The effect of substantia nigra stimulation and morphine on α-motoneurones and the tail-flick response

Rats were used to study the effect of unilateral stimulation of the substantia nigra on the reflex discharge of α-motoneurones and on the reaction time of the tail-flick response. In preparations with prenigral decerebration, nigral stimulation facilitated monosynaptic α-reflex activity ehilst γ-reflex activity remained unchanged. The facilitation of monosynaptic α-reflex activity was reduced by naloxone (1 mg/kg); morphine (2 mg/kg) did not change the number of α-reflex discharges, but it reduced the α-reflex latency, enhanced the effect of nigral stimulation on the latency and abolished the effect of naloxone on nigral facilatation. Nigral stimulation prolonged the reaction time of the tail-flick response in rats with an intact brain and after prenigral decerebration. Naloxone did not influence the anti-nociceptive effect of nigral stimulation, whilst morphine enhanced it in rats with an intact brain. The anti-nociceptive effect exerted by morphine in animals with an intact brain was abolished by prenigral decerebration, and an additional spinalization restored it. Inactivating the nigral neurones by unilateral microinjections of procaine or GABA into the substantia nigra depressed the nociceptive reflex. It is concluded that (1) activation of nigral neurones influenced mono- and polysynaptic reflexes in a reciprocal fashion by a pathway descending via brain stem relays to the spinal cord, (2) inactivation of nigral neurones produced similar changes in reflex activity by altering the function of the nigro-striatal feedback system, the outlet from the system to the spinal cord not being the substantia nigra, (3) morphine influenced the nociceptive reflex by an action at different levels of the central nervous system.     

The detection of pollutant impact in marine environments: Condition index, oxidative DNA damage, and their associations with metal bioaccumulation in the Sydney rock oyster Saccostrea commercialis

Specimens of the Sydney rock oyster Saccostrea commercialis were deployed for a 3-month period at control and sewage disturbed marine locations in the Hunter Region, New South Wales, Australia. The DNA damage product, 8-hydroxyguanine, was measured by GC/MS-SIM from chromatin extracts of the gill tissues of oysters to assess oxidative damage. The levels ranged from 11.5 to 18.8 modified bases per 10⁷ guanine bases. Although the condition indices were significantly different between the Redhead control site (178.3±3.6) and the Burwood sewage disturbed location (140.4±4.4), no significant differences in 8-hydroxyguanine concentrations were detected between the sites, and the concentration of 8-hydroxyguanine was not correlated to condition index. However, levels of the DNA base modification were correlated with the concentrations of bioaccumulated lead (r=0.84, P=0.036). This association provides in vivo evidence that the bioaccumulation of lead results in oxidative damage to DNA. An additional control and sewage disturbed site were included to investigate the relationship between heavy metal bioaccumulation and the condition index of deployed oysters. After the 3-month deployment period, the condition index was negatively correlated to concentrations of bioaccumulated mercury (r=–0.80, P<0.001), cobalt (r=–0.65, P<0.01), and nickel (r=–0.69, P<0.01), suggesting a strong negative influence of these metals at relatively low concentrations on the physiological condition of the oysters.     

Testicular cancer in US Navy personnel

Age-adjusted and age-specific incidence rates of testicular cancer in US Navy personnel did not differ significantly from those of the US population, and age-adjusted incidence rates did not increase with length of service in the Navy. There was a group of three occupations, however, which involved duties similar to those of the civilian occupation of automobile mechanic, and which had a significantly elevated age-adjusted rate of testicular cancer compared with the US population and the total Navy population. These occupations were aviation support equipment technician, engineman, and construction mechanic. All involve maintenance of internal combustion engines and exposure to the attendant lubricants, solvents, paints, and exhausts.