Examining the non-spatial pretraining effect on a water maze spatial learning task in rats treated with multiple intracerebroventricular (ICV) infusions of propionic acid: Contributions to a rodent model of ASD.

Propionic acid (PPA) is produced by enteric gut bacteria and is a dietary short chain fatty acid. Intracerebroventricular (ICV) infusions of PPA in rodents have been shown to produce behavioural changes, including adverse effects on cognition, similar to those seen in autism spectrum disorders (ASD). Previous research has shown that repeated ICV infusions of PPA result in impaired spatial learning in a Morris water maze (MWM) as evidenced by increased search latencies, fewer direct and circle swims, and more time spent in the periphery of the maze than control rats. In the current study rats were first given non-spatial pretraining (NSP) in the water maze in order to familiarize the animals with the general requirements of the non-spatial aspects of the task before spatial training was begun. Then the effects of ICV infusions of PPA on acquisition of spatial learning were examined. PPA treated rats failed to show the positive effects of the non-spatial pretraining procedure, relative to controls, as evidenced by increased search latencies, longer distances travelled, fewer direct and circle swims, and more time spent in the periphery of the maze than PBS controls. Thus, PPA treatment blocked the effects of the pretraining procedure, likely by impairing sensorimotor components or memory of the pretraining.

Propionic acid induced behavioural effects of relevance to autism spectrum disorder evaluated in the hole board test with rats.

Autism spectrum disorders (ASD) are a set of neurodevelopmental disorders characterized by abnormal social interactions, impaired language, and stereotypic and repetitive behaviours. Among genetically susceptible subpopulations, gut and dietary influences may play a role in etiology. Propionic acid (PPA), produced by enteric gut bacteria, crosses both the gut-blood and the blood-brain barrier. Previous research has demonstrated that repeated intracerebroventricular (ICV) infusions of PPA in adult rats produce behavioural and neuropathological changes similar to those seen in ASD patients, including hyperactivity, stereotypy, and repetitive movements. The current study examined dose and time related changes of exploratory and repetitive behaviours with the use of the hole-board task. Adult male Long-Evans rats received ICV infusions twice a day, 4 h apart, of either buffered PPA (low dose 0.052 M or high dose 0.26 M, pH 7.5, 4 µL/infusion) or phosphate buffered saline (PBS, 0.1 M) for 7 consecutive days. Locomotor activity and hole-poke behaviour were recorded daily in an automated open field apparatus (Versamax), equipped with 16 open wells, for 30 min immediately after the second infusion. In a dose dependent manner PPA infused rats displayed significantly more locomotor activity, stereotypic behaviour and nose-pokes than PBS infused rats. Low-dose PPA animals showed locomotor activity levels similar to those of PBS animals at the start of the infusion schedule, but gradually increased to levels comparable to those of high-dose PPA animals by the end of the infusion schedule, demonstrating a dose and time dependent effect of the PPA treatments.

Impaired Spatial Cognition in Adult Rats Treated with Multiple Intracerebroventricular (ICV) Infusions of the Enteric Bacterial Metabolite, Propionic Acid, and Return to Baseline After 1 Week of No Treatment: Contribution to a Rodent Model of ASD.

Propionic acid (PPA) is a dietary short chain fatty acid and an enteric bacterial metabolite. Intracerebroventricular (ICV) infusions of PPA in rodents have been shown to produce behavioral changes similar to those seen in autism spectrum disorders (ASD), including perseveration. The effects of ICV infusions of PPA on spatial cognition were examined by giving rats infusions of either PPA (0.26 M, pH 7.4, 4 µl/infusion) or phosphate-buffered saline (PBS, 0.1 M) twice a day for 7 days. The rats were then tested in the Morris water maze (MWM) for acquisition of spatial learning. After a recovery period of 1 week of no treatment, the rats were then tested for reversal of spatial learning in the MWM. PPA-treated rats showed impaired spatial learning in the maze, relative to controls, as demonstrated by increased search latencies, fewer direct and circle swims, and more time spent in the periphery of the maze than PBS controls. After a recovery period of 1 week of no treatment, these animals exhibited normal spatial reversal learning indicating that the behavioral cognitive deficits caused by PPA seem to be reversible.

Long-lasting auditory gating deficit accompanied by GABA(B) receptor dysfunction in the hippocampus after early-life limbic seizures in rats.

