The journal of physiological sciences : JPS
-
Gonadotropin-releasing hormone (GnRH) neurons represent the final output neurons in the central control of reproduction. gamma-Amino butyric acid (GABA), one of the major regulators of GnRH neurons, depolarizes GnRH neurons isolated from adult rats via GABA(A) receptors. The presence of GABA(A) receptors in GnRH neurons has also been demonstrated morphologically. Furthermore, the pineal hormone melatonin is involved in the regulation of reproductive function, including the timing of the luteinizing hormone surge. ⋯ These modulations were blocked by the melatonin receptor antagonist luzindole, suggesting an involvement of melatonin receptors. The modulation by melatonin was not observed in GnRH neurons isolated from infantile rats. These findings indicate that GABA affects the excitability of GnRH neurons in adult rats through GABA(A) receptors, and that melatonin modifies this excitability via melatonin receptors in a sex-specific manner.
-
We constructed a chassis that tightly fixes catheters for cannulation to the muscle. It can buffer pulling forces to avoid a mechanical tearing of the skin of mice as a result of movement. A simple hydraulic swivel was also made for blood pressure recording and drug infusion in freely moving mice.
-
Positive chronotropy induced by beta1-adrenergic stimulation is achieved by multiple interactions of ion channels and transporters in sinoatrial node pacemaker cells (SANs). To investigate the ionic mechanisms, we updated our SAN model developed in 2003 and incorporated the beta1-adrenergic signaling cascade developed by Kuzumoto et al. (2007). Since the slow component of the delayed rectifier K+ current (IKs) is one of the major targets of the beta1-adrenergic cascade, we developed a guinea pig model with a large IKs. ⋯ This was because the activation of IKs during the preceding action potential was negligibly small. However, IKs was important in counterbalancing the increase in ICaL and the Na+/Ca2+ exchange current (INaCa), which otherwise compromised the positive chronotropic effect by elongating the action potential duration. Enhanced Ca2+ release from the sarcoplasmic reticulum failed to induce an obvious chronotropic effect in our model.
-
Comparative Study
Forearm and calf tissue oxygenation in term neonates measured with near-infrared spectroscopy.
Peripheral tissue oxygenation has been studied with near-infrared spectroscopy (NIRS) on either the forearm or calf with questionable comparability. The aim was to compare forearm and calf tissue oxygenation in healthy term neonates measured with NIRS. Fractional oxygen extraction, tissue oxygenation index, and mixed venous oxygenation were similar in both extremities, whereas oxygen delivery and oxygen consumption of calf tissue were higher.
-
A head-down tilt posture, the Trendelenburg position, which could facilitate venous return from the splanchnic organs and lower extremities, is recommended for the treatment of anaphylactic shock. However, few data of animal studies support its effectiveness. We examined the effects of a head-down tilt maneuver on anaphylactic hypotension in BALB/c mice and Sprague-Dawley rats. ⋯ A head-down tilt maneuver in mice substantially attenuated the antigen-induced decrease in Sap throughout the 60 min measurements, though it aggravated slightly, but significantly, only at the late phase of after 25 min in rats. We conclude that a head-down tilt maneuver attenuates anaphylactic hypotension in anesthetized mice and rats. These beneficial effects were smaller in rats than in mice probably because of substantial portal hypertension, which might prevent the head-down tilt-induced increase in venous return from the splanchnic vascular bed.