Comparison of radial maze performance of rats after ibotenate and quisqualate lesions of the forebrain cholinergic projection system: effects of pharmacological challenge and changes in training regime

Rats with ibotenic or quisqualic acid lesions to cholinergic projections showed similar significant increases in both short-term working and long-term reference memory errors in radial maze spatial (place) and nonspatial (cue) tasks, throughout a period of 10 weeks after lesioning. All types of error were dose-relatedly reduced to a similar extent in lesioned rats after treatment with nicotine and the beta-carboline ZK93426. Performance of controls was not affected by nicotine, but errors were increased with the higher doses of ZK93426. In contrast, amphetamine increased errors in both control and lesioned rats. With extensive training, lesioned rats improved to control level, but were more disrupted than controls by a break in testing, which reinstated high error rates to an equivalent extent in lesioned groups. Choline acetyltransferase (ChAT) activity showed a comparable degree of depletion in quisqualate and ibotenate lesioned groups to around 60% of control level in cortex and 75% in hippocampus. These results indicate that at volumes and concentrations that produced an equivalent degree of ChAT depletion, detrimental effects of ibotenate and quisqualate lesions on radial maze performance were very similar. The time course of improvement with over-training and impairment after a break in training were also comparable with both lesioning agents. Reduced errors following compounds acting directly (nicotine) or possibly indirectly (ZK 93426) to enhance cholinergic function, but not after amphetamine, suggested that damage to cholinergic neurons contributed to the behavioural deficits induced by both ibotenic and quisqualic acid.     

Spontaneous exploration of a 6-arm radial tunnel maze by basal forebrain lesioned rats: effects of the benzodiazepine receptor antagonist β-carboline ZK 93 426

Nine days following ibotenic acid induced basal forebrain lesions or a sham-operation, rats were allowed to explore an automated six-arm radial tunnel maze. From each session, several measures of locomotor and exploratory activity were registered. Lesioned and sham-operated animals were treated with either the benzodiazepine receptor antagonist -carboline ZK 93 426 (5 mg/kg; IP) or vehicle (Cremofor EL 10% in saline; IP; n=10 for each group). Treatment was carried out 30 min before each session during acquisition (seven sessions) and reversals of the maze configuration (seven session). Eight days following the 14th session, the animals were retested without any further drug treatment. The main results suggest that the lesion resulted in locomotor hyperactivity, an increase in the number of blind arm entries, and of choice stereotypy. Treatment with ZK 93 426 attenuated the lesion-induced alterations of locomotor and exploratory activities. During the retest, the lesioned, previously vehicle-treated rats revisited arms which they had already explored during this session more frequently than the lesioned, previously ZK-treated rats; the latter group did not differ from the sham-lesioned controls. It is concluded that basal forebrain lesioned animals explored the tunnel maze less efficiently than sham-lesioned controls and that the lesioned animals benefited from the treatment with ZK 93 426. Although the specificity of the lesion in terms of destruction of cholinergic neurons remains unsettled, and although the psychological significances of the behavioral measures obtained from the tunnel maze are not yet fully understood, these results suggest that antagonists or partial inverse agonists at the benzodiazepine receptor may be able to normalize basal forebrain lesion-induced behavioral alterations.     

Interactions between the effects of propranolol and nicotine on radial maze performance of rats with lesions of the forebrain cholinergic projection system

This experiment investigated the hypothesis that nicotine-induced regional release of noradrenaline contributes to the improvements in radial maze performance following nicotine treatment in rats with lesions to the forebrain cholinergic projection system (FCPS), by examining whether pretreatment with the noradrenergic beta-receptor antagonist propranolol abolished the facilitative effects of nicotine. After S-AMPA (8.0mM) lesions to the nuclei of origin of the FCPS in the nucleus basalis and medial septal areas, rats displayed long-lasting impairment in long-term reference and short-term working memory in both spatial (place) and associative (cue) radial maze tasks. Performance of control and lesioned rats was assessed after administration of nicotine (0.1mg/kg), propranolol (either 0.5 or 5.0mg/kg) and both treatments. Nicotine reduced working memory error rates in lesioned animals, but did not affect the performance of controls. Propranolol dose-relatedly increased error rates in both control and lesioned animals. Adverse effects were more marked in controls, all four types of error being increased under the high dose of propranolol, whereas in lesioned rats significant increases in error rates above baseline were confined to working memory. The low dose of propranolol, in conjunction with nicotine, abolished the improvement in working memory seen with nicotine alone in lesioned rats. However, under joint treatment with the high dose, the substantial increases in working memory error rates seen in lesioned rats after propranolol alone were reduced to baseline level. In controls, reduction in errors to baseline was seen only in the cue task; place task errors remained significantly elevated. These results suggest that both cholinergic depletion and noradrenergic blockade exert disruptive effects on cognition, but that these effects are largely independent, since an additive or interactive mechanism would be predicted to produce greater disruption, following noradrenergic blockade, in lesioned rather than in control animals. Although facilitative effects of nicotine were abolished with the low dose of propranolol, the results further suggest that these effects are independent of release of noradrenaline, since nicotine continued to reduce errors in control and lesioned animals following blockade of beta receptors with the high dose of propranolol.     

