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Biomedical subjects

H Burton

Publications and source records attributed to H Burton.

At least 109 records · Page 6Linked to original sources
PubMed1978

The literature review: an integral part of the research process.

The importance of the review of literature, a component of any research study, has been relatively downgraded by occupational therapists because it is time-consuming. In order to encourage novice researchers and illustrate the importance of a comprehensive review of related literature, a review was carried out in the area of auditory feedback and the teaching of the use of myo-electrically controlled prostheses. This illustration of method in research includes initial ideas, assumptions and facts, the researchable question, the literature review and the conclusions drawn from the review which help guide the researcher in his potential study.

Amputees↗
PubMed1977

Cells of origin and terminal distribution of corticostriatal fibers arising in the sensory-motor cortex of monkeys.

The cells of origin of the corticostriatal projection have been identified in squirrel monkeys by the use of the retrograde horseradish peroxidase method. In the subfields of the somatic sensory, motor, parietal and frontal areas of the cortex, cells projecting to the ipsilateral striatum are relatively sparsely distributed and form a group of small- to medium-sized pyramidal cells with an average somal diameter from area to area of 14-16 mum. Such cells are found only in layer V of the cortex (mainly in the more superficial parts of the layer). Since they are consistently smaller than the pyramidal cells of layer V that project to the brainstem and spinal cord and since they lie outside layer VI which gives rise to corticothalamic axons, the corticostriatal axons are unlikely to be collaterals of axons projecting to other sites. The cells of origin of the crossed corticostriatal projection are also found in layer V and are pyramidal cells with somal diameters in the same range as above. They are found only in areas 4, 8, and 6. Studies with the anterograde, autoradiographic method in rhesus, cynomologous and squirrel monkeys, indicate that the somatic sensory areas project to most of the antero-posterior extent of the ipsilateral putamen. Subareas 3a, 3b, 1 and 2 of the somatic sensory cortex project to the same region and the projection overlaps similarly extensive projections from the motor and certain other areas of the cortex. However, in each case the pattern of terminal labeling is in the form of interrupted clusters, strips and bands. A single small injection of the cortex is associated with only one or two such clusters of terminal labeling. This seems to imply that individual corticostriatal fibers end in a very restricted manner and that the terminal ramifications of fibers from one cortical area may alternate in the putamen with those arising in other areas.

Animals↗
PubMed1976

Synaptic transmission between rat spinal cord explants and dissociated superior cervical ganglion neurons in tissue culture.

Physiological properties of the synapses formed between explants of spinal cord and dissociated autonomic ganglion neurons in tissue culture were studied using intracellular and extracellular stimulation and recording techniques (as well as iontophoresis) with a culture perfusion system allowing continuous microscopic observation during repeated changes of the bathing medium. The principal neurons of the superior cervical ganglion (SCGN) were dissociated from perinatal rats and the spinal cord explants were obtained from 15-day rat fetuses; these were allowed to mature for 3-10 weeks in co-culture. Recordings from over 1000 SCGN established that: (a) spontaneous small depolarizations and action potentials occurred in 20% of the SCGN studied, (b) the EPSPs observed in SCGN after spinal cord stimulation were sensitive to decreased Ca2+ and increased Mg2+, as well as to D-tubocurare, hexamethonium and mecamylamine, but not to atropine (at 10(-6) M concentration) or to the alpha-adrenergic blocking agents phentolamine or phenoxybenzamine; no potentiation of the EPSPs was seen with neostigmate or eserine, (c) acetylcholine directly applied to the SCGN was seen to mimic the responses seen after spinal cord stimulation; tetrodotoxin blocked both direct and iontophoretically fired action potentials, with only a suprathreshold acetylcholine potential remaining. These synapses were not sensitive to alpha-bungarotoxin. It is concluded that the synapses formed by spinal cord neurites on principal SCGN in tissue culture are nicotinic cholinergic, and that the evoked EPSPs recorded in this study are thus similar to the orthodromic fast EPSPs observed in vivo. No slow synaptic responses were observed and no demonstrable effects were noted that could be attributed to adrenergic transmission.

Acetylcholine↗
PubMed1976

Synaptic transmission between rat superior cervical ganglion neurons in dissociated cell cultures.

