Estrogen improves performance of reinforced T-maze alternation and prevents the amnestic effects of scopolamine administered systemically or intrahippocampally

In a previous study, administration of high doses of estradiol benzoate (100 microgram/kg for 3 days im) to ovariectomized Long-Evans rats counteracted impairments of reinforced T-maze alternation induced by systemic administration of scopolamine, a muscarinic receptor blocker. In the current study, daily administration of lower doses of estradiol benzoate (5 microgram/kg for 3 weeks sc) increased the number of correct reinforced alternations during T-maze acquisition in ovariectomized rats compared to oil-treated controls and prevented impairments of reinforced alternation induced by injection of scopolamine hydrobromide (0.2 mg/kg ip). Furthermore, scopolamine (20 microgram) delivered bilaterally to the dorsal hippocampus reduced reinforced T-maze alternation in ovariectomized rats previously trained to complete this task while daily treatment with estradiol benzoate (5 microgram/kg sc) for 1 week prior to scopolamine infusion counteracted this impairment. In summary, physiological levels of estrogen improved performance during acquisition of reinforced T-maze alternation and prevented impairments induced by scopolamine administered systemically or intrahippocampally.     

Effects of scopolamine on spatial double alternation in rats.

Developed and tested a method for training spatial double alternation in 3 experiments, with a total of 4 male albino Wistar rats and 10 male albino Sprague-Dawley rats. Responding on different components of the sequence was controlled by different interoceptive and exteroceptive stimuli. This base line was used to compare the effects of scopolamine (.25-1 mg/kg) on the 2 sorts of cued responding in the same S. The 2 types of response did not differ appreciably in susceptibility to disruption by scopolamine. An analysis of errors showed that both switching and perseverative errors were increased by scopolamine, and that no lever preferences developed. An analysis of the various response sequences shows that in the same S, the probability of some sequences decreased consistently with increasing dose level, some sequences increased, and others showed an inverted -shaped function. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estrogen effects on the hyperactivity induced by (+)-MDMA and cocaine in female rats.

This study compared the effects of estrogen (E) on the hyperactivity induced by (+)-3,4-methylenedioxymethamphetamine (MDMA) with E effects on cocaine-evoked hyperactivity in female rats. Sprague-Dawley rats were ovariectomized (OVX); half of them received a 17β-estradiol (E?) implant (OVX + E). Three weeks later, rats received saline, (+)-MDMA (1, 2, or 4 mg/kg) or cocaine (5, 10, or 20 mg/kg), and locomotor activity was monitored. OVX + E rats exhibited greater locomotor hyperactivity in response to both psychostimulants than did OVX rats. The enhanced response to cocaine appeared within 5 min following drug injection whereas the enhanced response to (+)-MDMA was delayed for approximately 30 min. The differential effects of E on hyperactivity may be due to the unique profiles of dopamine (DA) and serotonin (5-HT) in response to (+)-MDMA and cocaine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Priming effect" in conventionally reinforced rats.

Ran 15 male albino rats in alleys for water reinforcement with intertrial intervals (ITIs) similar to the intervals typically used in studies of intracranial reinforcement. When deprived over 15 hrs Ss ran faster with very short ITIs (7 sec) than with longer ITIs (95 sec). Comparisons with rats described in other studies running for intracranial reinforcement leads to the conclusion that, regardless of what kind of reinforcer is used, rats run faster for a reinforcer when ITIs are only seconds long rather than over a minute. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of effects of small lesions in posterodorsal septum on spontaneous and rerun correction (contingently reinforced) alternation in rats.

Compared characteristics of T-maze alternation behavior by giving 11 hooded rats 7 sessions under conditions of "rerun correction" (contingent reinforcement for alternation) and another 11 Ss the same number of sessions with noncontingent reinforcements (i.e., entering either goal arm of the –T maze was reinforced). Both groups alternated significantly above chance, and the difference in medians between groups was small but significant. However, Ss given rerun correction training quickly came against the "ceiling" of 100% alternation, and individual differences were small. Scores of Ss run under conditions of "spontaneous" alternation were more variable, both within and between Ss. In a 2nd part of the study, 6 Ss in each group received small electrolytic lesions in posterodorsal septum. There were 5 operated-control Ss from each group. After 2-wk recovery all Ss were again given 7 sessions in the –T maze. Under rerun correction procedure, controls retained near-perfect alternation scores. Most Ss with lesions dropped to chance levels but recovered to control level over the sessions. Ss tested under spontaneous alternation conditions behaved quite differently. Controls continued to alternate significantly, but Ss with lesions alternated significantly less and did not recover. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of spatial alternation and anxiety by septal scopolamine systemic diazepam in mice