Combined damage to entorhinal cortex and cholinergic basal forebrain neurons, two early neurodegenerative features accompanying Alzheimer's disease: effects on locomotor activity and memory functions in rats.

In Alzheimer's disease (AD), cognitive decline is linked to cholinergic dysfunctions in the basal forebrain (BF), although the earliest neuronal damage is described in the entorhinal cortex (EC). In rats, selective cholinergic BF lesions or fiber-sparing EC lesions may induce memory deficits, but most often of weak magnitude. This study investigated, in adult rats, the effects on activity and memory of both lesions, alone or in combination, using 192 IgG-saporin (OX7-saporin as a control) and L-N-methyl-D-aspartate to destroy BF and EC neurons, respectively. Rats were tested for locomotor activity in their home cage and for working- and/or reference-memory in various tasks (water maze, Hebb-Williams maze, radial maze). Only rats with combined lesions showed diurnal and nocturnal hyperactivity. EC lesions impaired working memory and induced anterograde memory deficits in almost all tasks. Lesions of BF cholinergic neurons induced more limited deficits: reference memory was impaired in the probe trial of the water-maze task and in the radial maze. When both lesions were combined, performance never improved in the water maze and the number of errors in the Hebb-Williams and the radial mazes was always larger than in any other group. These results (i) indicate synergistic implications of BF and EC in memory function, (ii) suggest that combined BF cholinergic and fiber-sparing EC lesions may model aspects of anterograde memory deficits and restlessness as seen in AD, (iii) challenge the cholinergic hypothesis of cognitive dysfunctions in AD, and (iv) contribute to open theoretical views on AD-related memory dysfunctions going beyond the latter hypothesis.     

Behavioral recovery following bilateral lesions of the nucleus basalis does not occur spontaneously

Recent studies have shown that rats given bilateral ibotenic acid lesions of the nucleus basalis (NBM) exhibit significant impairments on tasks requiring recent or trial-specific memory. However, despite the persistence of cholinergic deficiencies in the cortical projection area, the memory impairments gradually recover over a period of several months of training. Moreover, in one study, the behavioral recovery on a radial arm maze retention task was shown to generalize to a completely different behavior paradigm (passive avoidance) on which the animals had received no prior experience. The present study was performed to determine the extent to which this generalized recovery of performance on memory tasks is dependent upon extensive post-lesion training. Rats were given ibotenic acid lesions of the NBM and were then passively detained in their home cages for six months. Contrary to animals which had received post-surgical radial arm maze experience, the animals detained in their home cages displayed a significant retention impairment when tested on the passive avoidance task, suggesting that the experience the animals receive is an important factor for whether post-lesion functional recovery occurs. This study also confirms that the loss of cholinergic markers following bilateral, NBM lesions persists for at least several months, or longer.     

Differential effects of scopolamine on working and reference memory depend upon level of training.

Controversy exists whether the cholinergic system in the brain is involved in working memory (WM) selectively or in both WM and reference memory (RM). Rats were trained to obtain food from four baited arms of an eight-arm radial maze. The remaining arms were never baited. Three types of errors were recorded: entry into unbaited arms (RM errors), reentry into baited arms (WM errors), and reentry into unbaited arms (WRM errors). There were no differences among three control conditions: methyl scopolamine, physiological saline, and uninjected. Scopolamine increased WM but not RM errors. When rats were trained to a higher criterion of learning, however, both WM and RM were impaired. It appears that when baseline error rate is sufficiently low RM errors under scopolamine become observable. The results suggest that the cholinergic system is involved in both WM and RM, and the selective involvement of WM is the result of insufficient training. The controversy in the literature over the involvement of the cholinergic system in WM and RM was addressed.     

