Effects of streptomycin on the cortical neurons in the cat.

Data concerning the effects of streptomycin application on the brain cortex are very scarce and nonconcordant, despite routine intra-thecal administration of this drug. Experiments peformed in 15 adult cats permitted us to observed that application of streptomycin sulphate on the brain cortex leads to a real cortical depression, demonstrated by the disappearance of spontaneous spikes, lack of cortical fast activity and lack of hippocampal theta activity. The direct cortical response disappears too and sometimes even the transmission towards the deep structures of neuronal activation induced by high intensity or repetitive stimuli. The depressing activity of streptomycin resembles to a spreading depression, with an effect limited only to the hemisphere where the drug is applied. The difference between our results and those of other authors can be explained by the different degree of purity of the streptomycin used in the experiments.

Influence of temporal lobe lesions on photic-evoked responses in occipital visual areas.

In 20 patients with temporal lobe lesions and 10 controls, the averaged photic-evoked responses (APERs) and their dispersion pattern (DP) were investigated in inion-vertex-lead and bilaterally in inion-parietal leads (I-P3 and I-P4). The patients with temporal lobe lesions, regardless of lesion location in temporal areas, displayed either absence of APER (the whole APER or only the initial components) or a latency increase without amplitude changes. The DP was generally abnormal. The role of the temporal lobe in the organization of APER in visual areas is discussed.

Relations between the pulvinar-lateralis posterior complex of the thalamus and the hippocampus in wakefulness and sleep in cats.

Paucisynaptic connections between n. lateralis posterior (LP) and dorsal hippocampus (Hip) have been demonstrated in acute experiments. In the free moving cats, with chronic implanted electrodes on the neocortex, in LP, pulvinar (Pul), VA and VL nuclei of the thalamus and in the dorsal hippocampus (Hip), the theta waves recorded in LP, Pul and Hip were not of the same frequency and origin. In wakefulness and in slow-wave sleep, the theta waves were of 3.5-4 c/s and occurred exclusively or predominantly in Pul-LP, while in paradoxical sleep they were of 5-6 c/s, occurred' in Hip and invaded the Pul-LP. These two types of theta waves represent two distinct modalities of their organization and reflect the involvement of different mechanisms in the different phases of sleep.

Neocortical reactivity to peripheral stimuli in neurotics.

The averaged photic-evoked responses (APER) and their dispersion pattern (DP) were investigated in tired subjects, neurotics and patients with neurotic syndromes. The appearance of an ample late negative deflection (N3) followed by a deep positive one (P3) of APER and of an atypical DP in tired subjects, neurotics and in patients with neurotic syndromes, may be considered signs of tiredness and of attention lability. A lengthening of the latencies and decrease in amplitude of different APER components, found in neurotics and in patients with neurotic syndromes only, indicated abnormalities in the function of neuronal structures involved in the organizations of responses to peripheral stimuli.

Visual evoked responses and their dispersion pattern in frontal lobe tumours.

In patients with frontal lobe tumours the averaged visual evoked responses (AVER) and their dispersion pattern (DP) in visual areas were investigated before and at different periods after operation. Important changes in AVER (in amplitude and latency) were found in the patients with tumours on the midline or in one of the frontal lobes. The DP was abnormal in all the cases. There was no relation to visual acuity, tumour location and existance of intracranial hypertension. After operation, despite the clinical improvement, the alterations of AVERs or DPs were very marked and in some cases became even more important than before. The role of the frontal lobe in the organization of the responses to peripheral stimuli in the visual areas is discussed.

Visual evoked responses and their dispersion pattern in neurotic patients.

The AVER (averaged visual evoked responses) and the DP (a pattern of dispersion resulting from the variability of each time point locked to the stimulus onset: D = F [T]) were studied in neurotics in comparison with controls. In neurotics without depression and/or anxiety the AVERs were normal and the DPs showed a shortening of the second period; in neurotics with depression and/or anxiety the AVER'S were also normal but the second period of the DPs disappeared.