Differential synaptic processing separates stationary from transient inputs to the auditory cortex.

Sound features are blended together en route to the central nervous system before being discriminated for further processing by the cortical synaptic network. The mechanisms underlying this synaptic processing, however, are largely unexplored. Intracortical processing of the auditory signal was investigated by simultaneously recording from pairs of connected principal neurons in layer II/III in slices from A1 auditory cortex. Physiological patterns of stimulation in the presynaptic cell revealed two populations of postsynaptic events that differed in mean amplitude, failure rate, kinetics and short-term plasticity. In contrast, transmission between layer II/III pyramidal neurons in barrel cortex were uniformly of large amplitude and high success (release) probability (Pr). These unique features of auditory cortical transmission may provide two distinct mechanisms for discerning and separating transient from stationary features of the auditory signal at an early stage of cortical processing.

NR2B-containing NMDA autoreceptors at synapses on entorhinal cortical neurons.

We have previously shown that presynaptic N-methyl-D-aspartate receptors (NMDARs) can facilitate glutamate release onto principal neurons in the entorhinal cortex (EC). In the present study, we have investigated the subunit composition of these presynaptic NMDARs. We recorded miniature alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (mEPSCs), from visually identified neurons in layers II and V of the EC in vitro. In both layers, bath application of the NR2A/B subunit-selective agonist, homoquinolinic acid (HQA), resulted in a marked facilitation of mEPSC frequency. Blockade of presynaptic Ca(2+) entry through either NMDARs or voltage-gated Ca(2+) channels with Co(2+) prevented the effects of HQA, confirming that Ca(2+) entry to the terminal was required for facilitation. When the NR2B-selective antagonist, ifenprodil, was applied prior to HQA, the increase in mEPSC frequency was greatly reduced. In addition, we found that an NMDAR antagonist blocked frequency-dependent facilitation of evoked release and reduced mEPSC frequency in layer V. Thus we have demonstrated that NMDA autoreceptors in layer V of the EC bear the NR2B subunit, and that NMDARs are also present at terminals onto superficial neurons.

Activation of presynaptic group III metabotropic glutamate receptors depresses spontaneous inhibition in layer V of the rat entorhinal cortex.

Whole cell voltage clamp recording was used to investigate neurotransmitter release onto neurones in deep and superficial layers of rat entorhinal cortex in vitro. Activation of metabotropic glutamate receptors with the agonist (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid depressed spontaneous release of the inhibitory neurotransmitter GABA in layer V, but not in layer II. Depression of transmitter release did not persist in the presence of the sodium channel blocker tetrodotoxin. It seems likely that activation of presynaptic glutamate heteroreceptors inhibits action potential dependent release of neurotransmitter via a direct action at the presynaptic terminal. We confirmed that depression of inhibitory neurotransmission in layer V was mediated by group III metabotropic glutamate receptors using a specific group III antagonist, (RS)-cyclopropyl-4-phosphonophenylglycine. Application of the antagonist alone did not alter the frequency of spontaneous neurotransmitter release, suggesting that the metabotropic glutamate receptor is not tonically active. In layer V of the entorhinal cortex, activation of presynaptic metabotropic glutamate receptors enhances spontaneous glutamate release, and inhibits spontaneous release of GABA. These effects may combine to increase random action potential firing in this layer, thereby reducing its capacity for synchrony generation. Our results are consistent with an anticonvulsant action for group III metabotropic glutamate receptors in the entorhinal cortex.

Differential actions of PKA and PKC in the regulation of glutamate release by group III mGluRs in the entorhinal cortex.

In a previous study we showed that activation of a presynaptically located metabotropic glutamate receptor (mGluR) with pharmacological properties of mGluR4a causes a facilitation of glutamate release in layer V of the rat entorhinal cortex (EC) in vitro. In the present study we have begun to investigate the intracellular coupling linking the receptor to transmitter release. We recorded spontaneous alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated excitatory postsynaptic currents (EPSCs) in the whole cell configuration of the patch-clamp technique, from visually identified neurons in layer V. Bath application of the protein kinase A (PKA) activator, forskolin, resulted in a marked facilitation of EPSC frequency, similar to that seen with the mGluR4a specific agonist, ACPT-1. Preincubation of slices with the PKA inhibitor H-89 abolished the effect of ACPT-1, as did preincubation with the adenylate cyclase inhibitor, SQ22536. Activation of protein kinase C (PKC) using phorbol 12 myristate 13-acetate (PMA) did not affect sEPSC frequency; however, it did abolish the facilitatory effect of ACPT-1 on glutamate release. A robust enhancement of EPSC frequency was seen in response to bath application of the specific PKC inhibitor, GF 109203X. Both H-89 and the group III mGluR antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG) abolished the effects of GF 109203X. These data suggest that in layer V of the EC, presynaptic group III mGluRs facilitate release via a positive coupling to adenylate cyclase and subsequent activation of PKA. We have also demonstrated that the PKC system tonically depresses transmitter release onto layer V cells of the EC and that an interaction between mGluR4a, PKA, and PKC may exist at these synapses.