Effect of histamine on muscimol-induced working memory deficits in radial maze performance

We investigated the participation of gamma-aminobutyric acid (GABA) neurons of the medial septal area in eight-arm radial maze performance in rats. The intra-septal injection of muscimol, a GABA(A) agonist, caused an increase in total error and working memory error. On the other hand, no significant effect was observed with reference memory error. Donepezil and tacrine (cholinesterase inhibitors) antagonized the muscimol-induced spatial memory deficits. Histidine (1500 mg/kg, i.p.) also improved the total error and working memory error induced by muscimol. At this dose, histidine caused a significant increase in the histamine content of the cortex, hippocampus, and hypothalamus in rats. In addition, the intra-hippocampal injection of histamine also antagonized muscimol-induced spatial memory deficits. The practical conclusion is that the GABA(A) receptor of the medial septal area plays an important role in working memory, and also, the disturbance of working memory induced by muscimol is mediated not only by cholinergic but also by histaminergic systems in the spatial memory of rats.     

Akebia saponin D attenuates ibotenic acid-induced cognitive deficits and pro-apoptotic response in rats: involvement of MAPK signal pathway

Cholinergic deficit is one of the most remarkable symptoms and plays an important role in Alzheimer's disease. In the present study, the protective effects of Akebia saponin D (ASD) on learning and memory impairments induced by excitatory neurotoxin ibotenic acid injection were examined in vivo. Our findings suggest that ASD (90 mg/kg, p.o.) would exert a rescue effect on rats both in behavioral performances in Morris water maze and Y maze and cholinergic functions detected by chemical methods. We further investigated in the hippocampus and found ASD could regulate apoptosis-related proteins expression following ibotenic acid injection. Additionally, mitogen-activated protein kinase (MAPK) family phosphorylations were inhibited after ASD treatment, implicating that the MAPK signaling pathway could be involved in the mechanism underlying neuroprotection of ASD against ibotenic acid-induced excitotoxicity.     

Comparison of the effects of the 5-HT3 receptor antagonists WAY-100579 and ondansetron on spatial learning in the water maze in rats with excitotoxic lesions of the forebrain cholinergic projection system

The effects of the 5-HT₃ receptor antagonists, WAY-100579 and ondansetron (both at doses of 0.001, 0.01 and 0.1 mg/kg SC) and the muscarinic receptor agonist arecoline (1.0 mg/kg SC), on spatial learning and memory in the water maze were examined in rats after combined S-AMPA lesions to the nucleus basalis and medial septal brain regions. Lesioned rats showed substantially increased latency to find the submerged platform, and spent less time searching in the correct quadrant, and more time circling the periphery of the pool, relative to controls. Lesioned rats treated with WAY-100579, ondansetron and arecoline exhibited marked improvement in these parameters of learning relative to lesioned animals, with arecoline-treated animals showing the most substantial recovery. Linear dose-related trends of improvement were seen with both of the 5-HT₃ antagonists. In probe trials, testing retention of the platform position 24 and 72 h after the end of training, control rats exhibited substantial superiority relative to lesioned rats in accuracy of search in the training quadrant and former platform area, matched by rats treated with arecoline on the first, and by rats treated with the two higher doses of WAY-100579 and ondansetron on the second probe trial. These results are consistent with our previous studies which demonstrated that another selective 5-HT₃ receptor antagonist, WAY-100289, significantly reversed the cognitive deficits in water maze performance induced by ibotenic acid lesions of forebrain cholinergic projection system. Therefore, selective 5-HT₃ receptor antagonists may provide a novel effective therapy for treating cognitive deficits associated with degeneration of central cholinergic neurones, such as Alzheimer's disease or age-associated memory impairment.     

Estrogen improves working but not reference memory and prevents amnestic effects of scopolamine of a radial-arm maze

This study investigated the effect of estrogen treatment on working memory and reference memory of female rats. In addition, the impact of estrogen on the sensitivity of these two types of memory to the cholinergic antagonist scopolamine was investigated. At 35 days of ages, rats were ovariectomized and implanted chronically with Silastic capsules containing either 25% crystalline estradiol or 100% cholesterol. Thirty days after surgery, animals were trained on an eight-arm radial maze with four arms baited to assess both working and reference memory performance. Following training, females were given scopolamine hydrobromide (0.2 mg/kg i.p.) prior to retesting on the task. Results indicated that estrogen treatment improved working memory performance during maze acquisition but did not affect reference memory performance. Scopolamine treatment impaired performance on the working memory component, but not the reference memory component, while estrogen prevented the impairment of working memory by scopolamine. Results support previous evidence that estrogen selectively enhances performance on tasks that depend on working memory.     