In a previous study, we reported a rat model of early-life limbic seizures which resulted in a loss of GABA(B) receptor inhibition in the hippocampus. Since gating of auditory evoked potentials in the hippocampus (auditory gating) requires GABA(B) receptors and spatial behaviors depend on the hippocampus, we hypothesize that rats with early-life limbic seizures manifest deficits of auditory gating and spatial behaviors. Seizure rats were given a single injection of GABA(B) receptor antagonist CGP56999A (1-1.2 mg/kg i.p.) on postnatal day (PND) 15, which induced multiple limbic seizures in 8h; control rats were given saline injection. When tested at 3-9 weeks after seizure/control treatment, seizure as compared to control rats showed no difference in finding a hidden platform in the water maze, but were deficient in learning and maintaining consecutive criterion performance in the 8-arm radial arm maze. Auditory gating, as measured by paired-click (conditioning followed by test click) average auditory evoked potentials in the hippocampus, revealed a significant difference between seizure rats and controls. Seizure as compared to control rats showed an increased ratio of the test to conditioning click response as adolescents (50 days old) or adults (70 days old). Heterosynaptic electric paired-pulse depression of hippocampal population excitatory postsynaptic potential in freely moving rats, a measure of hippocampal GABA(B)-receptor mediated inhibition, was decreased in seizure as compared to control rats. Seizure as compared to control rats showed increased locomotor activity in a novel open field for the first 10 min, and decreased activity at 15-60 min. However, auditory prepulse inhibition, a measure of sensorimotor gating, revealed no difference between seizure and control rats. In conclusion, early-life limbic seizures induced a long-lasting deficit in auditory gating, likely caused by GABA(B) receptor-mediated inhibition loss in the hippocampus. Auditory gating loss is a symptom of schizophrenia, and thus GABA(B) receptor inhibition loss in the hippocampus provides a mechanism linking early-life seizures to a psychiatric symptom.

Effects of the enteric bacterial metabolic product propionic acid on object-directed behavior, social behavior, cognition, and neuroinflammation in adolescent rats: Relevance to autism spectrum disorder.

Recent evidence suggests that a variety of environmental factors, including dietary and gastrointestinal agents, may contribute to autism spectrum disorders (ASD). Here we administered propionic acid (PPA), a short chain fatty acid that is used as a food preservative and also is a metabolic end-product of enteric bacteria in the gut, to adolescent (41 ± 4 days) male rats in a study of restricted/repetitive behavior, social behavior, and cognition. The goal was to further evaluate the effects of PPA in young rodents. PPA (4 µl of 0.26 M solution) was administered intracerebroventricularly prior to each behavioral test. Rats treated with PPA displayed restricted behavioral interest to a specific object among a group of objects, impaired social behavior, and impaired reversal in a T-maze task compared to controls given phosphate buffered saline. Immunohistochemical analysis of brain tissue from PPA rats revealed reactive astrogliosis and activated microglia, indicating an innate neuroinflammatory response. These findings are consistent with our earlier findings of ASD-relevant behavioral and brain events in adult rats given PPA, and support further study of effects of PPA in young rodents by establishing similar effects in adolescent animals.

Intracerebroventricular injections of the enteric bacterial metabolic product propionic acid impair cognition and sensorimotor ability in the Long-Evans rat: further development of a rodent model of autism.

Propionic acid (PPA) is a dietary short chain fatty acid and a metabolic end-product of enteric bacteria. Intracerebroventricular (ICV) injections of PPA can result in brain and behavioral abnormalities in rats similar to those seen in humans suffering from autism. To evaluate cognition and sensorimotor ability in the PPA model, male Long-Evans hooded rats received ICV injection of PPA or control compounds prior to behavioral testing in water maze and beam tasks. Compared to controls, PPA-treated rats were impaired in the water maze task as indicated by an unusual pattern of mild or no impairment during spatial acquisition training, but marked impairment during spatial reversal training. PPA-treated rats were also impaired on the beam task. Neuropathological analysis from PPA-treated rats revealed an innate neuroinflammatory response. These findings add to evidence that PPA can change the brain and behavior in the laboratory rat consistent with symptoms of human autism.

Combined but not individual administration of beta-adrenergic and serotonergic antagonists impairs water maze acquisition in the rat.

