Cooperation and competition between the dorsal hippocampus and lateral amygdala in spatial discrimination learning

The conditioned cue preference (CCP) was used to study how rats discriminate between adjacent arms on a radial maze. Chai and White (Behav Neurosci 2004, 118:770-784) showed that an intact dorsal hippocampus is required to learn this discrimination and that an amygdala-based conditioned approach response that produces an equal tendency to enter both arms is simultaneously acquired. In the present experiments, rats were preexposed to the maze with no food and trained by alternately confining them at the ends of two adjacent arms, one that contained food and one that did not. When given a choice between these arms with no food present, the rats spent more time on their food-paired arms, suggesting they had learned to discriminate their locations. Temporary inactivation of the dorsal hippocampus with muscimol during confinement on the food-paired arm had no effect on the discrimination, but inactivation while on the no-food arm impaired it. This pattern of effects was reversed in rats with amygdala lesions (inactivation on the food-paired arm impaired, but inactivation on the no-food arm had no effect on the discrimination), showing that hippocampus-based and amygdala-based learning interact to influence the behavior of normal rats in this situation. The dorsal hippocampus learns about locations that contain food and about locations that do not contain food. The amygdala-based tendency to enter the food-paired arm cooperates with hippocampus-based foraging for food on the food-paired, but the amygdala-based tendency to enter the no-food arm competes with hippocampus-based learning about the absence of food on that arm.     

Unreinforced spatial (latent) learning is mediated by a circuit that includes dorsal entorhinal cortex and fimbria fornix

The relationship of the entorhinal cortex (EC) and fimbria-fornix (FF) in unreinforced spatial (latent) learning was studied using the conditioned-cue-preference task on an eight-arm radial maze. The maze was turned before every trial to eliminate the use of local cues. During three pre-exposure sessions, food-deprived rats explored the center platform and two adjacent arms of the maze. Since most of the same cues were visible from both arm locations, discriminating them required spatial learning. The rats were then alternately confined to the end of each arm over several days: one arm always contained food, the other was empty. Finally, the rats were allowed free access to both arms with no food present. Normal rats spent more time in their food-paired than in their unpaired arms showing that they learned to discriminate between the arm locations. Bilateral micro-injections of muscimol into the dorsal, but not into the ventral EC, given before the pre-exposure sessions only, impaired the discrimination. The discrimination was also impaired in rats with unilateral lesions of FF and contralateral injections of muscimol into the dorsal EC given before the pre-exposure sessions. Ipsilateral FF lesions and entorhinal inactivation had no effect. These results indicate that the acquisition of information during unreinforced exploration of a novel environment requires an intact circuit involving the dorsal EC and fimbria fornix. Together with previous reports, that this form of learning does not require a functional hippocampus, (Gaskin et al. (2005) Hippocampus 15:1085-1093) the findings also suggest that the acquisition of certain kinds of unreinforced information by this circuit is independent of the hippocampus.     

Involuntary,unreinforced (pure) spatial learning is impaired by fimbria-fornix but not by dorsal hippocampus lesions

Pure spatial learning occurs when rats acquire information about an environment while exploring it in the absence of reinforcers. We previously reported that voluntary, unreinforced exploration of a radial maze retards subsequent reinforced conditioned cue preference (CCP) learning in the same maze. In the present experiment, we examined the effects of involuntary, unreinforced pre-exposure to a radial maze. During pre-exposure, rats were moved by an experimenter between the ends of two arms of a radial maze five times in 30 min. This form of pre-exposure retarded CCP learning, whereas rats that were not pre-exposed and rats that were pre-exposed to a maze in a different room displayed normal CCP learning. These findings suggest that some information specific to the maze environment was acquired during involuntary unreinforced pre-exposure to it. In experiment 2, the retardation of reinforced CCP learning by involuntary unreinforced pre-exposure was eliminated by fimbria-fornix lesions made before pre-exposure but was unaffected by fimbria-fornix lesions made after pre-exposure but before training. Large neurotoxic lesions of the dorsal hippocampus made before pre-exposure had no effect on the retardation of CCP learning, but the rats with these lesions were impaired on a standard test of reinforced spatial learning in a water maze. The lesion effects in experiment 2 are similar to those previously reported for voluntary exploration and suggest that pure spatial learning may occur during both voluntary exploration of and involuntary exposure to an environment in the absence of reinforcers. Pure spatial learning can apparently occur with exposure to two different locations within an environment, but the rats do not have to move between the locations voluntarily. An intact fimbria-fornix is required for acquisition but not expression of this form of learning. The hippocampus is not involved in this form of learning.     

