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Tiospirone (TSP) is an atypical antipsychotic drug. It has 5HT-2 antagonistic properties as well as affinity for D2, 5HT-1a, 5HT-6 and sigma receptors. Behavioural studies in our laboratory, which used a 24h free access to food and fluids paradigm, showed a decreased alcohol and increased food intake after twice-daily administration of TSP; the maximal effect was obtained at a dose of 0.48 mg kg(-1). This study used the conditioned place preference paradigm to determine the effect of TSP on the reinforcing properties of cocaine. Intraperitoneal administration of 5.0 mg kg(-1) cocaine, but not saline, increased the time rats spent in the drug-paired compartment of a three-compartment shuttle box by 104.9%. Two doses of TSP, 0.143 and 0.48 mgkg(-1), were tested subcutaneously 60 min before saline or cocaine administration during the conditioning phase only. A dose-response effect was observed with a significant reduction in the time rats spent in the cocaine-paired compartment on the drug-free test day produced by the dose of 0.48 mg kg(-1) (an increase of only 38.1% when post-conditioned times were compared with preconditioned times). These findings suggest that TSP reduces the reinforcing properties of cocaine exhibited in the conditioned place preference paradigm.

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Amperozide (AMPZ) is a 5-HT2 receptor antagonist that can decrease consumption of ethanol and prevent cocaine conditioning of a place preference. Tiospirone (TSP) is a 5-HT2 receptor antagonist with affinity for D2, 5-HT1a, and 5-HT7, and sigma receptors, which can decrease consumption of ethanol while increasing food intake. Both drugs were tested for inhibition of food reinforced bar-pressing behavior. Fasted Sprague-Dawley male rats were trained daily on a 15-min FR-5 schedule. After response rates stabilized, each rat in one group received a 60-min pretreatment s.c. with saline, 0.25,0.75, or 2.5 microlmol/kg of AMPZ (injections were twice per week and counterbalanced). Each rat in a second group received a 60-min pretreatment with saline, 0.1,0.3, or 1.0 micromol/kg of TSP. The dose of 2.5 micromol/kg of AMPZ reduced the number of food reinforcements by 21% from saline. The effect was due to a greater decline in bar pressing during the last 5-min block. TSP, 0.3 and 1.0 micromol/kg, significantly reduced the number of reinforcements by 45 and 94% from saline, respectively. In a study of catalepsy, TSP at 0.3 and 1.0 micromol/kg produced akinesia and catalepsy, respectively. Our results indicate that AMPZ-induced reduction of alcohol intake is not due to a nonspecific effect on reward, but the akinetic effects of TSP masks whether or not it has effects on reward.

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Recent studies show that baclofen, a selective GABA(B) agonist, impairs different kinds of learning. In the present study we investigated the effect of microinfused baclofen into the hippocampus of male Wistar rats, on the performance in the Morris water maze. Rats of 8-10 weeks of age were implanted with cannulae aimed bilaterally at the hippocampal formation. Baclofen (1 microl of 0.2 mM, 2.0 mM, and 20.0 mM) or sterilized saline was microinfused 1 h before each daily session (3 trials/session, 1 session/day) for 4 days. On the fifth day, the animals did not receive drug or saline injections and the retention of the location of the escape platform was tested in a 30 s free swim trial. Results from the free swim trial indicate that the doses of baclofen used during training affected the ability of the rats to swim to the target quadrant. Although no significant difference compared with the saline group was observed, the experimental rats showed a more generalized swim trajectory in the area of the target and both adjacent quadrants. Moreover, 1 microl of 20.0 mM baclofen also impaired the acquisition. We suggest that baclofen has an impairing action on spatial learning, although more studies should be conducted to reach a more precise conclusion.

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Adult female rats, receiving a low protein diet at perinatal age and then recovered with balanced chow (D rats), were evaluated in the Open Field Drink Test (OFDT), after different acute and chronic treatments with benzodiazepines (BZD) ligands, as compared with control (C) female rats. Control and D rats showed similar reactivity to acute administration of diazepam (DZP, 1 mg/kg) and FG 7142 (2.5mg/kg), both BZD ligands with anxiolytic and anxiogenic effects, respectively. After chronic DZP treatment (3mg/kg/day i.p. for 3 weeks), C rats developed tolerance to the anxiolytic effect of DZP as well as withdrawal syndrome upon abrupt interruption of chronic treatment. On the contrary, D animals failed to develop tolerance to the anxiolytic effect of DZP, and did not show an increased anxiety upon withdrawal. The functionality of the GABAA receptor-complex, as measured by (36)Cl(-) uptake in cortical cerebral microsacs, was not altered in the DZP withdrawn rats. The lack of tolerance and withdrawal syndrome may be related to the incapacity of D rats to generate adaptive changes after chronic treatments. For instance, C rats showed a lower anxiety level in the OFDT after chronic vehicle administration, whereas D animals did not evidence such an adaptive response. Furthermore, D rats failed to respond to the anxiolytic effect of DZP after chronic vehicle treatment. These results reassert the deleterious effects of perinatal undernutrition on the capacity to develop adaptive responses to repeated drug administration or adequate stimuli.

