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K R Weiss

Publications and source records attributed to K R Weiss.

At least 91 records · Page 5Linked to original sources
PubMed1992

Distribution of buccalin-like immunoreactivity in the central nervous system and peripheral tissues of Aplysia californica.

The neuropeptide buccalin A was originally purified and sequenced from a nerve-muscle system used in feeding-related behaviors of Aplysia californica in which it has been proposed that it acts as a modulatory cotransmitter. The distribution of buccalin-like immunoreactivity in the central ganglia and in peripheral tissues of Aplysia californica was examined by whole mount immunohistochemical techniques. Immunoreactive material was located in specific cell bodies and clusters of neurons in each of the ganglia. Immunoreactive fibers were present in each of the connectives between ganglia, in tracts coursing through the ganglia, and in the majority of the peripheral nerves. Most fibers were smooth in contour, but some had regularly spaced swellings. Varicosities containing immunoreactive material were located on specific neuronal somata and on certain tissues associated with the feeding, circulatory, digestive, and reproductive systems. The specific and widespread distribution of buccalin-like immunoreactivity supports the hypothesis that members of the buccalin peptide family act as neuromodulators or neurotransmitters in a variety of central and peripheral circuits in Aplysia.

Animals↗
PubMed1992

Peptidergic co-transmission in Aplysia: functional implications for rhythmic behaviors.

Despite their ubiquitous presence in the central and peripheral nervous systems, the behavioral functions of peptide co-transmitters remain to be elucidated. The marine mollusc Aplysia, whose simple nervous system facilitates the study of the neural basis of behavior, was used to investigate the role of peptidergic co-transmission in feeding behavior. Several novel modulatory neuropeptides were purified, and localized to identified cholinergic motorneurons. Physiological and biochemical studies demonstrated that these peptides are released when the motorneurons fire at frequencies that occur during normal behavior, and that the peptides modify the relationship between muscle contraction amplitude and relaxation rate so as to maintain optimal motor output when the intensity and frequency of feeding behavior change.

Amino Acid Sequence↗
PubMed1992

Orientation of Aplysia californica to distant food sources.

The behavior of the marine mollusc Aplysia was examined under different experimental conditions designed to determine the food searching strategy of the animals. In a small, open field tank with still water, the animals took an average of 42 min to find a piece of seaweed, even though the stimulus was never located more than 30 cm away from the animal. Observations of the animals indicated that their search was not directed, without a clear tendency towards the food, and during the course of a search, they often crawled through most of the area of the tank. The search time, the distance travelled, and the strategy of the search of the animals was similar for different types of seaweed. If animals were aroused into activity by the presence of seaweed extract, the time for them to contact a piece of odorless glass fiber paper in the open field was not significantly different than that for a piece of seaweed. The probability at which the animals contacted the seaweed, as a function of the distance travelled, resembled the detection probability determined according to a theory of random search. We thus propose that the aroused animals move in a random pattern until they are very close to the food. This strategy can be advantageous in still water since chemicals do not provide distinct gradients that can serve as cues for chemotactic orientation from distances greater than a few centimeters from the source. In a Y-maze in still water, Aplysia did not perform above chance in selecting the arm that contained the seaweed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Localization of myomodulin-like immunoreactivity in the central nervous system and peripheral tissues of Aplysia californica.

The distribution of myomodulin-like peptides in the nervous system of Aplysia californica was examined by using immunocytochemical techniques. Neurons and cell clusters containing immunoreactive material were located in each of the major central ganglia. Myomodulin-like immunoreactivity was also present in fibers in each of the connectives between the ganglia and in peripheral nerves. Varicosities containing immunoreactive material were located on specific regions of peripheral tissues associated with the feeding, digestive, cardiovascular, and reproductive systems. Double-labeling experiments were used to demonstrate myomodulin-like immunoreactivity in two identified neurons, the motor neuron B16 in the buccal ganglion and the widely acting interneuron L10 in the abdominal ganglion. Structures in the eye and cerebral ganglion that may correspond to the optic circadian pacemaker system were also stained. The central and peripheral distribution of myomodulin-like immunoreactivity indicates that this family of neuropeptides is present in specific efferent, afferent, and interneuronal elements that participate in a diversity of neural circuits in Aplysia.

Amino Acid Sequence↗
PubMed1991

Activity of identified cerebral neuron correlates with food-induced arousal in Aplysia.

Firing of the cerebral-pedal regulator neuron, C-PR, evokes a constellation of responses which are characteristic of the food-induced arousal state that occurs following exposure of Aplysia to seaweed. To provide further evidence that C-PR plays a role in generating the food-induced arousal state, extracellular recordings from the cerebral-pedal connective, which contains the axon of C-PR, were obtained in freely moving animals. The C-PR spike in the connective recorded in vivo was then identified by comparing the wave form to the obtained by firing C-PR in an in vitro preparation. We report here that C-PR activity is evoked by food stimulation, and increased firing of the C-PR is closely correlated with appetitive head lifting, the first manifestation of the food arousal state.

