Insolation-paced sea level and sediment flux during the early Pleistocene in Southeast Asia.

Global marine archives from the early Pleistocene indicate that glacial-interglacial cycles, and their corresponding sea-level cycles, have predominantly a periodicity of ~ 41 kyrs driven by Earth's obliquity. Here, we present a clastic shallow-marine record from the early Pleistocene in Southeast Asia (Cholan Formation, Taiwan). The studied strata comprise stacked cyclic successions deposited in offshore to nearshore environments in the paleo-Taiwan Strait. The stratigraphy was compared to both a δ18O isotope record of benthic foraminifera and orbital parameters driving insolation at the time of deposition. Analyses indicate a strong correlation between depositional cycles and Northern Hemisphere summer insolation, which is precession-dominated with an obliquity component. Our results represent geological evidence of precession-dominated sea-level fluctuations during the early Pleistocene, independent of a global ice-volume proxy. Preservation of this signal is possible due to the high-accommodation creation and high-sedimentation rate in the basin enhancing the completeness of the stratigraphic record.

The 20-million-year old lair of an ambush-predatory worm preserved in northeast Taiwan.

The feeding behavior of the giant ambush-predator "Bobbit worm" (Eunice aphroditois) is spectacular. They hide in their burrows until they explode upwards grabbing unsuspecting prey with a snap of their powerful jaws. The still living prey are then pulled into the sediment for consumption. Although predatory polychaetes have existed since the early Paleozoic, their bodies comprise mainly soft tissue, resulting in a very incomplete fossil record, and virtually nothing is known about their burrows and behavior beneath the seafloor. Here we use morphological, sedimentological, and geochemical data from Miocene strata in northeast Taiwan to erect a new ichnogenus, Pennichnus. This trace fossil consists of an up to 2 m long, 2-3 cm in diameter, L-shaped burrow with distinct feather-like structures around the upper shaft. A comparison of Pennichnus to biological analogs strongly suggests that this new ichnogenus is associated with ambush-predatory worms that lived about 20 million years ago.

Resiniferatoxin combined with antidepressants preferentially prolongs sensory/nociceptive block in rat sciatic nerve.

BACKGROUND: Current techniques of peripheral nerve block have major limitations, including lack of differentiation between motor and sensory fibers and potential toxicity of local anesthetics. Recent studies have suggested that a nociceptive-selective nerve block can be achieved via a transient receptor potential vanilloid type 1 activator (capsaicin) along with local anesthetics. We hypothesized that the combination of potent transient receptor potential vanilloid type 1 agonist resiniferatoxin (RTX) and selected antidepressants (amitriptyline, doxepin, and fluoxetine, also potent sodium channel blockers) would produce prolonged and predominantly sensory nerve block. METHODS: Rats were anesthetized with isoflurane, and 0.2 mL of amitriptyline, doxepin, or fluoxetine was deposited next to the surgically exposed sciatic nerves (n = 8 per group). Some animals received a second injection containing RTX (n = 8 per group). The effect of nerve block was assessed by neurobehavioral tests of the motor function (extensor postural thrust) and the nocifensive reaction (mechanical pinch). RESULTS: A single application of RTX produced nociceptive-selective sciatic nerve block, whereas antidepressants produced nociceptive and motor block. The combined administration of RTX and antidepressant resulted in a predominantly nociceptive nerve block. Compared with antidepressants or RTX alone, the combination prolonged the nociceptive nerve block more than the motor block. CONCLUSIONS: The combined application of RTX and antidepressants produced a markedly prolonged nociceptive peripheral nerve block in rat sciatic nerves compared with either agent alone. However, the 2-drug regimen also elicited prolonged blockade of the motor function, although disproportionately less compared with the nociceptive modality, suggesting the existence of nontransient receptor potential vanilloid type 1-mediated mechanisms. The mechanisms through which RTX affects nociceptive signal transduction/transmission have yet to be fully elucidated.

Calcium chloride prolongs the effects of lidocaine and bupivacaine in rat sciatic nerve.

BACKGROUND AND OBJECTIVES: Elevated extracellular calcium ion has been shown to shift the voltage dependence of Na+- and K+-ion channels rightward, making the nerve less excitable. We hypothesized that calcium chloride (CaCl2) when used as an adjuvant prolongs and intensifies the block by local anesthetics (LAs). We investigated the effects of LAs combined with calcium in rat sciatic nerve blockade and in cultured rat GH3 cells expressing Na+ channels. Furthermore, we tested for histologic changes due to CaCl2. METHODS: We anesthetized rats with sevoflurane, exposed the sciatic nerves, and injected 0.2 mL of 1% lidocaine or 0.1% bupivacaine, alone or coadministered with 0.625%, 1.25%, 2.5%, or 5% CaCl2 (n = 8-10 per group). We assessed the complete-block time and complete-recovery time of proprioception, motor function, and nocifensive reaction. To elucidate the mechanism of nerve block, we performed electrophysiology experiments in cultured rat GH3 cells. Sciatic nerves were harvested at day 7 and stained with hemotoxylin/eosin. RESULTS: The addition of CaCl2 overall prolonged the duration of blockade by lidocaine or bupivacaine. Adding 10 mM CaCl2 to 300 microM lidocaine caused a right shift of the steady-state Na+-channel inactivation curve, indicating that the CaCl2 reduced the potency of lidocaine. Rat sciatic nerves treated with 1% lidocaine coadministered with 5% CaCl2 showed microscopic signs of neurotoxicity. CONCLUSIONS: The mechanism of prolonged nerve block of CaCl2 coadministered with LAs seems to be a raised threshold for nerve excitation. Major histopathologic changes at higher concentrations of CaCl2 are evident, and therefore, clinical application as an adjuvant to LAs seems unlikely.

Chronic intrathecal infusion of minocycline prevents the development of spinal-nerve ligation-induced pain in rats.

BACKGROUND AND OBJECTIVES: Minocycline is a second-generation tetracycline with multiple biological effects, including inhibition of microglial activation. Recently, microglial activation has been implicated in the development of nerve injury-induced neuropathic pain. In this study, the authors examined the effects of continuous intrathecal minocycline on the development of neuropathic pain and microglial activation induced by L5/6 spinal-nerve ligation in rats. METHODS: Under isoflurane anesthesia, male Sprague-Dawley rats (200-250 g) received right L5/6 spinal-nerve ligation and intrathecal catheters connected to an infusion pump. Intrathecal saline or minocycline (2 and 6 microg/h) was given continuously after surgery for 7 days (n = 8 per group). The rat right hind paw withdrawal threshold to von Frey filament stimuli and withdrawal latency to radiant heat were determined before surgery and on days 1 to 7 after surgery. Spinal microglial activation was evaluated with OX-42 immunoreactivity on day 7 after surgery. RESULTS: Spinal-nerve ligation induced mechanical allodynia and thermal hyperalgesia on the affected hind paw of saline-treated rats. Intrathecal minocycline (2 and 6 microg/h) prevented the development of mechanical allodynia and thermal hyperalgesia induced by nerve ligation. It also inhibited nerve ligation-induced microglial activation, as evidenced by decreased OX-42 staining. No obvious histopathologic change was noted after intrathecal minocycline (6 microg/h) infusion. CONCLUSIONS: In this study, the authors demonstrate the preventive effect of continuous intrathecal minocycline on the development of nociceptive behaviors induced by L5/6 spinal-nerve ligation in rats. Further studies are required to examine if continuous intrathecal minocycline could be used safely in the clinical setting.