The Milk-Ejection Reflex of the Rat: A 20- To 40-Fold Acceleration in the Firing of Paraventricular Neurones During Oxytocin Release

Wakerley, J. B.; Lincoln, D. W.

doi:10.1677/joe.0.0570477

Cited by 331 publications

(178 citation statements)

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“…Additionally, comparison of OVX and OVXϩE cells in the a.m. and the p.m. indicated changes in firing rates and patterns associated with estradiol negative and positive feedback, respectively, which were also consistent with the observed changes in LH levels. The relationship between electrical activity and hormone release has been demonstrated in magnocellular neurosecretory cells of the paraventricular (38,39) and supraoptic nuclei (40), as well as the GnRH system (41). Thus, it is likely that the changes observed here are directly related to, and indicative of, the increased GnRH release that is characteristic of the GnRH surge.…”

Section: Discussionmentioning

confidence: 56%

Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity

Christian

Mobley

Moenter

2005

Proc. Natl. Acad. Sci. U.S.A.

192

213

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A robust gonadotropin-releasing hormone (GnRH) surge is a prerequisite signal for the luteinizing hormone (LH) surge that triggers ovulation. In rodents, the GnRH surge is initiated by elevated estradiol and a diurnal switch in estrogen action from negative to positive feedback. The ability of constant estradiol treatment to induce daily LH surges was tested in adult mice that were ovariectomized (OVX) or OVX and treated with estradiol implants (OVX؉E). LH in OVX mice showed no time-of-day difference. In contrast, OVX؉E mice showed a large LH surge (8-to 124-fold relative to the a.m.) in p.m. samples on d 2-5 post-OVX؉E. Targeted extracellular recordings were used to examine changes in firing activity of GnRH neurons in brain slices. There was no time-of-day difference in cells from OVX mice. In contrast, OVX؉E cells recorded in the p.m. showed an increased mean firing rate and instantaneous firing frequency, which could increase GnRH release, and decreased duration of quiescence between bouts of firing, possibly reflecting increased pulse frequency, compared with cells recorded in the a.m. In the a.m., OVX؉E cells showed changes in GnRH neuron firing reflecting negative feedback compared with OVX cells, whereas in the p.m., OVX؉E cells exhibited changes suggesting positive feedback. These data indicate that differences in pattern and level of individual GnRH neuron firing may reflect the switch in estradiol action and underlie GnRH surge generation. The persistence of altered GnRH neuron activity in slices indicates that this approach can be used to study the neurobiological mechanisms of surge generation.luteinizing hormone ͉ mouse model ͉ surge ͉ electrophysiology ͉ neuroendocrinology

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Section: Discussionmentioning

confidence: 56%

Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity

Christian

Mobley

Moenter

2005

Proc. Natl. Acad. Sci. U.S.A.

192

213

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“…Among the most distinctive properties of MNCs is their capacity to generate repetitive bursts of action potentials (Poulain and Wakerley 1982). OT-secreting cells demonstrate brief (2-4 s), synchronized high-frequency bursts (40-80 Hz) during reflex milk ejections (Wakerley and Lincoln 1973). VP-secreting cells respond to changes in blood pressure and blood osmolality with a phasic firing pattern, or asynchronous, lower-frequency bursts (8-15 Hz) lasting tens of seconds and separated by silent intervals of similar durations (Brimble and Dyball 1977;Poulain et al 1977;Poulain and Wakerley 1982).…”

Section: Introductionmentioning

confidence: 99%

Somato-dendritic mechanisms underlying the electrophysiological properties of hypothalamic magnocellular neuroendocrine cells: A multicompartmental model study

2007

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Magnocellular neuroendocrine cells (MNCs) of the hypothalamus synthesize the neurohormones vasopressin and oxytocin, which are released into the blood and exert a wide spectrum of actions, including the regulation of cardiovascular and reproductive functions. Vasopressin-and oxytocinsecreting neurons have similar morphological structure and electrophysiological characteristics. A realistic multicompartmental model of a MNC with a bipolar branching structure was developed and calibrated based on morphological and in vitro electrophysiological data in order to explore the roles of ion currents and intracellular calcium dynamics in the intrinsic electrical MNC properties. The model was used to determine the likely distributions of ion conductances in morphologically distinct parts of the MNCs: soma, primary dendrites and secondary dendrites. While reproducing the general electrophysiological features of MNCs, the model demonstrates that the differential spatial distributions of ion channels influence the functional expression of MNC properties, and reveals the potential importance of dendritic conductances in these properties.

