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J B Wakerley

Publications and source records attributed to J B Wakerley.

At least 19 recordsLinked to original sources
PubMed1990

Facilitatory effect of hypothalamo-neurohypophysial tract stimulation on milk ejection frequency in the lactating rat.

The relative contribution of magnocellular and parvocellular neurones to the patterning of milk ejections was studied by activation of various parts of the hypothalamo-neurohypophysial tract. During suckling of anaesthetised lactating rats, electrical stimulation of the neurohypophysis/neural stalk (15 Hz, 1.5 s on/1.5 s off, 10 min) evoked an increased frequency of milk ejections as detected by intramammary pressure recording. Bilateral stimulation of the paraventricular nuclei produced a similar facilitation in the post-stimulus period, but stimulation of the supraoptic nuclei (with either low current or current sufficient to evoke peripheral oxytocin release) had no effect on the occurrence of milk ejections. These data are consistent with the hypothesis that parvocellular but not magnocellular neurones participate in the regulation of milk ejection frequency.

Animals↗
PubMed1990

Oxytocin excites neurones in the bed nucleus of the stria terminalis of the lactating rat in vitro.

Unit recordings were made in the bed nucleus of the stria terminalis in brain slices obtained from lactating rats. Addition of 10(-8) to 10(-6) M oxytocin to the perfusate caused a reversible and repeatable excitation in 28/53 (53%) of neurones. The excitatory effect of oxytocin was completely blocked in the presence of the antagonist [d(CH2)5,D-Tyr(OEt)2,Val4,Cit8]vasopressin (5 x 10(-7) M) and a smaller excitation was achieved with equimolar concentration of arginine vasopressin, implicating the involvement of an oxytocin receptor. This effect is discussed in relation to the actions of centrally administered oxytocin in the lactating rat.

Angiotensin Receptor Antagonists↗
PubMed1990

Role of the paraventricular nucleus in controlling the frequency of milk ejection and the facilitatory effect of centrally administered oxytocin in the suckled rat.

The milk-ejection reflex was studied in anaesthetized, lactating Wistar rats in order to evaluate the contribution of the paraventricular nucleus (PVN) to the patterning of milk ejection and the facilitatory action of centrally administered oxytocin. In the first series of experiments, radiofrequency lesions were performed and centred: (1) antero-dorsal to the PVN, damaging parts of the medial septum and anterior hypothalamus; (2) in the PVN, such that much of the parvocellular division was destroyed, but parts of the magnocellular division remained intact; or (3) in the PVN, destroying both parvocellular and magnocellular divisions. Suckling tests performed before and after lesioning showed that the milk-ejection interval was significantly increased (decreased frequency) after lesioning in groups 2 and 3, but that milk-ejection amplitude was significantly decreased only in group 3. These results suggest that damage to the parvocellular division of the PVN affects milk-ejection frequency, but that damage to the magnocellular PVN only affects amplitude. Subsequent tests on rats injected into the PVN with the neurotoxin N-methyl-D,L-aspartate revealed a fall in the amplitude and frequency of milk ejection, similar to that after complete radiofrequency lesions of the PVN. In the second series of experiments, the facilitatory action of centrally administered oxytocin (1 mU, 2.2 ng) was examined in animals bearing either sham or complete PVN lesions. In both groups, intracerebroventricular injection of oxytocin was able to increase the frequency of milk ejections, although the incidence of milk ejection was lower in the pre- and post-injection period in the PVN-lesioned animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Oxytocin release evoked by electrical stimulation of the medial forebrain in the rat: analysis of stimulus parameters and supraoptic neuronal activity.