This study examined the effects of serotonergic depletion and beta-adrenergic antagonism on performance in both visible platform and hidden platform versions of the water maze task. Male Long-Evans rats received systemic injections of p-chlorophenylalanine (500 mg/kg x 2) to deplete serotonin, or propranolol (20 or 40 mg/kg) to antagonize beta-adrenergic receptors. Some rats received treatments in combination. To separate strategies learning from spatial learning, half of the rats underwent Morris' water maze strategies pretraining before drug administration and spatial training. Individual depletion of serotonin or antagonism of beta-adrenergic receptors caused few or no impairments in either naive or pretrained rats in either version of the task. In contrast, combined depletion of serotonin and antagonism of beta-adrenergic receptors impaired naive rats in the visible platform task and impaired both naive and strategies-pretrained rats in the hidden platform task, and also caused sensorimotor impairments. This is the first finding of a 'global' water maze task/sensorimotor impairment with combined administration of two agents that, at the high doses that were given individually, produced few or no impairments. The data imply that (1) serotonergic and beta-adrenergic systems may interact in a manner that is important for adaptive behavior; (2) impairments in these systems found in Alzheimer patients may be important for their cognitive and behavioral impairments; and (3) the approach used here can model aspects of the cognitive and behavioral impairments in Alzheimer disease.

Neurobiological effects of intraventricular propionic acid in rats: possible role of short chain fatty acids on the pathogenesis and characteristics of autism spectrum disorders.

Clinical observations suggest that certain gut and dietary factors may transiently worsen symptoms in autism spectrum disorders (ASD), epilepsy and some inheritable metabolic disorders. Propionic acid (PPA) is a short chain fatty acid and an important intermediate of cellular metabolism. PPA is also a by-product of a subpopulation of human gut enterobacteria and is a common food preservative. We examined the behavioural, electrophysiological, neuropathological, and biochemical effects of treatment with PPA and related compounds in adult rats. Intraventricular infusions of PPA produced reversible repetitive dystonic behaviours, hyperactivity, turning behaviour, retropulsion, caudate spiking, and the progressive development of limbic kindled seizures, suggesting that this compound has central effects. Biochemical analyses of brain homogenates from PPA treated rats showed an increase in oxidative stress markers (e.g., lipid peroxidation and protein carbonylation) and glutathione S-transferase activity coupled with a decrease in glutathione and glutathione peroxidase activity. Neurohistological examinations of hippocampus and adjacent white matter (external capsule) of PPA treated rats revealed increased reactive astrogliosis (GFAP immunoreactivity) and activated microglia (CD68 immunoreactivity) suggestive of a neuroinflammatory process. This was coupled with a lack of cytotoxicity (cell counts, cleaved caspase 3' immunoreactivity), and an increase in phosphorylated CREB immunoreactivity. We propose that some types of autism may be partial forms of genetically inherited or acquired disorders involving altered PPA metabolism. Thus, intraventricular administration of PPA in rats may provide a means to model some aspects of human ASD in rats.

Retrosplenial cortex lesions impair water maze strategies learning or spatial place learning depending on prior experience of the rat.

There has been debate whether lesions strictly limited to retrosplenial (RS) cortex impair spatial navigation, and how robust and reliable any such impairment is. The present study used a detailed behavioral analysis with naive or strategies-pretrained rats given RS lesions and trained in a water maze (WM). Naive RS lesioned rats failed to acquire the required WM strategies throughout training. Strategies-pretrained RS lesioned rats were specifically impaired in spatial place memory without a WM strategies impairment. Additional training overcame the spatial memory impairment. Thus the behavioral consequences of the lesion depend on the specific previous experience of the animal. The use of appropriate training and testing techniques has revealed experience-dependant dissociable impairments in WM strategies learning and in spatial memory, indicating that RS cortex is involved in both forms of learning.

Thalamic and hippocampal mechanisms in spatial navigation: a dissociation between brain mechanisms for learning how versus learning where to navigate.

Various studies of hippocampus and medial thalamus (MT) suggest that these brain areas play a crucial, marginal, or no essential role in spatial navigation. These divergent views were examined in experiments using electrolytic Lesions of fimbria-fornix (FF) or radiofrequency or neurotoxic Lesions of MT of rats subsequently trained to find a stable visible (experiment 1) or hidden platform (experiments 2 and 3) in a water maze (WM) pool. Rats with electrolytic Lesions of FF or radiofrequency Lesions of MT were impaired in swimming to a stable visible platform, particularly the MT Lesion Group, suggesting impairment of WM strategies acquisition. Additional Lesioned rats were then tested in a hidden platform version of the WM task. Some rats were given Morris's nonspatial pretraining prior to Lesioning to provide them with training in the required WM behavioral strategies. Nonspatially Pretrained rats with FF Lesions eventually were able to navigate to the hidden platform, but the accuracy of place responding was impaired. This impairment occurred without problems in the motoric control of swimming or the use of WM behavioral strategies, suggesting that these rats had a spatial mapping impairment. Radiofrequency MT Lesions blocked acquisition of WM behavioral strategies by Naive rats throughout 3 days of training, severely impairing performance on all aspects of the hidden platform task. Nonspatially Pretrained rats given the same MT Lesions readily learned the hidden platform location and were indistinguishable from controls throughout spatial training. Rats given neurotoxic Lesions of MT for removal of cells were only mildly impaired and improved considerably during training, suggesting an important role for fibers of passage in WM strategies learning. The results provide a clear dissociation between a role for MT in learning WM behavioral strategies and the hippocampal formation in spatial mapping and memory. This is the first identification of a brain area, MT, that is essential for learning behavioral strategies that by themselves do not constitute the solution to the task but are necessary for the successful use of an innate learning ability: place response learning using spatial mapping.

