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Biomedical subjects

K R Weiss

Publications and source records attributed to K R Weiss.

At least 127 records · Page 7Linked to original sources
PubMed1986

Activity of an identified histaminergic neuron, and its possible role in arousal of feeding behavior in semi-intact Aplysia.

The possible functions of histaminergic neuron C2 were studied in an isolated head preparation from which it was possible to obtain intracellular recordings while the buccal mass exhibited feeding-like responses. Application of food to the lips of the isolated head preparation elicited rhythmic buccal movements that appeared to be ingestion responses, since they moved seaweed into the buccal cavity and towards the esophagus, and their frequency and regularity was similar to the ingestion responses studied in a group of intact animals. The ingestion responses of the buccal mass consisted of 2 main phases of movement of the radula from a middle rest position: forward and return to rest, and backward and return to rest. The relative magnitudes and timing of these 2 phases were variable. Intracellular recordings from C2 in the isolated head revealed that C2 is silent when the buccal mass is quiescent, but that it can be excited into spike activity, either by mechanical stimulation of the perioral zone or by chemostimulation that results in rhythmic movement. C2 fires a burst of spikes in phase with each protraction-retraction cycle, and, if the movements continue, C2 fires even when the eliciting stimulus has been removed. Activity of the cell was usually preceded by fast depolarizing responses that appeared to be blocked axon spikes. The evidence suggests that C2 is part of a positive feedback loop that may help maintain the persistence of arousal of feeding behavior beyond the time that food stimuli are removed.

Animals↗
PubMed1986

Sensory function and gating of histaminergic neuron C2 in Aplysia.

This paper explores the possible sensory function of the identified histaminergic neuron C2. Mechanical stimulation of a narrow region around the mouth of the animal (perioral zone) elicits brief depolarizing potentials in C2. Extracellular recordings from the peripheral axons of C2 indicate that the depolarizing potentials are due to action potentials that are conveyed from the periphery but do not invade the cell body, since they fail at a region with a low safety factor within the cerebral ganglion. These blocked axonal spikes (A-spikes) function as if they were excitatory synaptic inputs to C2, since the synaptic output of C2 does not occur unless the A-spikes succeed in evoking full action potentials in the soma (or an electrically close initial segment) of C2. Furthermore, like synaptic potentials, the A-spikes exhibit temporal and spatial summation, and facilitation. C2 receives both tonic and phasic inhibitory synaptic potentials, which can decrease the summation of A-spikes and thereby alter the frequency-filtering properties of C2 or block its synaptic output. Thus, C2 appears to be an unusual proprioceptive afferent that has a high degree of integrative function and may provide critical gating that is dependent on a variety of external and internal conditions.

Animals↗
PubMed1986

An identified histaminergic neuron modulates feeding motor circuitry in Aplysia.

An identified histaminergic neuron, C2, in the marine mollusk Aplysia is a complex mechanoafferent which appears to contribute to the maintenance of food arousal by means of its synaptic connections to the metacerebral cell (MCC). Because C2 also has extensive synaptic outputs to neurons other than the MCC, we studied its possible motor functions. We identified several synaptic followers of C2 and found that some were excitatory motor neurons for extrinsic muscles of the buccal mass, while others were modulatory motor neurons that inhibited contractions. In addition, we found that these neurons and other synaptic followers of C2 received powerful inputs during feeding motor programs. In order to determine the functional significance of the synaptic outputs of C2, we studied extrinsic buccal muscles (E4 and E5) whose motor neuron (C6) is excited by C2. Extracellular recordings from these muscles indicated that they receive input during swallowing and rejection, but not during biting movements. Lesions of these muscles, or of all extrinsic muscles, did not prevent animals from feeding, but decreased feeding efficiency, that is, the amount of seaweed an animal could ingest with each swallow. The data suggest that C2 is an integrative proprioceptive cell that functions as a premotor neuron. The non-MCC synaptic outputs of C2 may reinforce the actions of the central feeding motor program. Specifically, C2 appears to aid the functioning of muscles that produce fine adjustments of the buccal mass and contribute to the efficiency of feeding behavior, rather than in producing gross movements.

Animals↗
PubMed1985

The small cardioactive peptides A and B of Aplysia are derived from a common precursor molecule.

We have identified cells in the central nervous system of the marine mollusc Aplysia that react with antibody raised against the small cardioactive peptide B (SCPB). Antisera to this neuropeptide stained a subset of central neurons that include the large identified buccal neurons, B1 and B2. The distribution of SCP-containing neurons was used in a strategy to isolate a cDNA clone encoding the precursor protein for the peptide. RNA from neurons B1 and B2 and from cells that did not stain with SCPB antisera was used to direct the synthesis of radiolabeled cDNA probes. A cDNA clone complimentary to mRNA specifically expressed in the B1 and B2 cells was isolated by differentially screening a buccal cDNA library with these probes. The cloned cDNA segment is 1394 nucleotides in length and contains a 408-base-pair open reading frame. The predicted precursor protein is composed of 136 amino acids and has a characteristic hydrophobic leader sequence. The sizes of the precursor protein with and without this leader sequence agree with in vivo and in vitro labeling studies. The amino acid sequences for SCPB and a related peptide, SCPA, are present and are flanked by known proteolytic processing sites.

