Prior episodes of sodium depletion increase the need-free sodium intake of the rat.

Prior episodes of sodium depletion increase the daily 3% NaCl intake of rats. They ingest large volumes and continue to do so for as long as 3 months after recovery from sodium deficit while eating sodium-rich food and while plasma sodium concentration and renal function are normal. The increased daily intake of sodium is, therefore, need-free. There is a marked sex difference in the need-free intake of 3% NaCl. Female rats drink more salt than do male rats when they are sodium replete and depletion naive. Repeated depletions raise the need-free intakes of both sexes but the effect is greater in females. Plasma concentrations of angiotensin II and aldosterone, which are markedly elevated by each episode of sodium depletion, return to basal levels between and after depletions, and are not the cause of the chronically increased need-free salt intake of the multi-depleted rat. These results suggest that the persistent increase in daily 3% NaCl intake that occurs in the rat with a history of repeated sodium depletions is a permanent, nonpathological increase in avidity for the taste of salty substances that results in life-long overconsumption of salt. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bombesin suppresses need-free and need-induced salt intake in rats.

Evaluated whether the effects of bombesin are selective for the satiation of ingestive behaviors related to energy balance or if ingestive behaviors associated with sodium balance are also suppressed by bombesin. Injections of 4 and 8 μg/kg bombesin reliably reduced need-free and sodium deficiency-induced NaCl intake in male rats. The effects of bombesin on the sodium-deficiency-induced change in taste reactivity was assessed. Injections of 4 μg/kg and 8 μg/kg bombesin had no effect on the sodium deficiency-induced shift in taste reactivity. These data indicate that bombesin suppresses NaCl intake and that bombesin does not appear to interact with gustatory sensibility in exerting its behavior-controlling action. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual dimorphism in ultrasonic vocalizations of mice (Mus musculus): Gonadal hormone regulation.

Male mice, during courtship and sexual behavior, vocalize substantially more 70-kHz ultrasounds than do females. Four experiments conducted with 109 male and female DBA/2J and ADK2F? mice demonstrated that testosterone propionate (TP) substantially increased ultrasonic emissions and mounting by ovariectomized females and that long-term gonadectomized males and females increased their amount of ultrasound production in response to TP to approximately the same levels. From these results it is suggested that the sexual dimorphism normally seen in ultrasonic vocalizations can be accounted for by the activational effects of androgen in adulthood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibitory effects of estrogen on stimulated salt appetite in rats.

Adult male rats consumed 50–250% more 0.5 M NaCl solution than females did during a 7-hr drinking test when robust salt appetite was elicited by dietary sodium deprivation for 8 days, daily injections of deoxycorticosterone, or adrenalectomy followed by 2 days of sodium deprivation. In contrast, male rats drank much less saline after systemic treatment with the natriuretic agent furosemide, adrenalectomy followed by 1 day of sodium deprivation, or subcutaneous/ly (sc) treatment with colloid solution after 2 days of sodium deprivation, and female rats drank comparably small volumes. Conversely, 30-day-old prepubescent male and female rats showed equally robust salt appetites after 8 days of sodium deprivation. These and other findings support an inhibitory role of estrogen on salt appetite in rats, which appears to occur only when the appetite is especially pronounced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of gonadectomy in infancy and adulthood on handedness in male and female Mongolian gerbils

When assuming a species-typical tripodal posture, female Mongolian gerbils most often rest on their left forepaws and hold their right forelimbs aloft; male gerbils most often do the reverse. This experiment examined effects of gonadectomy, both in infancy and in adulthood, on the sexually dimorphic asymmetry in forelimb use by Mongolian gerbils when maintaining a tripodal stance. In adulthood, both male and female gerbils that had been gonadectomized at birth reversed their forelimb use while in a tripodal stance: Gonadectomized males used their forelimbs as did sham-operated females, and gonadectomized females used their forelimbs as did sham-operated males. Gonadectomy in adulthood abolished the sexual dimorphism in forelimb use seen in sham-operated subjects. It was concluded that gonadal hormones have organizational as well as possible activational effects on adult patterns of forelimb use by gerbils.     

Sodium appetite in lactating rats.