Activation of presynaptic group III metabotropic receptors enhances glutamate release in rat entorhinal cortex.

The role of group III metabotropic glutamate receptors (mGluRs) in modulating excitatory synaptic transmission was investigated in the rat entorhinal cortex (EC) in vitro. AMPA receptor-mediated excitatory postsynaptic currents (EPSCs) were recorded in the whole cell configuration of the patch-clamp technique from visually identified neurons in layers V and II. In layer V, bath application of the specific group III mGluR agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4, 500 microM) resulted in a marked facilitation of both spontaneous and activity-independent "miniature" (s/mEPSC) event frequency. The facilitatory effect of L-AP4 (100 microM) on sEPSC frequency prevailed in the presence of DL-2-amino-5-phosphonopentanoic acid (100 microM) but was abolished by the group III antagonist (RS)-cyclopropyl-4-phosphonophenylglycine (20 microM). These data confirmed that group III mGluRs, and not N-methyl-D-aspartate (NMDA) receptors were involved in the response to L-AP4. Bath application of the specific mGluR4a agonist (1S,3R,4S)-1-aminocyclopentane-1,2, 4-tricarboxylic acid (20 microM) also had a facilitatory effect on sEPSC frequency, suggesting involvement of mGluR4a. In layer II neurons, L-AP4 caused a reduction in sEPSC frequency but did not affect mEPSCs recorded in the presence of tetrodotoxin. These findings suggest that a group III mGluR with mGluR4a-like pharmacology is involved in modulating synaptic transmission in layer V cells of the EC. The effect on mEPSCs suggests that this receptor is located presynaptically and that its activation results in a direct facilitation of glutamate release. This novel facilitatory effect is specific to layer V and, to our knowledge, is the first report of a direct facilitatory action of group III mGluRs on synaptic transmission. In layer II, L-AP4 had an inhibitory effect on glutamate release similar to that reported in other brain regions.

Infantile osteopetrosis; bone marrow transplantation from a cousin donor.

The successful correction of infantile osteopetrosis in an Asian child by bone marrow transplantation (BMT) from an HLA-A,B matched cousin donor is reported. Retrospective HLA molecular analysis revealed that patient and donor were incompatible for HLA-DPB1. Donor type cells detected in the patient after transplantation indicate successful engraftment. The patient is currently alive and well.

Bone marrow transplantation for thalassaemia: experience of two British centres.

Bone marrow transplantation (BMT) was carried out on 38 patients with thalassaemia major over a period of 9 years; 30 were Asian. In all cases, the donor was an HLA-identical relative. The mean age at transplant was 6.4 years (range 0.5-20 years). Conditioning was busulphan and cyclophosphamide (CY). Cyclosporin (CsA) (n = 30), CsA + methotrexate (n = 6) or CsA + T cell depletion (n = 2) were used for prophylaxis against graft-versus-host disease (GVHD). Thirty-four patients successfully engrafted. Two patients required a second transplant and two achieved mixed chimerism, eventually rejecting their grafts. Nine patients (23.6) developed acute GVHD grade III-IV. Eleven patients (28.9) developed chronic GVHD. There were 11 deaths, 7 within the first 100 days post-BMT. Twenty-seven patients are alive from 156 to 3213 days post-BMT. The actuarial survival at 9 years post-BMT was 70%. The mortality is higher than in previously reported series; possible reasons for this are discussed.

Late spontaneous recovery of chronic thrombocytopenia.

Five cases are reported of spontaneous remission of chronic childhood thrombocytopenia four or more years after diagnosis. Other than typical features of chronic idiopathic thrombocytopenic purpura there were no obvious markers predictive of late remission, although a slow progressive recovery was common to four of the patients. In light of this experience splenectomy is not recommended in clinically mild thrombocytopenia.

HIV infection in haemophilia--a European cohort.

