Regulation of Oxytocin Release

Influence of ω3 fatty acids on maternal behavior and brain oxytocin in the murine perinatal period

INTRODUCTION

Perinatal women often experience mood disorders and postpartum depression due to the physical load and the rapid changes in hormone levels caused by pregnancy, childbirth, and nursing. When the mother's emotions become unstable, their parental behavior (maternal behavior) may decline, the child's attachment may weaken, and the formation of mother-child bonding can become hindered. As a result, the growth of the child may be adversely affected. The objective of this study was to investigate the effect of ω3 fatty acid deficiency in the perinatal period on maternal behavior and the oxytocin concentration and fatty acid composition in brain tissue.

MATERIALS AND METHODS

Virgin female C57BL/6 J mice fed a ω3 fatty acid-deficient (ω3-Def) or adequate (ω3-Adq) diet were mated for use in this study. To assess maternal behavior, nest shape was evaluated at a fixed time from gestational day (GD) 15 to postpartum day (PD) 13, and a retrieval test was conducted on PD 3. For neurochemical measurement, brains were removed from PD 1-6 dams and hippocampal fatty acids and hypothalamic oxytocin concentrations were assessed.

RESULTS

Peripartum nest shape scores were similar to those reported previously (Harauma et al., 2016); nests in the ω3-Def group were small and of poor quality whereas those in the ω3-Adq group were large and elaborate. The inferiority of nest shape in the ω3-Def group continued from PD 0-7. In the retrieval test performed on PD 3, dams in the ω3-Def group took longer on several parameters compared with those in the ω3-Adq group, including time to make contact with pups (sniffing time), time to start retrieving the next pup (interval time), and time to retrieve the last pup to the nest (grouping time). Hypothalamic oxytocin concentrations on PD 1-6 were lower in the ω3-Def group than in the ω3-Adq group.

DISCUSSION

Our data show that ω3 fatty acid deficiency reduces maternal behavior, a state that continued during pup rearing. This was supported by the observed decrease in hypothalamic oxytocin concentration in the ω3-Def group. These results suggest that ω3 fatty acid supplementation during the perinatal period is not only effective in delivering ω3 fatty acids to infants but is also necessary to activate high-quality parental behavior in mothers.

Neuroendocrine Mechanisms of Social Bonds and Separation Stress in Rodents, Dogs, and Other Species

Mammalian species form unique bonds between mothers and infants. Maternal care, including suckling, is necessary for infant survival, and the mother and, sometimes, the father require a lot of effort in nurturing infants. An infant's probability of survival depends on the extent of the investment of care by the mother. In parallel, mothers must identify their offspring and invest only in those who possess their genes to achieve evolutionary benefits. Therefore, they need to recognize their offspring and show a strong preference for them. For this reason, bond formation between mothers and infants is important. The mother monitors her offspring's physical condition and stays close to them. The offspring also form strong bonds with their mothers. Therefore, a separation between the mother and infant causes severe stress for both parties. Although it was initially thought that such bonds between mother and infant are limited to the same species, we have also observed a similar phenomenon in the human-dog relationship. In this article, we discuss the neuroendocrine mechanisms that underlie bond formation and separation based on findings of neurobiological research in mice and the relationship between humans and dogs.

The effect of changes in arterialPCO2on neuroendocrine function in man

There is evidence that changes in arterial P(CO(2)) (P(a,CO(2))), as well as P(O(2)), influence neuroendocrine function. The hyponatraemia and fluid retention (cor pumonale) seen in chronic obstructive pulmonary disease (COPD) and type II respiratory failure is associated with increased vasopressin release. This study examines the specific effects of altered P(a,CO(2)) on hormone release from the posterior and anterior pituitary. The study was performed in 20 ventilated ICU patients in the late recovery phase of their illness. None had primary respiratory disease. Control blood samples were taken and the alveolar ventilation was then adjusted to allow the P(a,CO(2)) increase or decrease for a period of 3 h, during which time further blood samples were taken for the determination, by radioimmmunoassy of vasopressin, oxytocin, growth hormone and cortisol. Urine output and electrolyte concentrations were also measured. Circulating concentrations of growth hormone and oxytocin increased with increasing P(a,CO(2)). Vasopressin release showed a similar pattern up to a P(a,CO(2)) of approximately 6.0 kPa, above which vasopressin concentrations were inversely related to P(a,CO(2)). There was no significant effect on cortisol concentrations. No significant effects were established in urinary parameters during the short period of this study. Thus an increase in CO(2) is associated with stimulated pituitary hormone release. The effect on the neurohypophysial hormones may account for the fluid retention and hyponatraemia seen in COPD and hence provide a rationale for treatment.

Brain substrates of infant-mother attachment: contributions of opioids, oxytocin, and norepinephrine

The aim of this paper is to review recent work concerning the psychobiological substrates of social bonding, focusing on the literature attributed to opioids, oxytocin and norepinephrine in rats. Existing evidence and thinking about the biological foundations of attachment in young mammalian species and the neurobiology of several other affiliative behaviors including maternal behavior, sexual behavior and social memory is reviewed. We postulate the existence of social motivation circuitry which is common to all mammals and consistent across development. Oxytocin, vasopressin, endogenous opioids and catecholamines appear to participate in a wide variety of affiliative behaviors and are likely to be important components in this circuitry. It is proposed that these same neurochemical and neuroanatomical patterns will emerge as key substrates in the neurobiology of infant attachments to their caregivers.

