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Biomedical subjects

P D Roberts

Publications and source records attributed to P D Roberts.

36 records · Page 2Linked to original sources
PubMed1975

Acute lymphoblastic leukaemia: cyclical chemotherapy with three combinations of four drugs (COAP-POMP-CART regimen).

Forty-two adults and children with previously untreated acute lymphoblastic leukaemia (ALL) were entered into a programme of chemotherapy in which three combinations, each of four drugs were administered in a predetermined cyclical rotation together with cranial irradiation and intrathecal injections of methotrexate. Forty-one patients (98%) entered remission and no patient developed neuroleukaemia. Relapse of ALL occurred in 10 patients, and three patients died during remission, while eight patients stopped treatment after two and a half years and have remained in remission for two to 26 months. Comparison of remission and survival experience in this mixed group of children and adults with the experience of children treated at Memphis and in the Medical Research Council's UKALL-I trial showed no significant differences. On the other hand, analysis by prognostic factors showed that neither age nor blast cell count at presentation had any adverse effect in patients treated in this study. No relapses occurred in nine patients with blast cell counts greater than 20 x 109/1 at presentation. This regimen is effective treatment for ALL and may be of special value in patients with poor prognoses. The regiment has not as yet proved superior for the treatment of children with ALL who do not have adverse prognostic features.

Adolescent↗
PubMed1973

Vitamin B 12 status in pregnancy among immigrants to Britain.

Haemoglobin, serum vitamin B(12), and serum and red cell folate levels have been measured in 322 pregnant immigrant women in London at their first booking and in a proportion at 34 weeks of gestation and postnatally. The Indian, East-African Indian, and Pakistani and Bangladeshi patients showed significantly lower initial mean serum vitamin B(12) levels than the European group, the levels being lower in Hindu and Sikh patients than in Moslems. The patients of West Indian, Indian, and East-African Indian origin showed significantly lower initial mean haemoglobin levels than the immigrants from European countries. Though there was no overall correlation between haemoglobin and serum vitamin B(12) level the incidence of hypersegmented polymorphs and macrocytosis in the peripheral blood was highest in the Indian and East-African Indian patients, and both these features were particularly frequent in patients with subnormal serum vitamin B(12) levels. Only one patient, however, had overt megaloblastic anaemia due to vitamin B(12) deficiency. The Indian patients whose red cell folate levels were less than 200 ng/ml also had a lower mean serum vitamin B(12) level than those with red cell folate levels greater than 200 ng/ml. The Indian patients had smaller babies than the Europeans but this was not related to the differences in vitamin B(12) status between the two groups. However, out of 39 babies of the Indian group 5 (13%) showed subnormal serum vitamin B(12) levels in the first 10 days of life, the lowest level being 120 pg/ml.Though there was an overall statistically significant fall in serum vitamin B(12) between first booking and 34 weeks of pregnancy there was no significant fall in serum vitamin B(12) in those who initially had subnormal levels. Thus many Indian women are vitamin B(12) deficient in pregnancy, and this is associated with morphological blood abnormalities in many cases, but megaloblastic anaemia due to this deficiency is relatively infrequent.

Africa, Eastern↗
PubMedDate not supplied

Computational consequences of temporally asymmetric learning rules: I. Differential hebbian learning.

Temporally asymetric learning rules governing plastic changes in synaptic efficacy have recently been identified in physiological studies. In these rules, the exact timing of pre- and postsynaptic spikes is critical to the induced change of synaptic efficacy. The temporal learning rules treated in this article are approximately antisymmetric; the synaptic efficacy is enhanced if the postsynaptic spike follows the presynaptic spike by a few milliseconds, but the efficacy is depressed if the postsynaptic spike precedes the presynaptic spike. The learning dynamics of this rule are studied using a stochastic model neuron receiving a set of serially delayed inputs. The average change of synaptic efficacy due to the temporally antisymmetric learning rule is shown to yield differential Hebbian learning. These results are demonstrated with both mathematical analyses and computer simulations, and connections with theories of classical conditioning are discussed.

Animals↗
PubMedDate not supplied

Computational consequences of temporally asymmetric learning rules: II. Sensory image cancellation.

The electrosensory lateral line lobe (ELL) of mormyrid electric fish is a cerebellum-like structure that receives primary afferent input from electroreceptors in the skin. Purkinje-like cells in ELL store and retrieve a temporally precise negative image of prior sensory input. The stored image is derived from the association of centrally originating predictive signals with peripherally originating sensory input. The predictive signals are probably conveyed by parallel fibers. Recent in vitro experiments have demonstrated that pairing parallel fiber-evoked excitatory postsynaptic potentials (epsps) with postsynaptic spikes in Purkinje-like cells depresses the strength of these synapses. The depression has a tight dependence on the temporal order of pre- and postsynaptic events. The postsynaptic spike must follow the onset of the epsp within a window of about 60 msec for the depression to occur and pairings at other delays yield a nonassociative enhancement of the epsp. Mathematical analyses and computer simulations are used here to test the hypothesis that synaptic plasticity of the type established in vitro could be responsible for the storage of temporal patterns that is observed in vivo. This hypothesis is confirmed. The temporally asymmetric learning rule established in vitro results in the storage of activity patterns as observed in vivo and does so with significantly greater fidelity than other types of learning rules. The results demonstrate the importance of precise timing in pre- and postsynaptic activity for accurate storage of temporal information.

Action Potentials↗