Water-deprived Rats Research Articles

Sham rehydration contributes to reduced Fos staining in the supraoptic nucleus (SON) after water deprivation.

This experiment tested the role of oropharyngeal and gastric afferents on Fos staining in the forebrain of dehydrated rats instrumented with gastric fistulae and allowed to drink water or isotonic saline. Rats were either treated with 48 h water deprivation (WD) or 46 h WD with 2 h rehydration (WDRH) in rats with gastric fistulae. WDRH rats were given water with fistulae open (SHAM) or closed (INGEST). An additional group of WDRH rats was given isotonic saline with fistulae open (WDRHS). WD increased c‐fos staining in the supraoptic nucleus (SON) and organum vasculosum of the lamina terminalis (OVLT). Both WDRH/INGEST and WDRH/SHAM rats had reduced c‐fos positive nuclei in the SON compared to WD rats but WDRHS rats remained elevated (CON 3 ± 1 WD 57 ± 10 WDRH/INGEST 2 ± 1 WDRH/SHAM 10 ± 1 WDRHS 52 ± 11). On the other hand, none of the WDRH treatments normalized c‐fos staining in the OVLT after two hours (CON 11 ± 3 WD 175 ± 21 WDRH/INGEST 205 ± 19 WDRH/SHAM 219 ± 15 WDRHS 214 ± 27). As expected, WD rats had increased and WDRH/INGEST rats had decreased plasma osmolality compared to controls (CON 296 ± 2 WD 307 ± 2 WDRH/INGEST 278 ± 2; mOsm). Meanwhile, RH/SHAM rats had normal osmolality and WDRHS rats had increased osmolality similar to WD rats (WDRH/SHAM 295±3 WDRHS 312±3; mOsm). The results show that sham water intake but not isotonic saline reduced Fos staining in the SON. (R01 HL062576)

Yoked delivery of cocaine is aversive and protects against the motivation for drug in rats.

In Experiment 1, water-deprived rats had 5-min access to saccharin followed by active or yoked intravenous delivery of saline or cocaine (0.33 mg/infusion). Both cocaine groups avoided intake of the saccharin cue following saccharin-cocaine pairings; however, the rats in the yoked condition exhibited greater avoidance of the taste cue than did the actively administering rats. Experiment 2 evaluated subsequent self-administration behavior on fixed- and progressive-ratio schedules of reinforcement. The results showed that prior yoked exposure to cocaine reduced subsequent drug-taking behavior on a progressive-ratio but not on a fixed-ratio schedule. Finally, Experiment 3 used a choice test to determine the impact of yoked drug delivery on the relative preference for cocaine versus water. The results showed that rats with a history of self-administering cocaine preferred to perform operant behaviors on the side of the chamber previously paired with cocaine, whereas the rats with a history of yoked delivery of cocaine avoided this side. These data show that, in most rats, the unpredictable, uncontrollable delivery of cocaine protects against the subsequent motivation for cocaine through an aversive mechanism.

Real-time One-dimensional Brain-Computer Interface (BCI) Using Prefrontal Cortex Neuronal Activities of Rats

The aim of this study is to verify the feasibility of control of one-dimensional (1-D) rotating machine using neural activities of Prefrontal cortex (PFC) in a BCI system. In this study, adult male Sprague-Dawley rats received bilateral implantation of recording micro-electrodes in PFC area. The spontaneous activities of a pair of PFC neurons of water-deprived rats were encoded and converted through a triple-step threshold comparator algorithm to three commands for one-dimensional movement control of a robotic wheel for accessing water. Averaged activities of two PFC neurons were quantized in every 200 ms to four ranges of activities around the mean firing rates (±0.5 SD) and were converted to four values. After comparison of the values of two chosen neuron units, direction and speed of rotation were decided. Rats were trained to complete one-dimensional control task to obtain water reward. The results indicated the percentage of stop event increased alone with more training. Different brain activity significantly influenced total water-drinking duration and non-water-drinking duration. Events generated from neuronal activity differed according to variant experimental sessions. Correlation between two signal units impacted controlling performance. Overall, the results of this study suggest that rats were able to manipulate the 1-D BCI system by differentially modulating PFC single neuron activities according to different circumstances. words: brain-computer interface, prefrontal cortex, rat, one-dimensional, single neu

