27 research outputs found
Inhibition by nociceptin of the light-evoked release of ACh from retinal cholinergic neurones
The retina possesses cholinergic amacrine cells which release acetylcholine (ACh) in response to flickering light. Using an eye-cup preparation in anaesthetized rabbits we found that when the retina was exposed to nociceptin, the light-evoked release of ACh was reduced in a concentration-dependent manner (IC(50) = 100ânM), the maximum effect being 60% inhibition. Opioid receptors were not involved in the inhibitory effect of nociceptin because its action was not blocked by naloxone (1âÎŒM) and furthermore ÎŒ-opioids enhanced the light-evoked release of ACh. Using rabbit retina homogenates we found that the retina possessed a substantial number of high-affinity binding sites for [(3)H]-nociceptin indicating the presence of ORL(I)-receptors. Since [des-Phe(1)]-nociceptin, which has no affinity for the ORL(I)-receptor, had no effect on the light-evoked release of ACh it is unlikely that the action of nociceptin was simply non-specific. We conclude that the inhibitory effect of nociceptin on retinal ACh release involves activation of the ORL(I) receptors
Understanding phosphorus mobility and bioavailability in the hyporheic zone of a chalk stream
This paper investigates the changes in
bioavailable phosphorus (P) within the hyporheic
zone of a groundwater-dominated chalk stream. In
this study, tangential flow fractionation is used to
investigate P associations with different size fractions
in the hyporheic zone, groundwater and surface
water. P speciation is similar for the river and the
chalk aquifer beneath the hyporheic zone, with
âdissolvedâ P (<10 kDa) accounting for ~90% of
the P in the river and >90% in the deep groundwaters.
Within the hyporheic zone, the proportion of
âcolloidalâ (10 kDa) and âparticulateâ
(>0.45 ÎŒm) P is higher than in either the groundwater
or the surface water, accounting for ~30% of
total P. Our results suggest that zones of interaction
within the sand and gravel deposits directly beneath
and adjacent to river systems generate colloidal and
particulate forms of fulvic-like organic material and
regulate bioavailable forms of P, perhaps through coprecipitation
with CaCO3. While chalk aquifers
provide some degree of protection to surface water
ecosystems through physiochemical processes of P
removal, where flow is maintained by groundwater,
ecologically significant P concentrations (20â30 ÎŒg/L)
are still present in the groundwater and are an
important source of bioavailable P during baseflow
conditions. The nutrient storage capacity of the
hyporheic zone and the water residence times of this
dynamic system are largel