As low-dose amphetamine stimulation of locomotor activity in the rat depends upon a mesolimbic dopaminergic substrate, neuroleptic antagonism of this behavior has been suggested as a model for ...studying antipsychotic activity. Animals in the present study received 21 days of chronic treatment with 1.0 mg/kg amphetamine, 0.1 mg/kg haloperidol or a combination of these two drugs. On day 21, mesolimbic (but not striatal) dopamine (DA) concentrations were positively related to locomotor activity in an open field. DA metabolites in this region were inversely correlated with the behavior. The combined drug group showed saline-like levels of both behavioral activity and mesolimbic DA. Metabolic indices in this group suggested that increased DA availability partially competed with the neuroleptic receptor blockade in mesolimbic regions. In contrast to tolerance previously observed with cataleptic doses of neuroleptics, 21 days of 0.1 mg/kg haloperidol did not induce behavioral or biochemical tolerance. This finding is consistent with the lack of tolerance development to antipsychotic effects and suggests that animal models incorporating chronic low-dose neuroleptic regimens may be useful for the study of chronic treatment issues.
Fourteen adult Sprague-Dawley rats received daily 3 mg/kg naltrexone (Group One, n = 7) or saline (Group Two, n = 7) injections for 24 days. During this time they underwent forced choice testing with ...0.125 mg/ml methadone (the unconditioned stimulus, UCS) versus taste-balanced 0.04 mg/ml quinine placebo solutions. The handling, injection ritual, and taste cues served as a conditioned stimulus (CS)-complex. While Group Two (CS-UCS paired) animals showed pronounced pharmacological methadone aversions, those in Group One (CS pre-exposed rats in which the effects of methadone were blocked by the naltrexone) maintained a moderate intake of the opiate solution. When the injection conditions were reversed for 10 days, no change in percent methadone solution occurred for either group; thus, Group One displayed a latent inhibition effect after the CS pre-exposure, while Group Two maintained its previously acquired aversion. Testing after a 3-month drug free period, however, revealed the acquisition of a comparable methadone aversion by Group One (hence, recovery from the latent inhibition observed in the first reversal phase). Parallels with latent inhibition and retention in conditioned taste aversion studies were drawn, and further support for generality in the laws of learning, suggested.
Fifteen adult female rats were subjected to one of the following surgical procedures: (1) bilateral neocortical ablation; (2) unilateral neocortical ablation; or (3) sham surgery. Following recovery, ...all rats were tested on a fixed-time 1-min food schedule for acquisition of schedule-induced polydipsia. Contrary to a previous report by Bigler, Fleming and Shearer 1, no attenuation of polydipsia was seen in either group of rats with neocortical damage.
Establishing tropical sea surface temperature (SST) during the Last Glacial Maximum (LGM) is important for constraining equilibrium climate sensitivity to radiative forcing. Until now, there has been ...little data from the central equatorial Pacific in global compilations, with foraminiferal assemblage‐based estimates suggesting the region was within 1°C of modern temperatures during the LGM. This is in stark contrast to multi‐proxy evidence from the eastern and western Pacific and model simulations which support larger cooling. Here we present the first estimates of glacial SST in the central equatorial Pacific from Mg/Ca in Globigerinoides ruber. Our results show that the central Pacific cooled by about 2.0°C during the LGM, in contrast with previous global compilations but in agreement with models. Our data support a larger magnitude of tropical LGM cooling, and thus a larger equilibrium climate sensitivity, than previous studies which relied on foraminiferal assemblages in the central tropical Pacific.
Plain Language Summary
Reconstructing how tropical Pacific climate changed during periods of variable atmospheric CO2 levels may improve our understanding of how this region will respond to anthropogenic forcing. The Last Glacial Maximum, (LGM, 19–23,000 years before present), is the most recent time in earth history when atmospheric CO2 was significantly different than pre‐Industrial values. Proxy‐based reconstructions of LGM sea surface temperatures (SSTs) are often used as a point of comparison with output from climate models. These models indicate ∼2°C cooling in the central equatorial Pacific during the LGM, in contrast with earlier microfossil‐based estimates which suggest very little LGM cooling. Here, we use the chemistry of unicellular protists called foraminifera to estimate SSTs during the LGM in the central equatorial Pacific. Our data show that the central equatorial Pacific cooled by about 2°C during the LGM, in agreement with models and supporting the notion that this region may be more sensitive to CO2 change than previously suggested.
Key Points
We present the first Mg/Ca data from the glacial Central Equatorial Pacific, which confirms cooling in agreement with model output
A compilation of tropical Mg/Ca records indicates larger glacial cooling than previous proxy compilations
Together these data suggest that Equilibrium Climate Sensitivity estimates based on earlier global proxy compilations may be underestimated
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