The role of the medial forebrain area (vertical limb of the diagonal band, medial septum and medial nucleus accumbens) in the control of oxytocin secretion in lactating rats was investigated. Electrical stimulation of the medial forebrain evoked a reproducible rise in intramammary pressure, equivalent to that caused by i.v. injection of 1 mU oxytocin. No pressor effect accompanied this response. Radioimmunoassay of plasma samples showed that stimulation caused a significant rise in the concentration of circulating oxytocin. The effects of changing the parameters of stimulation to the medial forebrain were compared with those evoked by stimulation of the neural stalk. The optimal frequency for stimulation of the forebrain was found to be four-fold lower (10-20 Hz) than that for stimulation of the neural stalk (50 Hz). During continuous prolonged stimulation of the forebrain (20 Hz; 2 min) only a single transient response was obtained, whereas a protracted response was obtained as a result of prolonged stimulation of the stalk. Recordings were made from antidromically identified neurosecretory cells in the supraoptic nucleus. Electrophysiological responses to electrical stimulation of the medial forebrain were characterized by two main features. (1) Single-pulse stimulation produced only a small excitation (one or two action potentials), while high-frequency trains produced a profound facilitation of this response, with each pulse evoking short-duration 'bursting' behaviour in the supraoptic neurons. (2) During long trains of stimulation this frequency-dependent facilitation declined and could only be renewed after a period of rest.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

Prolonged electrical stimulation of the nipples evokes intermittent milk ejection in the anaesthetised lactating rat.

Intermittent and continuous electrical stimulation of the nipples elicited milk-ejection responses in the lactating rat. The responses occurred intermittently, with similar amplitudes and periodicity as those seen in suckled rats. The responses were always associated with synchronization of the electroencephalogram (EEG), but some rats with synchronized EEG activity did not milk eject during stimulation. Since continuous stimulation also resulted in intermittent milk ejection it seems unlikely that the periodicity of the reflex in suckled rats depends upon changes in the intensity of sensory stimulation. The techniques of nipple stimulation may be a useful method with which to study neural pathways and other phenomena such as gating involved in oxytocin release and milk ejection. The success of the technique depends on a variety of factors such as parameters of the stimulation and state of anaesthesia.

Anesthesia↗
PubMed1986

Afferent projections from the mammary glands to the spinal cord in the lactating rat--II. Electrophysiological responses of spinal neurons during stimulation of the nipples, including suckling.

In lactating rats, the milk ejection reflex is evoked and maintained by stimulation of the nipples by the suckling young. In order to understand the processing of the suckling stimulus within the spinal cord, urethane-anaesthetized lactating rats were prepared for electrophysiological recording from the thoraco-lumbar spinal cord during stimulation of the nipples. Single shocks to inguinal or abdominal nipples evoked a cord dorsum potential, consisting of an early (2.6 ms) afferent volley followed by a negative wave (100-200 microV; latency 5-7 ms, duration 5-10 ms). Evoked potentials were also recorded at various depths within the spinal cord, with a maximum amplitude (200-400 microV) at a depth of 400-800 microns, 400-800 microns lateral to the mid-line. At a given recording site, the response was maximal for one particular nipple but submaximal potentials could be evoked from adjacent nipples. Simultaneous stimulation of adjacent nipples caused summation of the response. Unit recordings were made from 35 spinal neurons. Upon electrical stimulation of the nipples, the cells responded with an early train of spikes (latency 5-15 ms), and in 6 cells, a later response (140-180 ms), with a higher stimulation threshold, was also observed. All cells examined showed convergence and summation from different nipples. Twenty out of 27 cells were also activated by stretching of the nipples, which evoked a rapidly adapting response; rhythmical stretching produced a more sustained increase in activity. The cells also responded to other natural stimuli such as touch and pressure or stroking the hair around the nipple and had large receptive fields. Six cells were tested with the suckling stimulus. There was a brisk increase in firing as the pup grasped the nipple and then intermittent (every 18-30 s) episodes of enhanced activity, which directly correlated with the suckling movements. These episodes continued for the duration of the suckling test and were enhanced when a second pup was placed on an adjacent nipple. Finally, from a few experiments when a stimulating electrode was placed within the contralateral antero-lateral funiculus at the level of C2-C3 for antidromic identification, it was seen that some of the cells activated from the nipples projected to higher levels. The short latency responses to nipple stimulation, including suckling, suggest that the suckling stimulus reaches the spinal cord ungated.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Changing characteristics of the milk-ejection reflex during pregnancy, lactation and after weaning in the rat.