Amino Acid Sequence↗
PubMed1985

Biochemical and immunocytological localization of molluscan small cardioactive peptides in the nervous system of Aplysia californica.

High pressure liquid chromatography (HPLC) followed by bioassay on isolated snail hearts were used to locate two related peptides, termed small cardioactive peptides A and B (SCPA and SCPB) in each of the central ganglia of Aplysia. The peptides are most concentrated in the buccal ganglia, the ganglia involved in the control of feeding movements. Immunocytology with antisera raised to conjugated SCPB stained three groups of neurons in the buccal ganglia. One group consisted of relatively small neurons that were tightly clustered. The second group was comprised of larger neurons that were more scattered. The third group was made up of several neurons including the two largest in the ganglia, identified cells B1 and B2. B1 and B2 and other neurons in this group innervate the gut by way of the esophageal nerve. HPLC-bioassay of single, individually dissected B1 or B2 neurons demonstrated that the two peptides are present in a single cell. For B2, but not B1, choline injected into the cell body was converted to the conventional transmitter, acetylcholine. This indicates that, in addition to the two peptides, B2 also contains choline acetyltransferase, and raises the possibility that acetylcholine and the SCPs may act as co-transmitters in B2. Strong immunocytological staining of fibers and varicosities was observed in the neuropilar region of the cerebral, pleural, pedal, and abdominal ganglia. In addition to the buccal ganglia, immunoreactive neurons were observed in all of the other central ganglia. The high concentration of the SCPs and the relatively large number of immunoreactive neurons in the buccal ganglion suggest a particularly important role of these peptides specifically in feeding behavior. However, the widespread occurrence of the SCPs in fibers and neuronal cell bodies throughout the nervous system suggests that these peptides also may have additional behavioral functions in Aplysia.

Aplysia↗
PubMed1984

Internal stimuli enhance feeding behavior in the mollusc Aplysia.

The hypothesis that subsatiating levels of internal food stimuli can arouse and potentiate feeding behavior was examined in the mollusc Aplysia californica. Animals were fed a small quantity of seaweed and their latencies to show biting responses were determined after food arousal was permitted to partially decay. Control animals were stimulated with food, but were not permitted to ingest it, or were fed nonnutritive glass-fiber filter paper. Compared to controls, animals that were fed showed significantly shorter latencies to respond when tested up to 80 min after previous exposure to food. These results indicate that internal stimuli can function like external stimuli to enhance responsiveness to food and suggest the hypothesis that satiation may be viewed as an interactive process involving the interplay of excitatory and inhibitory influences arising from the alimentary system.

Animals↗
PubMed1984

Evidence for parallel actions of a molluscan neuropeptide and serotonin in mediating arousal in Aplysia.

The neuropeptide designated SCPB (small cardioactive peptide B), the sequence of which has recently been determined, was found in the accessory radula closer muscle, a muscle involved in biting movements. The ganglia and nerves that innervate the accessory radula closer muscle also contain SCPB. At nanomolar concentrations, it enhances the contractions of the muscle. The effect of SCPB on the muscle resembles the effect of an identified serotonergic neuron that previously was shown to mediate behavioral effects that reflect a food arousal state in Aplysia. Like serotonin, SCPB enhances contractions by a postsynaptic action, which appears to involve an increase in cAMP levels in the muscle. Our findings suggest that parallel peptidergic and serotonergic pathways may mediate similar aspects of arousal in Aplysia.

Animals↗
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

Lesion of a serotonergic modulatory neuron in Aplysia produces a specific defect in feeding behavior.

The serotonergic metacerebral cells (MCCs) of Aplysia were destroyed by intracellular injection of proteolytic enzyme. MCC-lesioned animals showed alterations of biting responses compared to MCC-sham and B-cell-lesioned control animals, as well as to their own preoperative behavior. The alterations of biting responses included a prolongation of the duration of radula protraction and a lengthening of interbite interval. No changes were observed in non-biting feeding responses and in behaviors unrelated to feeding.

Animals↗
PubMed1982

Activity of an identified serotonergic neuron in free moving Aplysia correlates with behavioral arousal.

Extracellular recordings of the metacerebral cell (MCC), a serotonergic neuron in Aplysia, were obtained in free moving, undrugged animals. MCC activity was evoked by exposure to food. Arousal level was manipulated by satiating the animals or exposing them to a noxious stimulus. We found that the amount of evoked MCC activity correlated with the level of arousal of the animal.

Animals↗
PubMed1982

Ultrastructure of a histaminergic synapses in Aplysia.

The ultrastructure of histaminergic synaptic terminals was studied by the means of intrasomatic injection of horseradish peroxidase into the identified histaminergic neuron C2 of Aplysia. The axonal tree of C2 was found to consist, in part, of varicosities that display putative release sites similar in morphology to those described in other neurons in Aplysia. The varicosities contain at least two populations of vesicles: a conspicuous class of of large vesicles with an electron-dense core that almost fills the entire vesicle and a heterogeneous class of large and small electron-lucent vesicles. The small lucent vesicles preferentially cluster near active zones.

