Alcohol consumption alters dopamine transporter sites in Wistar-Kyoto rat brain.

Even though animal and human studies show alterations in dopamine transporter (DAT) sites after alcohol withdrawal, the role of DAT in influencing either alcoholic or depressive behavior has not been examined extensively. Given that the Wistar-Kyoto (WKY) rat is a putative animal model of depressive behavior, the present study examined the effects of chronic alcohol consumption on DAT sites in WKY versus Wistar (WIS) rats. Brains from both strains were sectioned for autoradiographic analysis of [3H]-GBR12935 binding to DAT sites after 24 days of alcohol exposure. The results indicated that WKY rats consumed a greater amount of alcohol (P < 0.001) than WIS rats did throughout the experiment. Autoradiographic analyses of discrete brain regions indicated that alcohol consumption increased DAT sites in a greater number of brain areas in WKY compared to WIS rats. In WKY rats, the binding of [3H]-GBR12935 to DAT sites was increased in the basolateral, central and lateral nuclei of the amygdala, lateral nucleus of the hypothalamus, olfactory tubercle, caudate-putamen, nucleus accumbens and substantia nigra (P < 0.05) and decreased in the ventromedial nucleus of the hypothalamus and the CA1 region of the hippocampus. In WIS rats, alcohol consumption increased DAT sites in the CA1 region of the hippocampus, basolateral nucleus of the amygdala, ventral tegmental area and substantia nigra, and decreased DAT sites in the lateral and ventromedial hypothalamus and dentate gyrus. These results indicate a strain dependent alteration in DAT sites which may be related to altered dopamine neurotransmission in select brain regions following alcohol consumption.

The emergence test: effects of psychotropic drugs on neophobic disposition in Wistar Kyoto (WKY) and Sprague Dawley rats.

1. The Emergence Test (ET), a variation of the open field test in which the rat is not handled, and is purported to measure neophobia, was applied to Wistar Kyoto (WKY) and Sprague Dawley (S-D) rats. 2. While no-stress control WKY rats were less active in the ET, pre-treatment with shock stress exacerbated strain differences. WKY rats, previously exposed to shock, did not emerge from the home cage start box during repeated testing, whereas previously stressed S-D rats vacated the home cage quickly and revealed increasing behavioral agitation. 3. Diazepam reduced emergence latency only in S-D rats, whereas nomifensine significantly increased head poke responses in WKY rats. 4. WKY rats responded to the ET with characteristically depressive behavior, whereas S-D rats responded to the same ET with behavioral agitation and anxiety. The implications of these behavior patterns for discriminating between anxiety and depressive behavior are presented.

Paradoxical hormonal and behavioral responses to hypothyroid and hyperthyroid states in the Wistar-Kyoto rat.

Wistar-Kyoto (WKY) rats show endogenous depressive behavior that can be reversed by antidepressants. Given that WKYs exhibit decreased sensitivity to some antidepressants and treatment-resistant depressed patients often show hypothalamic-pituitary-thyroid (HPT) dysregulation, we examined the behavioral and HPT hormonal responses of WKYs to altered thyroid status. "Euthyroid" WKYs had elevated basal plasma TSH and T(3) levels as compared to Wistars. Hypothyroidism increased TSH levels more in WKYs than in Wistars and increased response latency in the open field test (OFT) of WKYs only. Administration of T(4) and T(3) suppressed plasma TSH equally in both strains. Wistars responded to increased T(3) levels with decreased response latency and increased activity in the OFT, but increased immobility in the forced swim test. In contrast, WKYs responded only to the high T(3) levels with decreased response latency in the OFT. These results suggest the existence of a decreased central nervous system sensitivity to thyroid hormones in WKYs that could be related to their depressive behavior.

Investigatory behavior of a novel conspecific by Wistar Kyoto, Wistar and Sprague-Dawley rats.

