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A characteristic feature of the class Theta glutathione S-transferase (GST) T1-1 is its ability to activate dichloromethane and dibromoethane by catalysing the formation of mutagenic conjugates. The level of the GSTT1 subunit within tissues is an important determinant of susceptibility to the carcinogenic effects of these dihaloalkanes. In the present study it is demonstrated that hepatic GST activity towards these compounds can be elevated significantly in female and male Fischer-344 rats by feeding these animals on diets supplemented with cancer chemopreventive agents. Immunoblotting experiments showed that increased activity towards the dihaloalkanes is associated with elevated levels of the GSTT1 subunit in rat liver. Sex-specific effects were observed in the induction of GSTT1 protein. Amongst the chemopreventive agents tested, indole-3-carbinol proved to be the most potent inducer of hepatic GSTT1 in male rats (6.2-fold), whereas coumarin was the most potent inducer of this subunit in the livers of female rats (3. 5-fold). Phenobarbital showed significant induction of GSTT1 only in male rat liver and had little effect in female rat liver. Western blotting showed that class Alpha, Mu and Pi GST subunits are not co-ordinately induced with GSTT1, indicating that the expression of GSTT1 is determined, at least in part, by mechanisms distinct from those that regulate levels of other transferases. The increase in amount of hepatic GSTT1 protein was also reflected by an increase in the steady-state level of mRNA in response to treatment with chemopreventive agents and model inducers. Immunohistochemical detection of GSTT1 in rat liver supported the Western blotting data, but showed, in addition to cytoplasmic staining, significant nuclear localization of the enzyme in hepatocytes from some treated animals, including those fed on an oltipraz-containing diet. Significantly, the hepatic level of cytochrome P-450 2E1, an enzyme which offers a detoxification pathway for dihaloalkanes, was unchanged by the various inducing agents studied. It is concluded that the induction of GSTT1 by dietary components and its localization within cells are important factors that should be considered when assessing the risk dihaloalkanes pose to human health.

To assess the effects of solitary, right-sided supratentorial intracranial tumours on language and communication function patients were assessed preoperatively using the Western Aphasia Battery (WAB) and Boston Naming Test (BNT). The impact of resective tumour surgery was evaluated prospectively by a comparison of test scores obtained at pre- and postoperative assessments. The WAB scores in 33 patients revealed that 21% were by definition dysphasic (i.e. Aphasia Quotient < 93.8) and 35% obtained an abnormal Language Quotient. Performance was particularly variable on the written picture description and word fluency WAB subtests. Using the BNT 21% of 47 patients were anomic. The tumours were evenly distributed throughout the frontal, temporal and parietal lobes, but none were in the occipital lobe. Reassessment approximately 6 days after excisional tumour surgery showed that mean scores for the BNT, Aphasia Quotient, and the WAB spontaneous speech and comprehension subtests had improved significantly despite a significant reduction in dexamethasone therapy. This study has demonstrated that right-sided intracranial tumours produce subtle, but specific language deficits of a type more usually associated with left-sided brain dysfunction. The pathophysiological basis of these deficits is unclear, but they are not attributable to either limited education or pre-existing dyslexia. Further studies using a discriminating and comprehensive assessment of language in the right hemisphere are required.

We have characterized a murine hybrid cell line, Bb1-3, generated by the fusion of mouse primary erythroblasts with MEL cells. It proliferated in serum-free medium and displayed a low level of spontaneous erythroid and megakaryocyte differentiation. Terminal erythroid differentiation could be induced with HMBA and DMSO and was enhanced by serum. Treatment with phorbol esters resulted in a high proportion of megakaryocytes and the expression of megakaryocytic specific lineage markers. Bb1-3 cells contain a human beta-globin transgene that was expressed at levels of 20-50% of the endogenous mouse globin genes. Initially, expression was largely limited to the beta-globin gene but after adaptation to serum free growth, equal expression of both the human gamma- and human beta-globin genes was observed. This cell line provides further evidence that the differentiation potential of mouse erythroleukaemia cells is not restricted to the erythroid lineage and should be useful to study the mechanisms underlying both developmental globin gene regulation and the terminal differentiation of bipotential erythroid/megakaryocytic progenitor cells.

The Expressed Sequence Tag database has been screened for cDNA clones encoding prostaglandin D2 synthases (PGDSs) by using a BLAST search with the N-terminal amino acid sequence of rat GSH-dependent PGDS, a class Sigma glutathione S-transferase (GST). This resulted in the identification of a cDNA from chicken spleen containing an insert of approx. 950 bp that encodes a protein of 199 amino acid residues with a predicted molecular mass of 22732 Da. The deduced primary structure of the chicken protein was not only found to possess 70% sequence identity with rat PGDS but it also demonstrated more than 35% identity with class Sigma GSTs from a range of invertebrates. The open reading frame of the chicken cDNA was expressed in Escherichia coli and the purified protein was found to display high PGDS activity. It also catalysed the conjugation of glutathione with a wide range of aryl halides, organic isothiocyanates and alpha,beta-unsaturated carbonyls, and exhibited glutathione peroxidase activity towards cumene hydroperoxide. Like other GSTs, chicken PGDS was found to be inhibited by non-substrate ligands such as Cibacron Blue, haematin and organotin compounds. Western blotting experiments showed that among the organs studied, the expression of PGDS in the female chicken is highest in liver, kidney and intestine, with only small amounts of the enzyme being found in chicken spleen; in contrast, the rat has highest levels of PGDS in the spleen. Collectively, these results show that the structure and function, but not the expression, of the GSH-requiring PGDS is conserved between chicken and rat.

Paired intracellular recordings in slices of adult rat neocortex with biocytin filling of synaptically connected neurons were used to investigate the pyramidal targets, in layer V, of layer III pyramidal axons. The time-course and sensitivity of excitatory postsynaptic potentials to current injected at the soma, and locations of close appositions between presynaptic axons and postsynaptic dendrites, indicated that the majority of contributory synapses were located in layer V. Within a "column" of tissue, radius < or = 250 microm, the probability that a randomly selected layer III pyramid innervated a layer V pyramid was 1 in 4 if the target cell was a burst firing pyramid with an apical dendritic tuft in layers II/I. If, however, the potential target was a regular spiking pyramid, the probability of connectivity was only 1 in 40, and none of the 13 anatomically identified postsynaptic layer V targets had a slender apical dendrite terminating in layers IV/III. Morphological reconstructions indicated that layer III pyramids select target layer V cells whose apical dendrites pass within 50-100 microm of the soma of the presynaptic pyramid in layer III and which have overlapping apical dendritic tufts in the superficial layers. The probability that a layer V cell would innervate a layer III pyramid lying within 250 microm of its apical dendrite was much lower (one in 58). Both presynaptic layer III pyramids and their large postsynaptic layer V targets could therefore access similar inputs in layers I/II, while small layer V pyramids could not. One prediction from the present data would be that neither descending layer V inputs to the striatum or thalamus, nor transcallosal connections would be readily activated by longer distance cortico-cortical "feedback" connections that terminated in layers I/II. These could, however, activate corticofugal pathways to the superior colliculus or pons, both directly and via layer III.

