Neonatal maternal separation enhances dopamine D2-receptor and tyrosine hydroxylase mRNA expression levels in carotid body of rats

Abstract

Adult male (but not female) rats previously subjected to neonatal maternal separation (NMS) are hypertensive and show a significant increase (25%) in their hypoxic ventilatory response. To begin investigating the mechanisms involved in this gender-specific disruption in cardiorespiratory regulation, we tested the hypothesis that NMS alters the expression of dopamine D(2)-receptors and tyrosine hydroxylase mRNA in 3 peripheral organs involved in cardio respiratory regulation: the carotid bodies, superior cervical ganglia, and adrenals. Pups subjected to NMS were placed in a temperature- and humidity-controlled incubator 3 h per day for 10 consecutive days (P3-P12). Control pups were undisturbed. Once they reached adulthood (8-10 weeks), male and female rats were anesthetised. The carotid bodies, superior cervical ganglia, and adrenals were harvested for semi-quantitative analyses of dopamine D(2)-receptors and tyrosine hydroxylase mRNA expression using reverse transcription-polymerase chain reaction (carotid bodies only) and Northern blot. In the carotid bodies, comparison of densitometric analyses showed that NMS enhanced tyrosine hydroxylase mRNA expression in male, but not female, rats. Neonatal maternal separation increased dopamine D(2)-receptor mRNA expression also, but the effect was not gender specific. No changes in mRNA expression related to dopaminergic neurotransmission were observed in superior cervical ganglia or the adrenals. These results indicate that subsequent mechanistic investigations should focus on the carotid bodies, as enhancement of dopaminergic neurotransmission within this organ likely contributes to the gender-specific effects of NMS on cardiorespiratory regulation.