To investigate the behavioral consequences of benzodiazepines in subjects whose septo-hippocampal cholinergic (ACh) activity was impaired, C57BL/6 mice received an injection of 2.5 microg/0.2 microl of scopolamine into the medial septal area with an i.p. injection of 0.5 mg/kg of diazepam. The consequences of these treatments administered in combination or alone were evaluated on anxiety measured in an elevated plus-maze and on spontaneous alternation carried out in a T-maze, using two different intertrial intervals (ITI: 5s or 30s). In these conditions, only the combined treatment provoked a decrease of the anxiety level, which was associated with an impairment of spontaneous alternation restricted to the 5s ITI. Because mice were not impaired during the sequential 30s ITI, this seems to rule out the possibility that this alternation deficit resulted from a working memory loss. These results suggest an involvement of a septal ACh-GABA-A/BDZ interaction in the exaggeration of cognitive deficits produced by benzodiazepines in patients characterized by a cholinergic hypofunction.     

Overshadowing and the outcome-alone exposure effect counteract each other.

Three conditioned lever-press suppression experiments with rats investigated the interaction between overshadowing and outcome-alone exposure effects. Experiment 1 found in first-order conditioning that combined overshadowing and outcome-preexposure treatments attenuate the response deficit produced by either treatment alone. Experiments 2 and 3 investigated the interaction between overshadowing and outcome pre- and postexposure effects in sensory preconditioning, varying retention intervals to engage recency and primacy effects with respect to treatment order. Contrary to when a solitary cue is conditioned, responding to a cue conditioned in compound appeared positively correlated with the context's associative status. These findings suggested that some of the basic laws of learning applicable to cues conditioned alone do not similarly apply to a component of a compound cue. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of low- and high-dose estrogen treatments on vascular responses in female rats

In an attempt to study the mechanisms by which estrogens affect vascular responses, we utilized aortic preparations from intact and ovariectomized female rats receiving low- and high-dose subcutaneous estrogen treatments. Oil-treated, as well as male rats, served as controls. In ovariectomized females, low-dose 17-beta-estradiol injections (5 microg/kg daily for two days) affected the basal release of nitric oxide, as evaluated by concentration-related curves to superoxide dismutase and N(G)-Methyl-L-arginine acetate, which was found to be greater in 17-beta-estradiol-treated females compared to oil-treated females or males. Conversely, the nitric oxide-related vascular relaxation evoked by acetylcholine and sodium nitroprusside was unchanged. Prostacyclin production was also evaluated. Aortic rings from ovariectomized 17-beta-estradiol-treated females released significantly more prostacyclin than those from oil-treated females. These results point out a possible role for nitric oxide and prostacyclin in the vascular protection brought about by physiological levels of estrogens. When intact females were treated with high doses of ethynilestradiol (100 microg/Kg daily for one month), a component of contraceptive pills, either the basal release of nitric oxide, or acetylcholine-induced relaxation underwent a significant decrease. Likewise, the relaxant responses to sodium nitroprusside were impaired in the aortic rings obtained from ethynilestradiol-treated animals when compared to controls. Similarly, the amount of prostacyclin released from aortic tissues obtained from ethynilestradiol-treated animals was significantly reduced. These results may provide a possible explanation for the higher incidence of cardiovascular disease in women who take contraceptive preparations containing high doses of estrogens.     

Temporal properties of gustatory spontaneous alternation in rats.

Describes 2 experiments in which female albino Sprague-Dawley rats (n = 24 each) drank a flavored solution for 1/2 hr. After a variable delay interval, Ss were allowed to choose for 15 min between the same solution and a differently flavored one. Ss drank more of the different solution after delays up to 4-6 hr. This result demonstrates spontaneous alternation for tastes, and confirms the long memory span previously observed in gustatory-visceral conditioning. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estrogen differentially modulates nicotine-evoked dopamine release from the striatum of male and female rats

BACKGROUND: Transluminal balloon angioplasty offers advantages to patch angioplasty. We evaluated the primary patency of thrombosed hemodialysis grafts that had undergone balloon angioplasty versus patch angioplasty as a salvage method. METHODS: We reviewed our experience with 22 consecutive intraoperative balloon angioplasties that were done in a 6-months period. The balloons used were noncompliant high pressure balloons. The balloon results were compared with those of 22 patients who had undergone patch angioplasties by the same surgeons. Age, gender, average time between graft insertion and revision, and number of prior revisions were analyzed. The two groups (patch and balloon) had similar ages (57 versus 58 years, respectively), gender distribution (12 women, 11 men versus 11 women and 11 men), average time of revisions before that particular procedure (15 versus 12 months), and average times of revisions before that procedure. RESULTS: Primary patencies of the patch and balloon group were respectively 86% versus 77% at 1 month, 45% versus 40% at 3 months, and 17% versus 28% at 6 months. There was no statistically significant difference between the two groups. Complications were comparable in both groups. CONCLUSION: Balloon angioplasty offers advantages to patch angioplasty, and we have shown similar patency rates. We recommend balloon angioplasty as a comparable method to salvage dialysis access grafts.     

