Evidence For Differences In Sensitivity Research Articles

Salinity and inundation effects on productivity of brackish tidal marsh plants in the San Francisco Bay-Delta Estuary

Plant productivity is central to numerous ecosystem functions in tidal wetlands. We examined how productivity of brackish marsh plants in northern California responded to abiotic stress gradients of inundation and salinity using two experimental approaches. In a greenhouse study with varying salinity, shoot production and biomass of Juncus balticus, Schoenoplectus acutus and S. americanus all declined monotonically with higher salinity, with evidence of differences in sensitivity among species by their varied functional responses. Salinity also negatively affected fecundity for the one species (S. americanus) that produced enough inflorescences during the experiment for analysis. In a field manipulation of inundation and initial pore water salinity, total end-of-season biomass and other metrics of growth in the high marsh species, J. balticus, had unimodal relationships with inundation. Root production tended to be greater strongly impacted by greater inundation than shoot production. The salinity treatment quickly dissipated for treatments that were flooded more frequently but persisted at a higher marsh elevation where it suppressed plant growth. These results suggest that both increased flooding and salinity associated with climate change and sea-level rise may negatively impact productivity of brackish marsh species, but with variable effects by species and stressor.

Effect of Menstrual Cycle Phase on Dopamine D2 Receptor Availability in Female Cynomolgus Monkeys

Sex differences have been reported in a variety of affective and neurodegenerative disorders that involve dysfunctional dopamine (DA) neurotransmission. In addition, there is evidence for differences in sensitivity to the abuse-related effects of psychostimulants across the menstrual cycle which may result from effects of ovarian hormones on DA function. The goal of the present study was to extend previous work examining menstrual cycle-related changes in DA D2 receptor availability in humans to drug-naive female cynomolgus monkeys (n=7) using the selective D2-like receptor ligand [(18)F]fluoroclebopride (FCP) and a high-resolution microPET P4 scanner. Menstrual cycle phase was characterized by daily vaginal swabs and measurements of serum progesterone levels. PET studies were conducted once during the luteal phase and once during the follicular phase. Regions of interest in the caudate nucleus, putamen, and cerebellum were defined on coregistered MRIs. Distribution volumes were calculated for FCP in each structure and the distribution volume ratio (DVR) for both brain regions relative to the cerebellum was used as a measure of D2 receptor availability. FCP DVRs were significantly higher in the luteal phase compared to the follicular phase in both the caudate nucleus (11.7% difference, p=0.02) and putamen (11.6% difference, p=0.03). These findings extend earlier work in humans and suggest that changes in DA receptor availability may be involved in the variation in symptoms of various neuropsychiatric disorders across the menstrual cycle, including differences in sensitivity to the abuse-related effects of stimulants.

Differential effects of Zn 2+ on the kinetics and cocaine inhibition of dopamine transport by the human and rat dopamine transporters

Zn 2+ may play a major role in the modulation of neurotransmission because it modulates membrane receptors and channels. Recent literature has shown Zn 2+ inhibits dopamine transport by the dopamine transporter (DAT), the main target of cocaine and some other drugs of abuse. Cocaine inhibits DAT and modulation of the DAT by Zn 2+ may alter effects of cocaine on dopamine neurotransmission. This study investigates how Zn 2+ changes DAT kinetics and its inhibition by cocaine. Steady-state and pre-steady-state kinetics of DAT activity were investigated using rotating disk electrode voltammetry. Values of K M and V max in hDAT and effects of cocaine match those in the literature. Zn 2+ allosterically inhibited transport in the human DAT (hDAT) with a K I = 7.9 ± 0.42 μM. Removal of endogenous Zn 2+ with penicillamine in hDAT increased transport values. In contrast, Zn 2+ did not alter transport by rat DAT (rDAT), with K M and V max values of 1.2 ± 0.49 μM and 15.7 ± 2.57 pmol/( s × 10 6 cells), respectively, and removal of Zn 2+ did not increase dopamine transport values. Zn 2+ allosterically reduced the inhibition by cocaine in hDAT. Results of pre-steady-state studies demonstrated that Zn 2+ increases the second order binding rate constant for dopamine to hDAT (3.5 fold to 19.2 × 10 6 M − 1 s − 1 for hDAT). In rat striatal homogenates Zn 2+ increased initial dopamine transport velocity and decreased cocaine inhibition providing evidence for differences in sensitivity to Zn 2+ between the three different preparations. Modulation of the DAT by Zn 2+ needs to be assessed further in development of cocaine antagonists.

Chlordiazepoxide normalizes behaviour and adrenal response abnormalities in septal rats in a dose and time dependent fashion

Rats lesioned in the septal nuclei display a dramatic syndrome characterized by hypoactivity in a novel environment, but exaggerated behavioural and corticosterone responses to environmental stimuli. These abnormal responses are normalized 2 hours following 15 mg/kg i.p. of chlordiazepoxide (Seggie, CCNP, 1980). The present study was undertaken to map the dose and time response characteristics of this effect and see if behaviour and corticosterone respond in parallel fashion. Chlordiazepoxide in doses of 7.5–30 mg/kg affected the hyperreactivity of septal rats is a ‘U’ shaped function without affecting the behaviour of non-lesioned rats. Corticosterone levels in non-lesioned rats were unaffected by chlordiazepoxide, while drug treated septal rats had corticosterone levels undistinguishable from non-lesioned control rats. The drug effects were transitory, maximal at 2 hours after injection, but absent as 48 hours after injection. General abnormalities of behaviour and corticosterone responsiveness were altered in parallel fashion by the drug, but some evidence of differences in sensitivity to the effect of the drug were noticed. Locomotion, was unaffected by the drug in lesioned and non-lesioned rats. The possibility of a GABA mechanism underlying the abnormalities of responsiveness, but not activity in septal rats is discussed.