Water deprivation increases Fos expression in hypothalamic corticotropin-releasing factor neurons induced by right atrial distension in awake rats

Atrial mechanoreceptors, sensitive to stretch, contribute in regulating heart rate and intravascular volume. The information from those receptors reaches the nucleus tractus solitarius and then the paraventricular nucleus (PVN), known to have a crucial role in the regulation of cardiovascular function. Neurons in the PVN synthesize CRF, AVP, and oxytocin (OT). Stimulation of atrial mechanoreceptors was performed in awake rats implanted with a balloon at the junction of the superior vena cava and right atrium. Plasma ACTH, AVP, and OT concentrations and Fos, CRF, AVP, and OT immunolabeling in the PVN were determined after balloon inflation in hydrated and water-deprived rats. The distension of the balloon increased the plasma ACTH concentrations, which were higher in water-deprived than in hydrated rats (P < 0.05). In addition, the distension in the water-deprived group decreased plasma AVP concentrations (P < 0.05), compared with the respective control group. The distension increased the number of Fos- and double-labeled Fos/CRF neurons in the parvocellular PVN, which was higher in the water-deprived than in the hydrated group (P < 0.01). There was no difference in the Fos expression in magnocellular PVN neurons after distension in hydrated and water-deprived groups, compared with respective controls. In conclusion, parvocellular CRF neurons showed an increase of Fos expression induced by stimulation of right atrial mechanoreceptors, suggesting that CRF participates in the cardiovascular reflex adjustments elicited by volume loading. Activation of CRF neurons in the PVN by cardiovascular reflex is affected by osmotic stimulation.

Associative interference in Pavlovian conditioning: A function of similarity between the interfering and target associative structures

Three lever-press suppression studies were conducted with water-deprived rats to investigate the role of similarity in proactive interference within first-order Pavlovian conditioning. Experiments la and 1b assessed the influence of stimulus complexity in proactive interference. Both experiments found greater interference when the interfering cue and target cue were composed of the same number of elements. Experiment 2 assessed the influence of context similarity in proactive interference and demonstrated that stronger proactive interference occurred when the interfering cue and the target cue were trained in the same context. The results in conjunction with other reports indicate that various types of cue interaction (e.g., interference and competition) are influenced by similarity of the interacting training events.

Muscarinic receptor antagonism causes a functional alteration in nucleus accumbens μ-opiate-mediated feeding behavior

Intra-nucleus accumbens (Acb) infusion of cholinergic muscarinic antagonist, scopolamine (10 μg/0.5 μl), markedly reduced fat intake elicited by intra-Acb treatment of the μ-opioid receptor agonist, DAMGO, with 30 min and 4 h pretreatment intervals. Intra-Acb scopolamine infusions also reduced food intake in food-deprived rats, but not water intake in water-deprived rats. Hence, Acb muscarinic manipulations exhibit some specificity for feeding, perhaps via interactions with the striatal opioid system.

Venous Gas Emboli in Normal and Dehydrated Rats Following Decompression from a Saturation Dive