Parallel processing of information about location in the amygdala,entorhinal cortex and hippocampus

The conditioned cue preference paradigm was used to study how rats use extra‐maze cues to discriminate between 2 adjacent arms on an 8‐arm radial maze, a situation in which most of the same cues can be seen from both arms but only one arm contains food. Since the food‐restricted rats eat while passively confined on the food‐paired arm no responses are reinforced, so the discrimination is due to Pavlovian stimulus‐reward (or outcome) learning. Consistent with other evidence that rats must move around in an environment to acquire a spatial map, we found that learning the adjacent arms CCP (ACCP) required a minimum amount of active exploration of the maze with no reinforcers present prior to passive pairing of the extra‐maze cues with the food reinforcer, an instance of latent learning. Temporary inactivation of the hippocampus during the pre‐exposure sessions had no effect on ACCP learning, confirming other evidence that the hippocampus is not involved in latent learning. A series of experiments indentified a circuit involving fimbria‐fornix and dorsal entorhinal cortex as the neural basis of latent learning in this situation. In contrast, temporary inactivation of the entorhinal cortex or hippocampus during passive training or during testing blocked ACCP learning and expression, respectively, suggesting that these two structures co‐operate in using spatial information to learn the location of food on the maze during passive pairing and to express this combined information during testing. In parallel with these processes we found that the amygdala processes information leading to an equal tendency to enter both adjacent arms (even though only one was paired with food) suggesting that the stimulus information available to this structure is not sufficiently precise to discriminate between the ambiguous cues visible from the adjacent arms. Expression of the ACCP in normal rats depends on hippocampus‐based learning to avoid the unpaired arm which competes with the amygdala‐based tendency to enter that arm. In contrast, there is cooperation between amygdala‐ and hippocampus‐based tendencies to enter the food‐paired arm. These independent forms of learning contribute to the rat's ability to discriminate among spatial locations using ambiguous extra‐maze cues. © 2013 Wiley Periodicals, Inc.     

Roles of movement and temporal factors in spatial learning

Previous experiments suggested that rats can learn to discriminate between adjacent arms of an eight-arm radial maze if they have an intact hippocampal system and are allowed to move around on the maze. These requirements are consistent with the hypothesis that this discrimination involves hippocampus-based spatial learning. We examined the importance of self-generated movement in this form of learning by moving rats manually (“passive movement”) between two adjacent maze arms within a single training trial. Rats moved passively between arms (only one of which contained food) within trials learned to discriminate between the arms, as measured by a conditioned preference for the food arm when both arms were empty. This form of learning was impaired by lesions of fimbria-fornix, but was unaffected by lesions of the lateral nucleus of the amygdala. Normal rats that were picked up and replaced on the same arm within trials and experienced their food and no food arms on different daily trials failed to learn the same discrimination. These findings suggest that self-generated movement is not required for spatial learning that may be mediated by a hippocampal system; rather, movement may simply serve to provide information from different locations about the cues in an environment. Hippocampus 1997;7:501–510. © 1997 Wiley-Liss, Inc.     

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

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

Reversible inactivation of hippocampus and dorsolateral striatum in C57BL/6 and DBA/2 inbred mice failed to show interaction between memory systems in these genotypes

C57BL/6 and DBA/2 mice with cannulae inserted bilaterally in the dorsal hippocampus or the dorsolateral striatum were released from the south arm of a cross maze and trained to find food in the east arm. Probe trials on which mice were released from the north arm were given following short or prolonged training. Prior to the probe trials, mice received intra-hippocampal or intra-striatal injections of lidocaine or saline. Results show that saline-injected C57BL/6 were fundamentally place learners whereas saline-injected DBA/2 mice did not engage any predominant system. Inactivating the hippocampus or the dorsolateral striatum in C56BL/6 mice disrupted place learning without promoting response learning. Inactivating the same brain sites in DBA/2 mice did not affect their behaviour. Thus, contrary to that observed in rats, disrupting the neural substrate of one memory system can abolish learning in that system but does not promote the use of another system in these genotypes.     