The assumption was made that investigatory behaviors (i.e., ano-genital and general body sniffing) of a female conspecific by a mature male rat, has positive hedonic characteristics. Because reduced interest in pleasurable events (i.e., anhedonia) is diagnostically related to depressive behavior, the hypothesis was advanced that less investigatory behavior would be observed in an animal model of depression, namely the Wistar Kyoto (WKY) rat strain. In Experiment 1, WKY, Wistar and Sprague-Dawley male rats were subjected, in the first test series, to three consecutive 2-min exposures to one intruder stimulus female, followed later by another three consecutive 2-min exposures to a second stimulus intruder female. On the second test series, 24 h later, the male rats were exposed to one female for 2 min, followed 6 min later to another 2-min exposure to another stimulus female. Half the male subjects were subjected to tail shock stress 2 h before the first test series. All males demonstrated a habituation of the investigatory response to the same stimulus female, but a dishabituation when subsequently exposed to a new stimulus female. Only WKY rats, exposed to prior stress, revealed a significant reduction in investigatory behavior. In Experiment 2, using only WKY and Wistar rats, a factorial design was used to observe any differences between two stressors, namely tail shock and water restraint, and also to observe possible differences in investigatory behavior towards male vs. female intruder rats. Restraint stress and shock stress elicited significant reductions in investigatory behavior for WKY rats, but not Wistar rats, when confronted with female intruder rats. Male intruders elicited more freezing behavior, as well as aggressive defensive fighting behavior from resident male rats. The results are interpreted to suggest that the significant decrease in investigatory behavior towards a female intruder, which was observed primarily in stressed WKY males, reflects the presence of anhedonia in stressed WKY rats, and reinforces our assertion that the WKY rat strain represents a useful animal model of depressive behavior.

Negative affect and voluntary alcohol consumption in Wistar-Kyoto (WKY) and Sprague-Dawley rats.

Based on the assumption that the Wistar-Kyoto (WKY) rat strain represents an animal model for depressive behavior, the purported relationship between depression and alcohol consumption was investigated in three experiments. WKY rats consumed more alcohol than Sprague-Dawley (S-D) rats when offered a choice between a 7% alcohol solution and tap water. Subsequently, the severity of stress-induced stomach ulcers was significantly less in WKY rats that had access to alcohol. In Experiment 2, WKY and S-D rats were assigned to either an alcohol access treatment or to a water-only treatment for 27 days and subsequently observed in the open-field test (OFT) and the elevated plus-maze (EPM). Access to alcohol reduced response latency in the OFT, and increased the percent time in the open arm and the total number of arm entries in the EPM for WKY rats. In Experiment 3, the antidepressant, imipramine, reduced alcohol consumption in both strains and significantly increased percent time in the open arms of the EPM for WKY rats. These studies support the assumption that depression and alcohol consumption may be related.

Gender differences in acute and chronic stress in Wistar Kyoto (WKY) rats.

While females are considered more susceptible to depressive behavior, this assertion is not strongly supported by the experimental literature. Since stress contributes to depressive behavior, male and female Wistar Kyoto (WKY) rats were exposed to either one session (acute stress) or 5 sessions (chronic stress) of restraint plus cold in order to study depressive behavior in male and female rats. After their respective treatment exposure, rats were tested in the open field test (OFT) and for retention of a passive-avoidance (P-A) task. One stress session resulted in significant immobility in the OFT for males, whereas 5 sessions were required to produce similar immobility in female rats. Acute stress interfered with the retention of the P-A response for males, while both acute and chronic stress produced poor P-A responses in female rats. Food consumption decreased progressively, as a function of stress sessions, in female rats, whereas feeding in males returned to control levels after five stress days. Both acute and chronic stress exacerbated the stress ulcer response in male rats, but not in female rats. Chronic, but not acute, stress resulted in an increase in serotonin transporter mRNA levels in the dorsal raphe nucleus of both male and female rats. The general consensus from these data suggested that female rats were more vulnerable to chronic stress and consequently supported the notion that females may be more susceptible to stress-induced behavioral depression. Key Words: WKY rats, acute and chronic stress, gender, passive avoidance, open field behavior, stress-ulcer, adrenal weight, serotonin, dorsal raphe nucleus

Differences in the stress response of Wistar-Kyoto (WKY) rats from different vendors.

