Sites of synaptic junctions established by a GABAergic basket cell on an interneuron in the CA1 area of the rat hippocampus.
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Animals↗
Biomedical subjects
S R Cobb
Publications and source records attributed to S R Cobb.
Synchronization of neuronal activity in hippocampus by individual GABAergic interneurons.
SYNCHRONIZATION of neuronal activity is fundamental in the operation of cortical networks. With respect to an ongoing synchronized oscillation, the precise timing of action potentials is an attractive candidate mechanism for information coding. Networks of inhibitory interneurons have been proposed to have a role in entraining cortical, synchronized 40-Hz activity. Here we demonstrate that individual GABAergic interneurons can effectively phase spontaneous firing and subthreshold oscillations in hippocampal pyramidal cells at 0 frequencies (4-7 Hz). The efficiency of this entrainment is due to interaction of GABAA-receptor-mediated hyperpolarizing synaptic events with intrinsic oscillatory mechanisms tuned to this frequency range in pyramidal cells. Moreover, this GABAergic mechanism is sufficient to synchronize the firing of pyramidal cells. Thus, owing to the divergence of each GABAergic interneuron, more than a thousand pyramidal cells may share a common temporal reference established by an individual interneuron.
Action Potentials↗
Properties of unitary IPSPs evoked by anatomically identified basket cells in the rat hippocampus.
Hippocampal pyramidal cells receive GABA-mediated synaptic input from several distinct interneurons. In order to define the effect of perisomatic synapses, intracellular recordings were made with biocytin-containing microelectrodes from synaptically connected inhibitory and pyramidal cell pairs in subfields CA1 and CA3 of the rat hippocampus. Subsequent physiological analysis were restricted to the category of cells, here referred to as basket cells (n = 14), which had an efferent synaptic target profile (n = 282 synaptic contacts) of predominantly somatic (48.2%) and proximal dendritic synapses (45.0%). Electron microscopic analysis revealed that in two instances identified postsynaptic pyramidal cells received a total of 10 and 12 labelled basket cell synapses respectively. At an average membrane potential of -57.8 +/- 4.6 mV, unitary inhibitory postsynaptic potentials (IPSPs; n = 24) had a mean amplitude of 450 +/- 238 microV, a 10-90% rise time of 4.6 +/- 3.2 ms and, measured at half-amplitude, a mean duration of 31.6 +/- 18.2 ms. In most instances (n = 19) the IPSP decay could be fitted with a single exponential with a mean time constant of 32.4 +/- 18.0 ms. Unitary basket cell-evoked IPSPs (n = 5) was extrapolated to be at -74.9 +/- 6.0 mV. Averages of unitary IPSPs had a mean calculated conductance of 0.95 +/- 0.29 nS, ranging from 0.52 to 1.16 nS. Unitary basket cell IPSPs (n = 3) increased in amplitude by 26.6 +/- 19.9% following bath application of the GABAB receptor antagonist CGP 55845A [correction of CGP 35845A] (1-4 microM), whereas subsequent addition of the GABAA receptor antagonist bicuculline (10-13 microM) reduced the IPSP amplitude to 13.5 +/- 3.1% of the control response. Rapid presynaptic trains of basket cell action potentials resulted in the summation of up to four postsynaptic responses (n = 5). However, any increase in the rate of tonic firing (2- to 10-fold) led to a > 50% reduction of the postsynaptic response amplitude. At depolarized membrane potentials, averaged IPSPs could be followed by a distinct depolarizing overshoot or postinhibitory facilitation (n = 4). At firing threshold, pyramidal cells fired postinhibitory rebound-like action potentials, the latter in close temporal overlap with the depolarizing overshoot. In conclusion, hippocampal basket cells have been identified as one source of fast, GABAA receptor-evoked perisomatic inhibition. Unitary events are mediated by multiple synaptic release sites, thus providing an effective mechanism to avoid total transmission failures.
Action Potentials↗
Hearing loss and temporal bone structure in achondroplasia.
