Agnès Gruart

Previous in vitro studies have characterized the electrophysiological properties and molecular events associated with long-term potentiation (LTP), but as yet there are no in vivo data from molecular-level dissection that directly identify LTP as the biological substrate for learning and memory. Understanding whether the molecular pathways required for learning are also those generating LTP when measured directly on the relevant circuit of a learning animal is clearly important, although so far has proved technically difficult. Here, for the first time, we combine highly defined genetic mouse models with behavior and in vivo recordings. We recorded the activity-dependent changes taking place at the CA3-CA1 synapses during the acquisition and extinction of a simple form of an associative learning task in mice carrying point mutations on specific docking sites of TrkB receptors (trkB(SHC), trkB(PLC)). The learning task consisted of a classical eyeblink conditioning using a trace parad...

In mature neurons, the number of synapses is determined by a neuronal activity-dependent dynamic equilibrium between positive and negative regulatory factors. We hypothesized that neuronal pentraxin (NP1), a proapoptotic protein induced by low neuronal activity, could be a negative regulator of synapse density because it is found in dystrophic neurites in Alzheimer's disease-affected brains. Here, we report that knockdown of NP1 increases the number of excitatory synapses and neuronal excitability in cultured rat cortical neurons and enhances excitatory drive and long-term potentiation in the hippocampus of behaving mice. Moreover, we found that NP1 regulates the surface expression of the Kv7.2 subunit of the Kv7 family of potassium channels that control neuronal excitability. Furthermore, pharmacological activation of Kv7 channels prevents, whereas inhibition mimics, the increase in synaptic proteins evoked by the knockdown of NP1. These results indicate that NP1 negatively reg...

The contribution of the orbicularis oculi muscle to the determination of lid position, and the putative role of eyelid proprioception in the control of reflex and conditioned eye blinks, were studied in alert behaving cats. Upper lid movements and the electromyographic activity of the orbicularis oculi muscle were recorded during reflexively evoked blinks and during the classical conditioning of the

Brain ischemia induces neuronal loss which is caused in part by excitotoxicity and free radical formation. Here, we report that mangiferin and morin, two antioxidant polyphenols, are neuroprotective in both in vitro and in vivo models of ischemia. Cell death caused by glutamate in neuronal cultures was decreased in the presence of submicromolar concentrations of mangiferin or morin which in turn attenuated receptor-mediated calcium influx, oxidative stress as well as apoptosis. In addition, both antioxidants diminished the generation of free radicals and neuronal loss in the hippocampal CA1 region due to transient forebrain ischemia in rats when administered after the insult. Importantly, neuroprotection by these antioxidants was functionally relevant since treated-ischemic rats performed significantly better in three hippocampal-dependent behavioral tests. Together, these results indicate that mangiferin and morin have potent neuroprotectant activity which may be of therapeutic val...

The extracellular levels of selected amino acids in the cerebellar posterior interpositus nucleus (PIN) during classical eyeblink conditioning was analyzed in alert cats using a delay paradigm. Animals were prepared for the chronic recording of eyelid movements (with the magnetic search-coil technique) and the electromyographic activity of the orbicularis oculi muscle. With the help of a guide and push–pull cannulae,

The nictitating membrane/eyelid motor system appears to be a suitable experimental model for the study of neural processing underlying the genesis and control of spontaneous, reflex and learned motor acts. A short review of available data regarding the kinematic, time domain, and frequency-domain properties of this motor system is presented. Lid movements seem to be generated by a 20 Hz

This chapter summarizes some of the recent findings regarding the use of the eyelid motor system as a model for the study of reflex and learned motor responses and on the role played by cerebellar structures in the genesis and control of both types of movement. The eyelid motor system of the cat is used for the study of the kinetic properties of reflex and conditioned lid movements and of the role played by the cerebellum in the acquisition and/or performance of both types of motor responses. Spontaneous blinks, eyelid reflex responses, eye-guided lid movements, and conditioned lid responses are recorded in alert cats in simultaneity with unitary and field electrical activity of cerebellar cortex and nuclear zones related to the eyelid motor system. The metric properties of eyeblinks seem to depend largely on the sensory modality used and the precise neural circuits involved in each particular movement. This diversity in eyelid motor responses can only be fully appreciated when lid position is recorded with the search-coil in a magnetic field technique.

