Tactile learning in rodents: Neurobiology and neuropharmacology

Comparative Genomics Provides Insights into Adaptive Evolution in Tactile-Foraging Birds

Tactile-foraging birds have evolved an enlarged principal sensory nucleus (PrV) but smaller brain regions related to the visual system, which reflects the difference in sensory dependence. The “trade-off” may exist between different senses in tactile foragers, as well as between corresponding sensory-processing areas in the brain. We explored the mechanism underlying the adaptive evolution of sensory systems in three tactile foragers (kiwi, mallard, and crested ibis). The results showed that olfaction-related genes in kiwi and mallard and hearing-related genes in crested ibis were expanded, indicating they may also have sensitive olfaction or hearing, respectively. However, some genes required for visual development were positively selected or had convergent amino acid substitutions in all three tactile branches, and it seems to show the possibility of visual degradation. In addition, we may provide a new visual-degradation candidate gene PDLIM1 who suffered dense convergent amino acid substitutions within the ZM domain. At last, two genes responsible for regulating the proliferation and differentiation of neuronal progenitor cells may play roles in determining the relative sizes of sensory areas in brain. This exploration offers insight into the relationship between specialized tactile-forging behavior and the evolution of sensory abilities and brain structures.

A case of visuo-auditory sensory substitution in rats

Sensory substitution refers to a process whereby an agent, by means of a removable specialized instrumentation, becomes capable of exploiting an available sensory modality in order to perceive properties of the environment which are normally accessible by means of a different modality. We describe a situation of visual-auditory sensory substitution in the rat. Rats were placed in complete darkness, and trained to follow a virtual path whose position was signalled by a sound activated by a video-tracking device. Our hypothesis was that the rats would be able to succeed in this task of spatial navigation, following the sound contour by means of sensory-motor coupling based on seeking the sound (all-or-none) and mastering the relation between their own actions and the expected sensory feedback. Our results confirm this hypothesis and show the progressive structuring of meaningful exploratory activity, leading from the appearance of stopping behaviour when the sound is lost or acceleration when the sound is discovered, up to a veritable sensory-motor strategy which maximizes the possibilities for discovering and following the sound path. Thus, the animals seem to have developed a new form of perception which translates in particular into motor behaviour adapted to the search for sound.

A Novel Method for Training Mice in Visuo-Tactile 3-D Object Discrimination and Recognition

Perceiving, recognizing and remembering 3-dimensional (3-D) objects encountered in the environment has a very high survival value; unsurprisingly, this ability is shared among many animal species, including humans. The psychological, psychophysical and neural basis for object perception, discrimination, recognition and memory has been extensively studied in humans, monkeys, pigeons and rodents, but is still far from understood. Nearly all 3-D object recognition studies in the rodent used the "novel object recognition" paradigm, which relies on innate rather than learned behavior; however, this procedure has several important limitations. Recently, investigators have begun to recognize the power of behavioral tasks learned through reinforcement training (operant conditioning) to reveal the sensorimotor and cognitive abilities of mice and to elucidate their underlying neural mechanisms. Here, we describe a novel method for training and testing mice in visual and tactile object discrimination, recognition and memory, and use it to begin to examine the underlying sensory basis for these cognitive capacities. A custom-designed Y maze was used to train mice to associate one of two 3-D objects with a food reward. Out of nine mice trained in two cohorts, seven reached performance criterion in about 20-35 daily sessions of 20 trials each. The learned association was retained, or rapidly re-acquired, after a 6 weeks hiatus in training. When tested under low light conditions, individual animals differed in the degree to which they used tactile or visual cues to identify the objects. Switching to total darkness resulted only in a transient dip in performance, as did subsequent trimming of all large whiskers (macrovibrissae). Additional removal of the small whiskers (microvibrissae) did not degrade performance, but transiently increased the time spent inspecting the object. This novel method can be combined in future studies with the large arsenal of genetic tools available in the mouse, to elucidate the neural basis of object perception, recognition and memory.

The effect of the anti-diabetic drug metformin on behavioral manifestations associated with ovariectomy in mice

The aim of this study was to evaluate the anti-diabetic drug metformin (Met) effects on the anxiety and cognitive impairment in ovariectomized mice. Thirty-two female adult mice were distributed into four groups: control, sham ovariectomy, ovariectomy + Met 7 mg/kg and ovariectomy + Met 15 mg/kg. The vaginal cytology was used to confirm the ovariectomy surgery. Anxiety was monitored using elevated plus maze test and cognitive function was assessed by novel object recognition task. Animal's brains were analyzed for the brain-derived neurotrophic factor (BDNF). Our results demonstrated that ovariectomy caused cognitive impairments and anxiety, as well as decreased BDNF levels. Moreover, administration of Met improves ovariectomy-related disorders such as cognitive impairments and anxiety, as well as increased BDNF levels. The results of the present study suggest that Met could be used as a novel therapeutic strategy for the treatment of ovariectomy-related conditions.

Protective effect of atorvastatin on d-galactose-induced aging model in mice

Atorvastatin (Ator), competitive inhibitors of 3-hydroxymethyl-3-glutaryl-coenzyme-A reductase, is a cholesterol lowering drug. Ator has been shown to have neuroprotective, antioxidant and anti-inflammatory properties making that a potential candidate for the treatment of central nervous system (CNS) disorders. Here we assessed the effect of Ator on the d-galactose (d-gal)-induced aging in mice. For this purpose, Ator (0.1 and 1mg/kg/p.o.), was administrated daily in d-gal-received (500mg/kg/p.o.) mice model of aging for six weeks. Anxiety-like behaviors and cognitive functions were evaluated by the elevated plus-maze and novel object recognition tasks, respectively. Physical power was assessed by forced swimming capacity test. Animals brains were analyzed for the superoxide dismutase (SOD) and brain-derived neurotrophic factor (BDNF). We found that Ator decreases the anxiety-like behaviors in d-gal-treated mice. Also, our behavioral tests showed that Ator reverses the d-gal induced learning and memory impairment. Furthermore, we found that Ator increases the physical power of d-gal-treated mice. Our results indicated that the neuroprotective effect of Ator on d-gal induced neurotoxicity is mediated, at least in part, by an increase in the SOD and BDNF levels. The results of present study suggest that Ator could be used as a novel therapeutic strategy for the treatment of age-related conditions.