Physiological responses of three marine microalgae exposed to cypermethrin.

The effects of cypermethrin on physiological responses of three typical marine microalgal species Skeletonema costatum (Bacillariophyceae), Scrippsiella trochoidea (Dinophyceae), and Chattonella marina (Raphidophyceae), were investigated by 96-h growth tests in a batch-culture system. The 96-h median inhibition concentrations (IC(50)) were 71.4, 205, and 191 µg L(-1) for S. costatum, S. trochoidea, and C. marina, respectively. Quick and significant physiological responses occurred when algal cells were exposed to cypermethrin, and all biochemical parameters varied significantly within 6- or 12-h exposure. Cypermethrin affected algal growth, protein content, and superoxide dismutase (SOD) activity by stimulation at low concentrations (1, 5 µg L(-1)) and inhibition at high concentrations (>50 µg L(-1)). A general increase in malondialdehyde (MDA) level was observed in all test groups, which suggested that the toxic effects of cypermethrin were probably exerted through free radical generation. These results suggest that the activation of SOD and promotion of protein at early exposure are important to counteract the oxidative stress induced by cypermethrin, and the inactivation of SOD may be crucial to the growth inhibition of microalgae by cypermethrin.

Toxicological effects of cypermethrin to marine phytoplankton in a co-culture system under laboratory conditions.

The growth of three marine phytoplankton species Skeletonema costatum, Scrippsiella trochoidea and Chattonella marina and the response of the antioxidant defense system have been investigated on exposure to commercial cypermethrin for 96 h and 32 days in a co-culture system. Growth of the three species was generally comparable over 96 h with an inoculation of 1:3:6.5 (C. marina:S. trochoidea:S. costatum), with stimulation at 5 µg l(-1) and inhibition under higher concentrations (50, 100 µg l(-1)). However, when inoculating at ratios of 1:1:1 during a 32 day test, S. costatum became the most sensitive species and was significantly inhibited in all test groups under the dual stresses of cypermethrin and interspecies competition. The growth of C. marina was significantly inhibited at the concentrations higher than 5 µg l(-1), while the growth of S. trochoidea was significantly promoted at low concentrations. Superoxide dismutase (SOD) activities significantly increased during 6-12 h exposure periods in test treatments at low concentrations, and enhanced in the control as well due to interspecies competition. The lipid peroxidation product malondialdehyde was enhanced at high concentrations, but did not increase in control and low concentration cultures with high SOD activities, indicating that algal cells activated the antioxidant enzymes promptly to protect the cells from lipid membrane damage. Results from this study suggested that cypermethrin pollution in maricultural sea waters might lead to a shift in phytoplankton community structure from diatom to harmful dinoflagellate species, and thus potentially stimulatory for harmful algal blooms.

The growth behavior of three marine phytoplankton species in the presence of commercial cypermethrin.

Toxicity of commercial cypermethrin on the growth of three marine microalgal species, Skeletonema costatum (Bacillariophyceae), Scrippsiella trochoidea (Dinophyceae) and Chattonella marina (Raphidophyceae) was separately investigated by 96 h and 24 d growth tests. The growth was stimulated at low concentrations and inhibited under high concentrations; however, overcompensation was observed at the late period of exposure under high concentrations in 24 d growth tests. The highest stimulation rates were obtained at concentration of 5 microg/L. The 24 h SC10 values were 0.91, 4.17 and 20.4 microg/L for S. costatum, S. trochoidea and C. marina, respectively. The 96 h IC50 values were 75.3, 227 and 114 microg/L for the three species, respectively. Results suggest that cypermethrin level used for sea lice controlling exert a stimulative effect on phytoplankton growth, and might result in the succession of phytoplankton community structure due to different sensitivity of species.

[Phentolamine antagonizes the effects of norepinephrine on the activity of pain-related neurons in the parafascicular nucleus of morphine-dependent rats].

OBJECTIVE: To examine the antagonization of phentolamine against the effects of norepinephrine (NE) on the activity of pain-related neurons in the parafascicular nucleus of morphine-dependent rats. METHODS: Electric impulses were applied as nociceptive stimulus to the right sciatic nerve of morphine-dependent rats, and the discharges of the pain-related neurons in the parafascicular nucleus were recorded by extracellular recording method with glass microelectrodes. RESULTS: Intracerebroventricular injection of norepinephrine resulted in the inhibition of evoked response of the pain-excited neurons as well as the excitation of evoked response of the pain-inhibiting neurons. Both the inhibitory effect on the electric discharges of the pain-excited neurons and the excitatory effect on the pain-inhibiting neurons of norepinephrine were almost completely blocked by intracerebroventricular administration of phentolamine. CONCLUSION: Phentolamine antagonizes the inhibitory effect of norepinephrine on the activity of pain-related neurons in the parafascicular nucleus in morphine-dependent rats, and norepinephrine may play an important role in the integration of the pain signal through the alpha-receptors.