In 228 patients, fetal blood pH, pCO2 and lactic acid were measured in two distinguishable parts of the second stage of labor. The 'first' part begins at full cervical dilatation and ends when the mother starts her first voluntary bearing down efforts. In our study, the fetal acid-base status did not change in this part, regardless of a late developing hypoxia. In contrast, higher levels of lactic acid and pCO2 and lower pH values were observed in the 'final' part of the second stage, indicating increasing acidosis. In this 'final' part, the fetuses with clinical signs of distress, as defined by an ominous Apgar score at birth, showed quicker and larger acid-base shifts than did the normal fetuses. Thus the two parts of the second stage of labor actually differ in their potential to stimulate fetal acidosis. Since such fetal acidosis may develop especially during the 'final' part of labor, we have concluded that special particular attention should be devoted to this part.

The purpose of this study was to investigate whether maternogenic fetal acidosis can occur at the time of labor and delivery and to evaluate the extent of the possible maternal contribution to fetal acidosis. We have therefore determined fetal and maternal lactate concentrations and acid-base status under various conditions in 589 women at the end of gestation and during labor. The results show that metabolic acidosis develops in all fetuses because of increased production of lactic acidosis is primarily of fetal origin: 1) the umbilical arteriovenous lactate differences were positive and large in steady-state conditions as well as in depressed newborns; 2) the conditions that could produce a net transfer of lactate from the mother to the fetus, namely a positive maternofetal gradient of lactate and proton, were rarely observed; and 3) the correlation between fetal and maternal lactate levels was very weak, with regression coefficients decreasing from near steady-state conditions to acute stress conditions, indicating that the increase in lactate in the fetus and mother occurs independently. This correlation indicates also that increased maternal lactate production under conditions of labor and delivery can make a contribution by affecting the rate of net transfer from fetus to mother. This is possible in approximately 6% of the fetuses.

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Several studies have reported that early life experiences significantly influence the learning process, especially avoidance behavior, at maturity. Most often it has been found that handling facilitates the acquisition of avoidance responses, although there are discrepancies in the data which may be attributable to procedural as well as strain differences (Ader, 1965;Denenberg & Karas, 1960;Denenberg & Smith, 1963;King & Eleftheriou, 1959;Levine, 1956;Levine & Wetzel, 1963). Extinction of avoidance behavior has not received comparable attention, nor has it been conclusively established that the observed effects are the result of early as distinguished from previous experience. In the present study we investigated the effects of handling and electric shock stimulation experienced before and after weaning on the extinction of an avoidance response conditioned in one trial. MethodLitters of Charles River (CD) rats were split within 24 h of birth and randomly divided into Handled (H), Shocked (S), and Control (C) groups. Half the Hand S groups were manipulated as previously described (Ader, 1965) during the first 21 days of life and half were manipulated during the 21 days immediately after weaning. The Ss were approximately 125 day old females randomly selected from this population and otherwise undisturbed until the beginning of avoidance training.Animals were placed on a 2 x 4 in. platform situated in the center and elevated 2 in. above the floor of a 9 x 8 x 8 in. Plexiglas chamber. The time required to descend from the platform to the grid floor with three paws was recorded. Animals received five training trials per day with an intertrial interval of 2 min. On the day after an animal left the platform in 5 sec or less on three consecutive trials (a criterion usually achieved within the first five trials), Psychon. Sci., 1968, Vol. 10 (7) it was returned to the apparatus and upon descending from the platform (with a latency:5 5 sec) was subjected to electric shock (1.0 mAl. In one experiment a single 1 sec shock was administered, and, in a second (variable shock) experiment, shock was administered continuously until the animal returned to the platform. Thereafter, no electric shock was applied in either procedure and each animal received one trial per day for 21 days. Animals were returned to their home cages upon descending from the platform or after a latency of 30 sec. ResultsThe rates at which the differentially manipulated animals reached the preshock criterion did not differ in either experiment. Significant differences in extinction were observed, and these data are shown in Fig. 1.The 1 sec shock and variable shock experiments were analyzed separately. Also, since the unmanipulated control animals could not be dichotomized on an "age at manipulation" continuum, separate analyses were used to compare the performance of H and S groups before analysis of any of the manipulated groups relative to the controls.Under the 1 sec shock procedure, S animals had longer latencies than H animals (F=15.49, df=1/23, p ...

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