Intradentate colchicine disrupts the acquisition and performance of a working memory task in the radial arm maze

Rats were given bilateral injections of colchicine into the dorsal and ventral hippocampus to study the role of the dentate gyrus granule cells in the acquisition and performance of a spatial, working memory task in the radial arm maze. Three weeks after intradentate injections, rats were trained in a task in which all eight arms were baited prior to each daily trail. For up to 20 days of training, colchicine-treated rats were significantly impaired in the performance of the task. In another study, rats received 20 days of training and then were given intradentate colchicine. Three weeks later, the performance of the colchicine-treated rats was impaired for up to 20 days of testing. A third experiment tested the ability of colchicine-treated rats to learn a task in which the same four arms of the maze were baited, while the remaining arms were never baited. Colchicine-treated rats were significantly impaired in their ability to perform this version of the task. Histological verification indicated that colchicine resulted in a relatively select loss of granule cells, while sparing pyramidal cells in the hippocampus. These data suggest that the hippocampus plays an integral role in the performance of the place tasks used in these experiments.     

Muscimol injections into the nucleus basalis magnocellularis of rats: selective impairment of working memory in the double Y-maze.

Anatomical and neurochemical results suggest that the cortico- and amygdalopetal cholinergic neurons of the nucleus basalis magnocellularis (NBM) may receive GABAergic inputs. The present experiments were undertaken to evaluate the possible influence of intra-NBM injections of the GABAA agonist, muscimol, on memory. In two experiments, rats were chronically implanted with guide cannulae placed bilaterally into the NBM. Rats were trained to a criterion of at least 83% correct on each component in a double Y-maze task that allowed a dissociation of working and reference memory. The task began with placement into one of the two end arms of the first Y-maze and the reference memory task was to go to the stem for food. Access to the second Y was then given and the working memory task was to go to the goal arm opposite the arm in the first maze from which that trial began. In experiment 1, pre-trained rats (n = 7) received muscimol (0.5 microliter) in doses of 0, 0.01, 0.1 and 1.0 microgram in a counterbalanced order with re-training to criterion between injections. In experiment 2, pre-trained rats (n = 8) received saline, muscimol (0.1 microgram), the GABAA antagonist, bicuculline (0.01 microgram), and muscimol + bicuculline. Results of experiment 1 revealed that intra-NBM muscimol produced a dose-dependent and differential impairment of working and reference memory. A dose of 0.1 microgram impaired working memory without significantly affecting reference memory; doses of 0.01 microgram and 1.0 microgram affected neither and both types of memory, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of injections of glucose into the dorsal striatum on learning of place and response mazes

The present experiment tested the hypothesis that facilitation of striatal function with intra-striatal glucose injections would facilitate learning a striatum-dependent response maze and impair learning a hippocampus-dependent place maze. Food-deprived Sprague-Dawley male rats were trained to find food in a Y-maze. In the place version of the maze, rats were rewarded for learning to go to an arm located in a fixed location while in the response task rats were rewarded for consistently turning in the same direction at the choice point. Artificial cerebrospinal fluid (1 microL) containing either 0.7 nmol of glucose (control) or 20 nmol of glucose was injected bilaterally into the dorsal striatum immediately before training. The animals were trained to a criterion of 9/10 correct choices. In the place maze, glucose injections impaired learning, as measured by number of trials required to reach 9/10 correct. However, in the response task, glucose injections did not enhance learning. A subsequent experiment examined the effects of intra-striatal glucose injections on acquisition of the response task under two different visual cue conditions, addition of an intra-maze light cue that predicted the correct arm or with removal of most visual extramaze cues. Glucose again failed to facilitate acquisition of the response task under these conditions. These findings suggest that facilitation of striatal function via intra-striatal glucose injections is sufficient to impair place learning but not to enhance response learning, perhaps separating the neurochemical mechanisms for striatal involvement in impairment of place and enhancement of response learning.     

