Reduced Oxytocin Release from the Neural Lobe of Lactating Rats is Associated with Reduced Pituitary Content and does not Reflect Reduced Excitability of Oxytocin Neurons

Higuchi, Takashi; Bicknell, R.J.; Leng, Gareth

doi:10.1111/j.1365-2826.1991.tb00278.x

Cited by 21 publications

(14 citation statements)

References 22 publications

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“…In pregnancy and lactation oxytocin and vasopressin responses were similar to those of the virgin mice, although oxytocin was previously reported to decrease in lactating mice (16). It is remarkable to note that the oxytocin concentration in lactating, suckled unstressed mice was lower than that in pregnant and virgin mice and may reflect minimal oxytocin secretion between milk ejection bursts during suckling (58) and depletion of the posterior pituitary store (59), as in rats.…”

Section: The Neurohypophysial Systemmentioning

confidence: 55%

Neuroendocrine Responses to Stress in Mice: Hyporesponsiveness in Pregnancy and Parturition

Brunton²,

et al. 2003

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Hypothalamo-pituitary-adrenal axis secretory responses to stress were compared in female virgin, late pregnant, parturient, and lactating mice. The basal plasma ACTH concentration was not different in pregnancy or lactation compared with virgins, but corticosterone concentration and corticosteroid-binding globulin capacity were greatly elevated in late pregnancy. Secretory responses to novel environment were attenuated in pregnant, but not lactating, mice compared with virgin females, whereas ACTH responses to forced swimming were attenuated in both groups. The expression of immediate early gene (nur77) mRNA increased in paraventricular nucleus neurons after stress exposure in virgin and lactating, but not pregnant, mice. During parturition, the basal ACTH concentration was similar to virgin and pregnant controls and did not increase with stress. Oxytocin secretion in response to either novel environment or forced swimming was unchanged in any reproductive group, whereas vasopressin secretion was decreased by both stressors, but only in virgins. Pretreatment with oxytocin receptor antagonist centrally had no effect on ACTH responses to stress in either virgin or pregnant mice. Pretreatment with an opioid receptor antagonist increased ACTH responses to stress in virgin mice, indicating opioid inhibition, but had no effect in pregnancy. Thus, in mice hypothalamo-pituitary-adrenal hyporesponsiveness in late pregnancy is a consequence of reduced responsiveness of paraventricular neurons, but inhibition by opioids or intracerebral oxytocin does not appear to be involved.

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Section: The Neurohypophysial Systemmentioning

confidence: 55%

Neuroendocrine Responses to Stress in Mice: Hyporesponsiveness in Pregnancy and Parturition

Brunton²,

et al. 2003

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“…However, although the decline in the overall secretion of the population (Figure 12C) begins at a time determined by the most active cells, heterogeneity in the input rates results in heterogeneity in depletion rates, which reduces the rate of the decline in the population signal. We know from experimental data [38] that, when tested over up to 4 days of stimulation, vasopressin secretion declines in proportion to pituitary content, but there is currently not enough data to make a more detailed quantitative comparison with the model.…”

Section: Resultsmentioning

confidence: 99%

“…This implies that in any secretory compartment, exocytosis is a stochastic process, and that the probability of release from a compartment depends on the content of a releasable pool in that compartment. On long timescales (tested over 4 days) the rate of secretion is proportional to the total gland content [38], suggesting that replenishment of the releasable pool (close to the plasma membrane) from a deeper store is also activity-dependent and probabilistic.…”

Section: Discussionmentioning

confidence: 99%

Spike Triggered Hormone Secretion in Vasopressin Cells; a Model Investigation of Mechanism and Heterogeneous Population Function