Reactivation treatment prevents the memory-impairing effects of scopolamine in preweanling rats.

The authors report that the expression of a conditioned odor aversion is impaired in preweanling rats when they are conditioned on Postnatal Day 12 and tested under the influence of scopolamine hydrobromide (0.2 or 0.5 mg/kg, intraperitoneal) after a 48-hr, but not after a 2-hr, retention interval (Experiment 1). This effect of scopolamine is not dependent on maturation of the cholinergic system between Days 12 and 14 (Experiment 2), nor is it due to peripheral mechanisms (Experiment 3). When pups are reexposed to the unconditioned stimulus (footshock) before drug administration, performance on the 48-hr retention test is not impaired by scopolamine (Experiment 4). These findings demonstrate that the cholinergic system may be critical for the retrieval and expression of long-term or weak memories in young rats. However, the expression of active memories (recent or recently reactivated) may not be dependent on the cholinergic system to the same extent as is the expression of inactive memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estrogen and the neural mediation of female–male mounting in the rat.

Sexually receptive females mount sexually sluggish males to entice them to copulate, and estrogen and male olfactory cues mediate this female–male mounting (FMM) in the rat. This study examined whether brain regions that concentrate steroid hormones and receive olfactory projections were important for the mediation of FMM. Fos induction was observed within the medial amygdala, medial preoptic area, and ventromedial hypothalamus of ovariectomized, hormone-primed rats that displayed FMM compared with rats that did not. Excitotoxic lesions of those regions eliminated FMM, whereas implants of crystalline estradiol benzoate to the ventromedial hypothalamus, but not the medial preoptic area or medial amygdala, restored FMM. These data indicate that the ventromedial hypothalamus is a critical area of convergence of hormonal, olfactory, and somatosensory inputs for FMM. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of scopolamine and hippocampal lesions on negative patterning discrimination performance in rats.

Rats were trained in operant chambers to perform an appetitive negative patterning successive discrimination. They were required to respond to the left in response to a tone or click and right to a tone-click compound. Scopolamine and methyl scopolamine impaired performance accuracy and increased response latency and response omissions. Subsequent hippocampal aspiration lesions initially impaired accuracy, which later improved. Lesions decreased response latencies. Finally, the effects of scopolamine and methyl scopolamine were shown to be similar in lesioned and control rats, suggesting that the hippocampus is not involved in the actions of these drugs on this task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of intracisternal 6-hydroxydopamine treatment on acquisition and performance of rats in a double T-maze.

136 male Sprague-Dawley rats in 4 experiments were subjected to various treatments with 6-hydroxydopamine (6-OHDA) to produce decrements in brain catecholamine content either before or after learning to respond in an appetitively motivated double –T maze task. Intracisternal injections of 6-OHDA not only impaired acquisition of the required behavioral response but also decreased performance of Ss which had previously acquired the task. Although reduced food consumption found in 6-OHDA-treated Ss may contribute to the observed deficits in –T maze responding, the behavioral deficit produced by 6-OHDA injection did not seem to be due only to a simple decrease in food intake. The decrements in acquisition and performance were clearly related to amount of central catecholamine depletion produced by 6-OHDA treatment. Further analysis suggested that the behavioral deficits were more related to the reductions in dopamine than they were to the depletion of brain norepinephrine. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of scopolamine on activity and passive avoidance learning in rats of different ages.

A total of 320 albino CFE Sprague-Dawley rats aged 16-17, 20-21, 24-25, 28-29, and 70-85 days old were injected intraperitoneally with either scopolamine hydrobromide (SCOP-HBr) or scopolamine methylnitrate (SCOP-Me-NO-3) at 4 levels (0, .5, 1.9, or 2.0 mg/kg. The SCOP-HBr but not he SCOP-Me-NO-3 disrupted passive avoidance in Ss aged 20-28 days. A subsequent replication at higher doses (4.0, 8.0, and 16.0 mg/kg) with 56 70-84 day old adults and 64 16-day-old pups indicated that SCOP-HBr could disrupt passive avoidance in the adults but not in the pups. Results are consistent with the hypothesis that a cholinergic inhibitory system which mediates passive avoidance develops in the rat 16-20 days postnatally. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of hippocampal microinjections of d-amphetamine and scopolamine on active avoidance behavior in rats.