Effects of vasopressin on histamine H(1) receptor antagonist-induced spatial memory deficits in rats.

The effects of [Arg(8)] vasopressin on histamine H(1) receptor antagonist-induced memory deficits were investigated using the eight-arm radial maze performance test in rats. Pyrilamine and diphenhydramine as well as scopolamine induced memory deficits characterized by increases in the number of total errors, reference memory errors and working memory errors. [Arg(8)] vasopressin improved not only scopolamine--but also pyrilamine--and diphenhydramine-induced memory deficits, although a high dose of [Arg(8)] vasopressin was needed to antagonize pyrilamine-induced memory deficits. The effects of pyrilamine on the brain [Arg(8)] vasopressin content were studied, and the hippocampus [Arg(8)] vasopressin content was shown to be decreased after pyrilamine injection. From these observations, it seems likely that [Arg(8)] vasopressin participates in not only the cholinergic system but also the histaminergic system in spatial memory.     

Castration in rats impairs performance during acquisition of a working memory task and exacerbates deficits in working memory produced by scopolamine and mecamylamine

Rationale Although much research has focused on the effects of ovarian hormones on learning and memory in females, less information is available regarding the effects of testicular hormones on learning and memory in males. Additionally, despite evidence of an interaction of testicular hormones and the cholinergic system in areas of the brain implicated in learning and memory, no information is available regarding the behavioral consequences of that interaction.Objectives We assessed the effect of castration in male rats on working memory during acquisition of a radial maze. We also assessed the interactive effects of castration and scopolamine, a muscarinic receptor antagonist, as well as mecamylamine, a nicotinic receptor antagonist, on behavior.Methods Young adult male rats were castrated or underwent sham surgeries. Beginning 10 days after surgeries, performance on a task of working memory was assessed across 24 days of acquisition in an eight-arm radial maze. Following acquisition, scopolamine and mecamylamine dose–effect curves were established.Results Castration of male rats significantly decreased arm-choice accuracy during acquisition. Castration significantly exacerbated impairments in arm-choice accuracy produced by scopolamine as well as mecamylamine, without altering the disruptive effects of the drugs on the rate at which rats entered the arms of the maze.Conclusions These results indicate that castration in male rats impairs working memory during acquisition of a spatial maze task. Additionally, these results suggest that the absence of testicular hormones increases the sensitivity of male rats to the impairing effects of scopolamine as well as mecamylamine on working memory.     

Effects of methanol extract of Uncariae Ramulus et Uncus on ibotenic acid-induced amnesia in the rat

In the present study, we investigated the effects of Uncariae Ramulus et Uncus (UR) on learning and memory in the Morris water maze task and the central cholinergic system of rats with excitotoxic medial septum (MS) lesion. In the water maze test, the animals were trained to find a platform in a fixed position during 6 days and then received a 60-s probe trial in which the platform was removed from the pool on the 7th day. Ibotenic lesion of the MS showed impaired performance of the maze test and severe cell losses in the septohippocampal cholinergic system (SHC), as indicated by decreased choline acetyltransferase-immunoreactivity and acetylcholinesterase-reactivity in the hippocampus. Daily administrations of UR (100 mg/kg, i.p.) for 21 consecutive days produced significant reversals of ibotenic acid-induced deficit in learning and memory. These treatments also reduced the loss of cholinergic immunoreactivity in the hippocampus induced by ibotenic acid. These results demonstrated that impairments of spatial learning and memory may be attributable to degeneration of SHC neurons and that UR ameliorated learning and memory deficits partly through neuroprotective effects on the central acetylcholine system. Our studies suggest that UR may be useful in the treatment of Alzheimer's disease.     