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We have previously reported that recovered adult rats undernourished at perinatal age failed to develop tolerance to the anticonflict effect of ethanol after chronic ethanol administration (1 g/kg/day during 30 days) (4). To further study the extent of this finding, we examined the effect of a similar chronic ethanol treatment on the hypothermic and anticonvulsant effects of ethanol in perinatally deprived rats. Hypoalgesic activity was assessed in ethanol treated rats during 15 days. After chronic ethanol treatment, a similar development of tolerance to the hypothermic effect of ethanol was observed in control and deprived rats. However, tolerance to the anticonvulsant and hypoalgesic effect of ethanol was significantly reduced in deprived as compared with control animals. Thus, early undernutrition differentially affects the development of tolerance elicited by chronic ethanol administration.

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Pregnant Wistar rats were treated on gestational day 8 (GD 8) with two IP injections of either ethanol (2.9 g/kg in 24% v/v saline solution) or saline. Offspring were tested in the water-maze task at 45 or 90 days of age. The escape latencies of rats trained with a submerged escape platform at a fixed location were similar between control and experimental rats. Analyses of responses on a probe trial carried out 10 days after the training period, revealed that 90-day-old females prenatally exposed to alcohol were less likely to swim in the target region. No differences were observed in this free-swim trial in 45- and 90-day-old male, and 45-day-old female animals. Binding studies of low-affinity GABAA sites in the hippocampus showed an increase in affinity of [3H]GABAA for their binding sites in 90-day-old female offspring prenatally intoxicated with ethanol. Our results demonstrate that acute intoxication with ethanol on GD 8 did not modify acquisition but impaired the retention of spatial learning only in adult female rats. It is possible that the impaired retention will be consequence of higher GABAA receptor affinity.

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The learning capacity of rats with an inborn high performance (HP) and low performance (LP) in an avoidance shuttle box paradigm, was evaluated in the Morris water maze. Escape latencies evaluated in HP and LP rats indicate that acquisition and retention of spatial information were not different from control animals. When a free swim trial was carried out, all groups showed a significant preference towards the target quadrant. Our results suggest that the altered hippocampal physiology described in HP and LP rats does not influence the performance of a spatial tasks such as the Morris water maze.

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Rats were trained in a water maze in a dark room with the extramaze cues restricted to only dimly back-lit shapes. We used lidocaine to reversibly lesion the dorsal hippocampus and this controlled-cue room in order to examine interhippocampal synthesis of lateralized place engrams. Experiment 1 showed that lidocaine injected into both hippocampi effectively abolished place navigation for up to 25 min but not at 45 min. In experiment 2, each day under lidocaine blockade of one hippocampus, pretrained rats were trained in the water maze to locate the target according to two cues (e.g., AB). Two hours later, the contralateral hippocampus was inactivated and the rats were trained to the same location with two other cues (CD). On day 5, intact brain retrieval was tested in one of three conditions: ACQ (e.g., AB), one of the pairs of cues used in acquisition training; SYNTH (e.g., AC), one cue from each of the pairs used in acquisition; CONT (e.g., AE), one cue that was used in acquisition training and a novel cue. The results show that the hippocampi learned the two tasks independently and similarly [latency (L) at the asymptote = 7 s]. Retrieval performance was at the asymptote for ACQ (AB) and SYNTH (AC) (L = 6 and 7, respectively) but was disrupted for CONT (L = 12). In experiment 3 as in experiment 2, the rats were trained, under unilateral blockade, to a new place for 4 days. On day 5, retrieval with the trained hippocampus blocked was worse (L = 11) than with the untrained side blocked (L = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

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Complex relational processes underlying place navigation learning were analyzed by minimizing the relational elements available to rats. The animals navigated in a standard water maze in darkness using controlled remote visual cues (back-lit shapes in opaque buckets aimed at the pool to keep the background dark) while being tracked by an infrared camera and computer. Learning was similar with 2 (AB) or 4 (ABCD) cues and as good as in a fully lit room with many cues (asymptotic escape time t = 5-7 s). The ABCD-trained rats were not impaired by removal of any 2 cues (t = 7). For AB-trained rats, adding 2 new cues (ABEF) or replacing AB with EF (EF) caused small (t = 11) or big disruptions (t = 20), respectively. By block 2, both groups (ABEF, EF) returned to asymptotic performance. But testing the ABEF rats on block 2 with only EF indicated that EF was learned (t = 12) but not as well as when only EF was present (t = 5). Thus transfer from a redundant to a minimal cue condition is immediate and easier than vice versa. Theoretical implications are discussed.

