Antidiuretic hormone and angiotensin II plasma concentrations in febrile Pekin ducks

Abstract

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.

Restraint increases afebrile body temperature but attenuates fever in Pekin ducks (Anas platyrhynchos)

“…A cotton string was tied loosely around the legs to prevent retraction of the legs underneath the trunk. The 8-h duration of restraint was chosen because it represents a time span that covers the peak elevation in T b in response to LPS (10,11,12,17) and is a duration that has been used in previous studies (10,11,12,17). The effect of diclofenac sodium on T b during restraint was evaluated by injecting diclofenac ϳ2 h after the ducks were placed in the stand.…”

“…Indeed, we are unaware of studies, even in mammals, that have examined whether superimposing a psychological stress on a fever alters the thermal response to the pyrogen. Therefore, the present study was designed with two objectives: 1) to determine whether sustained physical restraint has a more than transient effect upon normal T b and, if so, whether this restraint-induced effect is affected by the inhibition of PGs, known mediators of avian fever (12); and 2) to determine whether stress-induced changes in T b alter the time course and/or magnitude of a superimposed febrile response induced by lipopolysaccharide (LPS).To accomplish these objectives we carried out two series of experiments in adult Pekin ducks, an avian species that has been used frequently in thermoregulatory studies (10,11,12,17) and for which an extensive physiological database exists. In the first series, we compared the T b profiles of ducks when they were unrestrained to when they were held in restraints for 8 h, a time course that covers the normal avian fever response to LPS.…”

“…In particular, clarity is needed about how physical restraint influences thermal biology. Physical restraint is used in many mechanistic studies, for example, when regular blood sampling is required to measure the endocrine mediators of fever (10,11,17). If restraint induces a psychological stress resulting in elevated T b or fever, then results will be confounded by that response.…”

“…We also determined the effect of diclofenac sodium, a known inhibitor of PG formation and the febrile response in Pekin ducks (12) on the T b profiles of the ducks when they were restrained. In the second series, we compared the characteristics of the febrile response to LPS, an established pyrogen in Pekin ducks (10,11,12,17), in restrained and unrestrained animals.…”

“…To accomplish these objectives we carried out two series of experiments in adult Pekin ducks, an avian species that has been used frequently in thermoregulatory studies (10,11,12,17) and for which an extensive physiological database exists. In the first series, we compared the T b profiles of ducks when they were unrestrained to when they were held in restraints for 8 h, a time course that covers the normal avian fever response to LPS.…”