Dehydration may increase the risk for decompression sickness (DCS). Since DCS most probably is caused by endogenous gas phase formation, we hypothesized that decompression will induce more venous gas emboli (VGE) in dehydrated rats compared to controls. Two groups of rats were pressurized to 0.5 MPa (5 ATA) on heliox for 16 h, and thereafter decompressed to atmospheric pressure at a rate of 0.3 MPa x min(-1). The nine control rats had free access to water ad libitum whereas the eight dehydrated rats were water-deprived for 48 h before decompression. During and after decompression, VGE was measured in the vena cava for 60 min with the Doppler technique and graded into six bubble grade (BG) categories. Body mass (BM), and food and water intake were registered daily, and venous blood samples were taken before and after pressure exposure. Serum osmolality and hematocrit increased significantly in dehydrated rats (306 +/- 5.2 to 315 +/- 7.3 mosmol x kg(-1) and 39.3 +/- 4.9 to 49.6 +/- 5.2%) but not in controls (300 +/- 8.9 to 303 +/- 6.7 mosmol x kg(-1) and 40.3 +/- 5.2 to 41.4 +/- 6.1%). Plasma volume decreased by 9.2% (P < 0.05) and 2.8% (n.s.) in dehydrated and control rats. VGE were detected in all control animals (average BG: 2.8 +/- 1.9), but only in four water-deprived rats (BG: 1.6 +/- 2.2). This difference was not significant. Our experiments do not support the idea that dehydration increases circulatory VGE.

Activation of the serotonergic 5-HT 1A receptor in the paraventricular nucleus of the hypothalamus inhibits water intake and increases urinary excretion in water-deprived rats

The paraventricular nucleus (PVN) may be considered as a dynamic mosaic of chemically-specified subgroups of neurons. 5-HT 1A is one of the prime receptors identified and there is expressed throughout all magnocellular regions of the PVN. Several reports have demonstrated that a subpopulation of the magnocellular neurons expressing 5-HT 1A receptors are oxytocin (OT) neurons and activation of 5-HT 1A receptors in the PVN increases the plasma OT. Increasing evidence shows that OT inhibits water intake and increases urinary excretion in rats. The aim of this study was to investigate the role of serotonergic 5-HT 1A receptors in the lateral-medial posterior magnocellular region of the PVN in the water intake and diuresis induced by 24 h of water deprivation. Cannulae were implanted in the PVN of rats. 5-HT injections in the PVN reduced water intake and increased urinary excretion. 8-OH-DPAT (a 5-HT 1A agonist) injections blocked the water intake and increased urinary output in all the periods of the observation. pMPPF (a 5-HT 1A antagonist) injected bilaterally before the 8-OH-DPAT blocked its inhibitory effect on water intake and its diuretic effect. We suggest that antidipsogenic and diuretic responses seem to be mediated via 5-HT 1A receptors of the lateral-medial posterior magnocellular region of the PVN in water-deprived rats.

Water‐deprivation‐induced expression of neuronal nitric oxide synthase in the hypothalamic paraventricular nucleus of rat

This study was conducted to define the molecular mechanism by which dehydration induces expression of neuronal nitric oxide synthase (nNOS) in the hypothalamic paraventricular nucleus (PVN). Rats were deprived from water for 48 hr and then sacrificed immediately or 1 hr after ad libitum access to water. Another group of rats had free access to food and water and was included as euhydrate control group. The PVN sections fixed with 4% paraformaldehyde were processed for nNOS immunohistochemistry and NADPH-diaphorase (NADPH-d)/pCREB or NADPH-d/c-Fos double staining. nNOS-ir neurons significantly increased with water deprivation and decreased with rehydration, both in the posterior magnocellular (pM)- and the medial parvocellular (mP)-PVN. Most NADPH-d histostained neurons in the PVN appeared to exhibit pCREB-ir as well. Water deprivation markedly increased, and rehydration decreased, NADPH-d/pCREB neurons both in the pM- and in the mP-PVN. Gel shift assay demonstrated that dehydration may promote CREB binding to nNOS promoter in the PVN neurons. Significant amounts of NADPH-d-stained neurons in the PVN of water-deprived rats (67-68% in both the mP and the pM) exhibited c-Fos-ir. NADPH-d/c-Fos neurons in the pM-PVN were increased by water deprivation but not changed by rehydration. NADPH-d/c-Fos double-stained neurons in the mP-PVN did not significantly change depending on different water conditions. These results suggest that pCREB may play a role in dehydration-induced nNOS gene expression in the PVN neurons, and c-Fos might not be implicated in the regulatory pathway.