1. Dual intracellular recordings in the CA1 region of adult rat hippocampal slices and biocytin filling of synaptically connected cells were used to study the excitatory postsynaptic potentials (EPSPs) elicited in basket (n = 7) and bistratified interneurones (n = 7) by action potentials activated in simultaneously recorded pyramidal cells. 2. Interneurones could be subdivided according to their electrophysiological properties into classical fast spiking, burst firing, regular spiking and fast spiking cells with a rounded spike after-hyperpolarization. These physiological classes did not, however, correlate with morphological type. EPSPs were not recorded in regular spiking cells. 3. Average EPSP amplitudes were larger in bistratified cells (range, 0.5-9 mV) than in basket cells (range, 0. 15-3.6 mV) and the probability of obtaining a pyramidal cell-interneurone EPSP was also higher for the bistratified cells (1:7) than for the basket cells (1:22). EPSP 10-90 % rise times in bistratified cells (0.7-2 ms) and their widths at half-amplitude (3. 9-11.2 ms) were slightly longer than in basket cells (rise times, 0.4-1.6 ms; half-widths, 2.2-9.7 ms). 4. The majority of these EPSPs (6 of 8 tested) increased in amplitude and duration with postsynaptic depolarization, although in two (of 4) basket cells the voltage relation was conventional. 5. All EPSPs tested in both basket (n = 7) and bistratified cells (n = 5) decreased in amplitude with repetitive presynaptic firing. The average amplitudes of second EPSPs elicited within 15 ms of the first were between 34 and 94 % of the average amplitude of the first EPSP. Third and fourth EPSPs in brief trains were further depressed. This depression was associated with an increase in the incidence of apparent failures of transmission indicating a presynaptic locus.

1. In adult rat hippocampal slices, simultaneous intracellular recordings from pyramidal cells in CA1 and interneurones near the stratum oriens-alveus border revealed excitatory connections that displayed facilitation on repetitive activation in twelve of thirty-six pairs tested. 2. Postsynaptic interneurones were classified as horizontal oriens-alveus interneurones by the pronounced 'sag' in response to hyperpolarizing current injection, high levels of spontaneous synaptic activity and by the morphology of their somata and dendrites, which were confined to stratum oriens-alveus and their axons which projected to stratum lacunosum-moleculare where they ramified extensively, in the region of entorhinal cortex input to CA1. 3. Excitatory postsynaptic potentials (EPSPs) elicited by single pyramidal cells were 0 to 12 mV in amplitude. Mean EPSP amplitude (single spikes) was 0.93 +/- 1. 06 mV at -70 +/- 2.3 mV (n = 10). The rise time was 1.2 +/- 0.5 ms and the width at half-amplitude was 7.5 +/- 4.7 ms. 4. EPSPs fluctuated greatly in amplitude; the mean coefficient of variation was 0.84 +/- 0.37 for the first EPSP and 0.47 +/- 0.24 for the second. Apparent failures of transmission frequently occurred after first presynaptic spikes but less frequently after the second or subsequent spikes in brief trains. 5. EPSPs displayed facilitation at membrane potentials between -80 mV and spike threshold. Second EPSPs within 20 ms of the first were 253 +/- 48 % (range, 152-324 %) of the mean first EPSP amplitude. Third EPSPs within 60 ms were 266 +/- 70 % (range, 169-389 %) and fourth EPSPs within 60-120 ms were 288 +/- 71 % (range, 188-393 %). Both proportions of apparent failures of transmission and coefficient of variation analysis indicated a presynaptic locus for this facilitation.

The application of fluctuation analysis to studies of synaptic function in the neocortex is discussed. Analysis of failures of transmission has been valuable in indicating whether a presynaptic or a postsynaptic site is responsible for a change in synaptic efficacy. When combined with detailed ultrastructural verification of all synapses involved in an individual cell to cell connection, a reasonable estimate of quantal size and release probability under conditions of low frequency activity can be obtained. However, both the number of available release sites in functional terms and the probability that an action potential (AP) will release transmitter from any given site can vary from AP to AP at higher frequencies. A variety of presynaptic mechanisms that modulate release are now apparent. For example, one mechanism dominates release patterns at one class of connection which is insensitive to absolute firing frequency, but responsive to changes in frequency. At another class of connection, a different mechanism dominates, resulting in high sensitivity to frequency.

In this paper preliminary findings from the first stage of an English National Board (ENB) commissioned study investigating the educational needs of community practitioners in relation to their responsibilities for student learning are presented. A national postal survey of all educational centres offering nurse and/or midwifery education was undertaken in the latter half of 1993. Information was collected regarding the nature and planning of the community practice components of courses. The main methods of support for practitioners included the provision of the ENB 998/997 courses and liaison meetings between educational centres and community practice areas. Practitioners were often required to both supervise and assess students on practice placements, the length of these placements varying enormously. For those centres offering the mental health and learning disability branches of the Diploma in Higher Education in Nursing Studies (Project 2000), a significant proportion lacked teachers with specialist community qualifications. The investigation took place at a time of great upheaval, with 42% of centres reporting that they were in the process of amalgamation. The findings demonstrate that community nurses and midwives undoubtedly contribute to the education of nurse and midwife students and consequently have educational needs which must be addressed if they are to continue to supervise students.