The principal neurons of the rat superior cervical ganglion (SCGN) when established as dissociated cells in tissue culture form synapses among themselves. In the present study we have examined this synaptic interaction when these neurons are co-cultured with several other types of tissues. Dissociated SCGN were prepared from perinatal rats and studied, after 3-4 weeks maturation, with intracellular recording techniques. Synaptic interactions between sympathetic neurons were demonstrated when these cells were: (a) grown with explants from newborn rat thoracic spinal cord, (b) when the SCGN had survived for several weeks subsequent to removal of the spinal cord explants, and (c) when the SCGN were grown in the presence of an adrenergic target (interscapular brown fat cells). Unidirectional, reciprocal, recurrent and complex chemical synaptic networks, consisting of convergence and divergence, characterized connections between SCGN. All synaptic responses were cholinergic since they were reversibly blocked by hexamethonium or mecamylamine but were not sensitive to 10(-5) M phenoxybenzamine. Removal of the spinal cord explants did not significantly alter the proportion of chemical synaptic interactions between SCGN (more than 25%) from matched cultures. Anatomical observations established that in cultures with brown fat, innervating neurites appeared on the fat cells; these neurites frequently expanded to form varicosities that resembled the adrenergic terminals normally seen on brown fat in the animal. Synaptic profiles also occurred on the neurons in these cultures and some of these were shown to be cholinergic. The proportion of neuronal interactions in the combined SCGN + fat cultures was low, however, suggesting that co-culture with target tissue might influence the frequency of interconnections developed between SCGN in culture. Other factors, such as the presence of non-neuronal cells, degree of dissociation, cellular density, culture age and the survival of certain types of SCGN in culture are discussed as variables related to the formation of synapses between SCGN. Non-rectified electrical coupling between SCGN was also observed in 17 out of 679 pairs (2.5%) of neurons. Attenuation factor for electrically coupled action potentials ranged between 1 and 43.5.

Adipose Tissue, Brown↗
PubMed1976

Areal differences in the laminar distribution of thalamic afferents in cortical fields of the insular, parietal and temporal regions of primates.

A cytoarchitectonic parcellation has been made of the cortex of the insula and of the adjoining parts of the temporal and parietal lobes in rhesus and squirrel monkeys. In conjunction with this, the intracortical distribution of the thalamo-cortical fibers has been studied by the autoradiographic tracing technique. There is a systematic change in the density, laminar distribution and general character of the intracortical thalamic afferent plexus which seems to follow, in particular, the progressive differentiation of cortical layering that occurs in moving from insular through granular to homotypical cortex. In the dysgranular and granular insular areas in which cortical lamination is indistinct, the thalamic plexus as demonstrated autoradiographically is sparse and extends through much of layers III and IV. In the granular cortex (areas 3b and AI), the thalamic plexus is densest and coarsest; it fills all of layers IV and IIIB and extends into layer IIIA. In the "second" and "third" sensory areas, such as the second somatic sensory and many of the auditory fields, the density of the plexus and its coarseness diminish slightly and the deeper half of layer IV becomes free of terminals. In the homotypical cortex, the plexus becomes sparser, finer and strictly confined to layer IIIB. In many areas there are additional indications of thalamic terminations in deeper layers. Where layers V and VI are not divided into sublaminae (e.g.,in areas 3b and AI) there is labeling of the superficial half of layer VI. Where layers V and VI become subdivided in the homotypical cortex, the auditory and adjacent fields were only observed in cases in which the magnocellular nucleus of the medial geniculate body was involved by the injection of isotope. The boundaries of the cortical projection fields of individual thalamic nuclei, as determined autoradiographically, are remarkably sharp and invariably coincide with a sharp architectonic boundary or with a zone of maximal cytoarchitectonic change. Zones of apparent architectonic transition never showed overlap of thalamic afferents emanating from more than one nucleus. These results raise for discussion the significance of architectonic structure in relation to cortical connectivity and have a bearing upon those studies that have attempted to relate the terminals of thalamic afferents to particular classes of cortical neuron.

Animals↗
PubMed1976

The posterior thalamic region and its cortical projection in New World and Old World monkeys.

The posterior nuclear complex of the thalamus in rhesus, pigtailed and squirrel monkeys consists of the combined suprageniculate-limitans nucleus and an ill defined region of heterogeneous cell types extending anteriorly from the dorsal lobe of the medial geniculate body towards the posterior pole of the ventral nuclear complex. This region is referred to as the posterior nucleus. It is directly continuous with the ventroposteroinferior nucleus. The cortical projections of each of these nuclei, together with those of the adjacent ventral, pulvinar and medial geniculate complexes, have been studied by means of the autoradiographic tracing technique. The suprageniculate-limitans nucleus, the main input to which is the superior colliculus, projects upon the granular insular area of the cortex. The medial portion of the posterior nucleus projects to the retroinsular field lying posterior to the second somatic sensory area. There is clinical and electrophysiological evidence to suggest that the retroinsular area may form part of a central pain pathway. The lateral portion of the posterior nucleus which is closely related to certain elements of the medial geniculate complex, projects to the postauditory cortical field. The ventroposterioinferior nucleus, which may be involved in vestibular function, projects to the dysgranular insular field. The principal medial geniculate nucleus can be subdivided into a ventral division that projects to field AI of the auditory cortex and a dorsal division that merges with the posterior nucleus; it is further subdivided into an anterodorsal component that projects to two fields on the superior temporal gyrus, together with a posterodorsal component in which separate cell populations project to areas lying anterior and medial to AI. The magnocellular medial geniculate nucleus, sometimes considered a part of the posterior complex, appears to project diffusely to layer I of all the auditory fields. The auditory fields are bounded on three sides by the projection field of the medial nucleus of the pulvinar which also extends into the upper end of the lateral sulcus to bound the fields receiving fibers from the posterior nucleus. The topography of the areas receiving fibers from the posterior, medial geniculate and pulvinar complexes, taken in conjunction with the rotation of the primate temporal lobe, permits all of these fields to be compared with similar, better known areas in the cat brain.