The effect of intraperitoneal administration of leptin on short-term food intake in rats

The effects of intraperitoneal (i.p.) injection of leptin (1, 5, and 10 μg/kg) were investigated on the food consumption during a 60 min test meal in 21 h fasted rats. All doses of leptin produced significant reductions in cumulative food intake during the first 15 min and 30 min (at least, P < 0.05) after administration. Similarly, i.p., but not subcutaneous (s.c.), administration of leptin (25 μg/kg) reduced food intake in 21 h fasted rats. Leptin (10 and 25 μg/kg, i.p.) did not reduce water intake in 16 h water-deprived rats, nor did leptin (25 μg/kg) produce aversion in a two-bottle conditioned taste aversion test indicating that the hypophagic effect of leptin is (i) behaviourally specific for food and not water intake, and (ii) not due to drug-induced malaise. Moreover, leptin (10 and 25 μg/kg, i.p.) did not significantly alter food intake in non-deprived rats when measured at 30 min intervals over a period of 24 h. Chemical vagotomy with capsaicin abolished the inhibitory effects of leptin (25 μg/kg, i.p) on food intake in fasted rats and suggest that the hypophagic effect is dependent on intact vagal afferent nerves. Furthermore, the hypophagia induced by leptin (10 μg/kg, i.p.) in fasted rats was not attenuated by systemic administration of the peripherally acting cholecystokinin 1 receptor antagonist, 2-naphthalenesulphanyl- l-aspartyl-2-(phenethyl) amide (2-NAP; 2 mg/kg, i.p.), indicating that the suppressant effects of leptin on food consumption are not secondary to the release of endogenous peripheral cholecystokinin.

The reward system and maternal behavior in an animal model of depression: a microdialysis study

Flinders sensitive line (FSL) rats, an animal model of depression, display a different pattern of maternal behavior compared to Sprague-Dawley (SD) controls. In this study, we examined the rewarding value of mother-infant interaction for FSL dams. In the main study, we measured monoamine levels in the nucleus accumbens (NAc) of early postpartum FSL and SD dams during an interaction with pups, using the microdialysis technique. In addition, we compared the preference patterns of FSL and SD rats using the conditioned place preference paradigm, with pups as the unconditioned stimuli. Dopamine (DA) levels in dialysates from the NAc of SD dams but not FSL dams were elevated while interacting with pups but the metabolism of DA to dihydroxyphenylacetic acid was greater in FSL than in SD dams. While SD dams showed a conditioned preference for a region that was associated with SD pups, FSL dams did not show a preference for regions associated either with SD or FSL pups, but water deprived FSL rats demonstrated a preference to a region associated with water, eliminating an alternative explanation of learning deficit in FSL rats. Taken together, these results suggest that FSL dams are less rewarded by pups, compared to control dams.

Gastric emptying of ingested 0.15 M NaCl solution by rats with thirst and/or salt appetite.

Recent studies have indicated that salt appetite elicited by daily systemic treatment with deoxycorticosterone (DOCA) in rats is inhibited by two variables, one related to the concentration of the ingested saline solution and the other related to its volume. In the present experiments, the concentration of NaCl solution was held constant at 0.15 M NaCl but the basis for fluid consumption was varied. Specifically, rats were allowed to drink isotonic saline after receiving one of several treatments: DOCA, bilateral adrenalectomy, overnight water deprivation (WD), WD in DOCA-treated rats, and WD in rats maintained on sodium-deficient diet for 9 days. Each group of rats drank saline at a similar rate (∼1.8 ml/min), and the different amounts consumed in an initial bout reflected differences in bout duration. Gastric emptying of the ingested saline was similar across the five groups, too; despite intakes of up to 20 ml, only 3–6 ml of saline were retained in the stomach while the rest emptied into the small intestine. Fluid movement in the intestine, intestinal distension, and fluid absorption each increased similarly as a function of intestinal fluid volume. In addition, the linear relation between gastrointestinal (GI) fill and intake was identical across groups. These results indicate that the fate of ingested saline in the GI tract is not noticeably influenced by the current water or Na + needs of the animal. In other words, need influences ingestive behavior but not the physiological consequences of fluid ingestion in the GI tract. Supported by NIH Grant MH-25140.