Lactating rats that were given free access to sodium-deficient food, water, and 0.51 M NaCl solution showed no evidence of sodium appetite. The estimated daily loss of 1–2 mEq Na in milk was replaced by basal daily intake of 2–5 ml of saline. Sodium loss in urine was minimal, but milk sodium concentration was unchanged, and pups grew normally. Saline intake was enhanced when lactating rats that had been maintained on standard laboratory chow were injected with 30% polyethylene glycol solution to reduce plasma volume but no more so than when virgin female rats or male rats were similarly colloid-treated. Lactating rats markedly increased their intake of NaCl solution after simply depriving them of dietary sodium for 4 days, whereas male and virgin female rats did not. These findings indicate that pronounced sodium appetite does not invariably accompany lactation in rats, although it can occur whenever such animals become hypovolemic or sodium deficient. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Antagonism of clonidine injected intracerebroventricularly in different models of salt intake

Clonidine, an alpha 2-adrenergic agonist, injected into the brain inhibits salt intake of animals treated by the diuretic model of sodium depletion. In th present study, we address the question of whether central injection of clonidine also inhibits salt intake in animals deprived of water or in the need-free state. Saline or clonidine (30 nmol) was injected into the anterior third ventricle of 24-h sodium-depleted (furosemide + removal of ambient sodium), of 24-h water-deprived and of normovolemic (need-free state) adult male rats. Clonidine injected intracerebroventricularly (i.c.v.) inhibited the 1.5% NaCl intake for 1209 min by 50 to 90% in every model tested. Therefore, different models of salt intake are inhibited by i.c.v. injection of clonidine. Idazoxan, an alpha 2-adrenergic antagonist, injected i.c.v. at a dose of 160 nmol, inhibited the effect of clonidine only in the furosemide + removal of ambient sodium model of salt intake. This indicates that the antagonism of this effect by idazoxan is dependent on the body fluid/sodium status of the animal.     

Hormonal influences on sexual dimorphism in rate of extinction of a conditioned taste aversion in rats

The hormonal influences on the slow extinction rate of a conditioned taste aversion shown by male rats and the fast extinction rate shown by female rats were investigated. When males were castrated, they extinguished as quickly as females. When castrated males were given testosterone propionate replacement, they had a slow extinction rate. Castration had no effect on the extinction rate of females. But when testosterone propionate was administered to castrated or intact females, they had a slow, malelike extinction rate. Thus, sexual dimorphism in the extinction rate of a conditioned taste aversion seems to be due to the activational effects of testosterone.     

Amiloride increases sodium chloride taste detection threshold in rats.

The epithelial sodium-channel blocker amiloride has been shown to inhibit sodium responses in the 7th cranial nerve of the rat. In the signal detection task used in this study, amiloride (100 μM) treatment raised the NaCl threshold by ～1 log?? unit. The inhibition constant for amiloride was 1μM at 0.013 M NaCl. Because the NaCl intake of adult rats has been shown to be related to the level of dietary NaCl exposure early in development, rats were exposed by way of maternal diet to 1 of 3 diets (0.1% NaCl, n?=?8; 1.0% NaCl, n?=?8; 3.0% NaCl, n?=?9) from conception through weaning, to determine whether this treatment affects taste sensitivity. At Postnatal Day 30, rats were placed on 1.0% NaCl chow. This treatment did not affect NaCl detection or amiloride sensitivity in adulthood. The amiloride-induced shifts in NaCl sensitivity functions imply that the transcellular sodium transduction pathway is necessary for normal NaCl detection in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactive effects of fluid deprivation and testosterone on the expression of a sexually dimorphic conditioned taste aversion.

Conducted 3 experiments with 96 Wistar and 72 Sprague-Dawley rats to investigate the effects of fluid deprivation on the sexually dimorphic rate of extinction of a conditioned taste aversion. Under ad lib water conditions, males extinguished a conditioned taste aversion more slowly than females. However, when rats were fluid deprived, there was no difference in the extinction rates of females and males even when the more sensitive 2-bottle test was used. This absence of the sexual dimorphism was due to a differential effect of deprivation on females and males. Fluid deprivation increased the rate of extinction of the male but had no effect on the rate of the female. It is proposed that the more rapid extinction rate of the deprived male could be accounted for by a deprivation-induced change in a testosterone-dependent mechanism. This proposal was supported by demonstrating that injections of testosterone propionate blocked the effects of fluid deprivation on rate of extinction in the male rat. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Canine babesiosis in South Africa: more than one disease. Does this serve as a model for falciparum malaria?

The present study was carried out to determine whether the increased salt intake induce by increased specific sodium appetite in pregnant rats modifies water-salt homeostasis throughout pregnancy. Two groups of pregnant rats were used, one fed ad libitum with a normal sodium (NS) diet consisting of standard rat chow and distilled water, and the other fed with a high-sodium (HS) diet with free access to chow, distilled water plus saline solution (1.5% NaCl). Virgin rats in dioestrus were also studied as non-pregnant controls. Pregnant animals were studied on days 4, 9, 14, 20 and 21 of gestation at which time body weight, water and saline intake, sodium excretion, plasma atrial natriuretic peptide (ANP) and arginine vasopressin (AVP) concentrations, as well as plasma osmolality were determined. Data showed that water intake was higher in the NS group, but total fluid intake (water plus saline) was higher in the HS group throughout pregnancy. Dietary sodium intake was the same for both groups but total sodium intake (chow plus saline) was 60-98% higher in the HS rats. Pregnant HS rats excreted more fluid (35-50%) and sodium (up to 100%) compared with NS rats, indicating that the animals could change their renal excretion in response to a 2.5-fold higher dietary sodium intake compared with the control level. Salt satiety during pregnancy did not modify plasma ANP concentration. In both groups of pregnant rats ANP levels increased 3-fold on day 14 without significant alteration in sodium excretion, suggesting that the natriuretic action of ANP is attenuated at least after the second week of pregnancy. High sodium intake did not change plasma AVP concentration or osmolality and both groups showed the same gradual decrease in plasma osmolality (approximately 8 mosmol kg-1) at the end of pregnancy that was not accompanied by decreased plasma AVP concentration. The present data show that rats maintain the special homeostatic equilibrium that occurs in normal pregnancy even when they are allowed to increase sodium intake to satisfy their salt appetite during this period of the reproductive cycle.     