Animals↗
PubMed1976

Midbrain, diencephalic and cortical relationships of the basal nucleus of Meynert and associated structures in primates.

The structure and connectivity of the basal nucleus of Meynert, the substantia innominata in which it lies, and certain related areas have been examined in New World and Old World Monkeys, using retrograde and anterograde axonal transport methods. Experiments using the retrograde, horseradish peroxidase method confirm the observations of Kievet and Kuypers ('75) that the basal nucleus and substantia innominata project directly, heavily and with a somewhat crude topography upon the neocortex. Experiments involving the anterograde, autoradiographic method show that the basal nucleus and substantia innominata form part of a complex pathway that links them together with the lateral hypothalamus, certain parts of the amygdala and the peripeduncular nucleus of the midbrain. The peripeduncular nucleus is often regarded as a part of the central auditory pathway; it gives rise to a fiber bundle of considerable size that ascends on the dorsal surface of the ipsilateral optic tract and terminates ultimately in the lateral hypothalamic area of both sides. As well as distributing fibers to the basal nucleus, substantia innominata and lateral hypothalamus, this pathway provides a heavy projection to a cytoarchitectonically distinct posterior part of the lateral nucleus of the amygdala, the medial and intercalated nuclei of the amygdala and a less dense projection to the bed nucleus of the stria terminalis. Certain parts of the hypothalamus and possibly the preoptic areas give rise to a complementary descending pathway that distributes fibers to the ipsilateral basal nucleus, substantia innominata and amygdala, and ends in the peripeduncular nuclei of both sides. Decussating fibers in both the ascending and descending pathways cross in the ventral supraoptic commissure. It is concluded that the basal nucleus should include most of the aggregated and unaggregated large cells that lie in the substantia innominata and which in places intrude upon the preoptic regions and the nucleus of the diagnonal band of Broca. Together, these may form a complex that receives inputs from a variety of brainstem sources, and projects widely and diffusely upon all cortical structures of the telencephalon.

Amygdala↗
PubMed1975

Commissural and cortico-cortical "columns" in the somatic sensory cortex of primates.

Anatomical experiments demonstrate that commissural and cortico-cortical fibers arising and terminating in the somatic sensor- cortex of monkeys terminate in layers I through IV in a mosaic of precisely ordered vertical bands. The cells of origin of these fibers, found predominantly in layer III, are also arranged in vertical aggregations.

Animals↗
PubMed1975

Responses of spinal cord neurons to systematic changes in hindlimb skin temperatures in cats and primates.

Single-neuron recordings were made from the lumbar spinal cords of cats and squirrel monkeys. Recording sites were distributed throughout the dorsal horn and included Rexed's laminae I and III-VI in both species and laminae VII-VIII in cats. Activity was studied during systematic changes in skin temperature over the range of 15-49 degress C; this encompasses the perceptions of innocuous cooling and warming plus the initial stages of noxious heating. The experiment included studies in which the thermal stimulus was changed from various preadapting temperatures. In all cases, the sensitivity of an individual neuron to changes in skin temperature was associated with responses to various intensities of tactile stimulation which, for some neurons, could range from low to painful pressures. More than two-thirds of the neurons excited by innocuous temperature changes discharged to both cooling and warming, although the thresholds were much lower for cold temperature differecnes (less than or equal to 2 degrees C for cold steps as compared with more than 6 degrees C for warm steps). However, many neurons only responded to extreme cooling or, more frequently, noxious heating. The temperature response relationships of many neurons during cooling was best described in reference to specific cold-receptor activity because the discharge rates declined at extremely cold temperatures and because the slopes of the temperature-response functions were nearly identical when studied with different adapting temperatures. The responses of certain slowly adapting mechanoreceptors was considered in describing some of the spinal cord activity during extreme cooling. The responses to hot temperatures were attributed to activity in various receptors, including especially polymodal receptors. Activity during innocuous warming was ascribed to one population of peripheral warm receptors that do not show maximal static activity during innocuous warm stimuli. The significance of the extensive convergence in the spinal cord from mechanoreceptors and thermoreceptors was discussed in relation to thermal perception and the complexity of the information transmitted by the spinothalamic tract.

Adaptation, Physiological↗