Animals↗
PubMed1991

Egg laying hormone inhibits a neuron (C-PR) involved in multiple manifestations of food-induced arousal in Aplysia.

Egg laying behavior is known to suppress feeding in Aplysia, but both behaviors have common responses involving head movements and posture. Egg laying hormone (ELH) applied in vitro to the isolated nervous system of Aplysia reduces the spontaneous and the evoked activity of the C-PR, a neuron implicated in postural responses during feeding. The inhibitory effect of ELH on the C-PR appears to be mediated by interneurons primarily located in the pedal/pleural ganglia, which contain all the known direct follower cells of the C-PR. Our results do not support the idea that postural responses during feeding and egg laying are mediated by the activation of a common arousal element, the C-PR. In fact, the C-PR seems to be a specific element for the food-arousal state, and the inhibition of the C-PR by ELH may contribute to the suppression of appetitive feeding responses during egg laying.

Action Potentials↗
PubMed1991

R15 alpha 1 and R 15 alpha 2 peptides from Aplysia: comparison of bioactivity, distribution, and function of two peptides generated by alternative splicing.

The mRNA precursor encoded by the R15 gene is alternatively spliced in different neurons to form two related variants, R15-1 and R15-2 mRNA. One of the peptides encoded by the R15-2 mRNA, the R15 alpha 1 peptide, is expressed in the endogenously bursting neuron R15 and mediates some of its central and peripheral synaptic actions. In this study we found that the R15 alpha 2 peptide, which is encoded by the R15-1 mRNA, is synthesized in other neurons in the abdominal ganglion and is also bioactive. The R15 alpha 1 and R15 alpha 2 peptides were found to exert many similar actions on the cardiovascular, digestive, respiratory, and reproductive systems. However, the differences between many of the pharmacological effects of the R15 alpha 1 and R15 alpha 2 peptides indicate that alternative splicing in this system results in two functionally different peptides. Widespread immunoreactivity was found for an antibody directed against the R15 alpha 2 peptide, both in the central nervous system and the periphery. But because of the shared sequence with the R15 alpha 1 peptide, the antibody cross-reacts with the R15 alpha 1 peptide. To distinguish immunocytochemically between the two peptides, we also raised a second antibody that recognizes only the R15 alpha 1 peptide. This antibody labeled the cell body of only one neuron in the central nervous system, R15, although widespread immunoreactivity was found in axons and varicosities in the periphery.

Animals↗
PubMed1991

Identification and characterization of cerebral-to-buccal interneurons implicated in the control of motor programs associated with feeding in Aplysia.

We identified candidate neurons in the cerebral ganglion that regulate feeding responses mediated by the buccal ganglion. Backfilling the cerebral-buccal connectives revealed that each cerebral hemi-ganglion contains approximately 20 neurons that project axons to the buccal ganglion. Three M-cluster neurons (CBI-1, CBI-2, CBI-3) and one E-cluster neuron (CBI-4) were identified as cerebral-to-buccal interneurons (CBIs) based on position, morphology, synaptic connections, and ability to drive buccal motor programs (BMPs). CBI-1 responds to touch of the tentacles, lips, and buccal mass. It receives monosynaptic EPSPs from interganglionic, cerebral-to-buccal mechanoafferent (ICBM) neurons and monosynaptically excites buccal cells, some of which are also excited by the ICBMs. Tonic firing of CBI-1 usually evokes a single cycle of BMP activity. CBI-1 phase-shifts the rhythmic BMP driven by firing a dopaminergic neuron in the buccal ganglion. CBI-1 itself exhibits dopamine-like histofluorescence following formaldehyde-glutaraldehyde fixation. CBI-2 is excited by food stimuli applied to the lips. Constant-current intracellular stimulation of CBI-2 produces phasic firing of the cell that reliably evokes a rhythmic BMP that incorporates buccal and cerebral motor neurons, putative pattern-generating and pattern-initiating neurons, and neuromodulatory cells (metacerebral cells). CBI-4 also evokes a rhythmic BMP, but the details of its actions and synaptic effects differ from that of CBI-2. CBI-3 does not evoke a BMP, even though it is excited by food stimuli applied to the lips, and it makes monosynaptic connections (both excitatory and inhibitory) to many follower cells of the other CBIs. Firing of CBI-3 phase-delays the BMP driven by CBI-2. Since its activity is incorporated into BMPs and it provides direct inputs to elements of the feeding circuitry, it may play a role in pattern generation. The distinctive features of the CBIs suggest that the consummatory phase of feeding may be controlled by a population of interneurons that subserve different roles.