Wistar-Kyoto (WKY) rats are hyperresponsive to stress and prone to stress ulcer. However, some variability in these general findings has been reported. This variability may reflect differences in the rat stock from different WKY rat vendors. WKY rats from Taconic (WKY-T), Harlan Sprague-Dawley (WKY-H), and Charles River (WKY-CR) were observed in the open-field test (OFT) and the forced-swim test (FST), and subsequently exposed to ulcerogenic water-restraint stress. There were no differences between vendor stocks in the FST, but WKY-CR rats were significantly more immobile in the OFT as compared to WKY-T and a Wistar control group. WKY-CR and WKY-H rats revealed significantly more ulcers as compared to WKY-T and Wistar rats. The WKY inbreeding programs at Charles River and Harlan, as compared to the outbreeding practice at Taconic may contribute to these vendor differences. These data indicate that WKY rat sublines from different vendors represent an important source of variability when comparing studies of stress reactivity using WKY rats.

Developmental factors modify stress ulcer incidence in a stress-susceptible rat strain.

Our multifactor theory of stress ulcer assumes that environmental factors that operate during early growth stages influence the elaboration of stress ulcer in adult rats. The theory would predict that rats exposed to either neonatal handling, or raised in a stimulus enriched environment, would reveal differences in stress ulcer susceptibility. In study 1, some Wistar rats and ulcer-susceptible Wistar Kyoto (WKY) rats were handled daily from birth to day 21, whereas other rats from each strain were not disturbed. In study 2, Wistar and WKY rats were raised (3 months) in a large stimulus-dense enriched environment, whereas other rats from each strain were raised in standard rat cages where visual and auditory stimuli were minimized. At 3 months all rats were observed in the open field test (OFT), a test of emotionality, as well as the Porsolt forced swim test (FST), a test of behavioral depression, and subsequently exposed to the ulcerogenic water restraint procedure. Neonatal handling produced results suggesting increased wall climbing activity in the FST, reduced response latency in the OFT, increased body weight and reduced ulcer severity, but these differences were not significant. Rearing in an enriched environment produced similar results but these difference were more pronounced and significant in the Wistar rats as compared to the WKY rats. Thus early environmental manipulations can influence adult behavior and the elaboration of stress ulcer disease, but the impact of these manipulations is less salient in an organism with an endogenous susceptibility to the disease.

Effect of acute or repeated stress on behavior and brain norepinephrine system in Wistar-Kyoto (WKY) rats.

WKY rats develop more restraint-induced gastric ulcers and exhibit more depressive behavior compared to other rat strains. Exposure to novel stressors for 21 days exacerbates depressive behavior in WKY rats and alters beta-adrenoceptors (beta-ARs) and norepinephrine transporter (NET) sites in several limbic brain regions when compared to Sprague-Dawley rats. The present study examined whether these effects would be elaborated following an acute stressor and whether WKY rats would demonstrate adaptation after repeated stress. Rats were subjected to a 2-h supine restraint stress for either one or eight consecutive daily sessions. Open-field behavioral data were collected immediately after the daily stress sessions. Brains were sectioned for autoradiographic analysis of 125I-pindolol binding to beta-ARs and 3H-nisoxetine binding to NET sites in discrete brain regions. Acute 1-day stress resulted in a significant drop in body weight and an inhibition of behaviors in the open field. These effects were also sustained following 7 days of chronic restraint stress. In contrast, while acute stress had no effect on NET binding sites or beta-ARs, repeated stress decreased NET sites in the amygdala, hypothalamus, and locus coeruleus with little effect on beta-ARs in the brain regions examined.

