Effects of kainic acid in the parabrachial region for ongoing respiratory activity and reflexive respiratory suppression.
We previously reported that the electrical stimulation of gastrocnemius muscle nerve afferents given at a suprathreshold intensity for C-fiber afferents induces naloxone-reversible reflexive respiratory suppression ('after suppression'). The effects of kainic acid (KA) microinjections into the parabrachial area (nucleus parabrachialis lateralis: NPBL and nucleus parabrachialis medialis: NPBM) on (1) ongoing respiratory activity and (2) the 'after suppression' were studied in chloralose-urethane anesthetized, bivagotomized, paralyzed, and artificially ventilated cats. A large dose of KA (1.91 nmol in 0.1 microliters) microinjected into the unilateral NPBL induced significant long-lasting respiratory facilitation, while a subsequent KA injection into the ipsilateral NPBM induced significant, long-lasting respiratory depression. A small dose of KA (0.48 nmol in 0.1 microliters) into the unilateral NPBL (right side) induced significant respiratory facilitation, and the 'after suppression' effect was eliminated. A small dose into the unilateral NPBM (right side) caused initial transient respiratory facilitation followed by respiratory depression before 'after suppression' was restored. Subsequent KA injections into the NPBL on the other side (left side) significantly augmented respiration. The 'after suppression' effect was again eliminated after an injection of KA into the bilateral NPBL. It was concluded that NPBL may exhibit tonic inhibitory activities on respiration and play a critical role in the 'after suppression' effect, since an injection of KA into the NPBM counteracted both of these effects in the NPBL.
Hirano
T
T
Department of Neural Regulation, Nagoya University, Japan.
Simbulan
D
D
Kumazawa
T
T
D000818:Animals; D001049:Apnea / Q000188:drug therapy; D002245:Carbon Dioxide / Q000494:pharmacology; D002415:Cats; D004558:Electric Stimulation; D007608:Kainic Acid / Q000494:pharmacology*; D008845:Microinjections; D009270:Naloxone / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects; D010791:Phrenic Nerve / Q000187:drug effects; D011149:Pons / Q000187:drug effects*; D012137:Respiratory System / Q000187:drug effects*
D002245:Carbon Dioxide; D009270:Naloxone; D007608:Kainic Acid