Training memory without aversion: Appetitive hole-board spatial learning increases adult hippocampal neurogenesis

The Hole-Board Test in Mutant Mice

First described by Boissier and Simon in (Ther Recreat J 17:1225-1232, 1962), the hole-board has become a recognized test of anxiety and spatial memory. Benzodiazepines acting at the GABA_A-BZD site increase hole-pokes in rats and mice, indicating a loss in behavioral inhibition concordant with the behavior of mutant mice deficient in the GABA transporter. Hole-poking also depends on arousal mechanisms dependent on dopaminergic transmission, as indicated by drug and null mutant studies. In addition, the behavior is modified in natural and null mutants affecting the cerebellum as well as null mutants affecting neuropeptides, growth factors, cell adhesion, and inflammation. Further research is required to determine convergences between genetic and pharmacological effects.

Long-term consequences of alcohol use in early adolescent mice: Focus on neuroadaptations in GR, CRF and BDNF

Our aim was to assess the cognitive and emotional state, as well as related-changes in the glucocorticoid receptor (GR), the corticotropin-releasing factor (CRF) and the brain-derived neurotrophic factor (BDNF) expression of adolescent C57BL/6J male mice after a 5-week two-bottle choice protocol (postnatal day [pd]21 to pd52). Additionally, we wanted to analyse whether the behavioural and neurobiological effects observed in late adolescence (pd62) lasted until adulthood (pd84). Behavioural testing revealed that alcohol during early adolescence increased anxiety-like and compulsive-related behaviours, which was maintained in adulthood. Concerning cognition, working memory was only altered in late adolescent mice, whereas object location test performance was impaired in both ages. In contrast, novel object recognition remained unaltered. Immunohistochemical analysis showed that alcohol during adolescence diminished BDNF+ cells in the cingulate cortex, the hippocampal CA1 layer and the central amygdala. Regarding hypothalamic-pituitary-adrenal axis (HPA) functioning, alcohol abuse increased the GR and CRF expression in the hypothalamic paraventricular nucleus and the central amygdala. Besides this, GR density was also higher in the prelimbic cortex and the basolateral amygdala, regardless of the animals' age. Our findings suggest that adolescent alcohol exposure led to long-term behavioural alterations, along with changes in BDNF, GR and CRF expression in limbic brain areas involved in stress response, emotional regulation and cognition.

The 4-Hole-Board Test for Assessment of Long-Term Spatial Memory in Mice

The hole-board test has been used in rodents since the early 60s to measure exploratory behavior, locomotor activity and cognitive function. The test is based on rodents' natural curiosity and attraction for novelty. Basically, the hole-board consists of a small square arena with an extractable platform as floor, which has a set of equally spaced circular holes on its surface. In this article, we describe the protocol of a 4-hole-board test allowing the assessment of long-term spatial memory in mice without the employment of water or food restriction, painful stimuli (as electrical shocks) or any aversive condition (as forced swimming or exposure to intense light). Four holes are present on the floor of the square arena (one for each of its four quadrants). Mice released in the arena spontaneously approach the holes and explore them by briefly inserting the snout inside, a behavior defined as nose-poking (or head-dipping). If, after 24 hr, rodents are re-exposed to the hole-board, the novelty of the holes decreases. Animals with an intact long-term memory will show a reduction of the frequency of nose-poking into the holes. The total number of nose-pokes on day 1 is an index of exploration, while the percentage of decrease in nose-poking on day 2 represents an index of long-term spatial memory. Number of quadrant crossings is scored as a control measure for locomotor activity, which with the present protocol should remain stable across the days of testing. Indeed, the 4-hole-board test represents a stress-free and animal-friendly option to evaluate long-term spatial memory. In the present paper, we provide detailed description of the hole-board apparatus and step-by-step protocol for assessment of spatial memory in mice. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Validation of the 4-hole-board Basic Protocol 2: Evaluation of long-term spatial memory through the 4-hole-board test.

The presence of a social stimulus reduces cocaine-seeking in a place preference conditioning paradigm

BACKGROUND

One challenge in the treatment of substance use disorders is to re-engage the interest toward non-drug-related activities. Among these activities, social interaction has had a prominent role due to its positive influence on treatment outcome.