Dorsal hippocampal function in unreinforced spatial learning

This study examined learning about the spatial environment by rats during a single 10 min period of exploration on an eight-arm radial maze. Because no specific behaviors were learned during this procedure, the existence of learned spatial information was inferred from its retarding effect on subsequent conditioned cue preference (CCP) learning on the same maze. Previous experiments have shown that this form of spatial learning, measured in this way, requires an intact fimbriafornix and functional N-methyl-D-aspartate receptors. However, in the present experiments, large neurotoxic lesions of the dorsal hippocampus that impaired win-shift learning failed to eliminate the retarding effect of exploration on CCP learning. This result was obtained in three independent replications. These findings fail to confirm the hypothesis that the hippocampus is involved in spatial learning when that learning occurs in the absence of reinforcers and does not produce any specific learned behaviors. Previous work showed that this form of "pure" spatial learning requires an intact fimbria-fornix for acquisition but not for expression; the present findings suggest that the hippocampus is not required for either of these processes. The fimbria-fornix may interact with other temporal lobe structures in mediating this form of learning. The function of the hippocampus may be limited in some way to situations that involve reinforcers and/or situations in which specific behaviors are learned.     

Role of central noradrenaline neurons in the contextual control of latent inhibition in taste aversion learning

Three experiments were performed to examine the effects of noradrenaline (NA) depletion, using 3 different methods: lesions of the dorsal noradrenergic bundle (DB) with 6-hydroxydopamine (6-OHDA), lesions induced by neonatal treatment with 6-OHDA and lesions induced by systemic DSP4 upon latent inhibition, using the taste-aversion learning procedure. NA depleted and control (sham, vehicle or saline) rats were given pre-exposure trials to either novel saccharin or to novel saccharin in a novel type of drinking bottle (the noisy bottle). Later, during conditioning trials saccharin was presented in the noisy bottles for all the rats, followed by lithium chloride injections. Saccharin aversions, tested for in the noisy bottles, indicated considerably weaker saccharin aversions (i.e. more latent inhibition) by the control groups pre-exposed to both saccharin and the noisy bottles. These context-dependent latent inhibition effects were clearly attenuated by all 3 treatments that depleted central NA. Biochemical assays confirmed the NA depletions in each case. The results, demonstrating the intimate role of central NA neurons in contextual control of latent inhibition in taste-aversion learning, appear to conform with current attentional theories of NA function in the forebrain.     

Post-training intra-amygdala amphetamine injections given during acquisition of a stimulus-response (S-R) habit task enhance the expression of stimulus-reward learning: further evidence for incidental amygdala learning

The effect of post-training intra-amygdala amphetamine injections was examined on the acquisition and expression of a visual discrimination task. Rats were trained to enter four lit arms for food (stimulus-response) and avoid unlit arms on an eight-arm radial maze visual discrimination task. Post-training intra-amygdala amphetamine injections (10 microg) were given for 4 consecutive days during the mid-point of training (days 20-23). The number of lit arm entries was used as a measure of stimulus-response habit learning 24 h after each injection. Twenty-four hours after the last injection, a transfer test was run to assess the effect of the same post-training manipulation. This transfer test assessed the amount of time spent in the lit arms and was used as a measure of stimulus-reward learning. Compared to saline-injected rats, rats that received post-training amphetamine spent more time in lit as opposed to dark arms during the transfer test. This occurred in the absence of an increase in the number of correct arm entries during visual discrimination training. This suggests that post-training amphetamine strengthened a stimulus-reward association that did not immediately affect behavioral output. This association may reflect a mnemonic representation stored in an ensemble of amygdala neurons.     

The effects of delaying reward on choice preference in rats with hippocampal or selective septal lesions

Two experiments are reported in which rats were trained to choose one of two goal arms in a Y-maze, for water reward. In one arm, the rats always received water (the continuously reinforced-CRF-arm). In the other arm the rats only sometimes received water (the partially reinforced-PRF-arm). During the critical test phase in both experiments, we delayed the reward in the CRF arm only by 10 s. Experiment 1 tested intact rats given saline injections, or injections of chlordiazepoxide hydrochloride (Librium, 5 mg/kg), and rats with hippocampal or cortical control lesions. When reward was immediate in both arms all rats preferred the CRF arm. Once reward was delayed, the rats with hippocampal lesions switched their preference to the PRF arm, while the rats in the other treatment groups did not. Experiment 2 tested rats with medial septal lesions, lateral septal lesions or control operations in the same way. The rats with medial septal lesions, and to a lesser extent those with lateral septal lesions, switched their preference to the PRF arm when compared to the sham-operated controls. We conclude that damage to the hippocampus or its afferent pathway from the septum increases rats' sensitivity to temporal discontiguities between the outcome of a response and its emission.     