Sapid solutions and food intake in repeated dehydration and rehydration periods in rats.

Experiments were performed to ascertain whether food intake in thirsty rats is influenced by palatability of solutions and whether the availability of food during tests influences taste preference, acceptance, and total fluid intake. In five groups of rats, 2-bottle preference (Experiment 1) and 1-bottle acceptance tests (Experiment 2) in either 12, 24, 36, 48 h water deprived rats were performed; food was available during tests. Results showed that food availability during tests did not affect taste preference and acceptance. In Experiment1, after 36, 48 h water deprivation, rats drinking either NaCl or sucrose, they ate less food than rats drinking either HCl, quinine, or water. In Experiment 2, rats drinking NaCl as the only source of fluid ate significantly less food than all other groups. Two different post-ingestive effects (energetic; osmotic) may explain the same behavior for intake of sucrose or NaCl solutions. Since rats drinking either sucrose or NaCl ate less food but drank more fluid, they had a fluid/food ratio significantly higher than that of rats drinking either water, quinine, or HCl; these latters ate more food but drank less fluid. Taste, together with other factors, might inhibit or enhance the amount of fluid and food intake required to restore body weight and body fluid osmolality at the end of dehydration. During recovery periods, overeating is necessary to restore body mass, Na + and electrolytes; overdrinking corrects imbalance produced by excessive eating. In conclusion, food and fluid intake appears significantly related each other, even in dehydrated rats.

A parametric analysis of punishment frequency as a determinant of the response to chlordiazepoxide in the Vogel conflict test in rats

The Vogel conflict test has been widely used as a methodology for detecting anxiolytic-like effects of drugs with a broad spectrum of pharmacological activities. Despite widespread acceptance of the Vogel assay as a preclinical predictor of efficacy for anxiolytic-like compounds, detailed parametrics have not been reported on the optimization of this assay to determine how the schedule of reinforcement, the rate of responding and the frequency and temporal distribution of punishing events determine drug effect. The current report documents results of a systematic study of the relationship between number of shocks delivered and efficacy of the prototypical 1,4-benzodiazepine anxiolytic chlordiazepoxide (CDAP) in rats. Under this procedure, water-deprived rats were given access to water and during the later part of this access period, contacts with the drinking tube produced a brief electric shock. CDAP (5–20 mg/kg, i.p.) was first tested under a fixed-ratio 20 response schedule (every 20 th lick produced shock delivered via the sipper tube). CDAP produced dose-dependent increases in punished licking to approximately 275% of control at 20 mg/kg. Increasing the number of shocks during the first ten responses of the punishment component decreased the number of licks made under vehicle control conditions. The frequency of shock delivery produced both quantitative and qualitative changes in the effects of chlordiazepoxide ranging from no effect to 7000% increases in responding. The effects of chlordiazepoxide were dependent both on the control rate of responding and, independently, on the frequency of shock deliveries. Parametric variation under the Vogel conflict test may be useful in comparing the efficacy of novel approaches to the treatment of anxiety disorders.

Compartmentalization of hypothalamic TRPV4 in lipid rafts in the rat: putative role in the central control of body fluid homeostasis