Enhanced retrieval of unpleasant memories influenced by shock controllability, shock sequence, and rat strain.

The propensity to recall unpleasant events may be related to depression and posttraumatic stress disorder. This study examined the extent to which the recall of a previously unpleasant event (i.e., passive avoidance training) may be influenced by another aversive event. The other aversive event was tail shock. Since the Wistar Kyoto (WKY) rat strain has been proposed as an animal model of depressive behavior, this study was conducted with WKY and Wistar rats. Parameters manipulated included shock controllability, shock sequence (i.e., tail shock before avoidance training versus tail shock after training), and rat strain. Performance of the passive avoidance (PA) response was greater in WKY rats. Exposure to inescapable tail shock was related to greater PA performance compared to exposure to escapable or no-shock treatments. Tail shock prior to PA training led to a greater recall of the PA response. The magnitude of the PA response was influenced by the rat strain, shock controllability, and shock sequence. The applicability of these data to the memory bias phenomenon in depression is discussed.

Effect of stress on the behavior and 5-HT system in Sprague-Dawley and Wistar Kyoto rat strains.

The effects of chronic novel stressors, for 21 days, on the behavior and the serotoninergic (5-HT) system in Sprague-Dawley (SD) and Wistar Kyoto (WKY) rats were studied. Open-field and forced-swim tests revealed a significantly greater behavioral depression in the WKY strain. SD rats showed a decrease in 3H-DPAT binding to 5-HT1A receptors in the hippocampus, whereas WKY rats revealed an increase in 3H-DPAT binding in the hippocampus and hypothalamus. Stress did not appear to alter the binding of 3H-DPAT to 5-HT1A sites in the dorsal raphe or median raphe in either strains. SD rats revealed a modest increase in 5-HT transporter (5-HTT) sites in the cortex; WKY rats revealed a decrease in 5-HTT sites in the cortex and the hippocampus. Stress caused an increase in 3H-CNIMI binding to 5-HTT sites in the dorsal and median raphe nuclei in both strains. The results suggest that the greater susceptibility to behavioral depression in WKY rats may account for the differential effects on 5HT1A sites as well as 5-HTT sites in limbic regions and cell body area as compared to SD rats.

Effect of repeated novel stressors on depressive behavior and brain norepinephrine receptor system in Sprague-Dawley and Wistar Kyoto (WKY) rats.

This study compared the effects of repeated novel stressors on 'depressive behaviors', defined by the forced-swim and open-field tests, in Sprague-Dawley (S-D) and Wistar Kyoto (WKY) rats. Since stress appears to alter brain norepinephrine (NE) activity, this study also investigated the effects of the stressors on beta-adrenoceptors (beta-ARs), alpha 2-adrenoceptors (alpha 2-ARs) and NE transporter (NET) sites in S-D and WKY rats. Stress did not alter 125I-iodopindolol (125I-PIN) binding to beta-ARs, nor [3H]idazoxan ([3H]IDAZ) binding to alpha 2-ARs in S-D rats, compared to non-stressed controls. However, WKY-stressed rats showed a significant reduction in 125I-IPIN binding to beta-ARs in the cortex, hippocampus, amygdala and hypothalamus, and a reduction in [3H]IDAZ binding to alpha 2-ARs in the amygdala. [3H]nisoxetine ([3H]NIS) binding to NET sites in WKY-stressed rats was also reduced in the cortex, hippocampus and amygdala. When both strains were compared, the most surprising finding was a significantly higher density of NET sites in the hippocampus and amygdala in WKY rats compared to S-D rats. The results of this study indicate that stress, not only exacerbates depressive behavior in WKY rats, but also selectively alters beta-ARs, alpha 2-ARs and NET sites in limbic brain regions. Thus, the WKY strain may serve as a useful animal model for depressive behavior and for the investigation of novel antidepressant drugs.

