Isolated adult turtle brainstems exhibit central hypoxic chemosensitivity.

During hypoxia, red-eared slider turtles increase ventilation and decrease episodic breathing, but whether these responses are due to central mechanisms is not known. To test this question, isolated adult turtle brainstems were exposed to 240 min of hypoxic solution (bath PO = 32.6 ± 1.

Hypoxia switches episodic breathing to singlet breathing in red-eared slider turtles (Trachemys scripta) via a tropisetron-sensitive mechanism.

Hypoxia-induced changes in the chelonian breathing pattern are poorly understood. Thus, breathing was measured in freely swimming adult red-eared slider turtles breathing air prior to breathing nitrogen for 4h. Ventilation increased 10-fold within 10min due to increased breath frequency and tidal volume.

Regulation of respiratory-related hypoglossal motor output by α₁ adrenergic and serotonin 5-HT₃ receptor activation in isolated adult turtle brainstems.

The effects of brainstem α(1) adrenergic receptor activation on respiratory control in reptiles are poorly understood. Isolated adult turtle brainstems were exposed to phenylephrine (α(1) adrenergic agonist) and respiratory motor bursts were recorded on hypoglossal nerves. Phenylephrine acutely increased burst frequency, amplitude (low concentrations only), and regularity of the time interval between the start of respiratory events (single or clustered bursts), and decreased bursts/respiratory event.

5-HT3 receptor-dependent modulation of respiratory burst frequency, regularity, and episodicity in isolated adult turtle brainstems.

To determine the role of central serotonin 5-HT(3) receptors in respiratory motor control, respiratory motor bursts were recorded from hypoglossal (XII) nerve rootlets on isolated adult turtle brainstems during bath-application of 5-HT(3) receptor agonists and antagonists. mCPBG and PBG (5-HT(3) receptor agonists) acutely increased XII burst frequency and regularity, and decreased bursts/episode. Tropisetron and MDL72222 (5-HT(3) antagonists) increased bursts/episode, suggesting endogenous 5-HT(3) receptor activation modulates burst timing in vitro.

Excitatory and inhibitory effects of opioid agonists on respiratory motor output produced by isolated brainstems from adult turtles (Trachemys).

To determine how central opioid receptor activation alters turtle breathing, respiratory-related hypoglossal (XII) motor bursts were recorded from isolated adult turtle brainstems during 60 min bath applications of agonists for delta- (DOR), kappa- (KOR), or nociceptin/orphanin (NOR) receptors. DADLE (DOR agonist) abolished XII burst frequency at 0.3-0.