Contribution of sex differences in the acute stress response to sex differences in water maze performance in the rat.

Male rats outperform females in spatial tasks, such as the water maze (WM). Female rats are known to have higher basal serum corticosterone (CORT) levels and to manifest a more rapid and stronger CORT response to novel stressors. Sex differences in stress responses to the handling and forced swimming in the WM task might contribute to the sex difference in WM performance. In Experiment 1, naive females were found to be impaired relative to naive males in swimming to a visible platform in a WM pool due to strongly thigmotaxic swimming by females. In Experiment 2, serum CORT, a physiological measure of stress, was highly elevated during and after WM training, with female > male values and strong inverse correlations between CORT and measures of WM performance in females. Familiarization with the WM pool and test procedures by strategies pretraining prior to spatial training reduced or eliminated the sex differences in the stress response and WM performance. In Experiment 3, adrenalectomy to eliminate the stress response eliminated sex differences in WM performance. Taken together, the results suggest that male and female rats may harbor brain circuitry that is equally capable of accurate spatial navigation and memory in the WM but which may be impaired to different degrees by the differential stress responses triggered by WM testing.

Detailed behavioral analysis reveals both task strategies and spatial memory impairments in rats given bilateral middle cerebral artery stroke.

Middle cerebral artery occlusion (MCAO) impairs performance in the water maze task by rats. The purpose was to evaluate the effect of bilateral MCAO in naive and strategies-pretrained rats using a detailed behavioral analysis to further develop a water maze model of stroke. Rats were trained in either a simple swim-to-visible platform task or in a conventional spatial version with a hidden platform in the pool. In the visible platform task naive stroked rats were impaired because of a marked tendency to swim thigmotaxically on most trials. For the spatial learning experiment, some rats received Morris' water maze strategies pretraining prior to MCAO and subsequent spatial training to familiarize them with the general behavioral strategies required in the task. In the spatial learning task naive stroked rats had both strategies and spatial learning impairments but pretrained stroked rats were indistinguishable from sham controls on all behavioral measures. All stroked rats had comparable bilateral brain damage measured using a computerized volumetric measuring technique. These results indicate that in naive rats bilateral MCAO causes behavioral strategies impairments in the visible and hidden platform versions of the water maze as well as specific spatial learning impairments in the hidden platform version. The results also indicate that behavioral strategies pretraining allows stroked rats to acquire and remember sufficient strategies skills and spatial information to perform as well as sham controls during subsequent spatial training. These techniques appear to be capable of quantifying the effects of potentially protective treatments for stroke.

Methamphetamine exposure from postnatal day 11 to 20 causes impairments in both behavioral strategies and spatial learning in adult rats.

Spatial learning and memory deficits in a water maze have been observed in adult animals exposed to a regimen of 4 daily doses of d-methamphetamine (MA) at 2 h intervals from postnatal day 11 to 20. An interpretational issue for these long-term effects of MA is whether they are truly spatial deficits or are secondary to alterations in sensorimotor systems. In this experiment, we evaluated the effects of a pretraining procedure shown to minimize the influence of drug-induced sensorimotor deficits. Animals within a litter were treated with MA or saline. Animals were either pretrained for nonspatial task requirements in the water maze (i.e., swimming and platform climbing) or were nai;ve to the task. Animals that received the pretraining did better than the nai;ve animals. The nai;ve MA animals performed worse than the nai;ve control animals as previously observed. By contrast, no difference in search time was noted between pretrained MA- and SAL-treated animals during the acquisition phase of testing. When the platform was relocated in a novel position, spatial learning was impaired for MA animals, regardless of pretraining. No increase in the number of platform nonrecognition events (swimovers, deflections, or jump-offs) occurred among pretrained or nai;ve groups compared to controls. These data suggest that sensorimotor deficits do not account for the spatial learning and memory deficits in animals exposed neonatally to MA.