Hyponeophagia in Wistar Kyoto (WKY) rats.

Unconditioned suppression of feeding due to novelty (hyponeophagia) was studied in Wistar Kyoto (WKY), Lewis, Fischer 344, and Wistar rats. Fasted rats were given access to food either in home cages (controls) or to a single pellet fixed to the middle of a novel open field environment (experimental). The degree of feeding suppression was significantly greater in WKY rats compared to the other three strains. We suggest that this hyponeophagia resembles the reduced feeding frequently associated with behavioral depression, and that this behavior in WKY rats is another demonstration that this strain is very responsive to stressful stimulation and may serve as a useful animal model for depressive behavior.

Open field, learned helplessness, conditioned defensive burying, and forced-swim tests in WKY rats.

Wistar Kyoto (WKY) and Wistar rats were observed in four tests; the open field test (OFT), the conditioned defensive burying (DB) test, and two tests which are considered animal models of depressive behavior, namely the Porsolt forced-swim test (FST) and the shuttlebox escape responding following exposure to inescapable shock, that is, learned helplessness (LH). The four tests were administered according to a semirandomized schedule to control for sequence effects. All rats were later exposed to water-restraint stress and stomachs were subsequently inspected for ulcers. Stress ulcer severity was greater in WKY rats. WKY rats, as compared to Wistar rats, were hypoactive in the OFT, did not engage in DB, rapidly acquired the LH task, and were significantly more immobile in the FST. The FST was positively correlated with behaviors in the LH procedure and, to a lesser degree, with DB, but these relationships were observed only with WKY rats, not Wistar rats. The data suggested that the use of WKY rats represented a more sensitive procedure for detecting possible relationships between putative animal models of depressive behavior.

Strain differences in hypothalamic-pituitary-adrenal activity and stress ulcer.

Strain differences in stress responsiveness have been previously described, but specific components of the hypothalamic-pituitary-adrenal (HPA) axis responsible for stress hypo- or hyperactivity have not yet been characterized. This study proposed to analyze the effect of restraint stress on different measures of HPA function and stress ulcer in stress-ulcer prone Wistar-Kyoto (WKY) and Fisher 344 (F-344) rats and in the ulcer-resistant Wistar strain. Adult male rats of these strains were sham adrenalectomized, adrenalectomized, and adrenalectomized-replaced with corticosterone pellet. Ten days after surgery, animals were subjected to the 2-h ulcerogenic water-restraint stress and killed 2 h later. Intact WKY rats had dramatically more ulcers and higher anterior pituitary adrenocorticotropic hormone (ACTH) and proopiomelanocortin mRNA levels than the other two strains. In WKY rats, adrenalectomy increased ulcer incidence but did not affect thymus weight, ACTH content, or hypothalamic corticotropin-releasing factor mRNA levels, in contrast to the profound effects of adrenalectomy on these parameters in the other strains. Furthermore, corticosterone replacement was either without effect or enhanced the effect of adrenalectomy on these parameters in WKY rats, while it reversed the effects of adrenalectomy in the other strains. These data imply that WKY rats respond to stress with enhanced and prolonged changes in peripheral functions that are regulated by glucocorticoids, suggesting the presence of impaired efficacy of the glucocorticoid negative feedback on HPA function.

Restraint stress in biomedical research: an update.