Selective memory loss following nucleus basalis lesions: long term behavioral recovery despite persistent cholinergic deficiencies

Rats were trained for several months to perform a radial arm maze task and then given either sham or ibotenic acid lesions of the nucleus basalis magnocellularis (NBM), the primary cholinergic projection to the neocortex. The lesion produced a profound and apparently selective disturbance in memory for recent events. Further testing revealed that although the memory deficit persisted for several weeks, a gradual but complete recovery eventually occurred. Moreover, when these functionally recovered rats were later tested on a passive avoidance task that is normally sensitive to lesions of the NBM, no deficit was found. Thus, the post-lesion recovery of function generalized to a different memory test, upon which no post-lesion practice had been given. Post-mortem determinations revealed that the lesions caused marked neurodegeneration of the NBM, and decreases in both cortical choline acetyltransferase activity and high affinity choline uptake, but had no effect on density of muscarinic receptors. No evidence of neuronal recovery or neurochemical compensatory changes in the cholinergic system was found in the cortical projection areas, lesion site, or in parallel cholinergic systems terminating in the hippocampus or olfactory bulb. These results support the idea that the cortically-projecting cholinergic cells of the NBM normally play an important role in mediating recent memory. However, they also demonstrate that any simple relationship between the function of this brain region and the mediation of recent memory is unlikely. Finally, the results of this study direct attention toward issues related to the mechanisms involved with the recovery of function, and the extent to which degeneration of this brain area may contribute directly to the severe disturbance of cognitive function associated with certain neurodegenerative diseases (e.g., Alzheimer's, Pick's and Parkinson's disease).     

Effects of Yukmijihwang-tang derivatives (YMJd) on ibotenic acid-induced amnesia in the rat

The present study investigates the effects of Yukmijihwang-tang Derivatives (YMJd) on learning and memory through the Morris water maze task and the central cholinergic system of rats with excitotoxic medial septum (MS) lesion. In the water maze test, the animals were trained to find a platform in a fixed position for 6 d and then received a 60-s probe trial in which the platform was removed from the pool on the 7th day. Ibotenic lesion of the MS showed the impaired performance in the Morris water maze test and severe cell losses in the MS, as indicated by decreased choline acetyltransferase-immunoreactivity in the medial septum. Daily administrations of YMJd (100 mg/kg, i.p.) for 21 consecutive days produced significant reversals of ibotenic acid-induced deficit in learning and memory. These treatments also reduced the loss of choline acetyltransferase (ChAT) immunoreactivity in the MS induced by ibotenic acid. These results suggest that impairments of spatial learning and memory might be attributable to the degeneration of septohippocampal cholinergic (SHC) neurons and that YMJd treatment ameliorated learning and memory deficits partly due through neuroprotective effects on the central acetylcholine system. Our studies suggest that YMJd might be useful in the treatment of Alzheimer's disease.     

Effect of Polygala tenuifolia root extract on scopolamine-induced impairment of rat spatial cognition in an eight-arm radial maze task

The effects of Polygala tenuifolia root fractions and the acyl groups of its constituents on the retrieval process of spatial cognition in rats were studied using an eight-arm radial maze task. Oral administration of a precipitate fraction (PTB) obtained by concentration of the n-BuOH-soluble portion from the extract of the roots significantly decreased the number of total errors (TEs) and that of working memory errors (WMEs) at doses of 100 mg/kg and 200 mg/kg. However, it caused no significant decrease in the number of reference memory errors (RMEs). In addition, the saponin-rich fraction (PTBM) obtained by purification of PTB also showed significant decreases in TEs and WMEs at a dose of 100 mg/kg. Among the cinnamic acid derivatives present as the acyl groups in the P. tenuifolia constituents, sinapic acid (SNPA) significantly decreased TEs and WMEs at doses of 10 to 100 mg/kg. These results indicated that P. tenuifolia extracts, PTB and PTBM, and SNPA had a beneficial effect on the memory impairment induced by dysfunction of the cholinergic system in the brain. The memory improvement in the scopolamine-induced memory impairment seen in the radial maze performance was due to improvement in the short-term memory. A contribution of some constituents other than SNPA to the memory improvement was also suggested.     

Working and reference memory in rats in the three-panel runway task following dorsal hippocampal lesions.

Using a three-panel runway task, the influence of dorsal hippocampal lesions on working and reference memory in rats was investigated. Despite 20 postoperative training sessions, rats with hippocampal lesions were unable to perform the working memory task. In the acquisition process of the reference memory task, however, there was no significant difference between hippocampal- and sham-lesioned rats. On the other hand, rats trained preoperatively with a working memory procedure, and then subjected to hippocampal lesions, showed more errors (pushes made on the two incorrect panels of the three panel-gates located at four choice points) than did sham-lesioned rats. The increase in working errors induced by hippocampal lesions was not reduced during 10 subsequent re-training sessions. Hippocampal lesions had no effect on retention of the reference memory performance. The increase in working errors in hippocampal-lesioned rats was significantly reduced by treatment with the cholinesterase inhibitor physostigmine at 0.1 mg/kg and the cholinergic activating drug minaprine at 10 mg/kg. These findings suggest that lesions of the dorsal hippocampus selectively impair the ability to carry out the working memory task whether rats are trained preoperatively or postoperatively, and that the working memory loss in hippocampal-lesioned rats is mediated by lowering of the cholinergic function.     

