MESENCEPHALIC RETICULAR INFLUENCE ON ELECTRICAL ACTIVITIES OF THE PONTINE RETICULAR FORMATION

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Some characteristics of the electrical activities of the pontine reticular formation (PRF), recorded with gross- and micro-electrodes following stimulation of either the sciatic or the superficial radial nerve, were studied under the effects of stimulation of the mesencephalic reticular formation (MRF). The experimental animals were exclusively unanesthetized cats, immobilized with succinylcholine chloride or Faxédil.<BR>1. The peripherally evoked PRF potentials were composed of the initial positivity and the following negativity, this potential form being independent of the site of stimulation. The latency and the duration of the initial positive component were 10-20 msec and 10-30 msec, respectively, while the negative component had a duration of 40-75 msec. The MRF-induced, PRF potential was triphasic having the initial positivity. The threshold intensity of stimulus for eliciting the PRF potential was dependent on stimulating sites of the MRF.<BR>2. The peripherally evoked PRF unit response was classified into two types. The first type unit response occurred with an initial burst of spikes without being followed by after-discharges, whereas in the second type an initialburst of spikes continued to regular discharges with gradually decreasing frequencies. The mode of activation of the PRF unit was not essentially different between the MRF and the peripheral nerves. For a given stimulating point of the MRF, two types of the PRF unit were distinguished according to the threshold of activation (low-threshold and high-threshold). The discharge pattern of a given PRF unit to MRF stimulation was not fixed but variable depending on the site of stimulation.<BR>3. There are two types of spontaneous discharges in the PRF, the one with an irregular pattern of less than 10c/s and the other with a relatively regular pattern at 30-60 c/s. The firing rates of the PRF unit were mostly increased by MRF arousal stimulation.<BR>4. A single shock applied to the MRF with strengths sufficient for eliciting the PRF potential suppressed the peripherally induced, PRF potential for 10-40 msec.<BR>5. The peripherally induced, PRF potentials were suppressed during and after repetitive stimulation of the MRF, this being parallel to EEG arousal.<BR>6. Repetitive stimulation of the MRF increased the peripherally evoked, PRF unit response. The facilitatory effect was found more frequently in the high-threshold units than in the low-threshold ones, whereas this relation was reversed with the inhibition.<BR>7. It was suggested that the descending connection from the MRF is not diffuse, but rather specific.

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