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Biomedical subjects

P Andersen

Publications and source records attributed to P Andersen.

At least 379 records · Page 21Linked to original sources
PubMed1967

Some factors involved in the thalamic control of spontaneous barbiturate spindles.

1. The origin of thalamic and cortical spontaneous spindles was studied in cats anaesthetized with sodium pentobarbital.2. Complete removal of all cortical grey matter left the thalamic rhythmic spindle activity unchanged.3. Removal of the entire thalamus or pronounced oedema in the thalamus abolished completely the spindle activity in the corresponding hemisphere.4. In a neuronally isolated cortical area, a fast, low voltage background activity appeared, interrupted by occasional irregular rapid potential changes (sharp waves) of high voltage. Regular spindle rhythms were seldom observed unless excited by a depolarizing drug. Spontaneous spindles did not invade the isolated cortex via a bridge of intact cortical tissue.5. With increasingly larger destruction of the thalamus in a rostro-caudal direction, the activity in the post-cruciate cortex did not change until the anterior third of the thalamus was encroached upon. A transverse section in front of the thalamus nearly eliminated the cortical spindles.6. Complete removal of the mid line and intralaminar nuclei left the spontaneous rhythmic activity of the lateral thalamic nuclei and of the frontal cortex principally unchanged.7. Removal of the laterally located thalamic nuclei, including the n. ventralis posterolateralis (VPL), abolished virtually all spontaneous spindle activity of the frontal cortex, including the post-cruciate area.8. Local cortical cooling reduced the amplitude but not the frequency of the cortical spindles.9. Cooling of the whole brain reduced both the amplitude and the frequency of the spindles. At low temperatures, all spindle activity in the cortex disappeared, and occasional sharp waves occurred, as with de-afferentation.10. It is concluded that the rhythm of the cortical spontaneous barbiturate spindles is generated exclusively by thalamic neurones. The electromotive force of the corticographic waves, however, has a cortical origin.

Animals↗
PubMed1967

Nature of thalamo-cortical relations during spontaneous barbiturate spindle activity.

1. The relation between thalamic and cortical spontaneous spindles was investigated in cats anaesthetized with barbiturates.2. Simultaneous recordings with multiple electrodes in the thalamus and cortex revealed a high correlation between thalamic and cortical spindle activity, both with regard to the occurrence of the spindles as well as to their individual waves, provided a critical location of the electrodes was secured. The results indicate a point-to-point relation between a group of thalamic cells and a small cortical area to which these cells project. In the spontaneous rhythm, the cortical columns are probably individually controlled by a thalamic rhythmic entity. This point-to-point relation was found in all the major sensory projection systems and in one thalamic ;association' nucleus and its corresponding ;association' cortex.3. Cortical barbiturate spindles appeared either as local spindles in a restricted cortical area or as compound spindles in several areas. Spindles recorded from electrodes separated by 2 mm or more were clearly different with regard to intraspindle wave frequency, duration, and the time of start and stop of the spindle. These differences increased with increasing distance between the electrodes, and were most pronounced when the corticograms of the two hemispheres were compared.4. Spontaneous spindle activity interfered with orthodromic transmission through n. ventralis posterolateralis (VPL) and medial geniculate nucleus (MG), judged by depression of the thalamic and cortical responses to peripheral nerve volleys or clicks. Such inhibition required the afferent volley to be delivered at a particular time of the spontaneous oscillations. Further, orthodromic volleys reset the rhythmic spindle waves in the appropriate thalamic and cortical areas.5. These findings lead to a new concept of the thalamic pace-maker function. During barbiturate anaesthesia, small assemblages of thalamic neurones seem to have the ability to generate independent rhythmic discharges, and thereby control the rhythm of the particular cortical column to which this thalamic group projects.6. During barbiturate anaesthesia, many facultative pace-makers seem to be present in the thalamus. The total number may be as large as 25,000-35,000. Usually, many of these rhythmic thalamic units beat in synchrony or near synchrony.

Animals↗
PubMed1966

Rhythmic activity in a simulated neuronal network.