Effects of perinatal androstenedione on sexual differentiation in female rats.

Androstenedione was administered prenatally, postnatally, or both pre- and postnatally to female Sprague-Dawley rats. The extent to which reproductive morphology, ovarian functioning, and adult sexual behavior were masculinized and defeminized depended on the dosage, timing, and duration of the hormone treatment. The combined pre- and postnatal treatment resulted in the greatest degree of modification in that such females were anatomically masculinized and did not ovulate. When tested in adulthood, they showed a high potential for the male copulatory pattern and little lordotic behavior. It is concluded that androstenedione, while not as potent an androgen as testosterone propionate, nevertheless has the potential to participate in the process of sexual differentiation. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of intraventricular injections of tachychinin NK? and NK? receptor agonists on normal and sham drinking of NaCl by sodium-deficient rats.

The effects of lateral ventricular injections of succinyl-[Asp?, N-Me-Phe?]-substance P (SENK; 25,100,200 ng), a tachykinin NK? receptor agonist, and [Sar?, Met(O2)11]-substance P (Sar Met; 100, 200 ng), an NK? receptor agonist, on normal (gastric fistula closed) and sham drinking (gastric fistula open) of hypertonic NaCl by sodium-deficient rats were compared. Intraventricular injections of Sar Met had no effect on NaCl intake in either condition. Injections of 100 ng and 200 ng SENK caused an equal suppression of NaCl intake in the 2 fistula conditions. The latency to drink was not affected, but the initial lick rate was significantly lower and decayed more rapidly after 100 ng SENK than after saline or 25 ng SENK. The results show that (a) the tachykinin subtypes are not equally involved in the control of need-induced salt intake; (b) negative feedback from the stomach and distal gastrointestinal tract is not required for intraventricular injections of SENK to suppress sodium appetite; (c) the activation of NK? receptors decreases the oral excitatory influence of hypertonic: NaCl in sodium-deficient rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intraventricular neuropeptide Y decreases need-induced sodium appetite and increases pica in rats.

Neuropeptide Y (NPY) is a potent endogenous stimulator of food intake. In addition to stimulating increased food intake, when paired with a novel-flavored solution, NPY produces an aversion to that flavor. Hence, exogenous NPY elicits 2 seemingly opposing behaviors, increased feeding and the formation of a conditioned taste aversion. One interpretation of these data is that NPY produces some form of malaise or visceral illness. NPY's orexigenic and malaise-inducing properties were tested in rats with 2 measures sensitive to malaise, increased kaolin consumption (pica behavior) and failure to express need-induced sodium intake. Administration of NPY resulted in increased food intake, increased kaolin consumption, and decreased need-induced sodium intake. These data support the hypothesis that exogenous NPY has both orexigenic and malaise-inducing properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Application of time series spectral analysis theory: analysis of cardiovascular variability signals

The volume of the anteroventral periventricular nucleus (AVPv) of the rat hypothalamus is larger in females than in males. A preliminary study from this laboratory found that this sexual dimorphism develops between days 30 and 91. The present study was designed to confirm and extend these findings and to determine the role of endogenous gonadal steroids in the development of the AVPv postnatally. The results indicate that the sexual dimorphism in AVPv volume arises between days 30 and 40 and that the length of the nucleus becomes sexually dimorphic between days 60 and 80. Additionally, both AVPv volume and length increased between days 30 and 80 in females. Castration of male rats on the day of birth sex-reversed AVPv volume in adulthood and AVPv length was sex-reversed by castration of males 5 days after birth; ovariectomy of females at these ages had no effect on either parameter. Moreover, in both males and females, AVPv volume and length were unaffected by gonadectomy at later ages. That the AVPv appears to be influenced by testicular hormones neonatally, but changes structurally around the time of puberty in females, clearly challenges current concepts of sexual differentiation that limit the process to the early postnatal period.     

Effects of neonatal RU486 on adult sexual, parental, and fearful behaviors in rats.

