title: Inositol hexakisphosphate excites rat medullary sympathoexcitatory neurons in vivo.
abstract: Inositol hexakisphosphate (IP6) was microinjected into the rostral ventrolateral reticular nucleus or iontophoresed onto reticulospinal sympathoexcitatory neurons of the nucleus in anesthetized rats. IP6 (5-500 pmol) induced a dose-dependent potent and prolonged elevation of arterial pressure which was mimicked by microinjection of ethyleneglycol-bis (beta-aminoethylether)N,N,N',N'-tetraacetic acid (EGTA), while myo-inositol was ineffective. Iontophoretic application of IP6 and EGTA excited the medullary sympathoexcitatory neurons but myo-inositol had no effect. The effect of IP6 on firing rate of the sympathoexcitatory neurons was abolished by co-administration of Ca2+ ions onto these neurons. The results indicate that IP6 acts extracellularly to excite the medullary sympathoexcitatory neurons. The excitatory actions of IP6 may depend, at least in part, on a calcium-chelating action. Chelation of extracellular Ca2+ might be a physiological action of IP6.
authors.affiliation: Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021.
authors.forename: M K
authors.initials: MK
authors.lastname: Sun
authors.forename: C
authors.initials: C
authors.lastname: Wahlestedt
authors.forename: D J
authors.initials: DJ
authors.lastname: Reis
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D007294:Inositol / Q000494:pharmacology; D007478:Iontophoresis; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D008845:Microinjections; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology; D010833:Phytic Acid / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013564:Sympathetic Nervous System / Q000166:cytology / Q000187:drug effects* / Q000502:physiology
chemical_list: D002614:Chelating Agents; D007294:Inositol; D004533:Egtazic Acid; D010833:Phytic Acid; D002122:Calcium Chloride; D002118:Calcium