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Biomedical subjects

R G Morris

Publications and source records attributed to R G Morris.

241 records · Page 14Linked to original sources
PubMedDate not supplied

Weak before strong: dissociating synaptic tagging and plasticity-factor accounts of late-LTP.

Experiments were conducted using hippocampal slices in vitro to compare two accounts of the mechanisms by which input-specific protein synthesis-dependent long-term potentiation (late-LTP) may be realised. The synaptic tag hypothesis (Frey and Morris, 1997) predicts that the expression of early-LTP following a weak tetanus can be stabilised into late-LTP by subsequent strong tetanisation of a separate pathway, provided the interval between the two tetanisation episodes is within the decay time-course of a putative synaptic tag. An alternative plasticity-factors hypothesis requires that strong tetanisation should always precede weak tetanisation for stabilisation of early-LTP to occur. Our results indicate that weak tetanisation of pathway S2 at intervals of 5 min or 1 h prior to strong tetanisation on pathway S1 does result in late-LTP on pathway S2. Stabilisation was weaker or did not occur at intervals of 2 and 4 h. This stabilisation effect was shown to depend on protein synthesis during the strong tetanisation of S1. These findings uphold a key prediction of the synaptic tag hypothesis and have implications for the functional role of synaptic tagging for cortical plasticity.

Animals↗
PubMedDate not supplied

Selective impairment of learning and blockade of long-term potentiation by an N-methyl-D-aspartate receptor antagonist, AP5.

Recent work has shown that the hippocampus contains a class of receptors for the excitatory amino acid glutamate that are activated by N-methyl-D-aspartate (NMDA) and that exhibit a peculiar dependency on membrane voltage in becoming active only on depolarization. Blockade of these sites with the drug aminophosphonovaleric acid (AP5) does not detectably affect synaptic transmission in the hippocampus, but prevents the induction of hippocampal long-term potentiation (LTP) following brief high-frequency stimulation. We now report that chronic intraventricular infusion of D,L-AP5 causes a selective impairment of place learning, which is highly sensitive to hippocampal damage, without affecting visual discrimination learning, which is not. The L-isomer of AP5 did not produce behavioural effects. AP5 treatment also suppressed LTP in vivo. These results suggest that NMDA receptors are involved in spatial learning, and add support to the hypothesis that LTP is involved in some, but not all, forms of learning.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

A learning deficit related to age and beta-amyloid plaques in a mouse model of Alzheimer's disease.

Mice that overexpress the human mutant amyloid precursor protein (hAPP) show learning deficits, but the apparent lack of a relationship between these deficits and the progressive beta-amyloid plaque formation that the hAPP mice display is puzzling. In the water maze, hAPP mice are impaired before and after amyloid plaque deposition. Here we show, using a new water-maze training protocol, that PDAPP mice also exhibit a separate age-related deficit in learning a series of spatial locations. This impairment correlates with beta-amyloid plaque burden and is shown in both cross-sectional and longitudinal experimental designs. Cued navigation and object-recognition memory are normal. These findings indicate that A beta overexpression and/or A beta plaques are associated with disturbed cognitive function and, importantly, suggest that some but not all forms of learning and memory are suitable behavioural assays of the progressive cognitive deficits associated with Alzheimer's-disease-type pathologies.

Aging↗
PubMedDate not supplied

Prevalence of human papillomavirus types 16 and 18 in cervical adenocarcinoma and its precursors in Scottish patients.

Our aim was to determine the prevalence of human papillomavirus (HPV) types 16 and 18 in cervical adenocarcinoma (and its precursors) in Scottish patients. Nucleic acid was extracted from paraffin-embedded, formalin-fixed tissues. We examined 119 cases of invasive adenocarcinoma, 20 cases of adenocarcinoma in situ, and 16 cases of normal glandular epithelium. HPV DNA was detected by polymerase chain reaction using type-specific primers for the E6 and E7 genes of HPV-16 and HPV-18 with conformation of HPV genotype by subsequent restriction fragment length polymorphism. HPV DNA was identified in 87 (62.6%) cases, with HPV-16 being detectable in 65 (47%) cases and HPV-18 in 41 (29%) cases. All the cases of normal tissue tested negative for HPV-16 and/or HPV-18. No significant relation between infecting HPV type (16 or 18) and subtypes of disease (within the invasive category and between the preinvasive and the invasive categories) was noted. Our findings support that HPV-16, along with HPV-18, are likely to play a significant role in the pathogenesis of cervical adenocarcinomas and that cervical cancer screening strategies that incorporate oncogenic HPV testing, and prophylactic vaccines that target these types, will be beneficial for the reduction of adenocarcinoma and associated glandular precursors.

Adenocarcinoma↗
PubMedDate not supplied

Detection of human Ha-ras transcripts in tumor cells by in situ hybridization.

We demonstrate the development of a method for identification of human Ha-ras transcripts in cytological and histological preparations of rodent fibroblasts by RNA-RNA in situ hybridization. Fibroblasts, expressing human Ha- ras at high or a very low level, provide a biological model system to optimize in situ hybridization. For rapid detection we used the radiographic signal from cell smears, in directly overlaid x-ray film. Certain pretreatments of slides are shown to increase nonspecific probe binding. The methods described can be used for rapid detection of oncogene expression in small numbers of cultured cells, without prior extraction and purification of their RNA.

Genes, ras↗