Exposure to gonadal hormones during perinatal life influences later behavior. The finding that sex differences exist in progestin receptor expression in the perinatal rat brain suggests differential sensitivity of male and female brains to progesterone (C. K. Wagner, A. N. Nakayama, & G. J. De Vries, 1998). Because these sex differences are in neural sites that influence sexually differentiated sexual, parental, and fearful behaviors in adults, this study examined the effects of administering the progestin receptor antagonist RU486 for the first 10 days after birth on these behaviors in adulthood. Neonatal RU486 significantly reduced sexual behavior in males but did not impair reproduction in females. Neonatal RU486 did not affect parental responses of virgin rats exposed to pups (sensitization) but reduced fear in the elevated plus-maze in both sexes. Treatment of pups with RU486 affected neither mother–litter interactions nor plasma testosterone levels in males during or after treatment. These results suggest that neonatal exposure to progesterone, in addition to androgens and estrogens, influences behavioral development in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Seasonal testicular function in male rhesus monkeys

Some studies report seasonal patterns of testicular function in male rhesus monkeys even when they are housed away from females, while others suggest that exposure to sexually active females is essential for male seasonality. We conducted the present experiment (1) to test claims that seasonal testicular activation occurs in the absence of females and (2) to determine whether regular exposure to and copulation with females enhances, or is without effect upon, seasonal increases in testicular function. We studied two groups of male monkeys housed in a colony room containing no females. Males in the Female Exposure group (n = 7) were paired twice weekly with estradiol-implanted females and copulated vigorously. Males in the second group (n = 7) were placed in the same test chamber (at least 16 h after it had been scrubbed with disinfectant) but were never exposed to females. Serum testosterone levels and testis volume were monitored for both groups. Each group displayed a seasonal pattern of testosterone and of testis volume comparable in timing and magnitude to seasonal increases previously reported in group-housed males, but the two groups did not differ from each other. Our findings confirm that seasonal changes in testosterone and testis size occur in the absence of sexual interaction and demonstrate that moderate levels of sexual activity do not enhance this response.     

Relationship between absolute body-fluid deficits and fluid intake in the rat.

In 5 experiments acute absolute body-fluid deficits were induced in a total of 36 male albino Sprague-Dawley rats by injection of the diuretic drug furosemide, which caused up to 20% reduction of extracellular fluid volume and up to 2% reduction of intracellular fluid volume. Water and .3 M NaCl were subsequently made available to allow the Ss to replace their body fluids by drinking. The Ss increased their intake of both fluids, but replaced less than half of the total deficit, thereby tolerating larger and larger voluntary body-fluid deficits as the size of the diuretic fluid loss increased. Plasma measures showed that the Ss sustained hypovolemia after drinking, while intracellular fluid volume was apparently restored. Fluid-depleted Ss drank normally in response to intracellular dehydration induced by a sodium chloride load. Results demonstrate that incomplete restoration of body-fluid balance after body-fluid depletion is due to a failure to drink in response to extracellular dehydration. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sodium taste detectability in rats is dependent of anion size: The psychophysical characteristics of the transcellular sodium taste transduction pathway.

There are two known sodium transduction pathways in the rat gustatory system. The transcellular pathway is blocked by amiloride, and the paracellular pathway is limited by the anion gluconate. The contribution of each pathway to sodium detection was assessed. Sodium gluconate (NaGlu) and NaCl thresholds did not differ, implying that the paracellular pathway is not necessary for normal sodium detection. Adding 100 μM amiloride raised both NaCl and NaGlu thresholds but did not abolish all performance to NaGlu, indicating that some chemical cue was present at high concentrations. Rats were also exposed to one of three NaCl diets (0.12%. 1.0%, or 6.0% NaCl) through maternal and ad lib intake from Embryonic Day 1 through testing in adulthood. No differences across dietary groups were found for NaCl or NaGlu threshold with or without amiloride. Thus, this developmental dietary treatment does not appear to affect taste sensitivity to sodium subserved through either transduction pathway. Collectively, these data suggest that the transcellular transduction pathway is both necessary and sufficient for normal sodium detection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of the ionic specificity of sodium appetite in the rat pup

Sodium-deficient adult rats prefer NaCl to other monochloride salts (e.g., Denton, 1991; Schulkin, 1991). However, it is not known when or how this specificity develops. Our experiments charted the development of the ionic specificity of sodium appetite aroused by sodium depletion or intracerebroventricular injection of renin. We compared intake of 3% NaCl to three other monochlorides, potassium (K), ammonium (NH4), and lithium (Li), and calcium chloride (CaCl2) at various ages between 72 hr postnatal and weaning. This revealed a biphasic developmental scheme: The adult pattern of discrimination between the salts emerges between 3 and 18 days of age. Subsequently, the preference for Na over the other salts increases into adulthood.