Serotonergic and Peptidergic Modulation of the Buccal Mass Protractor Muscle (I2) in Aplysia

• Published in: Journal of neurophysiology 2000-12, Vol.84 (6), p.2810-2820
• Main Authors: Hurwitz, I, Cropper, E. C, Vilim, F. S, Alexeeva, V, Susswein, A. J, Kupfermann, I, Weiss, K. R
• Format: Article
• Language: English
• Subjects: Acetylcholine - metabolism; Acetylcholine - pharmacology; Animals; Aplysia; Dose-Response Relationship, Drug; Feeding Behavior - physiology; Ganglia, Invertebrate - physiology; Hexamethonium - pharmacology; Immunohistochemistry; In Vitro Techniques; Microelectrodes; Motor Neurons - cytology; Motor Neurons - drug effects; Motor Neurons - metabolism; Muscle Contraction - drug effects; Muscles - drug effects; Muscles - innervation; Muscles - physiology; Neuronal Plasticity - drug effects; Neuronal Plasticity - physiology; Neuropeptides - biosynthesis; Neuropeptides - metabolism; Neuropeptides - pharmacology; Neurotransmitter Agents - metabolism; Neurotransmitter Agents - pharmacology; Nicotinic Antagonists - pharmacology; Protein Isoforms - metabolism; Protein Isoforms - pharmacology; Serotonin - metabolism; Serotonin - pharmacology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2000.84.6.2810

  1 Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, New York 10029;   2 Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52 900, Israel; and   3 Center for Neurobiology and Behavior, College of Physicians and Surgeons, Columbia University, New York, New York 10032 Hurwitz, I., E. C. Cropper, F. S. Vilim, V. Alexeeva, A. J. Susswein, I. Kupfermann, and K. R. Weiss. Serotonergic and Peptidergic Modulation of the Buccal Mass Protractor Muscle (I2) in Aplysia . J. Neurophysiol. 84: 2810-2820, 2000. Plasticity of Aplysia feeding has largely been measured by noting changes in radula protraction. On the basis of previous work, it has been suggested that peripheral modulation may contribute to behavioral plasticity. However, peripheral plasticity has not been demonstrated in the neuromuscular systems that participate in radula protraction. Therefore in this study we investigated whether contractions of a major radula protraction muscle (I2) are subject to modulation. We demonstrate, first, that an increase in the firing frequency of the cholinergic I2 motoneurons will increase the amplitude of the resulting muscle contraction but will not modulate its relaxation rate. We show, second, that neuronal processes on the I2 muscle are immunoreactive to myomodulin (MM), RFamide, and serotonin (5-HT), but not to small cardioactive peptide (SCP) or buccalin. The I2 motoneurons B31, B32, B61, and B62 are not immunoreactive to RFamide, 5-HT, SCP, or buccalin. However, all four cells are MM immunoreactive and are capable of synthesizing MMa. Third, we show that the bioactivity of the different modulators is somewhat different; while the MMs (i.e., MMa and MMb) and 5-HT increase I2 muscle relaxation rate, and potentiate muscle contraction amplitude, MMa, at high concentrations, depresses muscle contractions. Fourth, our data suggest that cAMP at least partially mediates effects of modulators on contraction amplitude and relaxation rate.