Control of breathing in babies of narcotic- and cocaine-abusing mothers

Paternal preconception exposure to chronic morphine alters respiratory pattern in response to morphine in male offspring

The clinical use of opioids is restricted by its deleterious impacts on respiratory system. Gaining a better understanding of an individual's susceptibility to adverse opioid effects is important to recognize patients at risk. Ancestral drug addiction has been shown to be associated with alterations in drug responsiveness in the progenies. In the current study, we sought to evaluate the effects of preconception paternal morphine consumption on respiratory parameters in response to acute morphine in male offspring during adulthood, using plethysmography technique. Male Wistar rats administered 10 days of increasing doses of morphine in the period of adolescence. Thereafter, following a 30-day abstinence time, adult males copulated with naïve females. The adult male offspring were examined for breathing response to morphine. Our results indicated that sires who introduce chronic morphine during adolescence leads to increase irregularity of respiratory pattern and asynchronization between inter-breath interval (IBI) and respiratory volume (RV) time series in male offspring. These findings provide evidence that chronic morphine use by parents even before pregnancy can affect respiratory pattern and response to morphine in the offspring.

Spectral analysis of heart rate variability and respiration during sleep in cocaine-exposed neonates

This study's objective was to examine the autonomic control of heart rate and respiration during the neonatal period in human infants with prenatal exposure to cocaine. Four-hour daytime recordings of the electrocardiogram (ECG) were obtained from 15 cocaine-exposed and 13 non-exposed full-term neonates at 2 weeks of age during quiet sleep (QS) and active sleep (AS). For each 1-min epoch of sleep, the power spectrum of the R-R intervals was computed from the ECG to obtain the total power (0-2 Hz), and spectral power in the high-frequency (HFP, 0.3-2 Hz), mid-frequency (MFP, 0.1-0.2 Hz), and low-frequency (LFP, 0.03-0.1 Hz) bands. Respiration was also monitored and processed using similar spectral analysis procedures. Cocaine-exposed neonates showed enhanced heart rate variability reflected by an increase in spectral power across all frequency bands. Spectral power in LFP and MFP was higher in cocaine-exposed neonates during both sleep states, but only in HFP during QS. There were no respiratory patterning differences between the groups to account for these findings. The index of sympathovagal balance (LFP + MFP)/HFP, showed no differences between the groups. We conclude that infants exposed to cocaine in utero show differences in the modulation of heart rate reflecting an increase in both vagal and sympathetic influences.

Data Base of Studies on Prenatal Cocaine Exposure and Child Outcome

A computerized data base of characteristics and findings of the literature on prenatal exposure and child outcome was developed. The data base can be used to summarize and describe the literature resulting in a more objective understanding of the findings as well as to determine methodological problems that can shape the direction of future studies. Based on a literature search 99 studies were identified, 76 of which met methodological criteria and were included in the final data base. The data base shows that our knowledge base is limited, scattered, and compromised by methodological problems that mitigate any conclusions about whether or not or how prenatal cocaine exposure affects child outcome. Only a few studies have followed children beyond age 3. In addition, the cocaine problem is more complicated than first envisioned. It is a multifactorial problem including the use of other drugs and parenting and environmental lifestyle issues.

Prenatal cocaine: effect on hypoxic ventilatory responsiveness in neonatal rats

The effects of prenatal (embryonic days 7-21) cocaine (30 mg/kg b.i.d., s.c.) exposure on postnatal respiratory and behavioral responsiveness to acute hypoxia were investigated in 5-day-old (P5) rat pups. Control and cocaine-exposed pups were subjected to 20 min of 0.21 FIO2 followed by 20 min of 0.08 FIO2. Although all pups demonstrated the characteristic biphasic response to hypoxia, cocaine-exposed pups exhibited a blunted, initial response in minute ventilation (p < 0.05) and inspiratory drive (p < 0.05) as compared with control pups who showed increases in these measures (p < 0.01 and p < 0.05, respectively). The consequence of this apparent blunted ventilatory response was reflected in blood gas data gathered after 20 min of 0.08 FIO2:PCO2 (p < 0.05) and base-excess (p < 0.05) were increased and HCO3- (p < 0.05) and SO2 (p < 0.01) were decreased relative to control pups. Cocaine-exposed pups also exhibited behavioral evidence of decreased struggling (p < 0.001) in response to the hypoxic challenge. These data in the rat confirm our previous findings of altered ventilatory responsiveness to inspired hypoxia in the rabbit and extend our observations of a decreased ability to successfully compensate and behaviorally arouse following prenatal cocaine-exposure, thus underscoring the potential vulnerability of infants so exposed.

Prenatal cocaine exposure and postnatal hypoxia independently decrease carotid body dopamine in neonatal rats

The effects of prenatal cocaine exposure on the levels of carotid body dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were investigated in 5-day-old rat pups exposed to normoxic and hypoxic conditions. Timed-pregnant Sprague-Dawley rats were injected b.i.d. with either cocaine HCl (30 mg/kg) or isotonic saline (1 ml/kg) from gestational days 7-21. On the fifth postnatal day, pups were subjected to either 20 min of 0.21 or 0.08 fractional inspired oxygen (FlO2). Under a strictly timed protocol, both carotid bodies were removed from each pup, placed in an antioxidant solution to prevent DA breakdown, and subsequently analyzed via HPLC with electrochemical detection to determine carotid body DA and DOPAC content. Two-way ANOVA revealed decreases in DA in cocaine-exposed pups. No HVA was detectable in any of the samples. The 0.08 FlO2 condition decreased DA compared to 0.21 FlO2. The additive consequences of DA depletion resulting from the combination of prenatal cocaine and postnatal hypoxia decreased carotid body DA to 14% of control levels, with several animals exhibiting DA content below detection limits. Considering the role of the carotid body in the ventilatory response to hypoxia, these data suggest that prenatal cocaine exposure may adversely affect the normal chemoreceptive function of the carotid body.

