Central effects of catecholamines upon mammary contractility in rats are neurally mediated

Oxytocin Receptor Antagonist (Atosiban) in the Threat of Preterm Birth: Does It Have Any Effect on Breastfeeding in the Term Newborn?

AIM

Oxytocin is a hormone involved in the mechanism of breastfeeding, uterine contractions, and social relationships. Atosiban (competitive oxytocin antagonist) is one of the most commonly used tocolytics for the threat of preterm labor in Europe. The aim of this study is to determinate if the administration of atosiban has any influence in the type of feeding in the term newborn at discharge. The secondary objective is to verify its effectiveness for the prevention of preterm delivery and in the possibility of applying treatment to complete lung maturation.

MATERIALS AND METHODS

Retrospective cohort study carried out in a tertiary University Hospital distinguished by WHO-UNICEF as a Baby-Friendly Hospital Initiative. The analysis included 264 women exposed to atosiban during a period of 4 years. One hundred met inclusion criteria. Unexposed infants born right after and before the exposed ones were selected as the not exposed subgroup (n = 200).

RESULTS

Among women treated with atosiban, 82% maintained exclusively breastfed (EBF), 8% had mixed breastfeeding, and 10% had formula feeding at discharge. In the nonexposed group, 82% maintained EBF, 9.5% had mixed breastfeeding, and 8.5% had formula feeding at discharge (p = 0.84). 97.5% of pregnant women treated with atosiban received corticosteroid for lung maturation, and 49.5% completed gestation with term newborns.

CONCLUSION

There were no significant differences in the type of feeding at discharge between the atosiban group and the nonexposed group. In most cases, the administration of tocolytic therapy allowed to complete lung maturation.

The Association of Prenatal Tocolysis and Breastfeeding Duration

BACKGROUND

To date there are no clinical studies analyzing potential effects of tocolytics on breastfeeding duration in humans.

OBJECTIVES

The purpose of this study was to evaluate the association between beta 2 agonists prescribed for tocolysis during pregnancy and breastfeeding duration.

METHODS

We conducted a cross-sectional questionnaire study of 114 mothers and filled in the questionnaire developed to directly address the goals of the study.

RESULTS

There was a statistically significant difference between breastfeeding duration of mothers who were on tocolytics during pregnancy versus those who were not prescribed tocolytics (9.5 ± 5.7 months versus 4.5 ± 2.1 months) p < 0.001. In addition, hypogalactia was statistically significantly more prevalent in mothers with positive history versus mothers with negative history of tocolytic usage p < 0.001.

CONCLUSION

The results of our study indicate that tocolytic treatment in pregnancy is associated with shorter breastfeeding duration and hypogalactia.

Immunohistochemical Characterization of Sympathetic Chain Ganglia (SChG) Neurons Supplying the Porcine mammary Gland

The aim of this study was to investigate the chemical coding of mammary gland-projecting SChG neurons using double-labelling immunohistochemistry. Earlier observation showed that after injection of the retrograde tracer fast blue (FB) into the second, right thoracic mamma, FB+ mammary gland-projecting neurons were found in Th1-3, Th9-14 and L1-4 right SChG. The greatest number of FB+ nerve cell bodies was observed in Th10 (approx. 843) and Th11 (approx. 567). Neurons projecting to the last right abdominal mamma were found in L1-4 SChG. The greatest number of FB+ neurons was observed in L2 (approx. 1200). Immunohistochemistry revealed that the vast majority of FB+ mammary-projecting neurons contained immunoreactivities to TH (96.97%) and/or DßH (95.92%). Many TH/DßH-positive neurons stained for SOM (41.5%) or NPY (33.2%), and less numerous nerve cells expressed VIP (16.9%). This observation strongly corresponds to the results of previous studies concerning the immunohistochemical characterization of nerve fibres supplying the porcine mammary gland.

