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G Leng

Publications and source records attributed to G Leng.

At least 163 records · Page 9Linked to original sources
PubMed1984

Reversible fatigue of stimulus-secretion coupling in the rat neurohypophysis.

Single rat neurointermediate lobes were impaled on a stimulating electrode and continuously perifused with oxygenated medium. The secretion of oxytocin and vasopressin into the medium was measured by specific radio-immunoassays. The temporal profile of vasopressin release during a 20 min period of 13 Hz stimulation was compared with that of oxytocin. The results indicate that although the rate of secretion of both oxytocin and vasopressin declines over 20 min, the extent and time course of this fatigue is different for the two hormones. This difference could not be accounted for by differences in the rate of diffusion of released hormone from the tissue which was similar to the rate of wash-out of [14C]sucrose from the extracellular space in pre-labelled glands. In separate experiments glands were exposed to a prolonged period (60-70 min) of 13 Hz stimulation interrupted by brief silent periods (30 s-2 min duration). Some recovery from the fatigue of vasopressin secretion was evident after even the shortest of these silent periods. In further experiments glands were stimulated electrically for 18, 36, 54 and 72 s at 13 Hz: the order of presentation of the periods of stimulation was randomized between experiments. The vasopressin release rate declined markedly and progressively between 18 and 72 s. In contrast, the oxytocin release rate was relatively uniform throughout 72 s of stimulation. Thus vasopressin secretion is subject to a relatively rapid and dramatic fatigue. The results support the hypothesis that the phasic discharge patterns characteristic of vasopressin secreting neurones optimize the efficiency of vasopressin release from the nerve terminals in the neurohypophysis by avoiding the fatigue of stimulus-secretion coupling that accompanies continual stimulation.

Animals↗
PubMed1983

Oxytocin release is inhibited by opiates from the neural lobe, not those from the intermediate lobe.

Previous experiments have shown that the amount of oxytocin released by electrical stimulation from an isolated rat neurointermediate lobe is about doubled in the presence of the opiate antagonist naloxone. To test whether the opiates from the intermediate lobe inhibit the release of oxytocin, we performed similar experiments on the isolated neural lobe, after almost total removal of intermediate lobe tissue. The potentiating effect of naloxone upon oxytocin release was undiminished, suggesting that the endogenous opiate responsible for inhibiting oxytocin secretion comes from the neural lobe itself.

Animals↗
PubMed1983

Intercommunication in the rat supraoptic nucleus.

The vasopressin and oxytocin cells of the rat supraoptic nucleus fire in characteristic discharge patterns during hormone release. The present paper discusses the possible role of intercommunication between supraoptic neurones in determining these patterns. In contrast to earlier reports, recent electrophysiological and anatomical evidence suggests that strong coupling is not widespread within the nucleus. However, it remains possible that local release of a neuromodulator, perhaps vasopressin itself, may modify the phasic discharge patterns of the vasopressin cells. The neurosecretory cells project to areas outside the nucleus, and also to a few interneurones within the nucleus, which may mediate indirect communication between the supraoptic neurones.

Action Potentials↗
PubMed1982

Lateral hypothalamic neurones: osmosensitivity and the influence of activating magnocellular neurosecretory neurones.

1. The activity of single cells in the supraoptic nucleus and the lateral hypothalamus of urethane-anaesthetized rats was studied during electrical stimulation of the neural stalk.2. Neurones activated antidromically from the neural stalk were either unaffected or, rarely, slightly affected by single shocks or by brief trains of shocks presented at an intensity just below that necessary for antidromic invasion. Thus there does not appear to be a strong synaptic coupling between rat supraoptic neurones.3. In contrast, many lateral hypothalamic neurones, and particularly those in the perinuclear zone, were strongly affected by neural stalk stimulation, being either orthodromically excited or inhibited. Thus, rat magnocellular neurosecretory neurones appear to project, directly or indirectly, to the lateral hypothalamus.4. Thirty-one lateral hypothalamic neurones were studied following an I.P. injection of 1 ml. 1.5 M-NaCl. Eighteen neurones responded to this osmotic stimulus with a change of at least 1 spike/sec in mean firing rate.5. Fifteen of the thirty-one neurones were strongly affected by neural stalk stimulation (eight inhibited, seven excited). Ten of these fifteen neurones were affected in the same way by osmotic stimulation. The remaining sixteen out of thirty-one neurones were unresponsive to neural stalk stimulation, and of these, ten were also unresponsive to osmotic stimulation. Thus most lateral hypothalamic neurones responded in a similar way to neural stalk stimulation and to systemic osmotic stimulation.6. Thus the osmosensitivity of some neurones in the lateral hypothalamus may be mediated by synaptic input arising from the magnocellular neurosecretory neurones. However, the osmosensitivity of some lateral hypothalamic neurones cannot be explained in this way, and probably derives from osmoreceptors other than the magnocellular neurones.

Animals↗
PubMed1982

The supraoptic nucleus as an osmoreceptor.

The "Progress' review is written to challenge the prevalent belief that neurones of the supraoptic nucleus are not involved in the reception of osmotic stimuli. Evidence is presented that these neurones are depolarised by physiological increases in the osmotic pressure of the extracellular fluid. However, generation of action potentials in these depolarised cells still requires the presence of synaptic input from currently unidentified neurones. We suggest that the osmoreceptor regulating vasopressin secretion is probably composed of more than one type of neurone and discuss this suggestion in the context of selected experiments previously cited as evidence that the supraoptic nucleus is not involved in osmoreception.

