Adult behavior and adrenocortical function following neonatal morphine treatment in rats

Developmental, behavioral, and opiate receptor changes after prenatal or postnatal beta-endorphin, CRF, or Tyr-MIF-1

Developmental and long-term behavioral effects of perinatal injection of beta-endorphin (BE), CRF and Tyr-Pro-Leu-Gly-NH2 (Tyr-MIF-1) in male rats were investigated along with the possibility that opiate receptors may be altered by the injection of BE during this critical time. Daily injections of peptide were given to pregnant females (100 micrograms/rat) in the week before birth or to the offspring (50 micrograms/rat) of untreated mothers during the first week of life. Prenatal BE and CRF reduced body weight on day 1, in contrast to Tyr-MIF-1 which produced a significant increase over controls by day 7 as well as a slight but significant acceleration of eye opening. Among the postnatal treatments, CRF-treated animals showed the most dramatic changes. These included decreased body weight, accelerated eye opening, and, in adulthood, increased open field rearing behavior and a tendency for a monotonic body temperature response to low doses of morphine, in contrast to the biphasic response shown by controls. BE, when given to pregnant mothers, increased the number (Bmax) of [3H]naloxone-labeled (mu) receptors in whole brains of offspring assayed on day 14, but it did not significantly alter [3H]D-Ala-D-Leu-enkephalin-labeled (delta) receptors. In contrast, a significant decrease in both mu and delta receptors was observed on day 14 in rats given BE postnatally. These differences in receptors were no longer apparent in adulthood, and no significant differences in tail-flick response were detectable at this time. Nevertheless, some of the effects of these three peptides endured well beyond their presence, and for BE included changes in the number of opiate receptors.

Modulation of brain development by morphine: effects on central motor systems and behavior

Morphine administration to neonatal rats on days 1-7 after birth produced long-term changes in behavior and brain function. The pups were smaller than saline-treated littermates and showed retarded motor development. As adults, the morphine-treated rats had impaired motor coordination, altered gait, and altered patterns of activity in an open field. Several brain regions of the adult rats, including motor areas, had decreased metabolic activity as measured by the 2-deoxy-glucose technique, suggesting decreased functional activity in these areas. These results may be relevant to findings that children exposed in utero to narcotics tend to have impaired motor development.

Prenatal exposure to morphine in mice: enhanced responsiveness to morphine and stress

Some behavioral effects of prenatal morphine administration were studied in CD1 mice. Two sets of experiments were carried out. In a first set, which was performed during development: (a) measures of postnatal reflexes revealed only a light deficit in tests involving motor control, (b) activity measures showed a significant reduction of spontaneous activity which was evident only in the course of the first postnatal days. In a second set of experiments, in which adult mice were tested for activity, analgesia and passive avoidance learning: (a) no difference was observed, in baseline conditions, between the performances of the mice prenatally exposed to saline and those preexposed to morphine, (b) as compared with controls, enhanced responsiveness to morphine administration (for the activity and passive avoidance measures), and to morphine and stress (for the analgesic measures) were found.

Opiates, endorphins and the developing organism: a comprehensive bibliography

A comprehensive bibliography of the literature concerned with opiates, endorphins, and the developing organism is presented. A total of 1378 clinical and laboratory references, with citations beginning in 1875, are recorded. A series of indexed accompanies the citations in order to make the literature more accessible. These indexes are divided into clinical and laboratory topics. The clinical section is subdivided into: age of subject examined; maternal aspects; effects on the fetus; pharmacology, physiology, and the withdrawal syndrome; and "other" effects on the offspring. The laboratory section is subdivided into: type of opiate/endorphin studied; species utilized; and major subject areas explored.

Brain beta-endorphin-like immunoreactivity in adult rats given beta-endorphin neonatally

beta-endorphin-like immunoreactivity was measured by radioimmunoassay in the brains of adult rats treated neonatally with beta-endorphin, naloxone, or vehicle. After treatment with beta-endorphin, the decreases observed in beta-endorphin-like immunoreactivity in the hypothalamus, pineal, midbrain, pons-medulla, hippocampus, striatum, frontal cortex, occipital cortex, and posterior cortex were highly significant but the 23% decrease in the thalamus was not significantly different from that of control rats. Neonatal administration of naloxone only resulted in a significant decrease in beta-endorphin-like immunoreactivity in the hypothalamus. In contrast, no differences were discernible in content of either beta-endorphin-like immunoreactivity or ACTH-like immunoreactivity in the pituitary of rats treated with beta-endorphin, naloxone, or vehicle in the neonatal period. These same rats had shown an increased threshold to painful thermal stimulation by the tail-flick test after administration of either beta-endorphin or naloxone at birth. The results suggest that neonatally injected beta-endorphin may alter the levels of beta-endorphin-like immunoreactivity in rat brain as well as the response to pain.

Single-dose tolerance to morphine-induced analgesic and hypoactive effects in infant rats

A single injection of morphine or isotonic saline was administered to rats at either 1, 5, 9, ro 13 days of age. At 26-29 days of age, animals were tested for pain responsivity and activity following either morphine (5 mg/kg) or saline. Animals which received morphine at 1 day of age displayed tolerance at 26 days of age, whereas animals which received morphine at either 5, 9, or 13 days of age failed to display tolerance. This age-dependent change in susceptibility to single-dose morphine tolerance may involve alterations in opiate receptor ontogeny.