Ten haemophilia centres in northern Europe have pooled data on 202 haemophilic children who were infected with HIV between 1979 and 1986. All cases were under 16 years of age on 1 July 1985. The age at infection ranged from 1-15 years. Thirty seven cases (18%) had progressed to AIDS by 1 July 1991 and 15 of these have died. Persistent generalised lymphadenopathy has been noted in 102 patients of whom 18 (17%) have developed AIDS. Twenty three of the remaining patients (23%) have not. CD4+ T cell counts have fallen steadily. Of 36 patients who have had shingles since seroconversion, 19 (53%) had counts below 0.2 x 10(9)/l. Thirty five out of 145 patients without shingles (24%) had similar values. The mean IgA concentration in patients with CD4+ T cell counts above 0.5 x 10(9)/l was 2.38 g/l, between 0.2 and 0.5 was 3.07 g/l, and in those with CD4+ T cell counts below 0.2 x 10(9)/l the mean IgA concentration was 4.58 g/l. Treatment patterns have altered between 1989 and 1991, with increased use of zidovudine in patients without AIDS and a marked increase in primary prophylaxis against pneumocystis pneumonia. This has been associated with a decline in the incidence of pneumocystis as an indicator disease in new AIDS cases from 56% in 1989 to 20% in 1991. These observations indicate that persistent generalised lymphadenopathy does not worsen the outlook, but shingles does. Rising IgA concentrations are markers for disease progression. Modern prophylactic regimens are delaying the onset of indicator disease, but CD4 values continue to fall steadily.

Survey of oral anticoagulant treatment in children.

AIMS: To find out which children are treated with oral anticoagulants and how their treatment is controlled in the United Kingdom. METHODS: Two questionnaires were used. The first was sent to general haematologists and the other to paediatric cardiologists and cardiac surgeons. RESULTS: There were 273 (58%) replies to the first questionnaire. Most children were treated because of artificial cardiac valve replacement. The mean target International Normalised Ratio (INR) used was 2.73 to 4.0 for children with heart valves and 2.1 to 3.25 for children with venous thrombosis. The second questionnaire elicited replies from 11 of 22 cardiac centres. The mean target INR used for children with cardiac valves ranged from 2.59-3.77. Of 68 children covered in the survey, there have been two major bleeds and two thrombotic episodes: 78.8% of children were controlled with a venous prothrombin time and 21.2% with a capillary test. There was no consistency in the dose regimens used for the induction of oral anticoagulant treatment with warfarin. CONCLUSIONS: The levels of anticoagulation used for maintenance are similar to those recommended by the British Society for Haematology for adults (3.0 to 4.5). They seem to be safe for children too.

Diamond-Blackfan syndrome and neutropenia.

Neutropenia is a rare complication of Diamond-Blackfan syndrome (congenital hypoplastic anaemia). Three patients are reported: all had neutropenia as well as anaemia, and to investigate the cause of the neutropenia culture of bone marrow for granulocyte-macrophage colony forming cells (GMCFCs) was performed. Two cases had a low incidence of GMCFCs, but the third case had a high incidence. These findings suggest that myeloid precursors can be abnormal in Diamond-Blackfan syndrome and that the mechanism of neutropenia may, like that of anaemia, vary from patient to patient.

Bone-marrow transplantation for congenital erythropoietic porphyria.

Congenital erythropoietic porphyria, a disorder of haem synthesis, is caused by uroporphyrinogen III synthase deficiency in bone-marrow normoblasts. Uroporphyrins and coproporphyrins accumulate and cause oxidative damage to cells exposed to sunlight. Uroporphyrin overproduction was greatly reduced and skin changes reversed in a girl who received a bone-marrow graft from an HLA-identical sibling at 10 years of age. The patient died 11 months after transplantation because of severe progressive pneumonitis and encephalopathy associated with cytomegalovirus infection, but the encouraging response up to 8 months after engraftment indicates a possible benefit of bone-marrow transplantation in the treatment of this rare but usually fatal inherited disease.

Neutropenia associated with X-linked agammaglobulinaemia.

In a series of six cases of sex-linked agammaglobulinaemia neutropenia occurred as a presenting feature in four and during the presenting illness in the other two. The six patients all had low antibody titres and absent or low immunoglobulin concentrations with normal concentrations of T cells and absent B cells. The patients were all first seen with severe, acute infection, including septic abscesses and meningitis; neutropenia resolved as the infection and immunoglobulin deficiency were treated. Haematologists should be aware that neutropenia is a common association of infection in patients with immunoglobulin deficiency.