The molecular mechanisms underlying the osmotic sensitivity of hypothalamic neurons have not been fully described. Recent studies indicate that transient receptor potential (TRP) channels contribute to the intrinsic osmosensitivity of cells from the supraoptic nucleus (SON) and other osmotically sensitive parts of the forebrain. The impaired osmotic regulation in trpv4−/− mice suggests TRPV4 plays a role in osmotic signaling. Using different models of dehydration and bile duct ligations (BDL), a model of hepatic cirrhosis associated with elevated circulating vasopressin with hypo-osmolality, we tested the hypothesis that TRPV4 expression (western blotting) and compartmentalization could be regulated by changes in plasma osmolality. We found increased expression of TRPV4 in SON of 48 h water deprived rats and also in rats given 2% saline to drink for 10 days. The abundance of TRPV4 and nNOS was increased in the SON of BDL rats. Next we hypothesized that compartmentalization of the TRPV4 in the plasma membrane may play a role in its signaling. We have found that TRPV4 associates with lipid rafts (LR) in hypothalamus membranes (HM) from normal rats and a higher abundance of TRPV4 was associated in LR of BDL rats HM. When BDL rats were given 0.9% saline to drink, the abundance of TRPV4 associated with LR in HM returned to the control levels. In conclusion, our data suggest that changes in the expression and compartmentalization of TRPV4 in lipid rafts could alter the intracellular signaling of magnocellular neurons. (NIH HL062579 & DK57822).

Motivated attention and prepulse inhibition of startle in rats: Using conditioned reinforcers as prepulses.

In humans, prepulse inhibition (PPI) of startle is greater during attended prestimuli than it is during ignored prestimuli, whereas in rats, most work has focused on passive PPI, which does not require attention. In the work described in this article, researchers developed a paradigm to assess attentional modification of PPI in rats using motivationally salient prepulses. Water-deprived rats were either conditioned to attend to a conditioned stimulus (CS; 1-s, 7-dB increase in white noise) paired with water (CS(+) group), or they received uncorrelated presentations of white noise and water (CS0 group). After 10 conditioning sessions, startle probes (50 ms, 115 dB) were introduced, with the CS serving as a continuous prepulse. Three experiments examined PPI across a range of prepulse intensities (4-10 dB) and stimulus onset asynchronies (SOAs; 30-960 ms). PPI was consistently reduced in the CS(+) group, particularly with a 10-dB prepulse and a 60-ms SOA. Thus, PPI in rats differed between attended and ignored prestimuli, but the effect was reversed in the results of research with humans. A fourth study eliminated the group difference by reversing the CS-water contingency. Methodological and motivational hypotheses regarding the current findings are discussed.

AT1 and glutamatergic receptors in paraventricular nucleus support blood pressure during water deprivation

Water deprivation activates sympathoexcitatory neurons in the paraventricular nucleus (PVN); however, the neurotransmitters that mediate this activation are unknown. To test the hypothesis that ANG II and glutamate are involved, effects on blood pressure (BP) of bilateral PVN microinjections of ANG II type 1 receptor (AT1R) antagonists, candesartan and valsartan, or the ionotropic glutamate receptor antagonist, kynurenate, were determined in urethane-anesthetized water-deprived and water-replete male rats. Because PVN may activate sympathetic neurons via the rostral ventrolateral medulla (RVLM) and because PVN disinhibition increases sympathetic activity in part via increased drive of AT1R in the RVLM, candesartan was also bilaterally microinjected into the RVLM. Total blockade of the PVN with bilateral microinjections of muscimol, a GABA(A) agonist, decreased BP more (P < 0.05) in water-deprived (-29 +/- 8 mmHg) than in water-replete (-7 +/- 2 mmHg) rats, verifying that the PVN is required for BP maintenance during water deprivation. PVN candesartan slowly lowered BP by 7 +/- 1 mmHg (P < 0.05). In water-replete rats, however, candesartan did not alter BP (1 +/- 1 mmHg). Valsartan also produced a slowly developing decrease in arterial pressure (-6 +/- 1 mmHg; P < 0.05) in water-deprived but not in water-replete (-1 +/- 1 mmHg) rats. In water-deprived rats, PVN kynurenate rapidly decreased BP (-19 +/- 3 mmHg), and the response was greater (P < 0.05) than in water-replete rats (-4 +/- 1 mmHg). Finally, as in PVN, candesartan in RVLM slowly decreased BP in water-deprived (-8 +/- 1 mmHg; P < 0.05) but not in water-replete (-3 +/- 1 mmHg) rats. These data suggest that activation of AT(1) and glutamate receptors in PVN, as well as of AT1R in RVLM, contributes to BP maintenance during water deprivation.

