Vasotocin acts as a dipsogen in ducks at concentrations stimulating subfornical organ neurons in vitro

Schmid, Herbert; Simón, E.

doi:10.1007/bf00301129

Cited by 6 publications

(1 citation statement)

References 21 publications

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“…Possible mechanisms by which AVT may act as a cryogen include the inhibition of thyroid hormone secretion (John et al 1995) and/or the reduction of metabolic rate (John & George, 1992), which have been demonstrated to be effects of AVT in birds. Alternatively, it could be that the brain‐intrinsic vasotocinergic system (Berk et al 1982; Weindl & Sofroniew, 1982; Schmid et al 1995) is activated by circulating AVT at areas lacking a blood‐ brain barrier, such as the circumventricular organs (Schmid & Simon, 1996).…”

Section: Discussionmentioning

confidence: 99%

Antidiuretic hormone and angiotensin II plasma concentrations in febrile Pekin ducks

Gray

Maloney

1998

The Journal of Physiology

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Simultaneous whole‐cell voltage and Ca2+ fluorescence measurements were made from the distal apical dendrites and the soma of thick tufted pyramidal neurons in layer 5 of 4‐week‐old (P28–32) rat neocortex slices to investigate whether activation of distal synaptic inputs can initiate regenerative responses in dendrites. Dual whole‐cell voltage recordings from the distal apical trunk and primary tuft branches (540–940 μm distal to the soma) showed that distal synaptic stimulation (upper layer 2) evoking a subthreshold depolarization at the soma could initiate regenerative potentials in distal branches of the apical tuft which were either graded or all‐or‐none. These regenerative potentials did not propagate actively to the soma and axon. Calcium fluorescence measurements along the apical dendrites indicated that the regenerative potentials were associated with a transient increase in the concentration of intracellular free calcium ([Ca2+]i) restricted to distal dendrites. Cadmium added to the bath solution blocked both the all‐or‐none dendritic regenerative potentials and local dendritic [Ca2+]i transients evoked by distal dendritic current injection. Thus, the regenerative potentials in distal dendrites represent local Ca2+ action potentials. Initiation of distal Ca2+ action potentials by a synaptic stimulus required coactivation of AMPA‐ and NMDA‐type glutamate receptor channels. It is concluded that in neocortical layer 5 pyramidal neurons of P28–32 animals glutamatergic synaptic inputs to the distal apical dendrites can be amplified via local Ca2+ action potentials which do not reach threshold for axonal AP initiation. As amplification of distal excitatory synaptic input is associated with a localized increase in [Ca2+]i these Ca2+ action potentials could control the synaptic efficacy of the distal cortico‐cortical inputs to layer 5 pyramidal neurons.

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Section: Discussionmentioning

confidence: 99%

Antidiuretic hormone and angiotensin II plasma concentrations in febrile Pekin ducks

Gray

Maloney

1998

The Journal of Physiology

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Effects of angiotensin II and its blockers Sar1-lle8-angiotensin II and DuP 753 on drinking in ducks in relation to properties of subfornical organ neurons

Simón

Schmid

1996

J Comp Physiol B

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Properties of systemically applied angiotensin II in stimulating water intake of normally hydrated ducks were studied and the results compared with properties of angiotensin II-responsive neurons of the subfornical organ which are considered as targets for circulating angiotensin II acting as a dipsogen. Following intravenous infusion of hypertonic saline (2000 mosmol.kg-1 at 0.3 ml.min-1 for 1 h), intravenous infusion of 0.3 ml.min-1 isotonic saline with angiotensin II (200 ng.min-1), starting 1 h later, stimulated drinking in each case at an angiotensin II plasma level of about 1400 pg.ml-1. Without hypertonic priming, the same angiotensin II infusion did not stimulate drinking in each experiment; however, if effective, repeated infusions of ANGII induced stable dipsogenic responses. Angiotensin II infusions did not alter plasma levels of antidiuretic hormone. Sar1-Ile8-angiotensin II, a non-selective angiotensin II antagonist, acted weakly as a partial agonist when infused at a dose 200-fold higher than angiotensin II and effectively blocked the dipsogenic action of angiotensin II; this corresponds to the inhibition of angiotensin II-induced excitation by Sar1-Ile8-angiotensin II observed in duck subfornical organ neurons. DuP 753 (losartan), an angiotensin II antagonist specifically blocking AT1 receptors in mammals, had equivocal effects on angiotensin II-induced drinking in ducks at rates 50- and 200-fold higher than angiotensin II, which corresponds to the weak inhibitory action of this compound on angiotensin II-induced neuronal excitation in the duck SFO. Blood pressure was only marginally elevated by the applied angiotensin II dose and Sar1-Ile8-angiotensin II had no effect.

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Vasopressin and sensory circumventricular organs

Jurzak

Schmid

1999

Progress in Brain Research

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Vasotocin acts as a dipsogen in ducks at concentrations stimulating subfornical organ neurons in vitro

Cited by 6 publications

References 21 publications

Antidiuretic hormone and angiotensin II plasma concentrations in febrile Pekin ducks

Antidiuretic hormone and angiotensin II plasma concentrations in febrile Pekin ducks

Effects of angiotensin II and its blockers Sar1-lle8-angiotensin II and DuP 753 on drinking in ducks in relation to properties of subfornical organ neurons

Vasopressin and sensory circumventricular organs

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