Intracerebroventricular injection of choline increases plasma oxytocin levels in conscious rats

In the present study, we examined the effect of intracerebroventricularly (i.c.v.) injected choline on both basal and stimulated oxytocin release in conscious rats. I.c.v. injection of choline (50-150 micrograms) caused time- and dose-dependent increases in plasma oxytocin levels under normal conditions. The increase in plasma oxytocin levels in response to i.c.v. choline (150 micrograms) was greatly attenuated by the pretreatment of rats with atropine (10 micrograms; i.c.v.), muscarinic receptor antagonist. Mecamylamine (50 micrograms; i.c.v.), a nicotinic receptor antagonist, failed to suppress the effect of 150 micrograms choline on oxytocin levels. Pretreatment of rats with 20 micrograms of hemicholinium-3 (HC-3), a specific inhibitor of choline uptake into nerve terminals, greatly attenuated the increase in plasma oxytocin levels in response to i.c.v. choline injection. Osmotic stimuli induced by either oral administration of 1 ml hypertonic saline (3 M) following 24-h dehydration of rats (type 1) or an i.c.v. injection of hypertonic saline (1 M) (type 2) increased plasma oxytocin levels significantly, but hemorrhage did not alter basal oxytocin concentrations. The i.c.v. injection of choline (50, 150 micrograms) under these conditions caused an additional and significant increase in plasma oxytocin concentrations beyond that produced by choline in normal conditions. These data show that choline can increase plasma oxytocin concentrations through the stimulation of central cholinergic muscarinic receptors by presynaptic mechanisms and enhance the stimulated oxytocin release.

Pituitary portal plasma levels of oxytocin during the estrous cycle, lactation, and hyperprolactinemia

The median eminence receives fibers from both parvocellular and magnocellular OT neurons in the hypothalamus. The OT neuronal terminal in the median eminence is secretory and is the major source of the neuropeptide in the blood of pituitary portal vessels. The OT secretion into pituitary portal plasma increases by ovarian steroids, PRL, and the suckling stimulus. The OT secretion into the blood of pituitary portal vessels changes in parallel with the altered secretion of PRL from the pituitary. Because of correlative association between pituitary portal plasma OT and systemic plasma PRL and much abundant evidence for a direct stimulatory action of OT on PRL release, we propose that the pituitary portal vascular system serves as the window for the central OT neurotransmission to the pituitary lactotropes.

Reliving birth: maternal responses to viewing videotape of their second stage labors

To learn about women's responses to their second stage labors and the care they received, women (N = 20) whose second stage labors had been videotaped were interviewed postpartally and shown their videotapes. Often women found the videotape viewing to be intensely emotional, especially when they heard noises they made. Women frequently commented upon details they hadn't remembered, their reactivated memory for labor pain, and the "weird" experience of watching themselves in labor. The authors recommend that women who watch their labor videotapes do so with a caregiver or supportive companion. They should be forewarned that the experience may be intense; details of their labors may be vividly recalled or women may see labor events on the videotape of which they were previously unaware.

Multiple synapse formation: a possible compensatory mechanism for increased cell size in rat supraoptic nucleus

Abstract Magnocellular neuroendocrine cells of the rat supraoptic nucleus undergo numerous morphological changes during chronic dehydration of the animal. These changes include increases in cell size, the percentage of neuronal membrane in direct apposition and formation of new multiple synapses (i.e. terminals which form more than one synapse with adjacent somata and/or dendrites). Previous studies of multiple synapse formation in the supraoptic nucleus did not include adjustments for changes in somatic size, thus the full extent of synapse formation relative to increases in cell size was not known. That multiple synapse formation is a compensatory mechanism for increased somatic size was investigated by comparing animals that were either chronically dehydrated (by drinking 2% saline) or were well hydrated. Using morphometric techniques the percentage of somatic membrane contacted by single and multiple synapses was obtained. Estimates of somatic surface area were used together with stereologically derived estimates of the number of synapses per mum(2) to calculate the number of single and multiple axo-somatic synapses per neuron. Measures of soma-somatic and soma-dendritic membrane apposition and glial coverage were made to confirm earlier estimates of these parameters. Somatic surface area increased by more than 70% in dehydrated animals. Percentage of somatic membrane contacted by single synapses was lower (by 41%) and that contacted by multiple synapses was higher (by 100%) in dehydrated as compared to control animals. The number of single synapses was not different between the two groups but dehydrated animals had more multiple synapses per soma (23) than controls (6). With dehydration, there was an eight-fold increase in the percentage of somatic membrane contacted by adjacent somatic/dendritic membrane. The surface area per somain such direct apposition was fifteen-fold higher in dehydrates compared to controls. Glial processes covered the same proportion of somatic membrane in the two groups, while the actual area covered by glial processes per soma was higher in dehydrated animals. These results are consistent with the hypothesis that multiple synapse formation at least partially compensates for probable relative decreases in synaptic efficacy as synaptic density decreases when cells increase in size due to dehydration. This altered synaptic input as well as the increased direct apposition between adjacent neurons probably contribute to their enhanced activation during periods of increased hormone demand.