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“…Neurons were activated anlidromically by electrical stimulation of the neural lobe (2 ms pulses; < 1 mA intensity), and identified as putative oxytocin neurons by their continuous pattern of discharge activity ( 5 ) but the response was significantly lower in lactating rats ( n = 6 for both groups; **P <O.OI; ***P<O.OOl; r-test).…”

Section: Resultsmentioning

confidence: 99%

“…The oxytocin cells accelerate their firing rate by 20-to 40-fold at the milk ejection reflex (5). It remains striking that despite the reduced output of the oxytocin neurons in lactating rats to a variety of stimuli, sufficient oxytocin can Extracellular potassium concentrations in the neurohypophysis were measured as previously described (9,10).…”

Section: Discussionmentioning

confidence: 99%

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

Higuchi¹,

Bicknell²,

Leng³

1991

J Neuroendocrinology

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Lactating rats show reduced oxytocin release compared with virgin female rats in response to a variety of stimuli, including stress and osmotic stimulation. W e sought to establish whether this is a consequence of a reduced response in t h e oxytocin cells, or of a change in stimulus-secretion coupling at t h e level of t h e neurosecretory terminals in the neural lobe. Blood sampling experiments in anaesthetized rats showed that systemic administration of cholecystokinin resulted in significantly less oxytocin release in lactating rats than in virgin female rats. Electrophysiological recordings of single cells in the supraoptic nucleus, however, showed no difference in t h e responsiveness of oxytocin cells to this stimulus. Oxytocin release evoked by electrical stimulation or by depolarization with high potassium solutions was lower in isolated neural lobes from lactating rats than in glands from nonlactating rats, whereas evoked vasopressin release was similar in t h e two groups. The lactating rat neural lobes had a reduced oxytocin content: to study the consequences of depletion we compared hormone release evoked by electrical stimulation in vitro in neural lobes from normal male rats, and from male rats given 2% NaCl to drink for 2 or 4 days. Saline drinking resulted in a reduction in gland content of both oxytocin and vasopressin, and the evoked release of both hormones was also significantly reduced when expressed as a percentage of the gland content, as was also seen for oxytocin release for glands from lactating rats. Finally, measurement of t h e extracellular potassium response to stimulation of the isolated neural lobe as a n index of the excitability of neural lobe neurosecretory axons was unchanged in lactating rats compared with virgin female rats. Together, the data indicate that reduced oxytocin release observed in lactating rats is a simple consequence of reduced oxytocin content in the neural lobe rather than of a reduced excitability of the oxytocin neurons.Lactating rats exhibit a reduced oxytocin release in response to stress ( I , 2) and to osmotic stimulation (2). In addition, electrical stimulation of the region anterior and ventral to the third ventricle (which is essential for normal osmoregulation of oxytocin and vasopressin release; 3, 4). of the paraventricular nucleus, or of the neural lobe itself. all evoke less oxytocin release in lactating rats than in virgin female rats (2). This generalized reduced release of oxytocin appears paradoxical, since it occurs at a time when demand for oxytocin is high; oxytocin release in response to suckling is essential for efficient milk let-down (5-7). The release of oxytocin from the neural lobe of the pituitary is strongly dependent upon the parameters of stimulation, and is optimal in response to brief, high frequency episodes of stimulation similar to the intermittent bursting pattern of oxytocin cell activation observed during suckling (8). Facilitation of oxytocin release with increasing frequency of stimulation is a complex phen...

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The Milk-Ejection Reflex of the Rat: A 20- To 40-Fold Acceleration in the Firing of Paraventricular Neurones During Oxytocin Release

Cited by 331 publications

References 0 publications

Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity

Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity

Somato-dendritic mechanisms underlying the electrophysiological properties of hypothalamic magnocellular neuroendocrine cells: A multicompartmental model study

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

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