Biomedical subjects
Publications and source records attributed to G Benedek.
To analyse intrinsic sleep rhythms, transition probability functions were calculated from rat hypnograms. The method can be regarded as a generalization of Globus' binary autocorrelation analysis of sleep periodicity. It is useful for studying the construction of sleep cycles. The main advantage of the method is its insensitivity to random disturbances.
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The effects of high-frequency olfactory tubercle (TbOf) stimulations were studied on the EEG and behaviour of freely-moving cats. The results were as follows: (1) TbOf stimulation elicited sleep similar in every respect to physiological sleep; (2) statistical evaluation of the results showed that primarily the appearance and maintenance of slow wave sleep was facilitated by the stimulations. Stimulations during paradoxical sleep had no effect, but they did promote the recurrence of slow wave sleep after the paradoxical sleep. The effect of stimulations during wakefulness depended on the on-going activity; (3) TbOf stimulations brought about synchronization, which was characterized by a similar arousal threshold as for physiological sleep; and (4)atropine treatment prevented the behavioural effects and did not influence the EEG effects of the stimulations.
Vasodilatation in response to heat, the role of tail vasodilatation in thermolysis and the ability of the animals to use free water for evaporative cooling were studied in control and capsaicin-desensitized rats. 1) While vasodilatation in the tail began in the controls as soon as their temperatures reached 38.5-39 degrees C, in most of the desensitized rats the onset of this reaction was above a body temperature of 40 degrees C. 2) When exposed to 32 degrees C, desalivated capsaicin-treated rats showed a significant hyperthermia as compared to the controls. If the tails were amputated too, the temperatures of the controls rose to near those of the desensitized animals. 3) In the case of prolonged heat exposure or at a higher ambient temperature (38 degrees C), the desalivated tail-amputated controls still remained more tolerant to heat than the desensitized rats. 4) Even at an ambient temperature of 38 degrees C, desalivated controls without tails exhibited excellent thermoregulation when a water bath was present; they used the free water for evaporation. Capsaicin-treated rats neglected the water bath, and their temperatures rose continuously. 5) The results suggests that capsaicin treatment impaired reflex vasodilatation to heat and the behaviour of using free water for heat dissipation.
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The effect of repeated intravenous administration of 1 mg/kg atropine was studied on the synchronization elicited by low and high frequency electrical stimulation in the olfactory tubercle. The results showed that the synchronization of the cortical electrical activity could also be brought about during atropine administration, moreover, a gradual dose-dependent facilitation of the synchronizing effect was observed. Similar facilitation was obtained in cerveau isolé of the cats. Based on the experimental results it is concluded that the synchronizing effects of basal forebrain stimulation and the arousal effect of the activating system converge at a cortical level.
Noradrenaline (NA) and dopamine (DA) levels were studied in the forebrain of acute immobilized cats and in cerveau isolé preparations. A gradual decrease in NA and DA was observed one and two hours after high mesencephalic transection, while the amount of NA increased in acute immobilized cats after the cessation of ether anaesthesia. These changes in NA level are consistent with the observations suggesting an inverse relationship between NA and cortical deactivation. The decrease of DA with an exaggeration of spindle activity and increased synchronizing effect of basal forebrain stimulation indicate that the spindle-increasing effect of DA suggested by several authors requires the contribution of the brain stem.
Salivary thermolytic mechanisms (weight of salivary glands, effect of desalivation on water intake and body temperature, grooming activity) as well as escape behaviour and reaction to heat pain were studied in capsaicin-desensitized and control rats exposed to various warm ambient temperatures. Body temperature of the desensitized rats increased more than the controls' at all the ambient temperatures studied (32, 34 and 36 degrees C); however, significant differences in the mechanism of salivary cooling were obtained only at 34 and 36 degrees C. Central impairment of saliva spreading in desensitized rats seems evident. Complete surgical desalivation did not increase hyperthermia of control and desensitized animals in warm environments. Therefore other mechanisms, primarily vasodilatatory, must also be involved in the rat's thermolytic normal response. Although desensitized rats did not show a tendency to escape from the warm environment their response to heat pain was normal. In conclusion, it is suggested that heat perception in desensitized animals is impaired; however, the existence of some capsaicin-insensitive thermolytic mechanisms (prone extension of the body) cannot be excluded.
