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P Mares

Publications and source records attributed to P Mares.

At least 361 records · Page 20Linked to original sources
PubMed1976

Development of cerebellar somatosensory evoked potentials in the rat.

In lobule VIa of the vermis cerebelli of 69 male albino rats aged from 7 to 90 days we studied the somatosensory potential evoked by electrical stimulation of the sciatic nerve. A response consisting of a marked positive wave and a small negative wave was constantly present in the group of 9- to 10-day-old animals. At the end of the second week, an initial negative wave appeared. The response of 18-day-old animals consisted of 5 waves of alternating polarity and started with a small positive wave as in adult rats. During subsequent development only the relative size of the individual components changed, the later negative wave, N2, being the most marked component in adult animals. An attempted explanation of the possible origin of evoked potentials in young animals, based on the available data on the morphological development of the cerebellar cortex, is submitted. The latent periods, measured to the maxima of the individual waves, shorten abruptly between the 10th and 20th day and then undergo little change. Greater fatigability of the responses of young animals can be demonstrated by using rhythmical stimulation and paired stimuli. Somatosensory responses appear sooner than visual evoked potentials in the cerebellum, but they develop later than somatosensory evoked potentials in the cerebral cortex.

Aging↗
PubMed1975

Development of the interhemispheric response in rats.

In acute experiments on curarized rats, an interhemispheric response was observed for the first time at the age of 5 days. A stimulus of threshold intensity evoked both components of the response in the youngest animals, but only the negative phase of the evoked potential from the 9th day of age, with the initial positive phase appearing only after stimuli of high intensity. Upon using stimuli of double the value of threshold intensity, the responses had the same shape, i.e. positive-negative throughout the whole development. Marked changes in the latency of both components of the response were found during development. Up to 14 days latencies decreased rapidly; this was followed by a phase of relative stability and then, after the 19th day, by further, less pronounced decrease. An after-discharge, a late component of the response in adult animals, appeared for the first time in a mature form at 18 days. An after-discharge of a different shape was seen in young rats aged 7-14 days and none at all was observed in 5-day-old animals.

Age Factors↗
PubMed1975

Development of cortical somatosensory evoked potentials in rats.

The development of the contra- and ipsilateral cortical potential evoked by electrical sciatic nerve stimulation was studied in 77 male albino rats aged 5 to 45 days. A contralateral response was already recorded, as double negativity, in the youngest animals, while an ipsilateral evoked potential was not reliably present until the 10th day. At this time, however, both responses started with an inconstant positive wave and their shape was practically the same. During subsequent development the responses differed only in respect to their dominant component: in the contralateral response, the N1 wave had the highest amplitude for most of the time, while in the ipsilateral response the delayed N2 wave was the largest component. The latent periods of contralateral responses were somewhat shorter than those of ipsilateral evoked potentials. During development we noticed a phase of abrupt shortening of the latent period, which took place before the 15th day in the contralateral response and before the 20th day in the ipsilateral response. We also found a difference in the fatigability of the responses, which was greater in immature rats than in adult animals; in the ipsilateral evoked potential it approached adult values more slowly. The development of the ipsilateral response is thus delayed compared with the development of the contralateral response.

Age Factors↗