MacGregor

Leng

2013

PLoS Comput Biol

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Vasopressin neurons generate distinctive phasic patterned spike activity in response to elevated extracellular osmotic pressure. These spikes are generated in the cell body and are conducted down the axon to the axonal terminals where they trigger Ca2+ entry and subsequent exocytosis of hormone-containing vesicles and secretion of vasopressin. This mechanism is highly non-linear, subject to both frequency facilitation and fatigue, such that the rate of secretion depends on both the rate and patterning of the spike activity. Here we used computational modelling to investigate this relationship and how it shapes the overall response of the neuronal population. We generated a concise single compartment model of the secretion mechanism, fitted to experimentally observed profiles of facilitation and fatigue, and based on representations of the hypothesised underlying mechanisms. These mechanisms include spike broadening, Ca2+ channel inactivation, a Ca2+ sensitive K+ current, and releasable and reserve pools of vesicles. We coupled the secretion model to an existing integrate-and-fire based spiking model in order to study the secretion response to increasing synaptic input, and compared phasic and non-phasic spiking models to assess the functional value of the phasic spiking pattern. The secretory response of individual phasic cells is very non-linear, but the response of a heterogeneous population of phasic cells shows a much more linear response to increasing input, matching the linear response we observe experimentally, though in this respect, phasic cells have no apparent advantage over non-phasic cells. Another challenge for the cells is maintaining this linear response during chronic stimulation, and we show that the activity-dependent fatigue mechanism has a potentially useful function in helping to maintain secretion despite depletion of stores. Without this mechanism, secretion in response to a steady stimulus declines as the stored content declines.

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“…It is worth noting that basal plasma levels of OXT in these animals were found to be lower compared to those measured in male urethaneanesthetized rats (0.13 ± 0.01 vs. 0.24 ± 0.07 pg/dialysate, p < 0.05). This might be due to lower basal OXT levels in lactating rats [26,29] and/or to enhanced nona peptide release during urethane anesthesia [30, 31 but see 32]. The pulsatile release of OXT into blood during the 6-11 milk ejection reflexes occurring during the 30-min sampling period was reflected by an approximately 3-fold increase in the OXT content in microdialysates sampled from the jugular vein/right atrium.…”

Section: Discussionmentioning

confidence: 99%

Simultaneous Microdialysis in Blood and Brain: Oxytocin and Vasopressin Release in Response to Central and Peripheral Osmotic Stimulation and Suckling in the Rat

Ludwig²,

et al. 1993

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Simultaneous microdialysis in blood and brain has been used to monitor the release of both oxytocin and vasopressin into the systemic circulation (jugular vein/right atrium) and within the hypothalamic supraoptic nucleus of rats. Both home-made probes for blood and brain microdialysis revealed detectable nonapeptide concentrations under basal conditions and differential responses to a variety of stimuli. In urethane-anesthetized male rats, bilateral stimulation of the supraoptic nucleus by microdialyzing hypertonic medium (1 M NaCl) not only significantly increased the intranuclear release of both oxytocin and vasopressin (p < 0.05), but also their release from the neurohypophysis into blood (p < 0.05). In poststimulation microdialysates sampled from blood, the nonapeptides reached basal levels again, whereas intranuclear levels were further elevated. Intraperitoneal injection of hypertonic saline, on the other hand, resulted not only in the well-known increased peripheral release of oxytocin and vasopressin (p < 0.01 each), but also in a delayed increase in intranuclear oxytocin (p < 0.05). In contrast, intranuclear vasopressin release failed to change within the 90-min period following osmotic stimulation. In conscious lactating rats, suckling increased oxytocin contents in microdialysates sampled simultaneously in blood and the supraoptic nucleus (p < 0.05 each) further validating the microdialysis techniques used. The in vivo recovery in blood of approximately 65% determined using both radiolabeled and endogenous oxytocin provides a rough estimate to assess nonapeptide concentrations in plasma from 30-min or even 10-min blood microdialysis data. The results of the present study suggest that simultaneous microdialysis in blood and brain provides a useful tool to study patterns of peripheral and central release. Dependent upon the characteristics of the stimulus used, nonapeptide release into the different compartments may be either differentially regulated or coordinated.

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Reduced Oxytocin Release from the Neural Lobe of Lactating Rats is Associated with Reduced Pituitary Content and does not Reflect Reduced Excitability of Oxytocin Neurons

Cited by 21 publications

References 22 publications

Neuroendocrine Responses to Stress in Mice: Hyporesponsiveness in Pregnancy and Parturition

Neuroendocrine Responses to Stress in Mice: Hyporesponsiveness in Pregnancy and Parturition

Spike Triggered Hormone Secretion in Vasopressin Cells; a Model Investigation of Mechanism and Heterogeneous Population Function

Simultaneous Microdialysis in Blood and Brain: Oxytocin and Vasopressin Release in Response to Central and Peripheral Osmotic Stimulation and Suckling in the Rat

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