1. To compare the dynamics of synaptic transmission at different types of connection, dual intracellular recordings were made from pairs of neurones in slices of adult rat neocortex. Excitatory postsynaptic potentials (EPSPs) were elicited by single spikes, spike pairs and brief spike trains in presynaptic pyramidal cells and responses recorded in postsynaptic pyramidal cells and in interneurones. 2. Pyramid-pyramid EPSPs were strongly voltage dependent and this resulted in a range of paired pulse effects. At thirty-two of sixty-nine pyramid-pyramid connections, the 2nd EPSP was the same shape as the 1st, indicating minimal interaction between active synapses. In these thirty-two connections, paired pulse depression (PPD) was apparent (2nd EPSP integral 46 +/- 21% of the 1st, at 5-20 ms), which recovered within 60-70 ms. 3. In eleven additional pyramid-pyramid pairs, the 2nd EPSP was also the same shape as the 1st, but paired pulse facilitation (PPF, 149 +/- 32%) decaying within 50-60 ms was apparent. Even these connections displayed frequency-dependent depression, however, as 3rd EPSPs were smaller than 1st EPSPs at intervals < 100 ms. 4. At twenty-five pyramid-pyramid connections, 2nd EPSPs were broader than 1st EPSPs and in sixteen of these, voltage- and NMDA receptor-dependent enhancement was large enough to obscure the underlying PPD. PPD was revealed by postsynaptic hyperpolarization (4 pairs), N-methyl-D-aspartate (NMDA) receptor blockade (3 paris), or if Mg2+ was removed (in the one case studied). If synapse location allowed significant depolarization of one active site by another, voltage-dependent enhancement could produce supralinear EPSP summation and overcome PPD. Third EPSPs were, however, consistently smaller than 1st EPSPs. 5. In striking contrast, profound frequency-dependent facilitation, independent of voltage or NMDA receptors was seen at fifteen connections involving two classes of postsynaptic interneurones. 6. At these pyramid-interneurone connections, facilitation of the 2nd EPSP (655 +/- 380% at 5-20 ms) decayed rapidly, within 50-60 ms. Third and fourth EPSPs showed additional facilitation which decayed more slowly, within 90 ms and 2 s, respectively. Facilitation due to five to six spike trains was still apparent at 3 s. Therefore, once initiated by a brief high frequency spike train, facilitation was maintained at lower frequencies.

A prospective study of patients undergoing computerized tomography (CT)-guided stereotactic biopsy of nonpolar tumors in the dominant hemisphere was undertaken to determine if stereotactic biopsy caused a deterioration of language functions. Language was assessed using the Western Aphasia Battery (WAB) and the Boston Naming Test (BNT) before and after a biopsy sample was obtained. Of 16 patients studied, five (31%) were dysphasic preoperatively. After the biopsy the Aphasia Quotient (AQ), derived from the WAB, had significantly deteriorated in four (80%) of these patients, whereas in the fifth it remained relatively unchanged. One of these patients with an extensive infiltrating hemispheric oligoastrocytoma subsequently recovered normal language function after radiotherapy. In 10 of the 11 patients who had normal language function preoperatively there were no deleterious changes after biopsy in either the WAB subtest or BNT scores. In the other patient whose WAB score was normal preoperatively, there was a significant deterioration in postoperative AQ. This patient, who declined steroid therapy before and after biopsy, had a glioblastoma multiforme in Wernicke's area. A postoperative CT scan revealed no changes from what was shown on preoperative scan. This clinical study shows that CT-guided stereotactic biopsy of nonpolar tumors in the dominant hemisphere using the Brown-Roberts-Wells system and the Sedan-Nashold biopsy cannula carries a 9% risk (95% confidence intervals 0-26%) of impairing language functions if the patient is not dysphasic preoperatively. If the patient is dysphasic preoperatively, there is a very high risk of aggravating the dysphasia with stereotactic biopsy.

Objective: to ascertain who was providing antenatal care in the community in a defined geographical area in the north of England, and whether the care could achieve the government objectives presented in Changing Childbirth (DoH 1993)., Design: a questionnaire was used to obtain demographic information and semi-structured interviews were held with care providers in order to assess the perspective of those providing care., Participants: a purposive sample of nine community midwives and six general practitioners (GPs)., Findings: the midwife was the professional undertaking most of the antenatal care although in most instances there was a GP available on site if required. GPs saw the midwife as the main provider of care with themselves as 'back up'. Conflict over responsibility for care was an issue in some instances. Whilst changes in antenatal care provision had been, or were about to be made, only one midwife expressed a clear positive feeling towards midwife-led care. Giving women the opportunity for choice provoked an overwhelming feeling of helplessness for midwives. Midwives and GPs believed their education adequately prepared them to provide antenatal care in the community, however, GPs did not attend regular updating sessions., Implications for Practice: whilst it was recognised that midwives are taking increasing responsibility for antenatal care, GPs still believe that overall responsibility lies with them; therefore, there is a need to clarify roles. The majority of midwives expressed reservations about midwife-led care.

The Right Hemisphere Language Battery (RHLB) (Bryan, 1989) was devised to assess the presence of language disorders in patients with damage to the right cerebral hemisphere and to permit an evaluation of the efficacy of therapeutic techniques. To evaluate the utility and sensitivity of the RHLB in patients with solitary right hemispheric brain tumours 20 patients were assessed before and after neurosurgery. Twenty control subjects with no signs or symptoms of brain disease who were undergoing lumbar spinal surgery were also assessed. On six of the seven RHLB subtests there was no significant difference between the scores obtained preoperatively by patients with right hemispheric brain tumours and the control subjects. There was also no significant change in the scores of the patients with tumours before and after resection of the lesion. The RHLB is therefore not recommended for either evaluating communication deficits or for measuring the efficacy of therapeutic techniques in patients with right hemisphere brain tumours. This study does, however, show that there are statistically significant differences between the control and brain tumour groups on the discourse analysis subtest preoperatively. The implications of the study are discussed together with possible reasons for the findings.

Objectives: 1) to provide a descriptive analysis of women's views of the antenatal care provided in the study centre; 2) to identify which aspects of antenatal care were important to women; 3) to assess whether or not women 'booked' for delivery at the study centre would welcome the formal introduction of a midwifery-led service and 4) to audit sources of satisfaction and dissatisfaction identified in the survey., Design: descriptive survey using a self-administered questionnaire, and a self-administered audit questionnaire using a modified Measure of Satisfaction., Setting: the antenatal clinic of one teaching hospital in the north of England between July 1993 and August 1993. The audit was conducted between December 1994 and February 1995., Participants: 110 women attending four 'follow up' antenatal clinics participated in the survey and 151 women participated in the audit., Findings: many women felt they were already having midwifery-led care and that it was important to them to see a doctor during pregnancy. Generally the women were satisfied with antenatal care. Factors which caused dissatisfaction were, lack of continuity of care, quality of advice, waiting time and these were the focus of the audit., Implications for Practice: local needs should be assessed before implementing changes in service. Elements of good practice should be identified to ensure that they are not compromised in a changing service. Further evaluation of the changing maternity service is needed to monitor satisfaction and dissatisfaction.