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On stimulating various basal forebrain structures, characteristic cortical evoked potentials, basic elements of the synchronization elicited, were studied in acute immobilized cats. Stimulation of the LH/10 cps/ resulted in short latency positive-negative evoked potentials, similar responses of increased latency were elicited from the RPO and TbOf. The laterobasal RPO and TbOf, the only areas able to induce cortical synchronization upon high frequency stimulation, could be clearly distinguished on the basis of evoked potentials. The laterobasal RPO was characterized by short latency, long-lasting positive potentials, while stimulation of TbOf elicited negative-positive responses. The relationship between the evoked potentials and the synchronizing mechanism of the basal forebrain is discussed.
A study was made of the effects of high mesencephalic transection (cerveau isolé) and low doses of pentobarbital on the cortical synchronizations elicited in acute immobilized cats by (a) low frequency stimulation of the lateral hypothalamus (HL) and nucleus ventralis anterior thalami (VA) and (b) by low and high frequency stimulation of the laterobasal preoptic region (RPO) and olfactory tubercle (TbOf). The results obtained were as follows: (1) The synchronizations induced by basal forebrain stimulations were found to survive in acute cerveau isolé cats, moreover, even a facilitation of the synchronizing effect were observed. (2) A gradual facilitation was observed upon TbOf and RPO stimulation, while in the case of VA and HL stimulations, the facilitation appeared immediately after the transection. (3) Low doses of pentobarbital depressed the cortical effects of TbOf stimulation, while an increase of the synchronizing effect of low frequency VA and HL stimulation was found. The observations suggested that (i) the synchronizing mechanism in the ventral part of the basal forebrain (RPO and TbOf) differs from that of the thalamus and HL; (ii) the basal forebrain synchronizing mechanism is effective without the contribution of the brain stem; (iii) the mechanism responsible for the synchronizing effect of low frequency HL stimulation is similar as that described for the thalamus.
EEG changes as well as the mechanisms of the hyperglycaemic effect of triethyltinsulphate (TET), a compound known to induce brain oedema, were investigated in cats and rabbits, respectively. Considerable EEG alterations characterized by slow waves appeared in some minutes after TET administration. The hyperglycaemic effect of TET like that of epinephrine could be prevented by the administration of 1 mg/kg of the beta blocker, pindolol. It is suggested that the hyperglycaemic effect of TET is brought about by sympathetic activation.
Cortical synchronization characterized by frontal spindles and occipital slow wave activity was induced by bilateral thermal stimulation of 2--4 degrees C of the preoptic area in unanaesthetized immobilized rats. The synchronization was demonstrated by ECoG and its power density spectra. The ECoG of the synchronization was similar to that of slow wave sleep. Switching off the thermal stimulation the original activity was recovered in most of the cases. Frontal spindle activity and slow wave activity recorded over the posterior cortex seemed to be dissociated to some degree. Low frequency stimulation at the points of thermal stimulation resulted in frequency following synchronization. In some cases electrical and thermal stimulation induced gradually developing seizure activity.
The electroencephalographic effects of several doses of a brain edema inducing agent, triethyltinsulfate (TET), was studied by implanted epidural electrodes in cats. The effect of TET on the central nervous system was found to have two phases: 1. a six hours' acute toxic phase following TET administration, 2. An edematic phase developing on the 2nd to the 4th day. Similarly to our earlier observations brain edema induced by TET was found to be dose-dependent, as shown by EEG-s, and their analysis performed by computation.
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