100 male Sprague-Dawley rats received bilateral injections of 20 or 40 mg of dextroamphetamine or scopolamine into the dorsal or ventral hippocampus prior to each of 8 daily training sessions in a discriminated Y-maze active avoidance task. Scopolamine, but not dextroamphetamine, facilitated avoidance responding in both sites, with the effect being greatest following administration of 20 mg into the dorsal hippocampus. On Days 9 and 10, all Ss received saline injections and were tested for transfer of responding to the nondrug state. A decrement of performance occurred irrespective of whether the drug had facilitated avoidance responding. The performance changes were greater following termination of scopolamine than dextroamphetamine injections, and in no case were so great as those previously reported following peripheral injections of the drugs. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

No effect of neonatal estrogenic stimulation or hypophysectomy on spontaneous activity in female rats.

Ovariectomized 33 Sprague-Dawley rats on the day of birth and administered 0, 50, 100, 200, or 400 mg of estradiol benzoate (EB) on Days 2 and 4. In adulthood, estrogenic stimulation (15 and 250 mg/day of EB) significantly increased activity as measured in revolving drums. The adult activities of Ss given 0-200 mg of EB neonatally were equivalent; Ss given 400 mg of EB were the least reactive, suggesting neonatal desensitization The activity increase produced by 250 mg of EB was greater than that produced by 15 mg. Exp II examined the effects of EB in 10 hypophysectomized and ovariectomized Ss: Estrogen increased running in Ss demonstrating that the effects of estradiol on activity are not mediated by the pituitary. Similarities between the influence of perinatal steroids on spontaneous activity and mating behavior are noted. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Somatosensory determinants of lordosis in female rats: Behavioral definition of the estrogen effect.

By coating the ventral surface of 16 Sprague-Dawley male rats with a dye, regions of contact between males and females ( n = 76) during male mounting were recorded precisely on the female's hair and skin. Film analyses showed that the male's paws and pelvic thrusting stimulated the female's skin with dominant frequencies between 10 and 20/sec. Somatosensory stimuli were then applied to the female skin locations contacted by the male. Deflection of hair on the flanks or perineum alone did not cause lordosis. Light stimulation simultaneously on flanks and perineum caused lordosis only in some females given high estrogen dosages supplemented by progesterone. When flank stimuli were followed by pressure on the rump, tailbase, and perineum, lordosis was triggered reliably in hormone-treated females. In this case, the estrogen-dependence of the reflex was shown, and progesterone synergized with the estrogen effect. Among lordosis components, rump and head elevations in response to pressure stimuli on the rump, tailbase, and perineum appear to be hormone-sensitive. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postacquisition scopolamine treatments reveal the time course for the formation of lamb odor recognition memory in parturient ewes.

Within 4 hr after parturition, ewes learn to recognize the odor of their lamb. Whether scopolamine, a muscarinic antagonist, interferes with lamb odor retention was studied. After 4 hr of mother–young contact, ewes were separated from their lambs for 3 hr. During separation, they received intramuscular injections of saline, methylscopolamine (peripheral muscarinic antagonist), or scopolamine. Only scopolamine (100 μg/kg) prevented subsequent lamb recognition. To assess whether this effect depended on the duration of the learning phase, mothers remained with their lambs for 4, 8, or 16 hr before the 3-hr separation period and the scopolamine treatments. Ewes treated after 4 or 8 hr of contact displayed disturbed lamb recognition, whereas those having 16 hr of contact did not. Activation of central muscarinic receptors is therefore important for the formation of lamb odor recognition memory during a critical period of less than 16 hr postpartum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some effects of single alternation training of rats in a double runway.

Gave independent groups of male hooded rats (n = 30) either (a) single alternation (SA) of reward and nonreward in the 1st goal box of a double runway and 100% reward in the 2nd goal box, (b) concurrent SA in both goal boxes, (c) SA in the 1st goal box and no experience in the 2nd runway, or (d) random 50% reward in the 1st goal box accompanied by 100% reward in the 2nd goal box. SA training in the 1st or in both segments of the double runway yielded reliable SA patterning wherever such training occurred. Concurrent SA training in both segments yielded the fastest development of patterning. "Frustration effects" in the 2nd runway were consistently greater following SA in the 1st goal box than following random reward and nonreward. (PsycINFO Database Record (c) 2010 APA, all rights reserved)