for the cellular study of behavioral plasticity.

Animals↗
PubMed1979

Aplysia ink release: central locus for selective sensitivity to long-duration stimuli.

1. A behavioral and electrophysiological analysis of defensive ink release in Aplysia californica was performed to examine the response of this behavior and its underlying neural circuit to various-duration noxious stimuli. 2. Three separate behavioral protocols were employed using electrical shocks to the head as noxious stimuli to elicit ink release. Ink release was found to be selectively responsive to longer duration stimuli, and to increase in a steeply graded fashion as duration is increased. 3. Intracellular stimulation of ink motor neurons revealed that ink release is a linear function of motor neuron spike train duration, indicating that the selective sensitivity of the behavior to long-duration stimuli is not due to a nonlinearity in the glandular secretory process. 4. In contrast, electrophysiological examination of ink motor neuron activity in response to sustained head shock revealed an accelerating spike train. During the later part of the spike train, compound excitatory synaptic potentials show a positive shift in reversal potential. 5. Our results suggest a central locus for the mechanisms that determine sensitivity of inking behavior to stimulus duration. 6. In contrast to ink release, defensive gill withdrawal was found to be extremely sensitive to short-duration stimuli.

Aggression↗
PubMed1979

Biophysical mechanisms contributing to inking behavior in Aplysia.

1. The release of ink from the ink gland of Aplysia californica in response to noxious stimuli is mediated by three electrically coupled motor neurons, L14A, L14B, L14C, whose cell bodies are located in the abdominal ganglion. The initial synaptic input to the ink motor neurons is relatively ineffective in firing the cells. As a result, a pause of 1--3 s often occurs before the cells attain their maximum firing frequency and cause the release of ink. Using current and voltage-clamp techniques we have analyzed the mechanisms underlying the firing pattern of these cells. 2. The presence of a fast transient K+ current appears to play an important role in mediating the firing pattern of the ink motor neurons. Their high resting potential (-75 mV) ensures that the steady-state level of inactivation of the conductance channels for the fast K+ current will normally be low. Thus a train of EPSPs or a depolarizing current pulse can activate this current maximally, thereby reducing the initial effectiveness of the excitatory input. 3. In addition to the fast transient K+ current, four other currents were identified: 1) a fast transient tetrodotoxin-sensitive inward current, presumed to be carried by Na+; 2) a slower tetrodotoxin-insensitive inward current, presumed to be carried by Ca2+; 3) a slow transient outward tetraethylammonium- (TEA) sensitive current; and 4) a very slow TEA-insensitive outward current. 4. A decreased conductance EPSP, which turns on over a several-second period, contributes to a late acceleration of spike discharge in the L14 cells. 5. The results suggest that a unique combination of biophysical properties of the L14 cells and the features of the synaptic input cause them to act as a low-pass filter in the reflex pathway for inking. Their high resting potential, which ensures minimal inactivation of the fast transient K+ current channel, makes these cells preferentially responsive to strong and long-lasting stimuli. The delayed recruitment of a decreased conductance EPSP augments the tendency of the L14 cells to fire in an accelerating burst pattern.

Aggression↗
PubMed1977

Further identification of neurons in the abdominal ganglion of Aplysia using behavioral criteria.

This review is an updating of the paper by Frazier et at. 13 in which 30 individual cells and 8 cell clusters were identified in the abdominal ganglion of of Aplysia californica on the basis of morphological, physiological and pharmacological criteria. Since that time, a number of neurobiological studies have utilized the neurons of the abdominal ganglion for behavioral studies. Based on these new investigations, 32 additional cells and 2 additional cell clusters have been identified, bringing the total of identified cells in the ganglion to 62 individual cells and 10 cell clusters. Additional features of the previously identified cells have also emerged. Much of the new information concerns the role of identified cells in behavior. We have summarized the current list of identified cells in the abdominal ganglion emphasizing these behavioral features. We also review the known synaptic connections made by identified interneurons in the ganglion. Included are descriptions of 6 new interneurons that connect to other cells in the ganglion. A major conclusion from this survey is that behavioral criteria permit resolution between cells in identified cell clusters that could previously not be distinguished using other criteria.

Abdomen↗
PubMed1975

Neural control of circulation in Aplysia. III. Neurotransmitters.

In the abdominal ganglion of Aplysia californica, seven motoneurons have been described which modulate the myogenic heart beat and vasomotor tone (28). These neurons mediate their motor effects by chemical transmission. In this paper we have attempted to specify the transmitters of six of these motoneurons. We have 1) studied the effects of several common transmitters on the innervated structures and compared these effects with the effects of firing the motoneurons, 2) examined whether blocking agents influence similarly the effect of a putative transmitter applied to the innervated structure and the effect of firing a motoneuron, and 3) tested the capability of the motoneurons to synthesize the putative transmitters from precursors. The positive inotropic and chronotropic effects of firing the excitor motoneuron RB(HE) were mimicked by perfusion of the heart with serotonin at a low concentration. Cinanserin blocked both the effects of motoneuron excitation and serotonin perfusion. RB(HE) was also shown to synthesize [3H]serotonin from L-[3H]tryptophan injected directly into the cell body. The effects of firing the two LD(HI) heart-inhibitory motoneurons were mimicked by perfusion of the heart with acetylcholine. Benzoquinonium blocked the effects of the inhibitory motoneuron and acetylcholine perfusion. Perfusion with arecoline also inhibited the heart beat. Acetylcholine applied to the arteries mimicked the vasoconstriction caused by the LB(VC) motoneurons. Aortic constriction in response to activity in LB(VC) cells or to acetylcholine was blocked by hexamethonium and curare. The heart inhibitor and vasoconstrictor motoneurons synthesized [3H] acetylcholine from [3H] choline injected into their cell bodies. Thus, as in vertebrates, acetylcholine mediates inhibition to the heart. Unlike vertebrates, however, serotonin mediates excitation to the heart and acetylcholine mediates peripheral vasoconstriction.

Acetylcholine↗