alpha(2) Adrenergic receptors and the central control of breathing in the cane toad, Bufo marinus

The effect of adrenergic agents on the central control of breathing in the cane toad, Bufo marinus. was tested by applying adrenergic agents to the ve ntral medullary surface of decerebrate adult toads. Toads were unidirection ally ventilated while recording lung, buccal, and artery blood pressures (B PI), as well as heart rate (HR). Following a control period, filter paper p ledgets soaked in the appropriate solution (epinephrine - 0.023, 0.05, 0.10 , and 0.23 mM; norepinephrine - 0.002, 0.016, 0.032, and 0.16 mM; clonidine - 0.00375, 0.0375, and 0.375 mM: or yohimbine - 0.43) mM) were placed bila terally on the ventral medullary surface. Epinephrine significantly increas ed the number of breaths (26%), lung amplitude (9%). and episode duration ( 21%), but had no effect on BP or HR. The alpha (2)-agonist. clonidine, sign ificantly increased respiratory activity at moderate doses (0.0375 mM) and decreased activity at high doses (0.375 mM), however, it failed to elicit s ignificant changes in BP or HR. Pretreatment with the alpha (2)-adrenocepto r antagonist, yohimbine (0.43 mM), blocked the clonidine induced changes in respiratory activity. Yohimbine had no effect on cardiorespiratory paramet ers. Norepinephrine had no effect on either cardiovascular or respiratory v ariables. Thus, it appears that an alpha (2) adrenergic mechanism is involv ed in the central control of respiration in this lower vertebrate. (C) 2001 Elsevier Science B.V. All rights reserved.