AIMS AND METHODS

Our aim was to study whether the presence of a social stimulus during the cocaine-induced conditioned place preference test was able to reduce the time spent in the drug-paired compartment. For that purpose, mice were trained for four days on a conditioned place preference task with one compartment paired with cocaine and the opposite with saline. On the test day, we introduced an unfamiliar juvenile male mouse into the saline-conditioned compartment (inside a pencil cup) to analyse the animal preference towards the two rewarding stimuli (cocaine vs mouse). Additionally, to discard the possible effect of novelty, as well as the housing condition (social isolation) on social preference, we decided to include a novel object during the test session, as well as perform the same conditioned place preference protocol with a group of animals in social housing conditions.

RESULTS

The social stimulus was able to reduce the preference for cocaine and enhance the active interaction with the juvenile mouse (sniffing) compared to the empty pencil cup paired with the drug. The introduction of a novel object during the test session did not reduce the preference for the cocaine-paired compartment, and interestingly, the preference for the social stimulus was independent of the housing condition. c-Fos immunohistochemistry revealed a different pattern of activation based on cocaine-paired conditioning or the presence of social stimulus.

CONCLUSIONS

These results suggest that social interaction could constitute a valuable component in the treatment of substance use disorders by reducing the salience of the drug.

Where to place the rewards? Exploration bias in mice influences performance in the classic hole-board spatial memory test

The classic hole-board paradigm (a square arena with 16 holes arranged equidistantly in a 4 × 4 pattern) assesses both exploration and spatial memory in rodents. For spatial memory training, food rewards are hidden in a fixed set of holes. The animal must not visit (i.e. nose-poke) the holes that are never baited (reference memory; RM) nor re-visit a baited hole within a session (working memory; WM). However, previous exploratory bias may affect performance during reward searching. During habituation sessions with either all holes rewarded or all holes empty, mice intrinsically preferred poking peripheral holes (especially those located in the maze's corners) over centre holes. During spatial memory training, mice progressively shifted their hole pokes and staying time to the central area that contained hidden rewards, while mice exposed to the empty apparatus still preferred the periphery. A group of pseudotrained mice, for whom rewards were located randomly throughout the maze, also increased their central preference. Furthermore, reward location influenced memory measures. Most repeated pokes (WM-errors) were scored in the locations that were most intrinsically appealing to mice (i.e. the corner and wall-baited holes), supporting a strong influence of previous exploratory bias. Regarding RM, finding rewards located in the centre holes, which were initially less preferred, entailed more difficulty and required more trials to learn. This outcome was confirmed by a second experiment that varied the pattern of rewarded holes, as well as the starting positions. Therefore, reward location is a relevant aspect to consider when designing a hole-board memory task.

Donepezil improves the cognitive impairment in a tree shrew model of Alzheimer's disease induced by amyloid-β1-40 via activating the BDNF/TrkB signal pathway

Alzheimer's disease (AD) is a chronic neurodegenerative disorder which can contribute to memory loss and cognitive damage in the elderly; moreover, evidence from clinical and animal studies demonstrated that AD always exhibit severe cognitive deficits. However, the effects of donepezil medications on cognition are controversial. Additionally, it is unclear whether donepezil can protect neurons to improve cognitive function through the brain-derived neurotropic factor (BDNF)/tyrosine receptor kinase B (TrkB) signalling pathway in the tree shrew (TS), which has a closer evolutionary relationship to primates than rodents. Here, we designed a study on an amyloid-β_1-40 (Aβ_1-40)-induced TS model of AD and investigated the molecular mechanism by which donepezil protects neurons and improves cognitive function through activating the BDNF/TrkB signalling pathway. The results showed that donepezil could rescue Aβ_1-40-induced spatial cognition deficits, and reverse Aβ_1-40-induced temporal horn along with ADC enlargement in the TS brain. Meanwhile, it suppressed Aβ_1-40-induced neuronal damage and loss of body weight. Intriguingly, donepezil could increase the choline acetyl transferase (ChAT) expression level and reduce the fibrillary acid protein (GFAP) expression level in the hippocampus and cortex of TS. Additionally, donepezil significantly upregulated the expression level of BDNF, as well as the phosphorylated level of TrkB. These results suggested that donepezil could protect neurocytes from senility and ameliorate learning and memory impairment in the TS model of AD, which appeared to be through regulating the cholinergic system and inhibiting the BDNF/TrkB-dependent signalling pathway. Moreover, the study underlines the potency of TS to be a novel animal model for research on AD, and it deserves intensive attention.