Biomedical subjects

A Scheff

Publications and source records attributed to A Scheff.

9 recordsLinked to original sources

PubMed2000

A performance-dependent adjustment of the retention interval in a delayed non-matching-to-position paradigm differentiates effects of amnestic drugs in rats.

Operant delayed non-matching-to-position (delayed non-matching-to-position) tasks have been widely used as tests of working memory in rats, but have suffered some loss in sensitivity to differentiating selective mnemonic from non-mnemonic deficits due to floor and ceiling effects. To circumvent this problem, a novel delayed non-matching-to-position was developed in which the retention interval was adjusted on a trial-by-trial basis to hold performance accuracy at an intermediate value. The present study assessed the effects of three amnestic drugs in this delayed non-matching-to-position. Rats were administered (i.p.) NMDA receptor antagonist ((5R,10S)-(+)-5-Methyl-10, 11-dihydro-5H-dibenzo[a,d,] cyclohepten-5,10-imine (Dizocilpine or MK-801), muscarinic receptor antagonist (-)-scopolamine hydrobromide (scopolamine), or cannabinoid receptor agonist ((R)-(+)-[2, 3-Dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1, 4-benzoxazin-6-yl]-1-naphthalenylmethanone) (WIN 55, 212-2). At high doses, both MK-801 (0.12-0.25 mg/kg) and scopolamine (0.25 mg/kg) produced deficits not selective to working memory. At low doses, scopolamine (0.06-0.12 mg/kg) and MK-801 (0.06 mg/kg) produced no deficits in any mnemonic or secondary measures. WIN 55, 212-2 produced deficits at 2.0 mg/kg that were consistent with a specific impairment of working memory. Using this particular delayed non-matching-to-position revealed that consistent changes in performance accuracy at the short retention interval were evident for scopolamine and MK-801, at times in the absence of changes in response tendency, which are consistent with an interpretation that these drugs produce general deficits in reference or procedural memory. In contrast, cannabinoid-induced deficits in choice accuracy support previous reports of delay-dependent deficits. Together, these data suggest that this delayed non-matching-to-position task is able to differentiate deficit patterns of amnestic drugs, and isolate the effects of motivational side effects of drugs from working memory measurement.

Amnesia↗

PubMed2000

Specificity of memory measures in an adjusting delayed nonmatching-to-position task for rats.

While the delayed nonmatching-to-position (DNMTP) behavioral paradigm has often been used by neuroscientists to assess working memory in rats, its measure of working memory is compromised by floor and ceiling effects. Specifically, these floor and ceiling effects undermine the ability to detect a significant interaction in a two-factor repeated-measures ANOVA, which is required in order to conclude that impaired performance has resulted from disrupted working memory and not from a change in another psychological process (i.e. that the impairment is 'specific' to working memory). The present study was conducted to evaluate if these limitations could be overcome in a DNMTP by adjusting the length of time that the rat was required to remember (the 'delay') so as to avoid the floor and ceiling. The general procedure for two experiments presented subjects with trials where there was either a minimal (1 s) delay or a longer delay of varying length, with the goal of maintaining nonmatch-to-position accuracy near 75%. The procedure was such, that if the average accuracy was at or above 75%, then the next trial would be a long-delay trial. If it were below 75%, then the next trial would be a 1 s delay trial. In the first experiment, the subjects were presented with trials where the value of the longer delay was systematically varied between-sessions. This was done to simulate the faster rate of forgetting found in persons with amnesia. DNMTP accuracy diminished at the longer delay but not the short delay as the second interval was lengthened. However, other measures, including accuracy at the 1 s delay, discrimination accuracy during the sample phase, and the number of trials completed per session, did not change. This experiment suggested that this DNMTP could precisely measure small changes in the rate of forgetting. In a second experiment, a potential non-mnemonic confound, the level of motivation, was directly manipulated by giving the water-restricted subjects access to water immediately prior to the start of the session. The number of trials completed per session diminished, but the accuracy at both the 1 s and the longer delays did not change. These results indicated that the measures of working memory in this DNMTP were insensitive to changes in motivation. Together, these experiments confirmed that adjusting the delay in the DNMTP improves the validity of the measures in this task.

Animals↗

PubMed1997

Focal acute tubular necrosis in a renal allograft.

Nuclear imaging is used to evaluate renal allografts demonstrating delayed function after transplantation. Interpretation of the nuclear scan in the context of clinical data, provides helpful information in the management of the transplant recipient. The better quality of images obtained with technetium-99m mercaptoacetyltriglycine (Tc-99m MAG3) has made it the radiotracer of choice compared to technetium-99m diethylenetriamine pentaacetic acid (Tc-99m DTPA) for imaging of the renal allograft. Tc-99m MAG3 is cleared from the kidney by tubular secretion, whereas Tc-99m DTPA is cleared by glomerular filtration. In this report, we discuss a unique abnormality found on nuclear imaging of a renal allograft. Utilizing our understanding of the characteristic handling of various radiotracers by the kidney, we were able to demonstrate that the renal scan was consistent with an area of focal acute tubular necrosis in the newly transplanted kidney.

Adult↗

PubMed1996