Animals↗
PubMed1991

Synaptic actions of identified peptidergic neuron R15 in Aplysia. I. Activation of respiratory pumping.

The purpose of the study described in this and the following two companion papers was to determine the synaptic actions of neuron R15, an endogenously bursting neurosecretory cell in Aplysia, as a step toward determining its physiological function. The results described in this paper demonstrate that activity in R15 increases the frequency of bursting in the R25/L25 network that triggers respiratory pumping. This excitatory modulatory effect appears to be mediated by R15 alpha 1 peptide. R15 activates both strong and weak modes of respiratory pumping. In contrast, the two R20 cells, which are thought to use the neuropeptides SCPA and SCPB as transmitters, elicit only strong episodes of respiratory pumping. The synaptic actions of R15 also differ from those of the R20 cells in being longer lasting and in exhibiting profound desensitization. Chronic recording of R15 activity in vivo indicates that it does not burst spontaneously in the intact animal, so the synaptic actions of R15 are not chronically desensitized. The neuroendocrine bag cells, which initiate egg laying, had been shown by others to excite R15 and the R25/L25 network that triggers respiratory pumping. Our data indicate that the excitatory effects of the bag cells on the R25/L25 cells are mediated in part by R15.

Animals↗
PubMed1991

Synaptic actions of identified peptidergic neuron R15 in Aplysia. II. Contraction of pleuroabdominal connectives mediated by motoneuron L7.

The purpose of this study was to determine the synaptic actions of the bursting peptidergic neuron R15 in Aplysia. R15 is known to be excited by the neuroendocrine bag cells, which trigger egg laying. In the two companion papers, we show that R15 mediates some of the effects of the bag cells on respiratory and reproductive organs. In this paper, we demonstrate that R15 excites L7, a multimodal motoneuron located in the abdominal ganglion. Although L7 excites several types of muscle fibers as well as neurons, the excitation of L7 by R15 is probably strong enough to cause contraction only of the sheath muscle of the pleuroabdominal connectives, which has an exceptionally low threshold for activation. The excitatory actions of R15 on L7, which desensitize profoundly, appear to be mediated by R15 alpha 1 peptide. The synaptic action of R15 on L7 and on the respiratory pumping system (Alevizos et al., 1991a) can be fully expressed only if R15 is first silenced for 2 hr by injection of hyperpolarizing current. A similar protocol for eliminating desensitization may prove to be generally useful for revealing the synaptic actions of other spontaneously active neurons that have rapidly desensitizing postsynaptic actions.

Animals↗
PubMed1991

Synaptic actions of identified peptidergic neuron R15 in Aplysia. III. Activation of the large hermaphroditic duct.

The purpose of the study described in this and the preceding two companion papers was to determine the synaptic actions of neuron R15, an endogenously bursting neurosecretory cell in Aplysia, as a step toward determining its physiological function. The results described in this paper demonstrate that activity in R15 activates anterograde peristaltic movements in the segment of the large hermaphroditic duct through which eggs move during egg-laying behavior. This action is mimicked by R15 alpha 1 peptide, a putative transmitter of R15. The neuroendocrine bag cells, which initiate egg laying when they fire in a population burst, have been shown by others to excite R15. Our data suggest that R15 mediates excitatory effects of the bag cells on the large hermaphroditic duct. Taken with the results of the two companion papers, these data support the hypothesis that R15 integrates various aspects of egg-laying behavior. The desensitization of R15's postsynaptic actions may complement the long-lasting refractoriness of the bag cells described by others, with both effects contributing to the episodic nature of egg laying.

Animals↗
PubMed1990

Differential firing patterns of the peptide-containing cholinergic motor neurons B15 and B16 during feeding behavior in Aplysia.

During egestive responses neuron B16 fires at 20 Hz, while neuron B15 is not active. During ingestive responses B16 fires for 0.5-1.0 s at 15-20 Hz, then B15 and B16 fire together, with B15 firing at 7.5-12 Hz. The duration of activity during ingestive responses depends on consumption of food: when food is not consumed, bursts are shorter (e.g. 2 vs 4 s). This study establishes a basis for investigating the role of peripheral neuromodulation under physiologically relevant conditions.

Acetylcholine↗
PubMed1990

Buccalin is present in the cholinergic motor neuron B16 of Aplysia and it depresses accessory radula closer muscle contractions evoked by stimulation of B16.

The accessory radula closer (ARC) buccal muscle motor neuron B16 is buccalin-immunoreactive and it synthesizes a peptide with chromatographic properties identical to those of buccalin. Terminal varicosities in the ARC muscle are buccalin-immunoreactive, and buccalin reduces muscle contractions evoked by stimulation of neuron B16, probably by a presynaptic action.

