Walter T. Kyner

The Amplitude of Circadian Oscillations: Temperature Dependence, Latitudinal Clines, and the Photoperiodic Time Measurement

This paper develops several propositions concerning the lability of the amplitude of Drosophila circadian pacemakers. The first is that the amplitude of the pacemakers motion, unlike its period, is markedly temperature-dependent. The second is that latitudinal variation in pacemaker amplitude (higher in the north) is responsible for two very different sets of observations on Drosophila circadian systems at successively higher latitudes. One of these is a cline in D. aurarias phase-shifting response to light, which steadily weakens in a succession of more northerly strains. The other, concerning D. littoralis in the very far north, is a cline in the rate at which eclosion activity becomes arrhythmic (the circadian rhythm damps out) in constant darkness; damping is faster in the north. The third proposition concerns a plausible selection pressure for the cline in pacemaker amplitude that we propose underlies the two directly observed clines. Two points are emphasized: (1) The amplitude of the pacemakers daily oscillation declines as the duration of the entraining light pulse (photoperiod) is increased; and (2) the duration of the daily photoperiods throughout the breeding season is steadily increased as one moves toward the poles. Selection for conservation of pacemaker amplitude (during the breeding season) would produce the latitudinal cline we propose. The fourth, and final proposition is that since the amplitude of the pacemakers daily motion responds systematically to change in photoperiod, amplitude is clearly one way—and a temperature-dependent way—in which insect circadian systems may sense seasonal change. These propositions concerning the temperature and latitude dependence of pacemaker amplitude may be relevant to a wider array of circadian pacemakers than Drosophila.

Arginine vasopressin V1-antagonist and atrial natriuretic peptide reduce hemorrhagic brain edema in rats.

Background and Purpose: Injection of arginine vasopressin into the cerebral ventricles in animals with brain injury increased brain water, whereas injection of atrial natriuretic peptide reduced water content. Therefore, to determine the role of endogenous arginine vasopressin in brain edema, we attempted to inhibit edema from a hemorrhagic lesion with an arginine vasopressin V1 receptor antagonist or atrial natriuretic peptide. Methods: Adult Sprague-Dawley rats with hemorrhages induced by 0.4 IU bacterial collagenase were treated with 75 ng (n=9) or 8 μg (n=9) of the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)Arg, 3.2 μg (n=4) atrial natriuretic peptide injected intracerebrally, or 5 μg/kg per hour (n=7) atrial natriuretic peptide intraperitoneally. They were compared with control groups injected with 0.4 IU collagenase only. Brain water and electrolytes were measured 24 hours later. Brain uptake of [14C] sucrose was measured 30 minutes after lesions were induced by 0.4 IU collagenase alone (n=5) or after collagenase injection and 50 μg/kg per hour n=5) atrial natriuretic peptide injected intravenously. Results: The arginine vasopressin V1 receptor antagonist and atrial natriuretic peptide significantly (p<0.05) reduced water and sodium contents in the posterior edematous regions. Brain uptake of [14C] sucrose was significantly reduced by intravenous atrial natriuretic peptide. Conclusions: Antagonists to arginine vasopressin V1 receptors and atrial natriuretic peptide both significantly reduce hemorrhagic brain edema, and atrial natriuretic peptide appears to protect the blood-brain barrier.

Gray and white matter brain-blood transfer constants by steady-state tissue clearance in cat

Capillary transfer constants for gray matter have been measured by others from steady-state tissue clearance during ventriculocisternal perfusion. Similar studies in white matter, however, are complicated by the bulk flow of interstitial fluid (ISF). Recently we determined the velocity of bulk flow of ISF under normal conditions. We now report capillary transfer constants in gray and white matter by steady-state tissue clearance in the cat. Adults cats underwent a 2, 3, or 4 h ventriculocisternal perfusion with artificial cerebrospinal fluid containing [3H]sucrose and either [14C]urea or [14C]ethylene glycol. Diffusion coefficients and velocity of bulk flow were determined from tissue concentrations of the extracellular marker, sucrose. Steady-state tissue concentrations of urea and ethylene glycol were used to calculate transfer of those compounds from the brain to the blood. Urea reached steady-state by the third hour; capillary transfer constants were similar in gray and white matter. Ethylene glycol reached steady-state by the second hour; however, capillary transfer was more rapid in the gray matter than in white.

