Morphology of expiratory neurons of the Bötzinger complex: An HRP study in the cat

Abstract

In anesthetized and artificially ventilated cats, the physiological and morphological properties of expiratory neurons or their axons of the Bötzinger complex (BOT) were studied using intracellular recording and intracellular HRP labeling techniques. Thirteen expiratory neurons (nine cell somata and four axons) were successfully stained. Four of them were motoneurons, having relatively large cell somata in the retrofacial nucleus (RFN) and axons without any collaterals inside the brainstem. All the motoneurons showed a plateau shape of depolarization potentials during the expiratory phase. Any of the other nine expiratory neurons exhibited augmenting type firing or membrane potential changes during the expiratory phase. In five out of nine augmenting neurons, cell somata were stained and located ventral to the RFN. In four, only axons were stained. The majority of the augmenting neurons had two major axonal branches: one traveling toward the contralateral side and the other descending ipsilaterally in the brainstem. The most striking feature of the axonal trajectory was that all of the stained augmenting expiratory neurons, including the axons, had collateral branches with synaptic boutons in the BOT area, thus indicating that BOT expiratory neurons interact with some respiratory neurons in the BOT area and its vicinity.

Extensive monosynaptic inhibition of ventral respiratory group neurons by augmenting neurons in the Bötzinger complex in the cat

“…The presence of this potential was used, therefore, as a guide for further tracking (cf. Otake et al 1987). Only units which fired in expiration and showed an augmenting pattern of discharge i.e.…”

“…Antidromic mapping studies show that axons of Bot-Aug neurons often project to more than one region of the brainstem, including the DRG, caudal VRG and rostral pons, and to the spinal cord (Lipski and Merrill 1980;Fedorko and Lipski 1981;Bianchi and Barillot 1982;Fedorko and Merrill 1984;Bianchi et al 1988;Mateika and Duffin 1989). An intracellular labelling study by Otake et al (1987) demonstrated that most Bot-Aug neurons have two major axonal branches, one travelling to the contralateral side, and the other descending ipsilaterally.…”

Electrophysiological properties of rostral medullary respiratory neurones in the cat: an intracellular study.

“…One type corresponded to motoneurones of the retrofacial nucleus with either an augmenting or post-inspiratory pattern of activity (discharge or membrane potential) and not exclusively a 'plateau' as reported by Otake, Sasaki, Mannen & Ezure (1987). Another consists of expiratory interneurones with augmenting discharge patterns and located either ventromedial to the retrofacial nucleus or near the ventral surface of the medulla, (Grelot, Bianchi, Iscoe & Remmers, 1988).…”

Neuronal gagging activity patterns may be generated by neurons in the reticular area dorsomedial to the retrofacial nucleus in dogs

“…Each of these nonrespiratory neurons also exhibited the same firing pattern during expulsion. Recording sites of these neurons were distributed in the reticular area, which may correspond to the BÖT (Lipski and Merrill 1980;Fedorko and Merrill 1984;Otake et al 1987;Manabe and Ezure 1988;Miller and Nonaka 1990), and also in the medullar area, where isolation by partial cutting (Fukuda and Koga 1991), lesion by electrical coagulation, or destruction by kainic acid (Koga and Fukuda 1995) eliminates the retching and expulsion reflexes. Therefore, neuronal gagging activity patterns are thought to be produced in the BÖT.…”