Oxytocin-messages via the cerebrospinal fluid: behavioral effects; a review

The cerebrospinal fluid (CSF) usually is considered as a protective 'nutrient and waste control' system for the brain. Recent findings suggest, however, that the composition of CSF is actively controlled and may play an influential role in the changes in brain activity, underlying different behavioral states. In the present review, we present an overview of available data concerning the release of oxytocin into the CSF, the location of the oxytocin-receptive brain areas and the behavioral effects of intracerebroventricular oxytocin. About 80% of the oxytocin-receptive areas are located close to the ventricular or subarachnoid CSF, including the hypothalamic 'Behavior Control Column' (L.W.Swanson, 2003). As a conclusion we suggest that 'CSF-oxytocin' contributes considerably to the non-synaptic communication processes involved in hypothalamic-, brainstem- and olfactory brain areas and behavioral states and that the flowing CSF is used as a 'broadcasting system' to send coordinated messages to a wide variety of nearby and distant brain areas.

Suckling-induced activation of neural c-fos expression at lower thoracic rat spinal cord segments

Suckling stimulation is essential for neuroendocrine and sympathetic reflex activation during lactation. In the present study, the induction of c-fos gene expression was used to identify neuronal populations in the spinal cord activated by acute 5 min suckling or by electrical stimulation of the central stump of the first abdominal mammary nerve in lactating rats previously separated from their litters for 6 or 18 h. In addition, to investigate whether spinal sympathetic preganglionic neurons are activated by suckling, dual immunostaining (Fos and choline acetyltransferase) was performed. Fos was expressed at low levels in continuously suckled and 6 h nonsuckled mothers, but no expression was found after 18 h of nonsuckling. On the other hand, in 6 h nonsuckled rats, significant increments in Fos expression occurred in several regions after acute suckling and after electrical stimulation. Also, the pattern of Fos expression in each spinal laminae was different for the two stimuli, i.e. more intense effects of suckling in deep laminae V-X and more intense effects in laminae I-IV with electrical stimulation. Double-labeling after suckling was found only in sympathetic preganglionic neurons from the intermedio-medial cell column, whereas after electrical stimulation, double label was observed only in neurons from the intermedio-lateral cell column. On the other hand, no effect upon Fos protein expression was observed after suckling and only a minor effect after electrical stimulation of mammary nerve in 18 h nonsuckled rats. These results are consistent with previous findings on the sympathetic reflex regulation of the mammary gland, as well as on the importance of the nonsuckling interval for optimal functioning of lactation.

Transneuronal labelling of nerve cells in the CNS of female rat from the mammary gland by viral tracing technique

Using the viral transneuronal tracing technique, the cell groups in the CNS transneuronally connected with the female mammary gland were detected. Lactating and non-lactating female rats were infected with pseudorabies virus injected into the mammary gland. The other group of animals was subjected to virus injection into the skin of the back. Four days after virus injection, infected neurons detected by immunocytochemistry, were present in the dorsal root ganglia ipsilateral to inoculation and in the intermediolateral cell column of the spinal cord. In addition, a few labelled cells could be detected in the dorsal horn and in the central autonomic nucleus (lamina X) of the spinal cord. At this survival time several brain stem nuclei including the A5 noradrenergic cell group, the caudal raphe nuclei (raphe obscurus, raphe pallidus, raphe magnus), the A1/C1 noradrenergic and adrenergic cell group, the nucleus of the solitary tract, the area postrema, the gigantocellular reticular nucleus, and the locus coeruleus contained virus-infected neurons. In some animals, additional cell groups, among others the periaqueductal gray and the red nucleus displayed labelling. In the diencephalon, a significant number of virus-infected neurons could be detected in the hypothalamic paraventricular nucleus. In most cases, virus-labelled neurons were present also in the lateral hypothalamus, in the retrochiasmatic area, and in the anterior hypothalamus. In the telencephalon, in some animals a few virus-infected neurons could be found in the preoptic area, in the bed nucleus of the stria terminalis, in the central amygdala, and in the somatosensory cortex. At the longer (5 days) survival time each cell group mentioned displayed immunopositive neurons, and the number of infected cells increased. The pattern of labelling was similar in animals subjected to virus inoculation into the mammary gland and into the skin. The distribution and density of labelling was similar in lactating and non-lactating rats. The present findings provide the first morphological data on the localization of CNS structures connected with the preganglionic neurons of the sympathetic motor system innervating the mammary gland. It may be assumed that the structures found virus-infected belong to the neuronal circuitry involved in the control of the sympathetic motor innervation of the mammary gland.

beta-adrenergic mechanisms modulate central nervous system effects of prolactin on milk ejection