Ventral hippocampal alpha4beta2 nicotinic receptors and chronic nicotine effects on memory

Chronic nicotine administration has been repeatedly shown to facilitate working memory function in rats on the radial-arm maze. The critical neural mechanisms for this effect are still being discovered. The nicotinic nature of the chronic nicotine induced memory improvement is supported by the finding that it is blocked by chronic mecamylamine co-infusion. The hippocampus also appears to be critically important. Hippocampal ibotenic acid lesions block the effect. Within the hippocampus, we have found that the alpha4beta2 nicotinic receptor subtype is involved in memory functioning. Acute ventral hippocampal infusions of the alpha4beta2 nicotinic antagonist dihydro-beta-erythroidine (DHbetaE) significantly decreased working memory performance in the radial-arm maze. The aim of the current study was to determine the importance of alpha4beta2 receptors within the ventral hippocampus for the memory enhancing effects of chronic nicotine treatment. Adult female Sprague-Dawley rats were trained on the 8-arm radial maze and were cannulated bilaterally in the ventral hippocampus. Osmotic minipumps administering chronic nicotine at a rate of 5 mg per kg per day were also implanted in the nicotine treatment rats. Control rats received saline-only minipumps. For a period of 4 weeks after surgery, each rat received bilateral hippocampal infusions of 0, 2, 6 and 18 microg per side of DHbetaE and tested for memory performance on the radial-arm maze. Radial-arm maze choice accuracy was impaired by acute hippocampal DHbetaE infusion in a dose-related fashion. This acute hippocampal DHbetaE-induced choice accuracy impairment was eliminated by chronic systemic nicotine infusion. Chronic nicotine in combination with acute vehicle hippocampal infusion was not seen to alter choice accuracy. Response latency was not found to be altered by acute hippocampal DHbetaE in the absence of chronic nicotine administration, but it did attenuate the response latency reduction induced by chronic nicotine infusion. Wet dog shakes were not found to be affected by hippocampal DHbetaE when given without chronic nicotine. Wet dog shakes were significantly increased by chronic nicotine infusion. Intra-hippocampal DHbetaE significantly potentiated this effect. The results from the current study reinforce the hypothesis that ventral hippocampal alpha4beta2 nicotinic receptors are important for memory function. These receptors may also have a role to play in the development of other aspects of behavior associated with chronic nicotine treatment.     

Reversal of age-related cognitive impairments by an M1 cholinergic agonist, AF102B

This study examined the effect of a specific M1 cholinergic agonist, AF102B, on place learning of aged and young rats. Spatial reference memory was tested in the Morris Water Maze task, while spatial working memory was tested on an 8-arm radial maze. Both memory functions were impaired in aged rats compared to young animals. However, the administration of AF102B significantly reduced the age-related cognitive impairments observed in both tasks. This data supports the assertion of the "cholinergic hypothesis," namely that specific enhancement of cholinergic function may reverse geriatric cognitive deficits.     

Estrogen and NMDA receptor antagonism: effects upon reference and working memory.

Since both estrogen and NMDA receptor antagonists act on the hippocampus CA1 region and behaviorally affect hippocampal memory tasks, we examined how estrogen depletion (ovariectomy) and NMDA receptor antagonism interact upon spatial memory of the mouse. After ovariectomy or sham operation, mice were given a 2-week recovery before behavioral tests began under the influence of vehicle or (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP 2, 5 and 10 mg/kg) intraperitoneal injections. CPP is a competitive, full NMDA receptor antagonist. Spatial reference memory was tested by the water maze, spatial working memory was tested by the radial arm maze, while overall locomotive activity was monitored by the Y-maze. Results from the water maze and the Y-maze did not show any spatial reference memory or activity differences between sham-operated and ovariectomized mice. The radial arm maze, however, highlighted some working memory differences between intact and ovariectomized mice. CPP treatment impaired dose dependently--the performance of ovariectomy and sham-operated mice equally on both water maze and radial arm maze, while the drug had no effect on Y-maze performance. These results suggest that short term estrogen deprivation has no effect upon spatial-reference memory, while it impairs spatial working memory. This effect is probably not mediated by NMDA receptors.