Animals↗
PubMed1982

Intraneuronal injection of horseradish peroxidase labels glial cells associated with the axons of the giant metacerebral neuron of Aplysia.

After injecting the cell body of the giant serotonergic neuron (GCN) in the cerebral ganglion of Aplysia with horseradish peroxidase (HRP), we found that some glial cells were labeled along the cerebrobuccal connective and posterior lip nerve, the two nerves that contain the major axon branches of the injected neuron. Starting at a distance of about 3 mm from the site of the injection, only glial cells in the nerve that are close to an axon branch of the GCN contained HRP. Labeling appears to be selective because, at most, only one out of three glial cells was labeled within an area of 20 micrometer of the axon. Moreover, no HRP was detected in any of the many glial cells within the cerebral ganglion. Reaction product diffusely labeled the cytoplasm of glial cell bodies and processes after intraneuronal injection of HRP. This distribution was markedly different from that observed in glial cells after the uptake of HRP from the extracellular space; HRP, presumed to be taken up by endocytosis, was found to be localized to vesicles, tubules, and multivesicular bodies.

Animals↗
PubMed1979

Response properties and synaptic connections of mechanoafferent neurons in cerebral ganglion of Aplysia.

1. The cells of two clusters of small neurons on the ventrocaudal surface of each hemicerebral ganglion of Aplysia were found to exhibit action potentials following tactile stimuli applied to the skin of the head. These neurons appear to be mechanosensory afferents since they possess axons in the nerves innervating the skin and tactile stimulation evokes spikes with no prepotentials, even when the cell bodies are sufficiently hyperpolarized to block some spikes. The mechanosensory afferents may be primary afferents since the sensory response persists after chemical synaptic transmission is blocked by bathing the ganglion and peripheral structures in seawater with a high-Mg2+ and low-Ca2+ content. 2. The mechanosensory afferents are normally silent and are insensitive to photic, thermal, and chemical stimuli. A punctate tactile stimulus applied to a circumscribed region of skin can evoke a burst of spikes. If the stimulus is maintained at a constant forces, the mechanosensory response slowly adapts over a period of seconds. Repeated brief stimuli have little or no effect on spike frequency within a burst. 3. Approximately 81% of the mechanoafferent neurons have a single ipsilateral receptive field. The fields are located on the lips, the anterior tentacles, the dorsal portion of the head, the neck, or the perioral zone. Because many cells have collateral axons in the cerebral connectives, receptive fields elsewhere on the body are a possibility. The highest receptive-field density was associated with the lips. Within each area, receptive fields vary in size and shape. Adjacent fields overlap and larger fields frequently encompass several smaller ones. The features of some fields appear invariant from one animal to the next. A loose form of topographic organization of the mechanoafferent cells was observed. For example, cells located in the medial cluster have lip receptive fields, and most cells in the posterolateral portion of the lateral clusters have tentacle receptive fields. 4. Intracellular stimulation of individual mechanoafferents evokes short and constant-latency EPSPs in putative motor neurons comprising the identified B-cell clusters of the cerebral ganglion. On the basis of several criteria, these EPSPs appear to be several criteria, these EPSPs appear to be chemically mediated and are monosynaptic. 5. Repetitive intracellular stimulation of individual mechanoafferent neurons at low rates results in a gradual decrement in the amplitude of the EPSPs evoked in B cluster neurons. EPSP amplitude can be restored following brief periods of rest, but subsequent stimulation leads to further diminution of the response. 6. A decremented response cannot be restored by strong mechanical stimulation outside the receptive field of the mechanoafferent or by electrical stimulation of the cerebral nerves or connectives...

Animals↗
PubMed1979

Functional role of serotonergic neuromodulation in Aplysia.

The serotonergic metacerebral cell (MCC) of the mollusk Aplysia produces slow synaptic potentials in motor neurons of the buccal muscle, and increases the rate of ongoing rhythmic burst output of the buccal ganglion. In addition, the MCC acts peripherally to enhance the strength of buccal muscle contractions that are produced by firing of motor neurons. The potentiation of contraction is not associated with any detectable changes of resting membrane potential of muscle cells. Although MCC activity produces a small enhancement of excitatory junctional potentials, several experiments clearly indicate that the MCC has a direct potentiating effect on excitation-contraction coupling. The data suggest that potentiation of contraction might be mediated by cAMP. For example, activity of the MCC enchances the rate of accumulation of cAMP in buccal muscle, application of phosphodiesterase resistant analogs of cAMP potentiates muscle contraction, and a phosphodiesterase inhibitor enhances the effect of MCC stimulation. Recordings from free-moving animals indicate that the MCC becomes activated by exposure of the animal to food stimuli, and that the activation parallels the presence of a food-arousal state. Food-arousal is characterized by enhanced strength and increased frequency of biting responses. Both these effects can result from activity of the MCC. Thus, in this system, modulatory synaptic actions function to provide the substrate for a type behavioral modulation.

Animals↗