Biomedical subjects

E C Cropper

Publications and source records attributed to E C Cropper.

41 records · Page 3Linked to original sources

PubMed1987

Myomodulin: a bioactive neuropeptide present in an identified cholinergic buccal motor neuron of Aplysia.

When Aplysia are initially exposed to food stimuli, their biting responses show progressive increases in speed and strength. The accessory radula closer (ARC) buccal muscles have been used to study this phenomenon, and it has been shown that changes in ARC muscle contraction are partially due to activity of a serotonergic neuron that modulates this muscle, by both a direct action and an action on two ARC motor neurons (B15 and B16). The motor neurons use acetylcholine as their excitatory transmitter, but they also contain bioactive peptides that can potentiate muscle contractions when they are exogenously applied. Motor neuron B15 contains the structurally related small cardioactive peptides A and B, whereas motor neuron B16 contains a different peptide--termed myomodulin. In the present study we determined the full amino acid sequence of myomodulin. Myomodulin is present in the ARC muscle, and exogenous application of the peptide potentiates ARC muscle contractions in a manner similar to the potentiation by small cardioactive peptides A and B. The structure of myomodulin, however, bears little resemblance to the small cardioactive peptides. Thus it appears that ARC muscle contractions may be regulated by at least three distinct classes of neuromodulators: serotonin, the small cardioactive peptides, and myomodulin.

Amino Acids↗

PubMed1986

Localization of responses in the somatosensory thalamus of the rat.

In the monkey and cat electrophysiological studies have indicated that unit response characteristics can be correlated with anatomical divisions in the somatosensory thalamus. In the rat, however, one study has suggested that the ventrobasal (VB) and posterior (PO) complexes are not functionally distinct [7]. In the present study, therefore, an attempt was made to correlate anatomical localization and unit response characteristics in the rat. We found that in the VB complex, units responding to light touch (LT) were more common than in the PO complex (45% vs. 9%), while in the PO complex, nociceptive units were more numerous than in the VB complex (55% vs. 38%). In the VB complex LT units had a somatotopic organization; in the PO complex they did not. Within the VB complex all LT units in the ventral posteromedial nucleus had receptive fields on the head; most ventral posterolateral nucleus LT units had receptive fields on the body. These results indicate that a correlation between unit response characteristics and localization does exist in the rat.

Afferent Pathways↗

PubMed1984

An immunocytochemical study of the serotonergic innervation of the thalamus of the rat.

The serotonergic innervation of the rat thalamus was studied with an indirect immunocytochemical technique using an antiserum raised against a serotonin-hemocyanin conjugate in animals pretreated with L-tryptophan and a monoamine oxidase (MAO) inhibitor. When pretreatment was not used there was a decrease in the number of immunoreactive fibers observed in the thalamic region. Innervation was greatest in nucleus ventralis corporis geniculati lateralis, and in the following midline nuclei: nucleus periventricularis, nucleus rhomboideus, and nucleus reuniens. Also well labeled were nucleus anterior ventralis, the intralaminar nuclei, and nucleus lateralis dorsalis. Moderate innervation was found in nucleus reticularis, nucleus anterior dorsalis, nucleus ventralis medialis, nucleus lateralis pars posterior, the posterior complex, and in nucleus dorsalis corporis geniculati lateralis. Very few serotonergic fibers were observed in nucleus paratenialis, nucleus gelatinosus, nucleus anterior medialis, nucleus medialis dorsalis, nucleus ventralis, nucleus ventralis pars dorsomedialis, or in nucleus corporis geniculati medialis. Serotonin immunoreactivity was also noted in a number of fiber bundles in the thalamic region. These include the fasciculus retroflexus, the fasciculus mamillothalamicus, the stria medullaris, and the stria terminalis. These results differ from those of previous descriptions of the serotonergic innervation of thalamic nuclei most notably in the midline nuclei and in the posterior complex. In this study the midline nuclei, nucleus rhomboideus, and nucleus reuniens were more densely innervated than had been described, and in the posterior complex a moderate, rather than sparse, innervation was observed. The more densely innervated nuclei of the anterior and lateral nuclear groups, nucleus lateralis dorsalis and nucleus anterior ventralis, also contained a greater number of labeled fibers than had been indicated.

Animals↗

PubMed1984

5-HT-Immunoreactive fibers in the trigeminal nuclear complex of the rat.

The distribution of serotonin immunoreactive (5-HT-IR) fibers in the trigeminal nuclear complex of the rat was mapped. In the sensory nuclei, innervation appeared to be dense in areas primarily related to nociceptive afferent activity, and sparse in areas primarily related to nonnociceptive afferent activity. Specifically, the marginal and gelatinosa layers of the spinal subnucleus caudalis contained many 5-HT-IR fibers while few labeled fibers were seen in the magnocellular portion of subnucleus caudalis or in the principal sensory nucleus. The spinal subnuclei oralis and interpolaris were sparsely innervated except for a few areas which contained more 5-HT-IR fibers. The motor nucleus contained as many immunoreactive fibers as the subnucleus caudalis, although fibers in the motor nucleus were thicker and varicosities more irregularly spaced than in caudalis.

Animals↗

PubMedDate not supplied

Structure, bioactivity, and cellular localization of myomodulin B: a novel Aplysia peptide.

Important insights into mechanisms by which neuromuscular activity can be modulated have been gained by the study of experimentally advantageous preparations such as the ARC neuromuscular system of Aplysia. Previous studies have indicated that one source of modulatory input to the ARC muscle is its own two motor neurons, B15 and B16. Both of these neurons synthesize multiple peptide cotransmitters in addition to their primary neurotransmitter acetylcholine (ACh). Peptides present in the ARC motor neurons include SCPA, SCPB, buccalin A and B, and myomodulin A. We have now purified a novel neuropeptide, myomodulin B, which is structurally similar to myomodulin A. Myomodulin B is present in two identified Aplysia neurons that contain myomodulin A; the ARC motor neuron B16 and the abdominal neuron L10. Ratios of myomodulin A to myomodulin B are approximately 6:1 in both cells. Like myomodulin A, myomodulin B potentiates ARC neuromuscular activity; it acts postsynaptically, and increases the size and relaxation rate of muscle contractions elicited either by motor neuron stimulation or by direct application of ACh to the ARC. When myomodulin A is applied to the ARC in high doses (e.g., at about 10(-7) M), it decreases the size of motor neuron-elicited muscle contractions. This inhibitory effect is never seen with myomodulin B. Thus, despite the structural similarity between the two myomodulins, there exists what may be an important difference in their bioactivity.

Amino Acid Sequence↗