A high‐fat diet impairs learning that is dependent on the dorsal hippocampus but spares other forms of learning

Two experiments were conducted to evaluate the effects of a high‐fat diet (HFD) on two tasks that were either dependent on the dorsal hippocampus (DH) or independent of the DH. A total of 80 adult male Sprague Dawley rats were administered either a lard‐based HFD (60% of calories from fat) or a control diet (10% of calories from fat) for 8 weeks, and then were trained and tested on either the latent cue preference (LCP) task or the conditioned cue preference (CCP) task in a 3‐compartment box apparatus (2 end‐compartments and 1 middle‐compartment). The end compartments of the box apparatus contained either a single environmental cue (DH‐independent) or multiple environmental cues (DH‐dependent). During training trials for the LCP and CCP tasks, on alternating days, rats were given access to water in 1 of the 2 end compartments and no water in the opposite end compartment. Rats were water‐replete during LCP training and were water‐deprived during CCP training. During testing for both tasks, all rats were water‐deprived and given free access to all compartments while the amounts of time spent in each compartment were recorded. Results showed that rats given the HFD demonstrated no compartment preferences during both LCP and CCP testing when the compartments contained multiple cues, while rats fed the control diet demonstrated normal compartment preference behavior. However, when the compartments contained a single environmental cue, rats given either the HFD and control diet demonstrated normal LCP and CCP learning. These results demonstrate that consumption of a HFD disrupted both LCP and CCP learning in a multiple‐cue (DH‐dependent) environment, but did not impair either type of learning in a single‐cue (DH‐independent) environment. This may be due to selective impairment of the DH caused by increased oxidative stress, inflammation, and/or disrupted neurotransmission produced by consumption of the HFD. © 2015 Wiley Periodicals, Inc.     

Intra-hippocampal lidocaine injections impair acquisition of a place task and facilitate acquisition of a response task in rats

While hippocampal lesions impair learning and memory in many tasks, such lesions also enhance learning and memory in other tasks. The present experiment examines the effects of inactivation of the hippocampus with lidocaine prior to learning, to find food in a place or response version of a four-arm plus-shaped maze. Rats received lidocaine injections 6 min prior to training. Rats were trained in a single session to a criterion of 9/10 correct responses. Compared to artificial cerebrospinal fluid (aCSF)-injected controls, rats with intra-hippocampal injections of lidocaine exhibited significantly retarded acquisition of place learning. In marked contrast, rats with intra-hippocampal injections of lidocaine exhibited significantly enhanced acquisition of response learning compared to their controls. In addition to showing that the hippocampus is important for learning the place task, these findings suggest that processing of information by the hippocampus interferes with learning a task dependent on a different neural system.     

Hippocampus is necessary for spatial discrimination using distal cue‐configuration

The role of the hippocampus in processing contextual cues has been well recognized. Contextual manipulation often involves transferring animals between different rooms. Because of vague definition of context in such a paradigm, however, it has been difficult to study the role of the hippocampus parametrically in contextual information processing. We designed a novel task in which a different context can be parametrically defined by the spatial configuration of distal cues. In this task, rats were trained to associate two different configurations of distal cue‐sets (standard contexts) with different food‐well locations at the end of a radial arm. Experiment 1 tested the role of the dorsal hippocampus in retrieving well‐learned associations between standard contexts and rewarding food‐well locations by comparing rats with neurotoxic lesions in the dorsal hippocampus with controls. We found that the hippocampal‐lesioned rats were unable to retrieve the context‐place paired associations learned before surgery. To further test the role of the hippocampus in generalizing altered context, in Experiment 2, rats were trained in a task in which modified versions of the standard contexts (ambiguous contexts) were presented, intermixed with the standard contexts. Rats were able to process the ambiguous contexts immediately by using their similarities to the standard contexts, whereas muscimol inactivation of the dorsal hippocampus in the same animals reversibly deprived such capability. The results suggest that rats can effectively associate discrete spatial locations with spatial configuration of distal cues. More important, rats can generalize or orthogonalize modified contextual environments using learned contextual representation of the environment. © 2010 Wiley‐Liss, Inc.     