1. A digital computer has been programmed to simulate a neuronal network consisting of eighty cells with the following characteristics:(a) All cells in the network had a set random probability of discharge when not affected by other cells. The probability of discharge was chosen as one system parameter (PD).(b) Subsequent to the firing of any neurone in the network, a certain number of other neurones underwent a change in their probability of discharge, consisting of an inhibitory period followed by a period of increased excitability. The changes of excitability mimic the changes of the membrane potential recorded for spontaneously rhythmically active cells in the animal thalamus.2. Starting the network, a typical transient response appeared, consisting of a burst-like activity. The initial activity was followed, first by random fluctuations of the number of active cells, later by periods of spontaneous rhythmic activity that had several characteristics in common with the type of spontaneous activity seen in the animal thalamus.3. The parameters which affected the rhythmic activity of the network most strongly were the degree of the post-inhibitory increase of the probability of discharge and the degree of distribution of the inhibition to neighbouring cells.4. The results are compatible with the inhibitory phasing theory advanced by Andersen & Sears (1964) to explain the occurrence of spontaneous rhythmic activity in the animal thalamus. However, before sufficient experimental knowledge is available, it is difficult to establish whether the rhythmic activity in the network is of the same type as that of the animal thalamus.5. A closer study of the parameters governing the behaviour of the simulated network has given indications of some parameters to be more closely investigated in future animal experiments.

Journal Article↗
PubMedDate not supplied

Protein kinase C injection into hippocampal pyramidal cells elicits features of long term potentiation.

Long-term potentiation (LTP) in the hippocampus is an interesting example of synaptic plasticity because of its induction by physiological discharge rates and its long duration. Of the possible biochemical mechanisms that regulate prolonged changes in cell function, protein phosphorylation is a particularly attractive candidate. We have therefore examined the effect of intracellular injection of calcium/diacylglycerol-dependent protein kinase (protein kinase C (PKC] in CA1 pyramidal neurones in hippocampal slices. Injection of the active enzyme elicited long-lasting enhancement of synaptic transmission, similar to LTP, whereas inactivated kinase failed to do so. The observed changes included an increased amplitude of the excitatory post-synaptic potential (e.p.s.p.) and an increased probability of firing and a reduced latency of the associated actin potential.

Action Potentials↗
PubMedDate not supplied

Respiratory disease and lung function in a tobacco industry.

In a field study, 75 workers from a cheroot factory were compared with 50 reference workers from a large telephone company. Questionnaire responses revealed higher prevalences of cough and shortness of breath on exercise among the tobacco workers than controls. Cigarette smoking was the same in the two groups, but tobacco workers also smoked cheroots. Significantly decreased values (p less than .01) of forced expiratory volume in 1 sec (FEV1.0) and forced vital capacity (FVC) were found among tobacco workers compared to referents. After adjusting for number of cigarettes and cheroots smoked, there remained no significant differences. There was a suggestion (p less than .10) of decreased FEV1.0 among light or nonsmoking tobacco workers. When cigarette consumption only was considered, this difference was significant (p less than .01). Lung function values were not associated with the very low measured dust exposures. Bronchial reactivity to inhaled histamine, diurnal and weekly changes in FEV1.0, skin-prick tests with tobacco extracts, and precipitating serum antibodies to tobacco extracts and extracts of microorganisms were similar to that expected in a nonexposed population. Differences in lung function between the two groups may result from excess cheroot consumption and higher previous exposure to tobacco dust among the tobacco workers.

Adult↗
PubMedDate not supplied

Long-term potentiation is associated with new excitatory spine synapses on rat dentate granule cells.

To investigate possible morphological correlates to long-term potentiation (LTP), three-dimensional reconstruction of serial electron micrographs was employed. LTP was induced in the perforant path/dentate granule cell synapse in two rats. The surgically isolated contralateral side served as control, along with two untreated animals. Longitudinally sectioned and transversally sectioned dendrites were sampled from the middle fifth of the molecular layer and all visibly connected spines were identified. A mixed, unbalanced, nested variance component model was used to make a valid statistical comparison between the LTP and control groups. The spine density was higher in the experimental than in the control groups. The changes were statistically significant in both the longitudinal and transverse sample. In addition, spines with a divided stem and two heads (bifurcating spines) were seen at a higher frequency in the LTP material compared with the contralateral material. From a subset of dendrites all connected spines were reconstructed and detailed measurements of head, neck, and PSD dimensions were made. We failed to find significant differences following LTP on either of the dimensions measured. The results suggest that new spine synapses are formed following LTP, including some of the bifurcating type.

Animals↗