Injection of 5,7-dihydroxytryptamine into the B3 raphe region of neonatal rat pups induces hyperalgesia but only slight alterations in ingestion-related behaviors

Behavioural effects in adulthood of neonatal manipulation of brain serotonin levels in normal and androgenized females

5HT concentrations in the hypothalamus are higher in females than males over the second week of life and this differentiation is testosterone-dependent. We have investigated the possible influence of 5HT over this period on the development of systems that control adult behaviour, in particular those influenced by neonatal testosterone. Neonatal androgenization (250 micrograms/pup testosterone propionate; TP; on day 1 postpartum) induced a masculine pattern of behaviour in females ovariectomised in adulthood and bearing a TP implant. The neonatal treatment reduced exploration, motor activity and female sexual behaviour and increased anxiety, orientation toward the incentive female and male sexual behaviour. Depletion of 5HT by pCPA (100 mg/kg days 8-16 postpartum) enhanced the TP-induced increment in locomotion and female sexual behaviour and increased sexual orientation toward the incentive female, while 5HTP (20 mg/kg days 8-16 postpartum) antagonised the reduction in exploration by TP. Thus 5HT may normally exert an inhibitory control on the action of neonatal testosterone on exploration, motor activity and sexual behaviour. Neonatal PCPA treatment also had a marked anxiolytic effect which was independent of the presence of T as it was noted in normal and androgenized females and previously has been observed in intact males. This might indicate a primary control by a serotonergic system on the development of the systems controlling anxiety.

The effect of prenatal methadone exposure on development and nociception during the early postnatal period of the rat

The effects of prenatal exposure to methadone via Alzet osmotic minipump on early postnatal development and on nociceptive behavioral endpoints were assessed in Sprague-Dawley rat pups during the first three postnatal weeks. This treatment regimen appeared to produce no maternal toxicity, with dams developing and maintaining dependence upon methadone through parturition. Methadone-exposed dams exhibited a withdrawal syndrome consisting of wet-dog shakes, diarrhea, vocalizations and irritability when challenged with naloxone 24 h postpartum. Pups exhibited a similar withdrawal syndrome following naloxone challenge consisting of mouthing and licking, hyperactive response to touch and vocalizations 24 h postpartum. Although no significant difference in litter size was evident in methadone-treated litters, a 16% pup mortality rate was observed in these litters. Prenatal methadone-exposed pups exhibited a significant body weight reduction at birth that resolved by postnatal day 2 (P2) in males and P4 in females. Methadone-exposed pups exhibited significant developmental delay in the expression of the negative geotaxic response to a morphine challenge while, conversely, 21-day-old pups exhibited a significantly reduced analgesic response to this challenge. These studies indicate that this method of prenatal exposure to methadone can produce dependence in the dam and offspring without substantial mortality, induce developmental delay and alter analgesic responses to opiate challenge in exposed pups during the preweanling period.