1. Using dual intracellular recordings in slices of adult rat neocortex, twenty-four IPSPs activated by single presynaptic interneurones were studied in simultaneously recorded pyramidal cells. Fast spiking interneurones inhibited one in four or five of their close pyramidal neighbours. No reciprocal connections were observed. After recordings neurones were filled with biocytin. 2. Interneurones that elicited IPSPs were classified as classical fast spiking (n = 10), as non-classical fast spiking (n = 3, including one burst-firing interneurone), as unclassified, or slow interneurones (n = 8), or as regular spiking interneurones (n = 3), i.e. interneurones whose electrophysiological characteristics were indistinguishable from those of pyramidal cells. 3. All of the seven classical fast spiking cells anatomically fully recovered had aspiny, beaded dendrites. Their partially myelinated axons ramified extensively, varying widely in shape and extent, but randomly selected labelled axon terminals typically innervated somata and large calibre dendrites on electron microscopic examination. One 'autapse' was demonstrated. One presumptive regular spiking interneurone axon made four somatic and five dendritic connections with unlabelled targets. 4. Full anatomical reconstructions of labelled classical fast spiking interneurones and their postsynaptic pyramids (n = 5) demonstrated one to five boutons per connection. The two recorded IPSPs that were fully reconstructed morphologically (3 and 5 terminals) were, however, amongst the smallest recorded (< 0.4 mV). Some connections may therefore involve larger numbers of contacts. 5. Single axon IPSPs were between 0.2 and 3.5 mV in average amplitude at -55 to -60 mV. Extrapolated reversal potentials were between -70 and -82 mV. IPSP time course correlated with the type of presynaptic interneurone, but not with IPSP latency, amplitude, reversal potential, or sensitivity to current injected at the soma. 6. Classical fast spiking interneurones elicited the fastest IPSPs (width at half-amplitude 14.72 +/- 3.83 ms, n = 10) and unclassified, or slow interneurones the slowest (56.29 +/- 23.44 ms, n = 8). Regular spiking interneurone IPSPs had intermediate half-widths (27.3 +/- 3.68 ms, n = 3). 7. Increasingly brief presynaptic interspike intervals increased the peak amplitude of, but not the area under, the summed IPSP. Only at interspike intervals between 10 and 20 ms did IPSP integrals exhibit paired pulse facilitation. Paired pulse depression was apparent at < 10 and 20-60 ms. During longer spike trains, summing IPSPs decayed to a plateau potential that was relatively independent of firing rate (100-250 Hz). Thereafter, the voltage response could increase again. 8. Summed IPSPs elicited by two to fifteen presynaptic spike trains decayed as, or more rapidly than, single-spike IPSPs. Summed IPSPs elicited by > 20 spikes (> 150 Hz), however, resulted in an additional, more slowly decaying component (latency > 50 ms, duration > 200 ms). The possible involvement of GABAB receptors in this component is discussed. 9. It is suggested that three broad classes of interneurones may activate GABAA receptors on relatively proximal portions of neocortical pyramidal neurones. The different time courses of the IPSPs elicited by the three classes may reflect different types of postsynaptic receptor rather than dendritic location. An additional class, burst firing, spiny interneurones appear to activate GABAA receptors on more distal sites.

In adult rat hippocampus, simultaneous intracellular recordings from 989 pairs of CA1 pyramidal cells revealed nine monosynaptic, excitatory connections. Six of these pairs were sufficiently stable for electrophysiological analysis. Mean excitatory postsynaptic potential amplitude recorded at a postsynaptic membrane potential between -67 and -70 mV was 0.7 +/- 0.5 mV (0.17-1.5 mV), mean 10-90% rise time was 2.7 +/- 0.9 ms (1.5-3.8 ms) and mean width at half-amplitude was 16.8 +/- 4.1 ms (11.6-25 ms). Cells were labelled with biocytin and identified histologically. For one pair that was fully reconstructed morphologically, excitatory postsynaptic potential average amplitude was 1.5 mV, 10-90% rise time 2.8 ms and width at half-amplitude 11.6 ms (at -67 mV). In this pair, correlated light and electron microscopy revealed that the presynaptic axon formed two synaptic contacts with third-order basal dendrites of the postsynaptic pyramid, one with a dendritic spine, the other with a dendritic shaft. In the four pairs tested, postsynaptic depolarization increased excitatory postsynaptic potential amplitude and duration. In two, D-2-amino-5-phosphonovalerate (50 microM) reduced the amplitude and duration of the excitatory postsynaptic potential. The remainder of the excitatory postsynaptic potential now increased with postsynaptic hyperpolarization and was abolished by 20 microM 6-cyano-7-nitroquinoxaline-2,3-dione (n = 1). Paired-pulse depression was evident in the four excitatory postsynaptic potentials tested. This depression decreased with increasing inter-spike interval. These results provide the first combined electrophysiological and morphological illustration of synaptic contacts between pyramidal neurons in the hippocampus and confirm that connections between CA1 pyramidal neurons are mediated by both N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate receptors.

Intracellular recordings were obtained from a class of neuron defined electrophysiologically as burst firing interneurons in layers V and VI in slices of adult rat somatomotor cortex. Four of these cells were recovered histologically. These four cells had resting membrane potentials between -68 and -80 mV, a mean input resistance of 77 +/- 16.2 M omega (measured from the voltage deflection produced by a 100 ms, 0.5 nA hyperpolarizing pulse delivered from a membrane potential of -80 mV) and responded to injections of depolarizing current from membrane potentials negative of -70 to -75 mV with an initial burst of action potentials followed by a complex afterhyperpolarization. In response to injection of larger (0.5-1.5 nA) hyperpolarizing current pulses from membrane potentials between -60 and -70 mV, 15 of 20 burst firing cells (three of four recovered histologically) that were tested displayed delayed inward rectification, and in all 20 cells of this type, responses to large negative current pulses were followed by a rebound depolarization that could initiate action potentials. Filling of four of these cells with biocytin and subsequent histological processing revealed that they were bitufted with sparsely to medium spiny dendrites and extensive local axon ramifications. These neurons are similar to low threshold spiking cells [Kawaguchi (1993) J. Neurophysiol. 69, 416-431]. Ultrastructural examination of the axons of three cells revealed that of 53 labelled terminals studied, the majority formed synaptic contacts with dendritic shafts. Filling neurons with biocytin during paired intracellular recordings resulted in three well labelled interneurons, each of which was postsynaptic to a simultaneously recorded pyramidal neuron. In these pairs both cells were identified, but the presynaptic axon was poorly labelled in one. In one of the two pairs in which the pre- and postsynaptic neurons were fully recovered, light microscopic assessment indicated that the axon of the presynaptic pyramid formed 12 close appositions with dendrites of the postsynaptic interneuron. Six of these appositions were examined at the electron microscopic level and were identified as possible synaptic contacts. In the other pair three of six close appositions observed at the light level were verified as possible synaptic connections at the ultrastructural level. These correlated electrophysiological and anatomical studies provide the first evidence for connections from pyramid to burst firing interneurons in the neocortex and indicate that these connections can be mediated by multiple synaptic contacts. The accompanying paper describes the functional properties of these connections.