Characteristic temporal bone changes have recently been defined by high resolution CT in nine patients with achondroplasia (Cobb et al., Am J Neuroradiol 9:1195, 1988). These included narrowing of the skull base and "towering" petrous ridges resulting in abnormal orientation of the inner and middle ear structures. In order to determine whether these morphologic changes are the cause of the hearing deficit in achondroplasia, audiometric studies and ENT evaluation were performed in eight of the nine patients. All had a history of frequent otitis media and four had experienced tympanic membrane tube insertion. Three patients had significant sensorineural hearing loss, two had conductive hearing loss and one patient had combined hearing loss. None of the temporal bone morphologic changes were found to be correlated with the degree of either sensorineural or conductive hearing loss. Fusion of the ossicular chain was not present in any of our cases. Appropriate treatment of frequent acute otitis media and early awareness of middle ear effusions and conductive hearing loss in children with achondroplasia may be of great importance in preventing permanent hearing loss.
Achondroplasia↗
On a possible explanation as to why most people have small refractive errors.
The case is made that there must be a feedback mechanism operating during the development of the human eye which means that over a population most people have relatively small refractive errors. The possible feedback mechanisms are examined and the conclusion is drawn that chromatic aberration of the human eye may produce visual cues which could be utilized in such a feedback system.
Brain↗
Preoperative splenic artery occlusion as an adjunct for high risk splenectomy.
High risk splenectomy is often encountered in cases of hypersplenism with massive splenomegaly (10 times usual weight of 150-200 g) resulting from myelophthisic processes. Intra-operative ligation of the splenic artery through the lesser sac is a technically useful method of gaining vascular control prior to mobilizing the challenging spleen. However, a massive or inaccessible spleen imposes mechanical limitations during surgery and may be complicated by torrential intra-operative hemorrhage in the setting of severe thrombocytopenia refractile to platelet transfusions. The authors describe pre-operative intravascular proximal splenic artery control in four adult patients (3 men, 1 woman) with extreme splenomegaly (2,250-10,000 g). The massive splenomegaly in this group resulted from chronic myelogenous leukemia (n = 2), isolated splenic lymphoma (n = 1), and agnogenic myeloid metaplasia (n = 1). Chief symptom manifestations included left upper quadrant abdominal pain, early satiety, post-prandial emesis, dyspnea, petechiae, and associated easy bruising. Prior to surgery, all the patients were taken to the radiology suite where either detachable silastic balloons or stainless steel coils were placed selectively into the splenic artery under fluoroscopic guidance requiring approximately 35 minutes. Splenic artery occlusion aided normalization of thrombocytopenia (average increases 19,000/microliter to 215,000/microliter) with prolongation in survival of platelets. Successful splenectomy was subsequently performed with no additional transfusion requirements and was made technically easier by reducing splenic bulk. There were no adverse consequences of intravascular occlusion and no peri-operative morbidity or mortality. Preoperative intravascular selective splenic artery occlusion, used as an important potential adjunct to anticipated high risk splenectomy, is recommended.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Wallerian degeneration in a patient with Schilder disease: MR imaging demonstration.
Wallerian degeneration in the corticospinal tract was demonstrated by magnetic resonance (MR) imaging in a patient with Schilder disease. The histochemical stages of myelin breakdown that allow its demonstration by MR imaging are reviewed.
Adult↗
On a possible explanation of the unusually high rates of colour vision defects in some west of Scotland primary schools.
The rate of Colour Vision Defect in some West of Scotland Primary Schools can be nearly four times higher than the normal rate for European whites. Population isolates in Ireland at the time of the troubles when immigration to Scotland was occurring could be a possible explanation.
Child↗
Persistent trigeminal artery variant. Carotid-anterior inferior cerebellar artery anastomosis.
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Adult↗
Radiologic considerations in neurocysticercosis.
Radiologic imaging techniques play an important role in the diagnosis and management of neurocysticercosis. Cysticercal involvement of the central nervous system can be classified as parenchymal, ventricular, meningo-cisternal, spinal, and mixed, depending upon the site of involvement. Computerized tomographic scanning has replaced most of the previously used techniques for assessing parenchymal disease and diagnosis has been greatly improved. Ventriculography and myelography are still useful in cases of intraventricular and spinal disease respectively.