Animals↗
PubMed1990

An identified neuron (CPR) evokes neuronal responses reflecting food arousal in Aplysia.

Feeding behavior of Aplysia is associated with an arousal state characterized by a constellation of maintained behaviors and by a potentiation or depression of responses to specific stimuli. A neuron (the cerebral-pedal regulator or CPR) that has widespread actions on various systems connected with feeding has been identified. CPR excites neurons that modulate or drive (i) body posture, (ii) biting, and (iii) cardiovascular behaviors. CPR also inhibits neurons concerned with defensive responses. Food stimuli, which elicit food arousal in the animal, produce prolonged excitation of the CPR. The results suggest that the CPR may evoke a central motive state representing the neuronal correlate of feeding motivation.

Animals↗
PubMed1990

Multiple roles of a histaminergic afferent neuron in the feeding behavior of Aplysia.

The cellular and circuit properties of individual identified neurons in invertebrates can be readily studied; hence it is possible to determine how the complex properties of nerve cells function in the generation of behavior. Recent studies of the cellular basis of feeding behavior in the marine mollusc Aplysia have focused on a neuron, C2, that has a variety of complex properties that determine the behavioral functions of the neuron. C2 conveys mechanosensory information from the mouth of the animal. It receives a complex pattern of inputs during feeding behavior, and generates diverse outputs that may shape behavior. It can act to filter out slow or sporadic sensory inputs, and its own outputs can be 'gated' by synaptic input. C2 uses histamine as its transmitter, and some of its synaptic outputs are modulatory and contribute to the expression of an arousal state induced by food. Other outputs shape feeding behavior directly by affecting motor neurons, as well as presynaptically inhibiting the outputs of feeding motor programs. Thus, the complex properties of this neuron may contribute to the flexibility and adaptability of feeding in Aplysia. Studies of C2 have expanded our concepts of the properties of sensory neurons.

Action Potentials↗
PubMed1990

Protein synthesis during acquisition of long-term facilitation is needed for the persistent loss of regulatory subunits of the Aplysia cAMP-dependent protein kinase.

Depending on the number or the length of exposure, application of serotonin can produce either short-term or long-term presynaptic facilitation of Aplysia sensory-to-motor synapses. The cAMP-dependent protein kinase, a heterodimer of two regulatory and two catalytic subunits, has been shown to become stably activated only during long-term facilitation. Both acquisition of long-term facilitation and persistent activation of the kinase is blocked by anisomycin, an effective, reversible, and specific inhibitor of protein synthesis in Aplysia. We report here that 2-hr exposure of pleural sensory cells to serotonin lowers the concentration of regulatory subunits but does not change the concentration of catalytic subunits, as assayed 24 hr later; 5-min exposure to serotonin has no effect on either type of subunit. Increasing intracellular cAMP with a permeable analog of cAMP together with the phosphodiesterase inhibitor isobutyl methylxanthine also decreased regulatory subunits, suggesting that cAMP is the second messenger mediating serotonin action. Anisomycin blocked the loss of regulatory subunits only when applied with serotonin; application after the 2-hr treatment with serotonin had no effect. In the Aplysia accessory radula contractor muscle, prolonged exposure to serotonin or to the peptide transmitter small cardioactive peptide B, both of which produce large increases in intracellular cAMP, does not decrease regulatory subunits. This mechanism of regulating the cAMP-dependent protein kinase therefore may be specific to the nervous system. We conclude that during long-term facilitation, new protein is synthesized in response to the facilitatory stimulus, which changes the ratio of subunits of the cAMP-dependent protein kinase. This alteration in ratio could persistently activate the kinase and produce the persistent phosphorylation seen in long-term facilitated sensory cells.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Release of peptide cotransmitters from a cholinergic motor neuron under physiological conditions.

In previous studies, we demonstrated that B15, one of the two cholinergic motor neurons of the accessory radula closer muscle of Aplysia, synthesizes two peptides, small cardioactive peptides A and B (SCPA and SCPB), that, when exogenously applied, increase the size and relaxation rate of muscle contractions elicited by motor neuron stimulation. In the present experiments, we obtained evidence that the SCPs are released under physiological conditions. Specifically, we characterized firing patterns of motor neuron B15 during normal behavior, simulated them in vitro, and demonstrated that this type of neuronal activity produces decreases in SCP levels in neuronal processes and terminals. We also obtained evidence that suggests that enough SCP is released under physiological conditions to modulate neuromuscular activity in the accessory radula closer. We demonstrated that physiological activity of neuron B15 produces significant increases in muscle cAMP levels. Furthermore, increases in the size and relaxation rate of muscle contractions can be produced by changes in stimulation parameters that are also likely to maximize effects of released endogenous SCPA and SCPB.

Animals↗