Autoradiographic Patterns of Brain Interstitial Fluid Flow After Collagenase-induced Haemorrhage in Rat

Cerebral oedema accompanies intracerebral haemorrhage. We induced intracranial bleeding by the intracerebral injection of bacterial collagenase. There was oedema observed both at the haematoma site in the caudate/putamen and bilaterally in the hippocampal regions. To determine the role of vasogenic oedema spread from the site of injury, we studied by autoradiography the distribution of extracellular markers injected along with the collagenase. Both 14C-dextran (m.w. 70,000) and 14C-sucrose (m.w. 341) spread away from the injection site into both hippocampal regions in a similar pattern, suggesting bulk flow. Vasogenic oedema secondary to a haemorrhagic lesion in the caudate/putamen is an important cause of the oedema observed in both hippocampal regions in our model.

The effect of arginine vasopressin and V1 receptor antagonist on brain water in cat

Arginine vasopressin (AVP) is important in brain water regulation. To better understand the effect of AVP released by extrahypothalamic fibers in brain, we microinfused AVP into intact brain and studied its effect on brain water and electrolytes. Adult cats had 5 ng of AVP infused into the caudate nuclei. Four h after infusion the brains were removed for measurement of water and electrolyte contents. Animals infused with AVP were compared to controls infused with saline. AVP increased water content significantly in gray and white matter sites, while electrolyte content was unchanged. Another group of animals had intracerebral infusions with 5 ng of AVP and 50 ng of a V1 receptor antagonist, (d(CH2)5Tyr-(Me)AVP). The antagonist blocked the increase in water, suggesting a V1 receptor mediated the action.

The effect of increased CSF pressure on interstitial fluid flow during ventriculocisternal perfusion in the cat

Transependymal absorption of cerebrospinal fluid (CSF) in hydrocephalus is suggested by periventricular edema, but the necessary bulk flow of interstitial fluid (ISF) has not been found. We performed ventriculocisternal perfusions in adult cats using CSF with the extracellular marker [3H]sucrose. CSF pressure was maintained at -5(control), 20 or 40 cm H2O for 2 or 4 h. Some animals had perfusions with isotope for the full experiment while others had an isotope-free perfusion for 2 h followed by a delayed-pulse with isotope. Apparent diffusion coefficients and distribution spaces for sucrose were determined from depth of isotope penetration. White matter apparent diffusion coefficients were statistically increased compared to controls for the 4-h 20 cm H2O and 2-h 40 cm H2O experiments. Apparent diffusion coefficients for delayed-pulse experiments at increased pressure were greater than those of full-pulse. Sucrose distribution spaces were not enlarged at the various pressures. Alteration of ISF transport in periventricular white matter occurred with increased pressure. These time-dependent changes in bulk flow rate indicate either a decrease in normal ISF flow toward the ventricle or reversal of transependymal ISF flow.

Selective effect of mannitol-induced hyperosmolality on brain interstitial fluid and water content in white matter.

We studied the effect of mannitol-induced hyperosmolality on brain interstitial fluid (ISF) by autoradiography. Adult cats underwent intracerebral infusion of the extracellular marker,14C-sucrose. Nine animals were given 2 g/kg of mannitol intravenously, and another nine animals without mannitol were controls. Plasma and cerebrospinal fluid (CSF) osmolalities were measured. After 2 hr the brains were removed for determination of water and electrolyte content and for preparation of the autoradiograms. Diffusion coefficients were calculated for intracerebral transport with equations for radial diffusion. We found that mannitol increased the plasma osmolality but did not affect that of the CSF. Water and potassium contents were significantly lower in the white matter of mannitol-treated animals than in controls. Diffusion was reduced in the direction of gray matter into the white matter. We conclude that lower doses of mannitol control CSF pressure by selectively removing water from white matter, reducing the CSF volume, and affecting molecular transport at the gray/white interface.

Time course of blood-nerve barrier reconstitution after sectioning: Implications for xenograft studies

The time course of blood-nerve barrier recovery in mouse nerves was studied after proximal and distal segmental sciatic sections. Transfer constants for uptake of isotopically labeled sucrose and urea were determined. Sectioned segments were examined ultrastructurally. Marked alterations in isotope uptake for 2 months with gradual restoration of blood-nerve barrier by 6 months was found. Ultrastructure of sectioned segments showed increased numbers of perineurial compartments. Human nerve xenografts to immunosuppressed animals remain hypomyelinated for 6 months which may be related to damage to the blood-nerve barrier.

Effect of Mannitol-Induced Hyperosmolarity on Transport between Brain Interstitial Fluid and Cerebrospinal Fluid

Osmotic agents, such as urea18 and mannitol,52 have been used for over 20 years to treat increased intracranial pressure (ICP). The usefulness of the currently used agent, mannitol, had been limited by the fluid and electrolyte disturbances that occurred with the recommended dosages of 2–4 g/kg. To overcome these limitations, lower mannitol dosages of 0.25–1.5 g/kg have been tested in patients and found to be effective in temporarily controlling ICP.22, 26