In slices of adult rat somatomotor cortex, paired intracellular recordings determined the properties of a novel class of excitatory connection, that of presynaptic pyramidal axon collaterals onto burst firing, spiny inhibitory interneurons. Single axon excitatory postsynaptic potentials were brief in time course and displayed conventional voltage relations, increasing in amplitude with membrane hyperpolarization with no change in time course. Excitatory postsynaptic potential amplitude distributions were not skewed. Paired pulse facilitation was profound at interspike intervals < 50 ms, but not altered by raising extracellular [Ca2+] from 2.5 to 5 mM, despite an apparent increase in release probability. Raising presynaptic firing frequency did however produce an increase in excitatory postsynaptic potentials elicited by first spikes that was associated with a decline in excitatory postsynaptic potentials elicited by second and third spikes in brief trains of presynaptic spikes. That this pattern of synaptic activity may result from low probabilities of transmitter release is discussed. It is proposed that while raising Ca2+ and increasing presynaptic firing both increase release probability, repetitive presynaptic firing raises probability more effectively than does raising extracellular [Ca2+]. However, concomitant exhaustion of readily releasable transmitter at higher firing rates may partially obscure this effect. It is concluded that the major differences in the firing rate- and firing pattern-dependent properties of pyramid-pyramid and pyramid-interneuron connections are due to the typically lower release probability at synapses onto interneurons. The accompanying paper describes the morphology of these connections.

A gene-targeting suicide vector for Streptococcus bovis has been constructed using the Escherichia coli/Streptococcus shuttle plasmid, pMU1328, and a region derived from the broad host-range, Gram-positive transposon, Tn916. This suicide plasmid replicates autonomously in E. coli, but not in Strep. bovis or Strep. bovis Tn916. Under positive selection, the plasmid was shown to integrate into Strep. bovis Tn916 chromosomal DNA at a frequency of 3 x 10(-8) cell-1 and was stably maintained for at least 100 generations in the absence of selection. This is the first report of a recombination system in ruminal bacteria. The ability to target genes, knock out specific functions or introduce novel genes into these micro-organisms will allow ruminal species to be manipulated and may eventually lead to improved animal production.

Many of the different morphological types of interneurons in mammalian neocortex are presumed to be inhibitory, but to date, conclusive functional data have been lacking. Using paired intracellular recordings in slices of adult rat somatosensory cortex, we present a sparsely spiny, burst firing interneuron that elicits in a simultaneously recorded pyramid a fast inhibitory postsynaptic potential, reversing at -78 mV. Neither inhibitory postsynaptic potential time course, nor paired pulse depression (inter-spike interval 15-120 ms), was affected by addition of the GABAB antagonist/partial agonist 2-OH-Saclofen (250 microM), but increasing extracellular [Ca2+] enhanced inhibitory postsynaptic potential amplitude at low firing rates and increased paired pulse depression at higher rates. Light microscopic examination of the biocytin-filled neurons revealed the presynaptic cell to be a sparsely spiny interneuron and the postsynaptic to be a small pyramidal neuron, both in layer II. Ultrastructural examination of 16 terminals of the presynaptic interneuron revealed that they formed symmetric contacts with unlabelled neurons, four with neuronal somata, 10 with dendritic shafts and two with spine shafts. This, therefore, is the first report of the properties of a single axon inhibitory postsynaptic potential in neocortex resulting from action potentials in an electro-physiologically and morphologically identified interneuron. We propose that at least some of the sparsely spiny, burst firing interneurons inhibit pyramidal neurons via GABAA receptors.

1. Double intracellular recordings were made from 1163 pairs of pyramidal neurones in layer V-VI of the rat somatomotor cortex in vitro using sharp electrodes filled with biocytin. Monosynaptically connected pairs of cells were identified when an action potential in one could elicit a constant latency excitatory postsynaptic potential (EPSP) in the other and the cells were filled with biocytin. Labelled cells were subsequently identified histologically with avidin-horseradish peroxidase. 2. Thirty-four pairs of cells were found to be monosynaptically connected. Fifteen of these pairs were sufficiently stable for electrophysiological recordings and three of these were recovered sufficiently to permit full morphological reconstruction. 3. The EPSP recorded between the first pair of pyramids varied in amplitude between 0 and 3 mV (mean 1.33 +/- 1.06 mV) and fluctuated considerably (coefficient of variation, 0.796). This was largely due to a high incidence of apparent failures of transmission. On reconstruction two boutons from the presynaptic pyramid axon were in close apposition to the proximal portions of basal dendrites of the postsynaptic cell. 4. In the second pair of pyramids the EPSP had a mean amplitude of 1.06 mV, and displayed a 10-90% rise time of 2.8 ms and a width at half-amplitude of 23 ms. This EPSP did not alter significantly with changes in membrane potential at the soma. The presynaptic axon closely apposed the distal apical dendrite of the postsynaptic cell in eight places. 5. In the third pair of pyramids, the EPSPs, recorded at a relatively depolarized membrane potential, were long lasting and could elicit slow dendritic spikes with long and variable latencies. These slow spikes suggested that the postsynaptic recording site was dendritic and on reconstruction a possible location was identified on the apical dendrite. A total of five presynaptic boutons closely apposed three separate, proximal branches of the postsynaptic apical dendrite. 6. These results provide the first illustration of a morphological basis for variations in functional properties of pyramid-pyramid connections in the neocortex.

A large body of anatomical data has detailed many complexities of neocortical circuitry, and physiological studies have indicated some roles for this circuitry in the complex functions of the cortex. Until recently, however, we have little precise information about the spatio-temporal properties of synaptic connections between individual neocortical neurones. Studies of synaptic responses elicited in one neocortical neurone by action potentials in another, and parallel morphological studies that have identified these neurones and the synaptic connections between them, have now described these parameters for certain types of local circuit connection in the neocortex. Some of these studies confirmed previous observations and inferences, but others provided major surprises. Evidence indicates that the class of both the presynaptic and postsynaptic neurone together determine a wide range of synaptic properties, such as the type of postsynaptic receptors involved and the temporal pattern of transmitter release, so that each type of synapse displays unique properties. A role for retrograde diffusable messages in determining the temporal properties of these circuits is postulated.

