Identification of central mechanisms vital for breathing in the channel catfish, Ictalurus punctatus.

Abstract

To investigate central respiratory control mechanisms in channel catfish, microinjections of kainic acid (causing chemical lesion of neurons) or kynurenic acid (an antagonist of N-methyl-D-aspartate (NMDA), kainate and alpha-amino-3-OH-5-methyl-4-isooxazole-propionic-acid (AMPA) receptors) were made into the general visceral nucleus (nGV) of the medulla in anaesthetised spontaneously breathing animals. Kainic acid abolished the ventilatory movements, indicating that neurons in the nGV are crucial for maintaining normal breathing. Kynurenic acid did not affect normal breathing, but abolished the ventilatory responses to hypoxia, showing that ionotropic glutamate receptors in the nGV are vital for the production of oxygen chemoreceptor activated respiratory reflexes. In addition, immunohistochemistry of brain slices showed that interneurons and nerve fibres in the nGV display NMDA-immunoreactivity, which corroborates the physiological experiments. The results of this study suggest that neurons and glutamatergic pathways in the nGV are essential for ventilatory functions and hypoxic reflexes in channel catfish.