Since the publication of our initial review of restraint stress in 1986, much work has continued with this technique, either as a tool for the investigation of other pharmacological, physiological, or pathologic phenomena or with restraint stress itself serving as the object of the study. As we noted in 1986, the major use of restraint has been for the induction of stress responses in animals and, more specifically, for the investigation of drug effects, particularly as they affect typical stress-related pathology--gastrointestinal, neuroendocrine, and immunological agents have been extensively studied. In compiling this update on restraint stress and its effects, we noted an increasing emphasis on central nervous system mechanisms in peripheral disease, especially gastrointestinal disease. In particular, many CNS-active agents have been tested for their effects on gastric and duodenal lesion formation and gastric secretion, including antidepressants, antipsychotics, anxiolytics, noradrenergic, serotonergic, dopaminergic, and peptidergic compounds. Some of these agents are especially active in the gastrointestinal tract even when administered centrally, further solidifying the concept of a brain-gut axis. The present update includes studies of: methods and procedures, pre-restraint manipulations, post-restraint/healing effects, and drug effects. In addition, a current bibliography of reports that have employed restraint is included.

Sex differences and stress response of WKY rats.

Wistar Kyoto (WKY), Fischer-344 (F-344), and Wistar male and female rats during either proestrus-estrus or diestrus phases of the estrus cycle were exposed to the ulcerogenic procedure of water restraint. Both male and female WKY rats revealed significantly more stomach ulcers as compared to Wistar and F-344 rats of the same sex. No persistent sex difference was observed, but ulcer severity was more pronounced during the proestrus-estrus phase as compared to the diestrus phase of the estrus cycle particularly in WKY female rats. In the second study, WKY females were observed as more active in the open-field test (OFT), but more immobile in the forced swim test (FST), as compared to WKY male rats. In addition, proestrus-estrus WKY females were less active in the OFT and significantly more immobile in the FST as compared to diestrus females. Thus, proestrus-estrus WKY females were judged as more emotional in the OFT and as exhibiting more signs of behavioral depression according to the FST. These studies suggest that the steroid hormone milieu in WKY rats may be responsible for these behavioral changes as well as the stress responsiveness in this stress-susceptible rat strain.

Passive-avoidance behavior in Wistar-Kyoto (WKY), Wistar, and Fischer-344 rats.

In Experiment 1, Wistar-Kyoto (WKY), Wistar, and Fischer-344 (F-344) rats were tested on two passive-avoidance tasks: a platform step-down task and a one-way avoidance task. Wistars had shorter response latency scores in the step-down task, whereas F-344 rats had shorter scores in the one-way task. A subsequent ulcerogenic water-restraint stress produced significantly fewer ulcers in Wistar rats as compared to WKY and F-344 rats. In Experiment 2, rearings, grooming, ambulation, defecation, and response ambivalence behaviors were recorded in the one-way avoidance task in addition to response latency. WKY rats defecated more and produced lower scores on the three activity measures as compared to Wistar and F-344 rats. Response latency and ambivalence scores were higher for WKY rats. The subsequent ulcerogenic procedure also produced more ulcers in WKY rats. These data verify the ulcer susceptibility of WKY rats and underscore the assertion that their predominant stress coping behaviors are immobility and freezing. High ambivalence scores in WKY rats suggest behavioral inhibition, which is readily elicited by stressors. These behaviors resemble depressive behavior and suggest that WKY rat may be a useful animal model of depression.

Depressive behavior and stress ulcer in Wistar Kyoto rats.

Wistar Kyoto (WKY) rats, as compared to several other rat strains, are hypoactive in the open field test and in the defensive burying test. WKY rats readily acquire a learned helplessness task as well as a passive avoidance tasks. WKY rats also reveal a greater susceptibility to restraint-induced stress ulcer. The behavioral tests suggest the presence of depressive behavior in WKY rats. When exposed to the Porsolt forced-swim test of 'behavioral despair', WKY rats are judged as exhibiting more depressive behavior. Desipramine not only reduced immobility in the forced-swim test, but also diminished the severity of restraint-induced stress ulcer. These data suggested a heightened activity of the hypothalamic-pituitary axis. Basal plasma ACTH levels did not differ between WKY rats and Wistar rats, but serial plasma ACTH response to restraint stress was significantly greater for WKY rats. These data suggest that depressive behavior is a characteristic of WKY rats and this strain is a valuable model for studying depression which may be induced by an exaggerated stress response.