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International audience; The present work defines a simple behavioral paradigm to evaluate spatial representation in rats. In two experimental conditions differing in the richness of distal visual cues, rats learned to locate a food goal in a cross maze from various starting points. We conducted different challenges consisting of (i) reaching the same goal from a modified arrangement of the maze arms (geometric challenge), (ii) reaching the goal within a 90 degrees rotated maze, herein checking the use of a place strategy, and (iii) investigating the effect of central cholinergic blockade over the retention of the task. Results showed that rats needed 12-30 trials to learn a place response, depending upon the richness of the visual environment. The maze rotation did not produce any impairment whereas the geometric challenge affected the performance specifically under the visually richer environment. Scopolamine injection (i.p.) produced a significant impairment in place recognition. Our present work shows that this maze procedure constitutes a useful paradigm to assess learning and processing of a place representation by rats. Similarly to what has been shown in other popular maze paradigms, our results show that rats mostly rely on distal extra-maze cues to solve the task, but also compute intra-maze information.

Acetylcholine (ACh) is known to shape the adult neocortical activity related to behavioral states and processing of sensory information. However, the impact of cholinergic input on the neonatal neuronal activity remains widely unknown. Early during development, the principal activity pattern in the primary visual (V1) cortex is the intermittent self-organized spindle burst oscillation that can be driven by the retinal waves. Here, we assessed the relationship between this early activity pattern and the cholinergic drive by either blocking or augmenting the cholinergic input and investigating the resultant effects on the activity of the rat visual cortex during the first postnatal weekin vivo. Blockade of the muscarinic receptors by intracerebroventricular, intracortical, or supracortical atropine application decreased the occurrence of V1 spindle bursts by 50%, both the retina-independent and the optic nerve-mediated spindle bursts being affected. In contrast, blockade of acetylcholine esterase with physostigmine augmented the occurrence, amplitude, and duration of V1 spindle bursts. Whereas direct stimulation of the cholinergic basal forebrain nuclei increased the occurrence probability of V1 spindle bursts, their chronic immunotoxic lesion using 192 IgG-saporin decreased the occurrence of neonatal V1 oscillatory activity by 87%. Thus, the cholinergic input facilitates the neonatal V1 spindle bursts and may prime the developing cortex to operate specifically on relevant early (retinal waves) and later (visual input) stimuli.

It is well accepted that populations of neurons responsible for the onset and maintenance of paradoxical sleep (PS) are restricted to the brainstem. To localize the structures involved and to reexamine the role of mesopontine cholinergic neurons, we compared the distribution of Fos- and choline acetyltransferase-labelled neurons in the brainstem of control rats, rats selectively deprived of PS for approximately 72 h and rats allowed to recover from such deprivation. Only a few cholinergic neurons from the laterodorsal (LDTg) and pedunculopontine tegmental nuclei were Fos-labelled after PS recovery. In contrast, a large number of noncholinergic Fos-labelled cells positively correlated with the percentage of time spent in PS was observed in the LDTg, sublaterodorsal, alpha and ventral gigantocellular reticular nuclei, structures known to contain neurons specifically active during PS. In addition, a large number of Fos-labelled cells were seen after PS rebound in the lateral, ventrolateral and dorsal periaqueductal grey, dorsal and lateral paragigantocellular reticular nuclei and the nucleus raphe obscurus. Interestingly, half of the cells in the latter nucleus were immunoreactive to choline acetyltransferase. In contrast to the well-accepted hypothesis, our results strongly suggest that neurons active during PS, recorded in the mesopontine cholinergic nuclei, are in the great majority noncholinergic. Our findings further demonstrate that many brainstem structures not previously identified as containing neurons active during PS contain cholinergic or noncholinergic neurons active during PS, and these structures may therefore play a key role during this state. Altogether, our results open a new avenue of research to identify the specific role of the populations of neurons revealed, their interrelations and their neurochemical identity.