It is known that prolactin (PRL) is produced within the brain and numerous central actions of the hormone have been reported. In anesthetized lactating rats, central administration of PRL, i.e., intracerebroventricular (icv) or intrathecally (it), facilitated milk ejection (ME) by depressing the sympathetically mediated facilitatory tone of the mammary ductal system. However, it is not known whether or not the same effects and similar mechanisms take place in conscious rats after PRL administration. In the present study, the effects of centrally administered PRL, i.e., icv or it, on ME was determined in both conscious and anesthetized rats. In conscious rats, the rate of ME was determined by applying a 15-min period of suckling by the litter, following a 6-h period of isolation. In anesthetized rats, intramammary pressure (IMP) responses of the mammary glands to exogenous oxytocin (OT) were recorded. The results showed that, whereas in anesthetized rats, increased responsiveness of the mammary glands to OT were observed after PRL administration, an intense inhibition of ME occurred in conscious rats. Because, in conscious and anesthetized rats, these effects were prevented by prior administration of the beta-adrenergic blocker propranolol (PROP) to the mothers, this suggests that the PRL effects on ME are modulated through sympathomimetic and sympatholytic actions in conscious and anesthetized rats, respectively. Thus, as shown by ductal tone measurements, in conscious, but not in anesthetized rats, the effect of PRL was associated with increased ductal constriction within the mammary glands; an effect that was mimicked by icv administration of the beta-adrenergic agonist isoproterenol (ISOP) and that was prevented by PROP. Further, the sympatholytic action of icv-PRL in anesthetized rats prevented the effect on ductal tone of both icv-PRL in conscious rats and of ISOP in anesthetized rats. Taken together, these results clearly suggest that the central effects of PRL on ME are modulated by adrenergic mechanisms.

Sympathetic innervation of mammary glands mediates suckling-induced reflex inhibition of milk yield in rats

Previous work has shown that physiologic activation of the sympathetic system may inhibit milk yield (ME) in rats. Thus, adrenal catecholamines (CAs) are released by suckling, but it is not known whether such inhibition results also from reflex activation by the same stimulus of neural sympathetics upon the mammary gland. The present experiments were designed to determine whether suckling inhibits ME induced by oxytocin (OT) in the urethane-anesthetized lactating rat, and whether such inhibition results from adrenal and/or neurally released CAs. Rats were isolated (6 h) from their pups and then anesthetized. OT (0.8 mU every 2 min) was administered intravenously to the mothers during suckling. Rats were either chronically implanted with cannulae into the lateral cerebral ventricles (intracerebroventricularly), bilaterally adrenalectomized (ADX), hypophysectomized (HX), spinal cord transected (SCT: T3-T4), or had the nipple area (NA) locally anesthetized before suckling. MEs were low in control, sham, ADX and HX rats, but not in rats given the beta-adrenergic blocker propranolol (PROP; intravenously or intracerebroventricularly injected), nor in SCT, NA or PROP-HX rats. As revealed by ductal resistance measurements as an indicator of ductal tone, suckling-induced inhibition of ME was due to ductal constriction within the mammary glands. These effects of suckling, however, could be prevented by prior activation of ductal mechanoreceptors. Together, these results indicate that suckling inhibits ME through the reflex activation of neurally mediated central beta-adrenergic mechanisms, and that these effects, in turn, can be regulated by ductal mechanoreceptor activation.

Mammary type I deiodinase is dependent on the suckling stimulus: differential role of norepinephrine and prolactin

Mammary deiodinase type I (M-D1) is present only during lactation and exhibits a clear direct correlation with lactation intensity (size of litters). The present work shows that M-D1 is suckling dependent and that intervals between suckling periods no longer than 12 h are essential to maintain this activity. Moreover, we find that with only 15 min of resuckling in 12-h nonsuckled mothers, the 50% decrease in both M-D1 messenger RNA and enzymatic activity could be restored to control values. This restorative effect by suckling may involve pre- and posttranscriptional mechanisms in which norepinephrine and PRL play important roles. Norepinephrine elicits a potent stimulatory effect on M-D1 messenger RNA and enzyme activities, whereas PRL only increases M-D 1 activity and may modulate the enzyme response to norepinephrine. Oxytocin and GH had no effect. These data suggest that the adrenergic nervous system and PRL could directly participate in mammary energetic expenditure, regulating the local T3 supply.