1. In slices of rat sensorimotor cortex, dual intracellular recordings were obtained from 1,952 pairs of deep layer pyramidal neurons. Where action potentials in one neurone elicited excitatory postsynaptic potentials (EPSPs, n = 56) in the other, responses to different presynaptic firing rates and patterns and at different postsynaptic membrane potentials were recorded and on some occasions both neurons were filled with biocytin. 2. Slices were fixed, sectioned again at 60 microns, and incubated with Avidin horseradish peroxidase (HRP), which was then visualized using the 3,3'-diaminobenzidine tetrahydrochloride (DAB) method. All neurones reported here that were identified histologically were pyramidal cells with their somata in the deep layers (V and VI). 3. One in 70 of the tests performed revealed a synaptic connection, 25 of which were studied in detail. Mean EPSP amplitude was 1.67 +/- 1.66 (SD) mV, with some single sweep events as large as 9 mV. For some of the smaller EPSPs the amplitude distributions contained a clear peak around 0 mV, the coefficient of variation (CV) was large, and paired pulse facilitation was apparent. EPSPs with large average amplitudes displayed no apparent failures of transmission, EPSP amplitudes were fairly evenly distributed around the mean, CVs were small, and paired pulse depression was apparent in 2.5 mM extracellular Ca2+. When single sweeps were selected according to the size of the first EPSP, large second EPSPs were found to follow small first EPSPs and small second EPSPs to follow large first EPSPs. Paired pulse effects appeared, in the majority of tests, to be due to a change in presynaptic release probability. 4. Two EPSPs were recorded in three different extracellular Ca2+ concentrations. In 1 mM Ca2+, the first EPSP of a short interval pair was small and paired pulse facilitation was apparent. In 5 mM Ca2+, first EPSPs were between 2.5 and 4 times larger than in 1 mM Ca2+ and paired pulse depression was apparent. In all Ca2+ concentrations however, averaged third and fourth EPSPs of brief bursts were of similar amplitudes and smaller than second EPSPs. If presynaptic inhibition does contribute to paired pulse effects here, it is not overcome by a combination of raised extracellular Ca2+ and repetitive presynaptic firing. 5. These EPSPs displayed a wide range of time courses. The mean 10-90% rise time was 2.49 +/- 1.08 ms, the mean width at half amplitude was 15.39 +/- 5.42 ms (n = 22), and the mean EPSP latency was 1.59 +/- 0.68 ms (n = 18). (ABSTRACT TRUNCATED AT 400 WORDS)

Single axon excitatory connections between pairs of neocortical pyramidal neurons were studied using paired intracellular recordings in layers II/III and IV of coronal slices of adult rat somatosensory/motor cortex. Excitatory postsynaptic potentials evoked with different presynaptic firing patterns and at different postsynaptic membrane potentials were compared. Two methods of statistical analysis were used in attempts to determine whether changes in mean excitatory postsynaptic potential amplitude were due to presynaptic or postsynaptic modifications. Analysis of the decrease in mean excitatory postsynaptic potential amplitude associated with increases in presynaptic firing rate were consistent with a change in probability of transmitter release. Paired pulse depression appeared to exhibit both presynaptic and postsynaptic components when the interspike interval was < 10 ms, but could be explained simply by a decrease in probability of release with interspike intervals between 10 and 80 ms. Previous studies had demonstrated that these excitatory postsynaptic potentials are partially mediated by N-methyl-D-aspartate receptors. In contrast to the apparently presynaptic effects of firing pattern, postsynaptic membrane depolarization appeared to produce an increase in quantal amplitude. In addition to this increase at low frequencies, a form of frequency-dependent, self-potentiation involving the recruitment of an additional, longer-latency postsynaptic component occurred at higher presynaptic firing rates. The possibility is discussed that two different mechanisms are involved in the replacement of vesicles at release sites. Over a few tens of milliseconds (paired-pulse depression) availability of releasable transmitter may be determined by the rate of replacement of discharged vesicles from a readily releasable pool of vesicles. Over longer periods of firing at 0.33-2 Hz, the readily releasable pool may become exhausted and require replenishment. Postsynaptic depolarization increases the duration of these excitatory postsynaptic potentials, facilitating summation and enables two components of excitatory postsynaptic potential enhancement at N-methyl-D-aspartate receptor-mediated synapses; one that is present at all firing rates and relates simply to voltage dependent events and one that occurs at higher firing rates and involves a gradual, time dependent event. These data also indicate that the optimal pyramidal firing pattern if another pyramid is to be activated is a tonic, or brief burst pattern at relatively low repetition rates. Long bursts of many presynaptic spikes recruit little that is not activated by pairs of spikes. This situation is in stark contrast to the results obtained in the following paper in which excitatory inputs from pyramids to non-pyramids are described.

In slices of adult rat somatosensory/motor cortex, paired recordings were made from pyramidal and non-pyramidal neurons. Single axon excitatory postsynaptic potentials evoked in the non-pyramidal neuron by action potentials in the pyramidal neuron were large and fast and demonstrated large fluctuations in amplitude, with coefficients of variation between 0.1 and 1.25. Excitatory postsynaptic potential amplitude distributions included a large number of apparent failures of transmission as well as some extremely large events. This contrasted dramatically with the relatively narrow distribution of amplitudes for pyramid-pyramid connections in neocortex. Excitatory postsynaptic potentials increased in amplitude with postsynaptic membrane hyperpolarization. Very small changes in the coefficient of variation when mean amplitudes increased substantially were consistent with the increase being due to a change in quantal amplitude. These excitatory postsynaptic potentials displayed profound paired pulse facilitation. Moreover, third and fourth spikes in a presynaptic burst also evoked large responses. This facilitation was associated with a decrease in the proportion of apparent failures in transmission and a change in the shape of the excitatory postsynaptic potential amplitude distribution, both indicative of an increase in the probability of transmitter release. However a large change in the mean amplitude was not associated with a similar change in the inverse square of the coefficient of variation. The result of this third test, taken in isolation, might therefore suggest that quantal amplitude had increased with paired-pulse facilitation. However, of the three tests applied, this last is the most heavily model-dependent and produced a result inconsistent with the results of the other two tests. The possibility is therefore discussed that both the shape of the excitatory postsynaptic potential amplitude distribution and the failure of coefficient of variation analysis to detect an apparently presynaptic change might result from the release at these synapses being poorly fit by a simple model. Based on a more complex model of synaptic release proposed by Faber and Korn [Faber and Korn (1991) Biophys. J. 60, 1288-1294] and a hypothesis proposed by Scharfman et al. [Scharfman et al. (1990) Neuroscience 37, 693-707], two hypotheses arising from the present study are discussed: (i) that branch point failure contributes to the pattern of synaptic activation at these connections; and (ii) that both presynaptic pyramidal firing pattern and axonal geometry contribute to the selection of the type of postsynaptic neurone preferentially activated.(ABSTRACT TRUNCATED AT 400 WORDS)