Roles of learning and motivation in preference behavior: Mediation by entorhinal cortex, dorsal and ventral hippocampus

In the latent cue preference (LCP) task, water-deprived rats alternately drink a salt solution in one distinctive compartment of a conditioned cue preference (CCP) apparatus and water in the other compartment over 8 days (training trials). They are then given a choice between the two compartments with no solutions present (preference test). Previous findings showed that this training procedure results in two parallel forms of learning: conditioning to water-paired cues (a water-CCP) and latent learning of an association between salt and salt-paired compartment cues (a salt-LCP). Experiment 1 examined these two types of learning in isolation. Results showed that expression of the salt-LCP required salt deprivation during testing, but expression of the water-CCP did not require a deprivation state during testing. Other results showed that salt-LCP learning itself involves two distinct components: (1) the latent association among neutral cues in the salt-paired compartment, and (2) motivational information about salt deprivation during testing. Previous findings also demonstrated roles for the dorsal hippocampus (DH), ventral hippocampus (VH), and entorhinal cortex (EC) in salt-LCP learning. Experiment 2 examined the involvement of these structures during acquisition or expression of salt-LCP learning. Rats with cannulas aimed at DH, VH, or EC were given infusions of muscimol, either before exposure to the salt-paired, but not the water-paired, compartment during training or before the preference test. Inactivation of the DH or EC impaired both acquisition and expression of the association between salt and salt-paired compartment cues, while inactivation of the VH disrupted the influence of motivational information about salt deprivation required to express the salt-LCP. These results suggest unique roles for the EC-DH circuit and VH in salt-LCP learning, as well as a functional dissociation between the DH and VH.

Similarity in spatial origin of information facilitates cue competition and interference

Two lick suppression studies were conducted with water-deprived rats to investigate the influence of spatial similarity in cue interaction. Experiment 1 assessed the influence of similarity of the spatial origin of competing cues in a blocking procedure. Greater blocking was observed in the condition in which the auditory blocking cue and the auditory blocked cue originated at the same spatial location. Recent investigations have demonstrated that manipulations that impact competition between cues trained together have similar effects on interference between cues trained apart. Therefore, Experiment 2 investigated the influence of similarity of the spatial origin in proactive interference of Pavlovian conditioning by separately pairing two auditory cues with a common outcome, originating at the same spatial location or different spatial locations. Greater proactive interference was observed in the condition in which the interfering cue and target cue originated at the same spatial location. The results are considered in light of the possibility that a similar mechanism may underlie interference between cues trained apart and cue competition between cues trained together.

Effects of nitric oxide on expressions of nitrosocysteine and calcium-activated potassium channels in the supraoptic nuclei and neural lobe of dehydrated rats

Nitric oxide (NO) is an important gas mediator in the signal transduction cascade regulating osmotic function in the hypothalamo-neurohypophysial system. We previously found that increased nitric oxide synthase (NOS) activity in the supraoptic nuclei (SON) and neural lobe following osmotic stimulation and NO could regulate the expression of Ca 2+-activated K + channel (BK channels) protein in the magnocellular system during dehydration. The aim of the current study is to examine the role of NO in the regulation of nitrosocysteine and BK channel protein in the magnocellular system in dehydrated animals. Using Western blot analysis and quantitative immunofluorescent staining study, we found that water deprivation in rats significantly enhanced the expression of nitrosocysteine protein in SON and neural lobes. Immunohistochemistry study indicated that dehydration significantly increased the profiles of SON neurons co-expressing nitrosocysteine with BK-channel protein. Intracerebroventricular administration of L-NAME (an inhibitor of NO synthase) significantly reduced the neuronal profiles of nitrosocysteine, as well as their co-expression with BK-channel in SON of dehydrated rats. However, treatment of sodium nitroprusside (a donor of NO) increased this co-expression. Our results indicate that NO signaling cascade may control the expression of BK channels through the regulation of nitrosocysteine in SON and neural lobe of rats during osmotic regulation.