Robert W. Reynolds

A general procedure for estimation of corticosteroid response in individual rats

A procedure is presented whereby microliter volumes of plasma, obtained rapidly and repeatedly from the tail vein of unanesthetized rats, can be analyzed for corticosterone. Preliminary results suggest that (1) basal levels are considerably lower and (2) the latency to corticosteroid stress response is shorter than previously reported.

Rapid pulsatile corticosterone response in unanesthetized individual rats

Plasma corticosterone concentrations were determined by radioimmunoassay of blood samples obtained rapidly and repeatedly from individual unanesthetized rats at time intervals of approximately 10 seconds. Results confirm that corticosterone release is pulsatile, as has been reported previously, but with a much faster time course and a pulse frequency close to one pulse per minute. Such a release pattern is consistent with and required by the theory that there are rate sensitive hormone receptors. Failure of others to observe such a rapid response is presumably attributable to their use of much longer intervals between samples or of sampling procedures and techniques that obliterate any variation from a preconceived smooth function.

Estrogenic effects on behavioral thermoregulation and body temperature of rats

Abstract Estradiol benzoate increases responding for heat reinforcement of ovariectomized female and intact and castrate male rats placed in the cold. In females, both pre- and postsession rectal temperatures are depressed by the steroid. The maintenance of low temperatures despite increased heat intake suggests that body temperature is regulated at a lower level as a result of estradiol-induced increases in heat loss or decreases in heat production.

Hypothalamic metallic deposition and the production of experimental obesity

Abstract The effectiveness of the deposition of metallic ions in the medial hypothalamus in producing experimental obesity in rats was investigated. Both the direct deposition to the hypothalamus of Fe +++ (as FeCl 3 · 6H 2 O) or Cu ++ (as CuCl 2 · 2H 2 O) via bilateral stainless steel cannulae or via anodal electrolysis with stainless steel or copper electrodes resulted in similar significant increases in daily weight gain and the development of obesity. NaCl deposition via cannulae, sham lesions, and empty cannulae insertion were all ineffective in altering body weight. These results suggest that: (a) the electrical events associated with anodal direct current lesions using stainless steel or copper electrodes are secondary to the deposition of metallic ions in the production of experimental obesity; and, (b) the tissue destruction in the ventromedial hypothalamic region coupled with the presence of heavy metal ions apparently ‘add’ to produce a very high probability of the development of experimental obesity.

Comparison of plasma corticosterone- and progesterone-binding activity in rat and human

Corticosterone-and progesterone-binding activity were measured by saturation analysis, with dextran-charcoal separation, in plasma obtained from male and female rats, and a normal male and female human. In plasma from normal male and female rats, progesterone was much less effective than corticosterone in displacing 3H-corticosterone from plasma protein binding sites although the parallelism of the displacement curves indicated competition for the same binding sites. In plasma from the normal male human, corticosterone and progesterone were equally effective in displacing 3H-corticosterone. However, 3H-progesterone showed no apparent binding to either rat or human plasma proteins, suggesting that dextran-charcoal effectively removed progesterone from transcortin binding sites at 4 degrees C. This observation was confirmed by multiple equilibrium dialysis. In dialysis, 3H-corticosterone and 3H-progesterone were bound equally by human plasma, but rat plasma bound 3H-corticosterone to a much greater extent than it did 3H-progesterone. These data indicate that, in contrast to human plasma, rat plasma has much greater affinity for corticosterone than for progesterone.