Lateralization of motor reactions and formation of behavioural tactics during learning in the eight-arm radial maze in adolescent and adult rats

The problem of motor lateralization in ontogenesis is important for understanding adaptation development. In our experiment adolescent (P28–P30) and adult (P120) rats were trained in an eight-arm radial maze and their motor behaviour compared during training. During learning, the adult rats typically started by moving either left or right direction in the central arena in choosing the way in the maze. The adult rats also developed behavioural tactics to enter maze arms at 45° or 90° relative to the previously visited arm. The adolescent rats showed no directional preference and no clear behavioural tactics when entering maze arms. Based on our findings, we propose that motor lateralization increases the efficacy of food search and leads to the elaboration of behavioural tactics. Data obtained may reflect the fact that motor behaviour specialization develops gradually during ontogenesis and is helpful for adaptation to the environment.     

The anxiolytic effect of chronic inositol depends on the baseline level of anxiety

Inositol, a precursor for membrane phosphoinositides involved in signal transduction, has been found to be clinically effective in a number of psychiatric disorders and to reverse behavioural effects of lithium. To gain insight into the mechanism of action of inositol, it is critical to establish its efficacy in animal models. Following the initial report by Cohen et al. (1997b) that inositol was anxiolytic in the elevated plus maze model of anxiety, the effect of chronic intraperitoneal and chronic dietary inositol administration in rats was tested in four experiments. There was a significant increase in closed arm and total arm entries following chronic injection of inositol, but no effect of inositol when it was given chronically in rat chow. Because the first 2 experiments suggested that the mode of drug administration affected the control levels of anxiety (open arm entries and time in open arms) in control groups, the effect of chronic dietary inositol was tested in rats that were exposed to a mild and a more severe form of stress. Chronic saline injections elevated anxiety in the plus maze, which was only marginally affected by chronic dietary inositol. Following 3 weeks administration of 5% dietary inositol rats were pre-exposed to a cat. There was a clear increase in number of entries into open arms, suggesting an anxiolytic effect of inositol.     

Biological sex influences learning strategy preference and muscarinic receptor binding in specific brain regions of prepubertal rats

According to the theory of multiple memory systems, specific brain regions interact to determine how the locations of goals are learned when rodents navigate a spatial environment. A number of factors influence the type of strategy used by rodents to remember the location of a given goal in space, including the biological sex of the learner. We recently found that prior to puberty male rats preferred a striatum‐dependent stimulus‐response strategy over a hippocampus‐dependent place strategy when solving a dual‐solution task, while age‐matched females showed no strategy preference. Because the cholinergic system has been implicated in learning strategy and is known to be sexually dimorphic prior to puberty, we explored the relationship between learning strategy and muscarinic receptor binding in specific brain regions of prepubertal males and female rats. We confirmed our previous finding that at 28 days of age a significantly higher proportion of prepubertal males preferred a stimulus‐response learning strategy than a place strategy to solve a dual‐solution visible platform water maze task. Equal proportions of prepubertal females preferred stimulus‐response or place strategies. Profiles of muscarinic receptor binding as assessed by autoradiography varied according to strategy preference. Regardless of biological sex, prepubertal rats that preferred stimulus‐response strategy exhibited lower ratios of muscarinic receptor binding in the hippocampus relative to the dorsolateral striatum compared to rats that preferred place strategy. Importantly, much of the variance in this ratio was related to differences in the ventral hippocampus to a greater extent than the dorsal hippocampus. The ratios of muscarinic receptors in the hippocampus relative to the basolateral amygdala also were lower in rats that preferred stimulus‐response strategy over place strategy. Results confirm that learning strategy preference varies with biological sex in prepubertal rats with males biased toward a stimulus‐response strategy, and that stimulus‐response strategy is associated with lower ratios of muscarinic binding in the hippocampus relative to either the striatum or amygdala. © 2012 Wiley Periodicals, Inc.