Adolescent↗
Exchange threshold colorimeter and analytical anomaloscope of class I and class II subjects and colour defectives.
The spectral absorption curve of 'red' cones erytholabe and the 'green' cones chlorolabe are examined by these techniques. Evidence is elicited for a fourth photopic response peaking at approximately 570 nm.
Color Perception↗
A model for colour vision defect.
The Unique Green phenomenon whereby the wavelengths of light which are judged neither blue-green nor yellow-green show a distinct genetic polymorph. Amongst the males there is a clear bimodality whereas there is a near normal distribution amongst the females. The classification of the types of person so produced breeds true apparently in the X-chromosome. This phenomenon now having been confirmed is impossible to fit into the strict Walraven model of colour vision without modification. The modification that would be used is discussed and it is shown that a number of other difficulties within the Walraven model model can also be resolved.
Color Perception↗
Evidence for an effect by colour defect on personality.
This paper discusses whether defective colour vision affects the type of personality of the individual. Three pieces of recent research are examined. Pickford and Cobb (1974) found a positive relation between colour defect and type of personality when they tested a sample of students in psychology. However, two later studies of school children did not demonstrate such a relationship. It is postulated that the contradiction in results between the first and the last two studies can be explained by the assumption that the effects of colour defect on the personality do not occur until later in life.
Adaptation, Psychological↗
Red/green colour defect among the Roman Catholic and non-denominational population.
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Catholicism↗
Study of foveal tritanopia.
This paper discusses the possibility there is a difference between men and women in foveal tritanopia. The discussion is based on a study carried out by Cobb and McCrossan in 1973 in which they measured the luminosity curves of the fovea in five women and five men. The instrument used was a Wright colorimeter which measured the luminosity curves with a 2 degree 12' field and a 0 degree 12.5' field. Comparison shows a loss of sensitivity to blue for the curve obtained with the 0 degrees 12.5 relative to the curve obtained with the 2 degree 12' field. Male subjects obtained two maxima with the 0 degree 12.5' field, usually at 555 nm and 595 nm, whereas for females on maximum, usually at 555 nm and from 555 nm to the long wavelength end of the spectrum, curves followed loosely the curve obtained with the 2 degree 12' field. Thus, a significant difference was found between the males and the females in their response to the longer wave-lengths when the 0 degree 12.5' (0 degree 12.5') field was used. In addition to this there were also large individual differences in the matching points obtained by the males while the differences among the females were much smaller.
Adult↗
Examination of class I, class II, normals and colour defectives on exchange threshold colorimeter and analytical anomaloscope.
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Color Perception Tests↗
Resolution acuity in astigmats: evidence for a critical period in the human visual system.
Astigmats, who have been fully optically corrected, show an acuity configuration highly characteristic of the uncorrected astigmatism when they are tested with gratings of different orientations. This phenomenon, which is called meridional amblyopia, has been supposed to be neural in origin. This paper attempts to show that there is evidence for a critical period in the visual system of humans. In the experiment described here twelve astigmatic subjects were tested against a control group of six non-astigmatic (emmetropic) subjects. The astigmatic subjects differed in the ages at which they had been initially optically corrected. Square-wave gratings were used to test the subjects and measures of acuity for different orientations were recorded. It was found that those astigmatic subjects corrected above the age of seven showed the usual acuity decrement while those corrected below seven showed significantly smaller meridional amblyopia. The age of seven, therefore, was taken to mark the end of a critical period in the development of the human visual system, after which the system ceases to be structurally influenced by visual input.
Adult↗
The effect of exposure time upon perceived size.
An experiment whereby a standard filled circle is exposed for 100-1000 msec on the tachistoscope for ten subjects. Each is asked to choose a comparison circle, which appears to be the same size, out of a series of eleven filled circles of various angular subtenses larger and smaller than the standard filled circle in the tachistoscope. The results indicate that exposure time has a role in the perception of size.
Adult↗