Pulmonary edema induced by intracranial carbachol infusion in rabbits and rats

Abstract The pulmonary edema produced by Maire and Patton [6] by electrolytic lesions of the lateral preoptic area (LPO) of the hypothalamus can be reproduced by carbachol infused intracranially through cannulae chronically implanted in the LPO of rats and rabbits. Control infusions of saline or mammalian Ringer-Locke solution preceded all infusions of the reagents used, with each animal serving as his own control. Infusions of discrete volumes of nembutal, L-norepinephrine bitartrate, or carbachol preceded by either intracranial or systemic intraperitoneal atropine, failed to produce signs of pulmonary edema in any of the animals. When carbachol infusions were not preceded by atropine, animals with cannulae in LPO demonstrated evidence of intense behavioral and autonomic activation and pulmonary edema. Microscopic examination of lung tissue from 20 animals which died following unilateral carbachol infusion demonstrated evidence of pulmonary edema in the lung ipsilateral to the cannulae. The contralateral lung was only slightly involved in all cases. Animals with no signs of pulmonary edema under any of the infusion conditions had cannulae located outside the LPO. Lung tissue from these animals was indistinguishable from tissue of rabbits which had been infused only with saline or mammalian Ringer-Locke solution. The data indicate that pulmonary edema following intracranial carbachol infusion is a result of an excitatory muscarinic action of carbachol on the cells of the LPO. They also suggest that the pulmonary edema produced by electrolytic lesions in LPO may have been due to something other than simple removal of LPO tissue.

Circadian Fluctuations in Plasma Corticosterone, Corticosterone-Binding Activity and total Protein in male rats: Possible Disruption by Serial Blood Sampling

Male rats were bled serially every 6 h for 48 consecutive hours. Plasma so obtained was assayed for corticosterone (B), corticosterone-binding activity (CBA) and total plasma protein (TPP). Although the averaged data indicated a significant circadian rhythm in plasma B, inspection of the circadian changes in individual animals showed that 40% had irregular or aberrant patterns of plasma B. Additionally, circadian fluctuations in plasma CBA were approximately 3-fold lower in magnitude than previously reported, and there was no significant circadian change in TPP. Running wheel activity during the 48 h blood sampling period decreased by over 50% indicating that the serial sampling procedure caused disruption of the activity cycle. However, the majority of wheel-running activity occurred during the dark portion of the day-night cycle. Because circadian fluctuations in plasma proteins, including corticosteroid binding globulin (CBG), may be directly related to changes in locomotor activity, it is suggested that the attenuation of circadian changes in CBA and TPP were due to disruption of the daily cycle of locomotor activity. The abnormal circadian patterns in plasma B observed in some animals also may have been caused by disruption of the activity cycle in spite of the fact that the rats did not appear to be stressed as evidenced by concentrations of plasma B that were well within the normal range.

Rapid corticosterone pulses

If micro-sampling techniques are used in conjunction with a highly sensitive radioimmunoassay procedure, it is possible to obtain repeated rapid measurements of plasma corticosterone concentrations from unanesthetized rats. Such a procedure reveals the existence of rapid corticosterone pulses with a duration of less than 60 s and amplitudes as great as 250 ng/ml. Several procedures were employed to determine that the pulses were not simply artifacts of the measurement and sampling methods. The existence of such rapid pulses provides for a duality of glucocorticoid function consisting of a rapid dynamic response capable of functioning simultaneously with, but independently of a slower long term regulatory response.

Thiosemicarbazide Injection Followed by Electric Shock Increases Resistance to Stress in Rats

Adult rats that had been raised with a minimum of stimulation were injected with thiosemicarbazide, a drug that lowers y-aminobutyric acid concentrations. Fifteen minutes later the animals were given 30 mild electric shocks over a half-hour period. Two. weeks later they were tested for their resistance to gastric ulceration induced by immobilization. The experimental animals showed a much greater resistance to stress than did the appropriate control groups. A replication confirmed the results of the first study.

Rapid corticosterone pulses: Confirmation by an alleged disconfirmation?

Data from a paper reporting a failure to confirm our report of rapid corticosterone pulses and suggesting that our data were artifactual were reanalyzed and reevaluated. It is shown that these data actually appear to confirm our original report. Artifacts in their procedure tend to introduce smearing that minimizes the observed effect. In addition, their method of data presentation combined with the lack of appropriate data analysis apparently led to their failure to draw the proper conclusions.