The pattern of reflex milk ejection during suckling was investigated in anaesthetized Wistar rats at various stages of pregnancy, lactation and after weaning. Milk-ejection responses were measured using intramammary pressure recordings, and the amount of oxytocin released was estimated from log dose-response lines compiled from the mammary responses to exogenous oxytocin. The number of rats showing intramammary pressure responses to oxytocin increased on Day 22 of pregnancy (the day of parturition) and decreased at 8 days after weaning. The dose-response lines from pregnant animals were shallow, but steepened and shifted to the left during lactation and after weaning. Reflex milk-ejection responses during suckling were detectable in primigravid animals, indicating that birth of the litter and previous suckling experience are unnecessary for the immediate functioning of the reflex. Reflex milk-ejection responses improved during early lactation (such that the frequency and the amount of oxytocin released at each response were maximal at Day 10 of lactation), and subsequently declined in late lactation. Although the frequency of responses in animals 2 and 4 days after weaning was similar to that in late lactating animals, the amount of oxytocin released at each response had risen again to mid-lactation values. In animals undergoing a second pregnancy and lactation the pattern of change in the milk-ejection responses was similar to that of primiparous animals.

Animals↗
PubMed1985

Reappraisal of the influence of mammary distension on the frequency of milk ejection in the rat.

Experiments were performed to reinvestigate the importance of mammary engorgement for activation of the milk-ejection reflex in the rat. Reflex milk ejection (measured by intramammary pressure recordings during a 2-h suckling test under anaesthesia) was compared in rats with engorged mammary glands (15-h separation from the pups, followed by sham-removal of milk) and in rats with drained mammary glands (15-h separation, followed by milk removal using a foster litter and exogenous oxytocin). In experiment 1, multiple small (2 mu.) doses of oxytocin were used for milk removal: these were effective in emptying the mammary glands and caused no subsequent impairment or change in sensitivity of the mammary response to oxytocin. Using this draining procedure, no significant differences were observed in either the number or relative amplitude of the milk ejections, or the occurrence of pup stretch reactions between engorged and drained rats. Similar results were seen in experiment 2, where an identical draining protocol was used, but the rats were pretreated with propranolol before the suckling test. In experiment 3, large (250 mu.) oxytocin doses were used for milk removal, as in previous studies. Again mammary draining had no effect on milk ejection in a subsequent suckling test (with propranolol pretreatment). However, the number of stretch reactions shown by the pups was significantly (P less than 0.001) reduced from 8.6 +/- 1.4/2 h to 1.9 +/- 0.6/2 h. This effect probably related to long-term impairment of the oxytocin response of the mammary glands following the draining procedure, and could not be attributed to the draining per se.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Extrinsic control of phasic supraoptic neurones in vitro: burst initiation and termination following brief changes in excitatory drive.

Experiments were performed to investigate the responses of phasic supraoptic cells in hypothalamic slices to brief (2-3 sec) changes in excitatory drive, induced by varying the level of local glutamate stimulation. A brief increase in excitation during a silent period immediately triggered a prolonged burst of firing, similar in duration to the ongoing phasic bursts. A transient decrease in excitation during a phasic burst evoked a protracted quiescence, reminiscent of a typical silent period. These results support the idea that in phasic cells the effects of brief synaptic inputs may be amplified in time to produce a prolonged change in electrical activity and associated hormone release.

Afferent Pathways↗
PubMed1983

Effects of morphine and D-Ala, D-Leu enkephalin on the electrical activity of supraoptic neurosecretory cells in vitro.