Animals↗
PubMed1981

The effects of neural stalk stimulation upon firing patterns in rat supraoptic neurones.

Antidromically identified neurones were recorded from the supraoptic nucleus of urethane-anaesthetized rats. In test periods of about 10 min, each recorded action potential was followed 1 ms later by a shock to the neural stalk. In phasically firing cells, this stimulation consistently modified the observed firing pattern: burst length was shortened but intraburst activity was unchanged. The stimulation invaded most supraoptic neurones antidromically, but antidromic spikes evoked in the recorded neurone were extinguished by collision. Thus, the observed changes in firing pattern were probably the consequence of interaction between the recorded unit and other neurones projecting to the neural stalk--most probably other supraoptic neurones. The behaviour of continuously firing supraoptic neurones was studied following single shocks and following trains of shocks. The results suggest that the widely reported evidence for recurrent inhibition in the rat supraoptic nucleus has been misinterpreted, and that inhibition cannot be demonstrated in most supraoptic neurones following single shocks to the neural stalk. However, the experiments using trains of shocks produced evidence consistent with a complex interaction between magnocellular neurosecretory cells involving both excitation and inhibition.

Action Potentials↗
PubMed1981

Threshold sensitivity of the auditory pathway: effects of worsening signal-to-noise ratio in the auditory nerve.

Perfusions of scala tympani with high potassium solutions increase spontaneous activity of auditory nerve fibres without affecting their threshold sensitivity. In these circumstances, however, the signal-to-noise ratio of the auditory nerve response to a given stimuli is worsened. Recordings from cochlear nucleus neurones during such perfusions indicate that this worsening is critical for threshold sensitivity at higher levels in the auditory pathway.

Acoustic Stimulation↗
PubMed1981

Relative efficiency of neural firing patterns for vasopressin release in vitro.

Single rat neurohypophyses were impaled on a platinum electrode, perifused with isotonic medium and fractions of perifusate collected each minute. Arginine vasopressin content of the fractions was measured by radioimmunoassay. The basal release of arginine vasopressin varied from 50 to 350 pg (0.02-0.14 mU/min) between individual neurohypophyses. Recordings previously obtained from rat supraoptic neurones provided the patterns for electrical stimulation. 8-min segments of a phasically and a continuously firing neurone were selected such that each was firing at a mean rate of 6 spikes/s and possessed very similar overall distributions of interspike intervals. In 15 experiments individual neurohypophyses were stimulated with the phasic pattern, followed by the continuous pattern, or vice versa, separated by an 8-min unstimulated period. In either case, significantly more hormone was released during phasic stimulation than during continuous stimulation. It is concluded that the phasic firing pattern typical of vasopressin neurones is highly efficient for the release of vasopressin from the neurohypophysis, but that its effectiveness does not lie in an increased preponderance of short interspike intervals.

Animals↗
PubMed1981

Effects of neural stalk stimulation on phasic discharge of supraoptic neurones in Brattleboro rats devoid of vasopressin.

Brattleboro rats, homozygous for diabetes insipidus, and Long-Evans rats were anaesthetized with urethane, and antidromically identified neurons were recorded from the supraoptic nucleus. Phasically firing neurones were studied during repeated electrical stimulation of the neural stalk, whereby most supraoptic neurones, but not the recorded neurone, were activated antidromically. Such stimulation consistently modified the discharge pattern of phasic neurones in Long-Evans rats, but was relatively ineffective in Brattleboro rats. These results suggest that the effects of neural stalk stimulation on discharge patterns in Long-Evans rats may be substantially mediated by the evoked release of vasopressin or neurophysin.

Action Potentials↗
PubMed1981

The effects of frusemide, bumetanide and piretanide on the quinea pig cochlea and auditory nerve.

Frusemide, bumetanide and piretanide were introduced into scala tympani of the guinea pig cochlea by perfusion. The short-term effects of these drugs on the cochlear microphonic, the compound action potential and on the activity of single auditory nerve fibres were studied. the compound action potential was more sensitive to the action of the above compounds than was the cochlear microphonic. Single auditory nerve fibres showed a marked increase in threshold and generally a fall in spontaneous firing rate. A deterioration in in tuning was observed which in some cases, was not invariably accompanied by a rise in threshold. Histological examination revealed oedematous changes in stria vascularis and in supporting cells following cochlea perfusion with the above compounds.

Animals↗
PubMed1980

The Davis theory: a review, and implications of recent electrophysiological evidence.

The Davis theory of mechano-electrical transduction asserts that the endocochlear potential and the hair cell resting potential summate to provide a driving force for current flow through the hair cell. However, while a variety of agents which depress the endocochlear potential simultaneously depress auditory nerve sensitivity and reduce the cochlear microphonic, recent reports suggest that the hair cells may be depolarised without such effects ensuing. The relevant literature is reviewed.

Animals↗
PubMed1980

Kanamycin ototoxicity and pigmentation in the guinea pig.

Cochleas from albino and pigmented guinea pigs were examined histologically following chronic administration of Kanamycin. In pigmented animals, damage was concentrated amongst hair cells towards the base, but in albinos, hair cell damage was diffusely spread. These observations support suggestions that melanin is implicated in Kanamycin ototoxicity.

Animals↗