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Biomedical subjects

J B Wakerley

Publications and source records attributed to J B Wakerley.

At least 55 records · Page 3Linked to original sources
PubMed1976

Plasma concentrations of prolactin and thyrotrophin during suckling in urethane-anaesthetized rats.

Plasma levels of prolactin and TSH were determined by radioimmunoassay in urethaneanaesthetized lactating rats during suckling. Oxytocin release was monitored by recording intramammary pressure. Application of ten pups, 3 h after administration of urethane (1-1 g/kg, i.p.), evoked a parallel rise in prolactin and TSH concentrations which reached a maximum during the 3rd hour of suckling and then declined. Peak hormone concentrations represented a 25-fold increase in prolactin and a ten-fold increase in TSH. Suckling also elicited a pulsatile (every 5-10 min) release of 0-5--1-0 mu. oxytocin. The gradual rise in prolactin and TSH occurred between the 1st and 20th oxytocin pulses. Intravenous injection of thyrotrophin-releasing hormone (TRH) into unsuckled, anaesthetized lactating rats resulted in a 7- to 30-fold increase in TSH concentration, whereas prolactin levels showed no substantial change. These results indicate that suckling releases TSH as well as prolactin in the urethaneanaesthetized rat. However, the absence of prolactin release after injections of TRH makes it unlikely that both endocrine responses are regulated solely by the actions of this one releasing hormone.

Anesthesia↗
PubMed1975

Pattern of sucking in the infant rat during spontaneous milk ejection.

Two methods are described for measuring the sucking of rat pups on the nipples of the mother. The first uses pressure recording of the cannulated teatduct; the second uses direct observation of sucking behavior. Using these methods, the sucking behavior of the pups during sequences of milk ejections was investigated. Pressure recordings of the sucking of individual pups on the nipple showed that between milk ejections the pups sucked intermittently in bursts. During milk ejection itself there was a longer period of vigorous and continuous sucking. Behavioral observations on the level of sucking in whole litters of pups showed that the background bursts of sucking from the litter as a whole were randomly distributed in relation to the inferred time of oxytocin release. These results indicate that once the pups are sucking on the nipples, variations in the sucking behavior of the litter have no role in the timing of milk ejections in the mother.

Animals↗
PubMed1975

Factors governing the periodic activation of supraoptic and paraventricular neurosecretory cells during suckling in the rat.

1. One hundred and thirty-two antidromically identified paraventricular (PV) and supraoptic (SO) neurones were studied during milk ejection evoked by the suckling of the young, in thirty-four lactating rats anaesthetized with urethane (1.1 g/kg I.P.). The spike activity of these neurones was analysed to determine some of the factors governing their orthodromic activation. Changes in spike activity were compared with the amount of oxytocin released from the neurohypophysis, as measured by the rise in intramammary pressure at milk ejection. 2. Sixty-five units, from both the PV and SO nuclei, displayed a characteristic burst of accelerated activity 12-18 sec before milk ejection. With a suckling stimulus of nine or ten pups, these neurosecretory responses were both regular in their occurrence (recurring evey 4-8 min) and uniform in character, i.e. all responsive cells accelerated to 30-80 spikes/sec for 1-4 sec. Two units deviated from this pattern and both were recorded in animals which failed to display a detectable milk ejection...

Action Potentials↗
PubMed1974

Electrophysiological evidence for the activation of supraoptic neurones during the release of oxytocin.

1. Antidromically identified supraoptic (SO) units were recorded in lactating rats anaesthetized with urethane (1.1 g/kg), and their activity was studied during milk ejection evoked by the suckling of the young. Fifty-eight SO units were recorded through 174 milk ejections. Each milk ejection was the result of a neurohypophysial release of an oxytocin pulse of 0.5-1.5 m-u.2. Fifty-five of the SO units displayed background activity and three were silent. The firing rates ranged from 0 to 15.4 spikes/sec, the distribution was exponential with 26% of the units firing at < 1 spike/sec. Sixteen (28%) of the SO units displayed a phasic pattern of activity characterized by periods of activity (6-132 sec) and silence (4-71 sec).3. Twenty-five of the non-phasic units displayed a large and stereotyped acceleration in spike activity some 10.5-17.4 sec before the rise in intramammary pressure at milk ejection. Units accelerated to rates between 9-66 spikes/sec, an increase of about thirtyfold (median) on background activity. The response was brief (0.9-4.7 sec) and was followed by a period of after-inhibition.4. It was concluded from studies of double recordings and observations of multi-unit activity that all the responsive units were synchronously activated. The mean latency of 13.3 sec between the onset of the neurosecretory response and milk ejection was similar to that observed following the experimental release of endogenous oxytocin by electrical stimulation of the neurohypophysis (50 pulses/sec for 2-4 sec).5. Four of the phasically active units were correlated with the oxytocin release for milk ejection. Three of these units displayed a burst of activity superimposed on the terminal portion of an active phase, some 10.2-14.7 sec before milk ejection. The fourth unit, recorded in conjunction with a responsive non-phasic unit, consistently switched from silence to activity coincident with the onset of the SO activation.6. The remaining SO units and a further ten units that were not antidromically activated by neurohypophysial stimulation displayed no change in activity during either the period of neurosecretory activation or the period of after-inhibition.7. This activation of the SO neurones, in the formulation of oxytocin release and milk ejection, is the same as that we have previously observed in recordings from the paraventricular (PV) region, and the proportion of neurones displaying the response is similar: 48% in the SO nuclei, 58% in the PV nuclei. We conclude, since the SO nuclei contain 80% of the neurosecretory cells that project to the neurohypophysis, that the SO nuclei are as important, if not more so, than the PV nuclei in the control of oxytocin release.

Action Potentials↗