Evidence for a Distributed Respiratory Rhythm Generating Network in the Goldfish (Carsssius auratus)

Abstract

Central pattern generators located in the brainstem regulate ventilatory behaviors in vertebrates. The development of the isolated brainstem preparation has allowed these neural networks to be characterized in a number of aquatic species. The aim of this study was to explore the architecture of the respiratory rhythm-generating site in the goldfish (Carassius auratus) and to determine the utility of a newly developed isolated brainstem preparation, the Sheep Dip. Here we provide evidence for a distributed organization of respiratory rhythm generating neurons along the rostrocaudal axis of the goldfish brainstem and outline the advantages of the Sheep Dip as a tool used to survey neural networks.

Control of Breathing in In Vitro Brain Stem Preparation from Goldfish (Carassius auratus; Linnaeus)

“…Consequently, the pontine area from which the VII nucleus originates also integrates sensory and motor information related to taste, swallowing, and feeding, thus making it possible that the motor output recorded from this nerve reflects nonrespiratory motor behaviors (Milsom et al 2004). While the mean bursting frequency calculated from all our experiments (32 ‫ע‬ 2 bursts min Ϫ1 ) is comparable with previous results obtained in vitro under similar experimental conditions (44.1 ‫ע‬ 7.5 bursts min Ϫ1 ; Duchcherer et al 2010), proper investigation with other approaches (e.g., semi-intact preparations) is necessary to ascertain that the bursting activity recorded is in fact respiratory related. Nevertheless, several lines of evidence give us confidence that this was the case.…”

“…The brain was irrigated with artificial cerebrospinal fluid (aCSF) at room temperature (20Њ-22ЊC) throughout and after the dissection procedure, which took place in the recording chamber. The composition of the aCSF consisted of (in mM) 120 NaCl, 3.5 KCl, 1.3 MgCl 2 , 11 D-glucose, 13 NaHCO 3 , 1.25 NaH 2 PO 4 , 2.0 CaCl 2 (Duchcherer et al 2010). Tissue Po 2 was not measured in this study.…”

“…However, evidence supporting the presence CO 2 /H ϩ -sensitive chemoreceptors in the CNS of fish is limited and controversial, even in air-breathing species (Wilson et al 2000;Milsom 2002Milsom , 2010Milsom et al 2002). A recent in vitro study on goldfish (Carassius auratus) isolated brain stems has found evidence of a distributed respiratory-generating network in fish (Duchcherer et al 2010), but the presence of chemosensitive structures in this neural network that would be able to modulate the respiratory rhythm in response to variations of the brain Po 2 and Pco 2 levels, as well as the mechanisms underlying respiratory rhythm generation, is still debated. To address this gap of knowledge, one of the goals of this study was to take advantage of the recently revived isolated brain stem from goldfish (Duchcherer et al 2010) to address this issue by testing the hypothesis that the goldfish possesses central chemoreceptors that modulate the frequency and amplitude of respiratory motor output in response to hypoxia or hypercapnia.…”

Diving into the mammalian swamp of respiratory rhythm generation with the bullfrog

“…In a recent study using the sheep dip preparation to investigate the rhythm generator responsible for gill ventilation in the teleosts Carssius auratus (a type of carp), we recorded the motor pattern of gill ventilation from the trigeminal nerve while progressively blocking synaptic activity from the caudal to rostral brainstem (Duchcherer et al, 2010). We found that the motor pattern gradually deteriorated as the functional region was reduced.…”

“…The en bloc preparation is amenable for use with a variety of techniques including intracellular recording using sharp microelectrodes, voltage-dependent optical recording of large populations of neurons on the ventral surface and functional transection studies with resolution of 10's of microns that are probably impossible to do in vivo (Duchcherer et al, 2010;Galante et al, 1996a;Oku et al, 2008;Wilson et al, 1999). This preparation generates a close facsimile of the motor pattern recorded in more intact preparations but it has a mildly hypercapnic and acidic core (Torgerson et al, 1997b).…”