Experiments were performed to investigate the effects of morphine and [D-Ala2, D-Leu5]enkephalin on supraoptic cells in hypothalamic slices in vitro. To ensure the presence of a steady background activity, the cells were recorded with glutamate-filled glass microelectrodes and the level of activity was controlled by selecting a suitable retaining current (0.1-9.8 nA). Under these conditions, supraoptic cells showed either the non-phasic (65%) or phasic (35%) firing pattern previously associated with oxytocin or vasopressin cells, respectively. During perifusion of the slice with morphine (10 microM), 10 out of 17 non-phasic supraoptic cells were profoundly inhibited, five cells showed no response and the remaining 2 cells were excited. Similarly with [D-Ala2, D-Leu5]enkephalin (10 microM), 11 out of 15 non-phasic cells were inhibited, 3 cells showed no response and 1 cell was excited. The inhibition produced by morphine or [D-Ala2, D-Leu5]enkephalin could be reversed by concomitant application of naloxone (10 microM). In contrast to the profound effects seen in the non-phasic cells, only 1 out of 13 phasic cells tested with either morphine or [D-Ala2, D-Leu5]enkephalin was inhibited. The remaining 12 phasic cells showed no change in either their overall firing rate or pattern of activity during opiate perifusion. These results provide further evidence that, in addition to their inhibitory effects within the posterior pituitary, opiates can directly suppress the electrical activity of magnocellular neurosecretory cells at the level of the hypothalamus. However, the absence of an opiate effect on the phasic cells might suggest that the action of opioid peptides within the hypothalamus would be exerted predominantly on the oxytocin, rather than the vasopressin cells.

Animals↗
PubMed1978

Comparison of firing patterns in oxytocin- and vasopressin-releasing neurones during progressive dehydration.

The electrical activity of neurosecretory cells in the supraoptic nucleus of the urethane-anaesthetized lactating rat was examined after periods of water deprivation ranging from 0-24 h. Supraoptic units were identified by antidromic activation following stimulation of the neurohypophysis, and classified as oxytocin or vasopressin cells according to their response during reflex milk ejection. In 65 vasopressin cells, dehydration increased the mean firing rate from 2.1 spikes/sec at 0 h to 6.8 spikes/sec at 24 h and caused a change from a slow irregular to a phasic firing pattern. Thus, after 6 h or more of dehydration, 84-100% of the vasopressin cells fired phasically, compared to 12% under normal conditions. In phasic vasopressin cells , the intraburst firing rates were closely related to the stages of dehydration, rising from a mean of 6.3 spikes/sec at 6 h to 12.0 spikes/sec at 24 h. However, no systematic relationship was observed between the stages of dehydration and the mean burst or silence durations. In 77 identified oxytocin units, dehydration increased the firing rate from 0.9 spikes/sec to 2.8 spikes/sec after 24 h, but only 3 (4%) of the cells showed phasic firing. Instead, the oxytocin units changed from a slow irregular to a fast continuous discharge. In conclusion, both vasopressin and oxytocin neurones are activated during chronic dehydration, but there is a marked difference in the pattern of their response. The phasic firing of the vasopressin cells may be important in increasing the occurrence of short interspike intervals and thus facilitating hormone release.

Action Potentials↗
PubMed1978

Relationship between the suckling-induced release of oxytocin and prolactin in the urethane-anaesthetized lactating rat.

The effects of changes in the intensity of the suckling stimulus on the reflex release of oxytocin and prolactin were compared in urethane-anaesthetized lactating rats. Mothers which had previously suckled 12 pups (Group 1) showed a graded increase in the amount of oxytocin released during a 3 h suckling test when the number of pups applied to the nipples was increased from six to eight or ten. Mothers which had suckled six pups during their lactation (Group 2) appeared to show a maximum frequency of milk ejection whether six, eight or ten pups were applied to the nipples. The release of prolactin was not elicited from either Group 1 or Group 2 mothers when six pups were applied to their nipples. With eight pups suckling, the Group 1 mothers again showed no evidence of prolactin release. In contrast, the Group 2 mothers showed a significant increase in the level of prolactin in the plasma during the 3 h suckling test. With ten pups suckling the release of prolactin was evident in both groups of mothers, although the response was earlier and more pronounced in Group 2 than Group 1. These results suggest that in the urethane-anaesthetized rat, the threshold for the suckling-induced reflex release of oxytocin is distinct from the threshold for the release of prolactin and that these thresholds are, at least in part, set by the preceding suckling experience of the mothers. In those animals which showed both reflex milk ejection and prolactin release there was a linear relationship between the magnitude of the two endocrine responses.

Animals↗