RESUMO
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 240â¯min of hypoxic solution (bath PO2â¯=â¯32.6⯱â¯1.2â¯mmHg) and spontaneous respiratory-related motor bursts (respiratory event) were recorded on hypoglossal nerve roots. During hypoxia, burst frequency increased during the first 15â¯min, and then decreased during the remaining 35-240â¯min of hypoxia. Burst amplitude was maintained for 120â¯min, but then decreased during the last 120â¯min. The number of bursts/respiratory event decreased within 30â¯min and remained decreased. Pretreatment with either prazosin (α1-adrenergic antagonist) or MDL7222 (5-HT3 antagonist) blocked the hypoxia-induced short-term increase and the longer duration decrease in burst frequency. MDL7222, but not prazosin, blocked the hypoxia-induced decrease in bursts/respiratory event. Thus, during bath hypoxia, isolated turtle brainstems continued to produce respiratory motor output, but the frequency and pattern were altered in a manner that required endogenous α1-adrenergic and serotonin 5-HT3 receptor activation. This is the first example of isolated reptile brainstems exhibiting central hypoxic chemosensitivity similar to other vertebrate species.
Assuntos
Tronco Encefálico/fisiopatologia , Hipóxia/fisiopatologia , Tartarugas/fisiologia , Animais , Nervo Hipoglosso/fisiopatologia , Receptores Adrenérgicos alfa 1/metabolismo , Receptores 5-HT3 de Serotonina/metabolismo , RespiraçãoRESUMO
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. Breaths/episode decreased by â¼50% within after 1h of hypoxia while the number of singlet breaths increased from 3.1±1.6singlets/h to a maximum of 66.1±23.5singlets/h. Expiratory and inspiratory duration increased during hypoxia. For doublet and triplet breaths, expiratory duration increased during the first breath only, while inspiratory duration increased for all breaths. Tropisetron (5-HT3 receptor antagonist, 5mg/kg) administration prior to hypoxia attenuated the hypoxia-induced increase in singlet breath frequency. Along with results from previous in vitro studies, this study suggests that 5-HT3 receptor activation may be required for the hypoxia-induced increase in singlet breathing pattern in red-eared slider turtles.
Assuntos
Antiarrítmicos/farmacologia , Hipóxia/fisiopatologia , Indóis/farmacologia , Ventilação Pulmonar/fisiologia , Respiração/efeitos dos fármacos , Tartarugas/fisiologia , Animais , Relação Dose-Resposta a Droga , Feminino , Masculino , Nitrogênio/farmacologia , Ventilação Pulmonar/efeitos dos fármacos , Fatores de Tempo , TropizetronaRESUMO
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. Burst frequency and timing changes persisted during a 2.0 h washout. Acute increases in burst frequency and amplitude were blocked by prazosin (α(1) adrenergic antagonist). Pretreatment with prazosin and tropisetron (5-HT(3) antagonist) blocked the increase in respiratory event regularity, but did not alter the decrease in bursts/respiratory event. Intermittent phenylephrine application (4 × 5.0 min separated by 20 min) did not produce long-lasting changes in burst frequency and amplitude, bursts/respiratory event, or respiratory event regularity. Thus, sustained α(1) adrenergic receptor activation in turtle brainstems produces acute and long-lasting changes in respiratory burst frequency and pattern.
Assuntos
Tronco Encefálico/fisiologia , Nervo Hipoglosso/fisiologia , Sistema Respiratório/inervação , Tartarugas/fisiologia , Agonistas de Receptores Adrenérgicos alfa 1/farmacologia , Antagonistas de Receptores Adrenérgicos alfa 1/farmacologia , Animais , Tronco Encefálico/efeitos dos fármacos , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Nervo Hipoglosso/efeitos dos fármacos , Indóis/farmacologia , Fenilefrina/farmacologia , Prazosina/farmacologia , Respiração/efeitos dos fármacos , Sistema Respiratório/efeitos dos fármacos , Antagonistas da Serotonina/farmacologia , TropizetronaRESUMO
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. Tropisetron blocked all mCPBG effects, and the PBG-induced reduction in bursts/episode. Tropisetron application following mCPBG application did not reverse the long-lasting (2h) mCPBG-induced decrease in bursts/episode. We conclude that endogenous 5-HT(3) receptor activation regulates respiratory frequency, regularity, and episodicity in turtles and may induce a form of respiratory plasticity with the long-lasting changes in respiratory regularity.
Assuntos
Potenciais de Ação/fisiologia , Receptores 5-HT3 de Serotonina/fisiologia , Respiração , Centro Respiratório/fisiologia , Tartarugas/anatomia & histologia , Potenciais de Ação/efeitos dos fármacos , Vias Aferentes/fisiologia , Animais , Biguanidas/farmacologia , Relação Dose-Resposta a Droga , Nervo Hipoglosso/fisiologia , Técnicas In Vitro , Indóis/farmacologia , Estimulação Física/métodos , Respiração/efeitos dos fármacos , Centro Respiratório/citologia , Agonistas do Receptor 5-HT3 de Serotonina , Antagonistas do Receptor 5-HT3 de Serotonina , Serotoninérgicos/farmacologia , Fatores de Tempo , Tropanos/farmacologia , TropizetronaRESUMO
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 0.3-0.5 microM. DPDPE (DOR agonist) increased frequency by 40-44% at 0.01-0.1 microM and decreased frequency by 88+/-8% at 1.0 microM. U-50488 and U-59693 (KOR agonists) decreased frequency by 65-68% at 100 and 50 microM, respectively. Orphanin (NOR agonist) decreased frequency by 31-51% at 1.0-2.0 microM during the first 30 min period. Orphanin (0.5 and 2.0 microM) increased bursts/episode. Although morphine (10 microM) abolished frequency in nearly all brainstems, subsequent co-application of phenylephrine (alpha(1)-adrenergic agonist, 20-100 microM) with morphine restored activity to 16-78% of baseline frequency. Thus, DOR, KOR, and NOR activation regulates frequency and NOR activation regulates episodicity, while alpha(1)-adrenergic receptor activation reverses opioid-induced respiratory depression in turtles.