Ruminant production is a major focus of Australian agriculture. The ability of ruminant animals such as sheep and cattle to make productive use of low quality plant materials depends on the activity and efficiency of the anaerobic microbial population that resides in the rumen. Factors that affect ruminant production include the ability of cellulolytic microorganisms to digest plant structural polysaccharides (primarily cellulose and hemicellulose), the capacity of microorganisms to metabolise and detoxify otherwise inhibitory plant products and the efficiency of nitrogen utilisation by ruminal organisms. This review will consider some current Australian research programs aimed at improving ruminant production efficiency by genetic engineering of ruminal bacteria.

These experiments combined electrophysiological recordings from hippocampal slices with application of drugs to and sampling of extracellular fluid from a restricted region of the slice using a push-pull cannula placed under the slice in an interface chamber. Stable and apparently normal extracellular and intracellular recordings could be obtained directly over the tip of the cannula and solutions changed without disturbing the recording. Relatively rapid effects (1-5 min) were observed when TTX, CNQX, or medium containing 50 mM K+ were applied via the cannula and recovery from these effects was achieved. In addition, effects were restricted to the immediate vicinity of the cannula; neurones recorded several hundred micrometers away were apparently unaffected. Samples of extracellular fluid obtained as minute fractions during the application of high K+ containing medium contained higher concentrations of GABA, aspartate and glutamate than control fractions but the same levels of other amino acids, e.g., isoleucine and leucine. With appropriate design of push-pull cannula and recording chamber, therefore, stable electrophysiological recordings can be combined with localized extracellular fluid sampling and rapid and localized application of test solutions in an interface slice chamber.

Activity-dependent changes in synaptic efficacy may underlie the acquisition of memory. Much interest has centred on the involvement of NMDA (N-methyl-D-aspartate) receptors in the induction of long-term potentiation (LTP), but since activation of this receptor alone results only in short-term enhancement, other receptors are clearly involved. This paper describes a novel form of lasting synaptic enhancement requiring concomitant activation of both NMDA and metabotropic quisqualate, or Qp receptors for induction. Neither high frequency presynaptic activity, co-activation of many presynaptic axons, postsynaptic depolarization, nor blockade of inhibition were required. However, repetitive, though relatively low frequency activity of the presynaptic axon appeared to be necessary. We suggest, tentatively, that presynaptic activity may be directly involved in priming the recently active terminal to respond to postsynaptic changes.

Spike triggered averaging was used to record local circuit connections between pairs of CA1 pyramidal neurons in isolated slices of rat hippocampus. Of 795 pairs of neurons tested, six were connected. These epsps were only partially blocked by 2-amino-5-phosphonovalerate (AP-5), which decreased the amplitude and half width of the epsp, but did not affect the early rising phase. In contrast, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked all phases of the epsp and combinations of AP-5 and CNQX blocked the epsp almost entirely. These results indicate that these epsps were mediated by both N-methyl-d-aspartate (NMDA) and non-NMDA excitatory amino acid receptors. Moreover, they exhibited a voltage relation typical of neuronal responses to NMDA, increasing in amplitude and duration as the postsynaptic cell was depolarized. These epsps were brief (10 - 90% rise time < 5 ms, width at half amplitude < 20 ms), indicating a proximal location. Increasing presynaptic firing rate (1 - 4 spikes/s) reduced average epsp amplitude by almost 50%. When epsps were evoked by pairs of spikes (interval 3 - 25 ms), a large response to the first spike precluded a large response to the second. No evidence for selective enhancement of the NMDA receptor component by paired spike activation was found. It is concluded that a significant NMDA receptor mediated input to CA1 is provided by local circuit CA1 - CA1 connections and that these synapses can be demonstrated under control conditions.

Recently there has been much research effort directed towards the development of immunosensors. Optical technologies are currently proving very attractive for the construction of such sensors. The fluorescence capillary fill device (FCFD) has been designed to fulfil these needs. The development of an assay for human chorionic gonadotrophin (hCG) in the FCFD for a variety of body fluids (whole blood, serum, urine and saliva) demonstrates the versatility and assay performance of the device.

Lasting enhancement of minimal Schaffer collateral epsps in CA1 pyramidal neurons was induced when these epsps were coactivated with putative local circuit N-methyl-d-aspartate (NMDA) receptor-mediated epsps. In transverse slices of hippocampus, minimal epsps were evoked by stimulating the Schaffer collateral/commissural pathway within CA3 stratum radiatum and the local circuit axons were stimulated within CA1 stratum oriens or alveus using fine, two barrel glass micropipettes. Minimal Schaffer collateral epsps were insensitive to d-2-amino-5-phosphonovalerate (AP-5) and displayed conventional voltage relations. Local epsps were sensitive to AP-5 and increased in amplitude and duration with membrane depolarization. High frequency tetanic stimulation of the minimal Schaffer collateral epsps induced no lasting enhancement. However, pairing of the Schaffer epsp with a frequency potentiated local epsp resulted in a delayed, but lasting increase in the Schaffer epsp. When the local epsp did not exhibit frequency potentiation during pairing, no enhancement resulted. When either epsp was contaminated with an ipsp, no lasting increase resulted. When transmission through the alveus was blocked by focal application of local anaesthetic, traditional protocols for long-term potentiation (LTP) induction were relatively ineffective. These results indicate that a significant source of the NMDA receptor activation required for the induction of LTP in the Schaffer collateral input to CA1 derives from local circuit connections between CA1 pyramidal neurons and, moreover, that lasting enhancement can be induced with low frequency activation, at postsynaptic resting potential, in the presence of Mg2+ and with local inhibition intact.

Deoxyribonuclease activity was surveyed in 22 strains belonging to 12 species of rumen bacteria, with lambda bacteriophage DNA as substrate. Activity was readily detected in broken cell preparations from 15 of these strains. Particularly high levels of activity were present in cells and culture supernatant of all 5 strains of Bacteroides succinogenes, and 2 out of 6 strains of Bacteroides ruminicola, examined.