Interleukin-10 (IL-10) is a cytokine classically linked with anti-inflammatory and protective functions in the central nervous system (CNS) in different neurodegenerative and neuroinflammatory conditions. In order to study the specific role of local CNS produced IL-10, we have created a new transgenic mouse line with astrocyte-targeted production of IL-10 (GFAP-IL10Tg). In the present study, the effects of local CNS IL-10 production on microglia, astrocytes and neuronal connectivity under basal conditions were investigated using immunohistochemistry, molecular biology techniques, electrophysiology and behavioural studies. Our results showed that, in GFAP-IL10Tg animals, microglia displayed an increase in density and a specific activated phenotype characterised by morphological changes in specific areas of the brain including the hippocampus, cortex and cerebellum that correlated with the level of transgene expressed IL-10 mRNA. Distinctively, in the hippocampus, microglial cells adopted an elongated morphology following the same direction as the dendrites of pyramidal neurons. Moreover, this IL-10-induced microglial phenotype showed increased expression of certain molecules including Iba1, CD11b, CD16/32 and F4/80 markers, "de novo" expression of CD150 and no detectable levels of either CD206 or MHCII. To evaluate whether this specific activated microglial phenotype was associated with changes in neuronal activity, the electrophysiological properties of pyramidal neurons of the hippocampus (CA3-CA1) were analysed in vivo. We found a lower excitability of the CA3-CA1 synapses and absence of long-term potentiation (LTP) in GFAP-IL10Tg mice. This study is the first description of a transgenic mouse with astrocyte-targeted production of the cytokine IL-10. The findings indicate that IL-10 induces a specific activated microglial phenotype concomitant with changes in hippocampal LTP responses. This transgenic animal will be a very useful tool to study IL-10 functions in the CNS, not only under basal conditions, but also after different experimental lesions or induced diseases.

Reelin, an extracellular protein essential for neural migration and lamination, is also expressed in the adult brain. To unravel the function of this protein in the adult forebrain, we generated transgenic mice that overexpress Reelin under the control of the CaMKIIalpha promoter. Overexpression of Reelin increased adult neurogenesis and impaired the migration and positioning of adult-generated neurons. In the hippocampus, the overexpression of Reelin resulted in an increase in synaptic contacts and hypertrophy of dendritic spines. Induction of long-term potentiation (LTP) in alert-behaving mice showed that Reelin overexpression evokes a dramatic increase in LTP responses. Hippocampal field EPSP during a classical conditioning paradigm was also increased in these mice. Our results indicate that Reelin levels in the adult brain regulate neurogenesis and migration, as well as the structural and functional properties of synapses. These observations suggest that Reelin controls developmental processes that remain active in the adult brain.

The activity of deep cerebellar nuclei neurons was recorded in the alert cat and related to the respiratory cycle. Respiration-related neurons (RRNs, n = 29), located in the rostral fastigial and interpositus nuclei, were classified as inspiratory (24%) or expiratory (76%). Nine RRNs were antidromically activated from the red nucleus, but none from the inferior olive. Half of the RRNs showed well defined proprioceptive inputs of a rather broad origin. Other RRNs (27%) showed a respiration-related pattern independent of respiratory movement performance. Repeated electrical stimulation of the inferior olive exerted a synchronizing effect on the firing rate of 24% of the RRNs. It is proposed that cerebellar nuclear RRNs are involved in locomotor re-adjustments of the respiratory musculature.

Learning-related changes in strength in selected hippocampal synapses have been described recently. However, information is scarce regarding the spatial-temporal sequence of changes in synaptic weights taking place during the acquisition of a classical conditioning task and the contribution of both context (environmental details) and cues (conditioned and unconditioned stimuli: CS, US) to those activity-dependent changes. We recorded in rabbits the monosynaptic field excitatory postsynaptic potentials (fEPSPs) evoked at 6 different hippocampal synapses during the acquisition and extinction of a classical eyeblink conditioning using trace or delay paradigms, as well as during pseudoconditioning and in the absence of CS and US presentations (context). Context and pseudoconditioning training evoked early, lasting changes in synaptic strength in perforant pathway synapses in dentate gyrus (PP-DG), and hippocampal CA3 (PP-CA3) and CA1 (PP-CA1) areas. Pseudoconditioning also evoked early, nonlasting changes in strength within the intrinsic hippocampal circuit (CA3-CA1 and CA3-cCA1 synapses). In contrast, during both trace and delay training sessions, synaptic changes in strength were mostly noticed within the intrinsic hippocampal circuit (DG-CA3, CA3-CA1, CA3-cCA1). The response of hippocampal synapses to afferent impulses seems to be modulated by both context and cues during associative learning in behaving rabbits.