Cardiac and respiratory patterns during sleep in cocaine-exposed neonates

Four-hour recordings of heart rate and respiration during spontaneous sleep and wakefulness were obtained from 17 cocaine-exposed and 14 control infants at 2 weeks of age. The median values for heart and respiratory rate and variability were determined for each 1-min epoch of quiet and active sleep. Overall mean rates and variabilities were determined for each state. The cocaine-exposed infants showed significantly greater sleep state effects on heart rate relative to the control infants. Recency of cocaine exposure was not a factor in the differences; even those cocaine-exposed infants who tested negative for the drug perinatally differed significantly from those who had never been exposed. Heart rate variability was increased in cocaine-exposed infants relative to controls in both sleep states. Respiratory rate and variability were not significantly different in the cocaine-exposed and control infants. These results suggest differences in cardiovascular control in infants of cocaine-abusing mothers compared to infants without cocaine exposure. The mechanism responsible for these differences is unclear and may reflect cocaine-induced changes in the autonomic physiology of developing infants or some indirect effect of maternal cocaine use.

Deficient hypoxia awakening response in infants of smoking mothers: possible relationship to sudden infant death syndrome

OBJECTIVE

To determine whether fetal exposure to cigarette smoke impairs postnatal chemoreceptor control of ventilation and hypercapnic and hypoxic awakening responses.

STUDY DESIGN

Smoking (n = 13) and nonsmoking (n = 34) women were recruited during pregnancy. Serum cotinine levels were measured to assess level of nicotine exposure. The infants were studied at 2 to 3 months of age for ventilatory and awakening responses to hypoxia (17%, 15% and 13% inspired O2) and hypercapnia 4%, 6%, and 8% inspired CO2). Continuous measures were analyzed with unpaired t tests and analysis of variance for repeated measures. Proportions of awakening and periodic breathing were analyzed by means of a comparison of proportions.

RESULTS

The infants of smokers had lower birth weights (3022 +/- 566 vs 3518 +/- 491 gm; p < or = 0.005) and were older at the time of study (10.4 +/- 2.8 vs 8.7 +/- 1.3 weeks; p < 0.01) than the control infants. Maternal cotinine levels were higher in smokers (97.8 +/- 107 ng/ml vs no cotinine; p < 0.0001). More infants of smokers failed to awaken with hypoxia than did control infants (54% vs 15%; p = 0.006). The ventilatory responses to hypoxia and hypercapnia were similar in the two groups. All infants awakened with hypercapnia, and there was no difference in the awakening threshold for carbon dioxide (50.3 +/- 4.5 vs 48.3 +/- 5.4 mm Hg; p = 0.28).

CONCLUSION

Infants of mothers who smoked during pregnancy have deficient hypoxic awakening responses, which may contribute to the increased risk of sudden infant death syndrome in infants of smoking mothers.

Opioid depression of respiration in neonatal rats

1. The effects of opioid receptor agonists and antagonists on the breathing pattern of neonatal rats were studied. Three experimental approaches were taken. In the first approach, the effects of opioid agonists and antagonists on the spontaneous respiratory neural activity generated by brainstem-spinal cords isolated from neonatal rats aged 0-4 days postnatal (P0-4) maintained in vitro were studied. Secondly, similar studies were performed utilizing medullary slice preparations consisting of respiratory rhythm-generating regions (pre-Bötzinger complex). Thirdly, whole-body plethysmographic recordings were obtained from unanaesthetized neonatal (P0-18) rats before and after I.P. administration of opioid-receptor agonists and antagonists. 2. The mu-receptor agonists morphiceptin and DAGO (Tyr-D-Ala-Gly-[NMePhe]-Gly-ol), when added either to the solutions bathing the brainstems of neonatal rat brainstem-spinal cord preparations or bathing the medullary slice preparations, resulted in a naloxone-reversible, dose-dependent decrease in the frequency of respiratory rhythmic discharge. 3. The respiratory burst frequency and amplitude in vitro were unaffected by the addition of the delta-opioid receptor agonist DPDPE ([D-pen2,5]-enkephalin) and the kappa-opioid receptor agonist U50488 (trans-[+]-3,4-dichloro-N-methyl-N-(2-[1- pyrrolidinyl]cyclohexyl) benzene-acetamide) or the opioid receptor antagonist naloxone. 4. Intraperitoneal administration of the mu-opioid receptor agonist fentanyl resulted in a naloxone-reversible, dose-dependent decrease in the frequency and amplitude of breathing of unanaesthetized neonatal rats (P0-P10). I.P. administration of the delta-opioid receptor agonist DPDPE did not affect breathing of neonatal rats until the second week postnatally. 5. We conclude that opioids suppress the frequency of neonatal rat respiration by acting via mu-opioid receptors located within regions of the ventral medulla containing respiratory rhythm-generating centres (the pre-Bötzinger complex). delta-Opioid receptor activation does not affect breathing in neonatal rats until approximately the second week postnatally.