In isolated slices of hypothalamus, suprachiasmatic nucleus (SCN) neurons were recorded intracellularly. Blockade of Ca++ channels increased spike duration, eliminating an early component of the afterhyperpolarization (AHP) that followed evoked spikes. The duration and reversal potential of AHPs were, however, unaffected, suggesting that only an early, fast component of the AHP was Ca(++)-dependent. Unlike other central neurons that exhibit pacemaker activity, therefore, SCN neurons do not display a pronounced, long-lasting Ca(++)-dependent AHP. Extracellular Ba++ and intracellular Cs+ both revealed slow depolarizing potentials evoked either by depolarizing current injection, or by repolarization following large hyperpolarizations. They had different effects on the shape of spikes and the AHPs that followed them, however. Cs+, which blocks almost all K+ channels, dramatically reduced resting potential, greatly increased spike duration (to tens of milliseconds), and blocked AHPs completely. In contrast, Ba++ had little effect on resting potential and produced only a small increase in spike duration, depressing an early Ca(++)-dependent component and a later Ca(++)-independent component of the AHP. The relatively weak pacemaker activity of SCN neurons appears to involve voltage-dependent activation of at least one slowly inactivating inward current, which brings the cells to firing threshold and maintains tonic firing; both Ca(++)-dependent and Ca(++)-independent K+ channels, which repolarize cells after spikes and maintain interspike intervals; and Ca++ channels, which contribute to activation of Ca(++)-activated K+ currents and may also contribute to slow depolarizing potentials. In the absence of powerful synaptic inputs, SCN neurons express a pacemaker activity that is sufficient to maintain an impressively regular firing pattern. Slow, repetitive activation of optic input, however, increases local circuit activity to such an extent that the normal pacemaker potentials are overridden and firing patterns are altered. Since SCN neurons are very small and have large input resistances, they are particularly susceptible to synaptic input.

Responses of neocortical pyramidal cells to excitatory amino acids were recorded intracellularly. Agonists and antagonists were applied electrophoretically from a separate multibarrel pipette and care taken to ensure that the pipette was positioned to evoke optimal responses to N-methyl-D-aspartate (NMDA), or homocysteic acid, before control responses were recorded. Responses to NMDA, but not those to alpha-amino-3-hydroxy-5-methyl-4-isoxazdepropionic acid (AMPA) or quisqualate, were enhanced when glycine was co-applied. Responses to AMPA, quisqualate and NMDA were reduced by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) applied either electrophoretically, or in the bathing medium, with responses to quisqualate being the least and those to AMPA being the most sensitive to CNQX. The blockade of NMDA responses by CNQX was selectively reversed by additional glycine confirming that CNQX blocks NMDA receptor-channel complexes at the glycine, rather than at the NMDA site. Under control conditions, responses to glutamate resembled responses to quisqualate, and were relatively insensitive to CNQX, 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-l-phosphonic acid and 2-amino-5-phosphonovalerate, while responses to homocysteic acid resembled responses to NMDA and were blocked by these antagonists. This suggested that homocysteic acid acted at NMDA receptors, while glutamate acted primarily at non-NMDA receptors. However, responses to both glutamate and homocysteic acid were augmented by additional glycine when these transmitter candidates were applied close to a "hot spot" for NMDA receptor activation. The glycine enhancement of responses to glutamate was sensitive to NMDA antagonists, indicating that glutamate can activate NMDA receptors in an intact preparation if glycine levels are high enough.

669 boys and 753 girls born in 1962 and living at home were observed at approximately half-yearly intervals from 9 to 17 years of age. Mean ages of reaching various developmental stages were calculated for voice change and facial hair in boys, menarche and breast development in girls, and for axillary hair in both sexes. Peak height velocity and age at which it occurred were also calculated for both sexes. Means were generally in good agreement with those found about 15 years previously in the Harpenden Growth Study. Most pubertal changes in the present study showed gradients by social class; in boys, development was later in those with fathers in unskilled manual occupations, whereas in girls the greatest differences, where found, were between those with fathers in non-manual occupations and the remainder.

In isolated slices of rat thalamus, inhibitory postsynaptic potentials evoked by electrical stimulation of the nucleus reticularis, were recorded intracellularly in relay neurons in the anterior part of the thalamus. These inhibitory postsynaptic potentials were found to have reversal potentials close to the resting potential of the recorded cell, to reduce neuronal excitability and to be sensitive to electrophoretic application of the GABA antagonists bicuculline and picrotoxin, indicating that they were GABA-activated, chloride mediated events. Voltage sensitive responses of relay neurons evoked by current injection and by inhibitory postsynaptic potentials were then compared. Hyperpolarizing current pulses and hyperpolarizing inhibitory postsynaptic potential trains elicited from membrane potentials positive to -70 mV resulted in rebound slow spike activation on repolarization. Depolarizing current pulses and depolarizing inhibitory postsynaptic potential trains evoked slow spikes when elicited from membrane potentials negative to -60 mV. There was, however, one major difference, the slow spikes evoked by inhibitory postsynaptic potentials were always delayed to the end of the train. Reversal potentials of evoked inhibitory postsynaptic potentials were found to depend on the potential at which the membrane was held immediately before the inhibitory postsynaptic potential was evoked, indicating that passive distribution of chloride ions contributes to their equilibrium potential. Evoked inhibitory postsynaptic potentials consisted of at least two components with different reversal potentials although current voltage relations indicated that similar decreases in membrane resistance were associated with both components and that they shifted approximately in parallel when inhibitory postsynaptic potentials were evoked from different holding potentials. Trains of GABA-mediated inhibitory postsynaptic potentials, similar to those recorded during spindling, will evoke slow spikes in almost all thalamic relay neurons irrespective of other synaptic inputs. This response will effectively synchronize burst firing in all cells receiving the same inhibitory input.

Weights and a number of linear measurements were related to crown-heel length in fresh apparently normal foetuses ranging from 8 to 21 weeks' post-menstrual age. The average relationships agreed remarkably well with results reported many years ago on the basis of preserved specimens mostly from spontaneous abortions. There was no evidence of sex differences.

In isolated slices of rat cortex, intracellularly recorded responses of pyramidal neurones to N-methylaspartate (NMA) and glutamate and responses to stimulation of the underlying white matter were compared and challenged with the sigma opiate cyclazocine. Cyclazocine blocked responses to iontophoretically applied NMA and one component of the postsynaptic response to stimulation, but left other postsynaptic events and responses to glutamate intact. These results are consistent with the view that sigma opiates act as selective NMA antagonists and block synaptic events mediated by NMA receptors.