Effect of novocaine block of limbic system formations of the brain, hypothalamus and reticular formation on evoked potentials in the ventrobasal thalamic nucleus of the rat

The effect of novocain on evoked potentials (EP) recorded from the ventrobasal complex (VBC) of rats thalamus has been studied during a single pulse stimulation of the contralateral hind paw immobilized with curare. It has been established that significant sinchronized decrease of amplitudes of all the three early components of EP has been observed during the novocain administration in the reticular thalamic nucleus, lateral amygdaloid area and septum. During the blocking of the anterior and posterior hypothalamus the amplitude of the second negative component of EP in VBC decreases, while during the blocking of the dorsal hypothalamus an increase of the amplitudes of all the three early components of EP is mainly observed.     

Effect of local cooling of the cortex on evoked potentials in the reticular formation in response to somatosensory stimulation

Potentials evoked in nuclei of the reticular formation by electrodermal stimulation of the limbs were investigated in acute experiments on unanesthetized, immobilized rats during cooling of the somatosensory cortex in the area of representation of one forelimb. Evoked potentials in the reticular formation were found to depend on the degree of cold inhibition of the cortical primary response to the same stimulation. The peak time of the main negative wave increased from 40–50 to 60–80 msec with a simultaneous decrease in its amplitude or its total disappearance in the case of deep cooling of the cortex. Cooling of the cortex had a similar although weaker effect on the earlier wave of the evoked potential with a peak time of 14 msec, recorded in the ventral reticular nucleus. In parallel recordings of potentials evoked by stimulation of other limbs they remained unchanged at these same points of the reticular formation or were reduced in amplitude while preserving the same temporal parameters. Cooling of the cortex thus selectively delays the development and reduces the amplitude of the response to stimulation of the limb in whose area of representation transformation of the afferent signal into a corticofugal volley is blocked. Consequently the normal development of both late and early components of the potential evoked in the reticular formation by somatic stimulation requires an additional volley, descending from the cortex, and formed as a result of transformation of the same afferent signal in the corresponding point of the somatosensory cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 32–38, January–February, 1981.     

Changes in the hypothalamus, reticular formation and pituitary of rats during development of subcutaneous tumors]

Dynamics of structural changes was studied in the hypothalamus, reticular formation and the hypophysis of rats, depending on the phases of development in them of 9m10-dimethyl-1,2-benzanthracene-induced tumours. The phase of subcutaneous tumours appearance proved to be accompanied by structural and functional changes in the hypothalamus, reticular formation and the hypophysis.     

Investigation of the stability of the potentials of the dorsal surface evoked by single and paired stimulations of the afferent nerve

In spinal and anesthetized cats in the region of the lumbosacral thickening we have recorded the potentials of the dorsal surface (PDS) in response to single or paired stimulation of the peripheral nerves. The intervals between the stimuli were 400, 100, and 20 msec. The recording was made once every 15 sec. We have constructed the histograms of the changes in the N₁-component recorded on conditioning and single stimulation. After conversion of the histograms for single responses we established agreement of the newly obtained histograms with those constructed for the conditioned responses. The coefficients of variance for both cases proved to be practically identical. In applying single stimulation of different strengths the coefficient of variance increased if the amplitude of the responses fell. The coefficient of variance for the low amplitude responses did not change on conditioning unlike that for the responses evoked by weak single stimulation. It has been shown that the confidence limits of change in the coefficient of variance for a confidence probability of 0.99 and 0.95 obtained in experiments with conditioning practically concur with the intervals for the single stimulation. It is concluded that presynaptic inhibition has no appreciable antifluctuation influences on the N₁-component of the PDS.Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 10–16, January–February, 1970.     

Dynamics of potentials evoked in the auditory pathway and reticular formation of the cat. Studies during waking and sleep stages

Averaged evoked potentials in the inferior colliculus (IC), medial geniculate nucleus (MG) and reticular formation (RF) of chronically implanted and freely moving cats were measured using auditory step functions in the form of tone bursts of 2000 Hz. The most prominent components of the AEP of the inferior colliculus were a positive wave of 13 msec and a negative wave of 40–55 msec latency. The AEP of the medial geniculate nucleus was characterized by a large negative wave peaking at 35–40 msec. During spindle sleep and slow wave sleep stages changes in the AEPs of both nuclei occured.Transient evoked responses of the inferior colliculus, medial geniculate nucleus and reticular formation were transformed to the frequency domain using the Laplace transform (one sided Fourier transform) in order to obtain frequency characteristics of the systems under study. The amplitude characteristics of IC, MG. and RF obtained in this way revealed maxima in alpha (8–13 Hz), beta (18–35 Hz) and higher frequency (50–80 Hz) ranges. During spindle sleep stage a maximum in the theta frequency range (3–8 Hz) and during slow wave sleep maximum in the delta (1–3 Hz) frequency range appeared in the amplitude characteristics of these nuclei.The amplitude characteristics of the inferior colliculus and medial geniculate nucleus were compared with the amplitude characteristics of other brain structures. The comparison of AEPs and amplitude frequency characteristics obtained using these AEPs reveals that the existence of a number of peaks (waves) with different latencies in the time course does not necessarily indicate the existence of different functional structures or neural groups giving rise to these waves. The entire time course of evoked potentials and not the number and latencies of the waves, carries, the whole information concerning different activities and frequency selectivities of brain structures.Supported by Turkish Scientific and Technical Research Council Grant TAG-266.Presented in Part at the VIIIth International Congress of Electroencephalography and Clinical Neurophysiology in Marseilles, September 1–7, 1973.     

Changes in evoked potentials during differentiation inhibition

Evoked responses (EPs) of the auditory and the sensorimotor cortical areas were studied in experiments on cats during formation of a positive food-procuring conditioned reflex to a rhythmic sequence of clicks and during formation of the differentiation inhibition in response to the clicks of the same parameters, but with different frequency. In the positive conditioned reflex the EPs amplitude in the sensorimotor cortex increases; they are enriched by late components and in their general configuration they become much similar to EPs in the auditory area. The EPs patterns both in the auditory and in the sensorimotor areas considerably change in response to the differentiation stimulus, but differently in each of the sites.     

Modulation of the photically evoked potentials in the motor cortex of cats by influences of the somatosensory system and the reticular formation]

The influence of somatosensor stimulation and electric stimulation in the mesencephalic reticular formation upon evoked potentials (EP) of the motor cortex (MC) produced by electric stimulation of the Chiasma opticum and the Corpus geniculatum laterale, respectively, was investigated in unnarcotized, immobilized cats. By preliminary electrical stimulation of the contralateral front limb, intensity-dependent changes of the early positive component of the EP in the MC could be produced. Similar changes were found after passive movement of the limb and following electrical stimulation in the reticular formation of the mesencephalon. The EP in the MC completely disappeared after i.v. administration of 15 mg/kg Nembutal. It is concluded that the impulses reaching the MC after stimulation in the visual system can be modulated in various ways, and thus exhibit a relatively high information content. Possible mechanisms of the modulating influences and their significance are discussed.