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Contribution of visual and nonvisual mechanisms to spatial behavior of rats in the Morris water maze was studied with a computerized infrared tracking system, which switched off the room lights when the subject entered the inner circular area of the pool with an escape platform. Naive rats trained under light-dark conditions (L-D) found the escape platform more slowly than rats trained in permanent light (L). After group members were swapped, the L-pretrained rats found under L-D conditions the same target faster and eventually approached latencies attained during L navigation. Performance of L-D-trained rats deteriorated in permanent darkness (D) but improved with continued D training. Thus L-D navigation improves gradually by procedural learning (extrapolation of the start-target azimuth into the zero-visibility zone) but remains impaired by lack of immediate visual feedback rather than by absence of the snapshot memory of the target view.

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Learning ability of adult rats undernourished at perinatal age and nutritionally recovered (D-rats) was assayed in the Morris water maze test as compared with controls (C-rats). D-rats showed longer escape latencies to locate a hidden platform in absence of proximal cues during the acquisition period. Swimming pre-training experience did not improve this shortcoming. Retention scores obtained 1, 3, 10 and 30 days after training showed that spatial information was efficiently consolidated after acquisition since D-rats performed as well as C-rats on retention tests. A cue learning task revealed no significant differences between both groups. These results suggest that perinatal undernutrition induces, even after a long period of nutritional recovery, a deficit in efficient place navigation in adult rats.

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Learning ability of adult rats undernourished at perinatal age and nutritionally recovered (D-rats) was assayed in the Morris water maze test as compared with controls (C-rats). D-rats showed longer escape latencies to locate a hidden platform in absence of proximal cues during the acquisition period. Swimming pre-training experience did not improve this shortcoming. Retention scores obtained 1, 3, 10 and 30 days after training showed that spatial information was efficiently consolidated after acquisition since D-rats performed as well as C-rats on retention tests. A cue learning task revealed no significant differences between both groups. These results suggest that perinatal undernutrition induces, even after a long period of nutritional recovery, a deficit in efficient place navigation in adult rats.

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We further investigated the effect of diazepam on the processing of spatial information in a water maze task. Diazepam significantly impaired the retention of spatial information in a group of rats trained to locate a hidden platform. In a free swim trial carried out after training, diazepam-treated rats showed no bias to the target quadrant. There was no effect of diazepam on retrieval of spatial information in well-trained rats, and diazepam was devoid of any effect on cue learning in the water maze. However, diazepam blocked latent place learning during cue training in the water maze. Our results indicate that the GABA-BZD receptor modulates spatial information processing and that diazepam specifically impairs the retention of spatial information without affecting retrieval or cue learning.

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The effect of flumazenil, a benzodiazepine-receptor antagonist, was evaluated in a spatial-reference memory procedure in a water maze. Flumazenil (1.0, 3.0, and 10.0 mg/kg, ip) did not modify acquisition of spatial information. Retention was similar between control and experimental rats 24 h after the training phase, as all groups showed bias to the target quadrant in a free swim trial. However, 10 days later, only flumazenil-injected rats (3.0 mg/kg) showed bias to the target quadrant. Flumazenil did not affect retrieval of spatial information in a group of well-trained rats. These results suggest that a benzodiazepine-receptor mediated endogenous mechanism is activated during learning of spatial tasks and that its blockade facilitates retention of spatial information.

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The effect of diazepam (0.3, 1.0, and 3.0 mg/kg) on the acquisition and retention of place learning was evaluated. The analysis of escape latencies indicates that 1.0 and 3.0 mg/kg diazepam significantly impaired the retention of spatial information. When a free swim trial was carried out only control animals showed spatial bias to the target quadrant. The absence of spatial bias in the group that received 0.3 mg/kg suggests that the amnesic effect of diazepam can be seen at doses similar to or even lower than the anxiolytic ones, and that the GABA/benzodiazepine receptor complex is highly sensitive to the cognitive impairment induced by diazepam in spatial tasks.

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