Learning-associated functional plasticity at hippocampal synapses remains largely unexplored. Here, in a single session of reward-based trace conditioning, we examine learning-induced synaptic plasticity in the dorsal CA1 hippocampus (dCA1). Local field-potential recording combined with selective optogenetic inhibition first revealed an increase of dCA1 synaptic responses to the conditioned stimulus (CS) induced during conditioning at both Schaffer collaterals to the stratum radiatum (Rad) and temporoammonic input to the lacunosum moleculare (LMol). At these dCA1 inputs, synaptic potentiation of CS-responding excitatory synapses was further demonstrated by locally blocking NMDA receptors during conditioning and whole-cell recording sensory-evoked synaptic responses in dCA1 neurons from naive animals. An overall similar time course of the induction of synaptic potentiation was found in the Rad and LMol by multiple-site recording; this emerged later and saturated earlier than conditioned behavioral responses. Our experiments demonstrate a cued memory-associated dCA1 synaptic plasticity induced at both Schaffer collaterals and temporoammonic pathways.
Animals ; CA1 Region, Hippocampal/physiology* ; Male ; Association Learning/physiology* ; Neuronal Plasticity/physiology* ; Cues ; Memory/physiology* ; Synapses/physiology* ; Conditioning, Classical/physiology* ; Excitatory Postsynaptic Potentials/physiology* ; Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors* ; Rats ; Optogenetics

OBJECTIVE: To explore the characteristic changes of the peripheral chorda tympanic nerve (CT) electrophysiological responses to salty stimulus and other taste stimuli in rats with the conditioned taste aversion to saltiness. METHODS: Fourteen adult SD male rats were divided into a conditioned taste aversion to salty group (CTA) and a control group (Ctrl) (n=7/group). On the first day of the experiment, rats were given a 0.1 mol/L NaCl intake for 30 min, then, the rats in CTA and Ctrl groups were injected intraperitoneally with 2 ml of 0.15 mol/L LiCl and the same amount of saline respectively. On day 2, 3 and 4, the 30 min consumption of NaCl and distilled water was measured for both groups of rats. On the 4th day after the behavioral test of that day, CT electrophysiological recording experiments were performed on CTA rats and control rats. RESULTS: Compared with the rats in Ctrl group, the electrophysiological characteristics of CT in CTA group rats did not change significantly the responses to the series of NaCl and other four basic taste stimuli (P＞0.05). The amiloride, the epithelial sodium channel blocker, strongly inhibited the response of CT to NaCl in CTA and Ctrl group rats (P＜0.01). CONCLUSION The electrophysiological responses of CT to various gustatory stimuli do not significantly change in rats after the establishment of conditional taste aversion to the saltiness.
Amiloride ; pharmacology ; Animals ; Chorda Tympani Nerve ; physiology ; Conditioning, Classical ; Electrophysiological Phenomena ; Male ; Rats ; Rats, Sprague-Dawley ; Sodium Chloride ; Taste ; physiology

Rac1 belongs to the family of Rho GTPases, and plays important roles in the brain function. It affects the cell migration and axon guidance via regulating the cytoskeleton and cellular morphology. However, the effect of its dynamic activation in regulating physiological function remains unclear. Recently, a photoactivatable analogue of Rac1 (PA-Rac1) has been developed, allowing the activation of Rac1 by the specific wavelength of light in living cells. Thus, we constructed recombinant adeno-associated virus (AAV) of PA-Rac1 and its light-insensitive mutant PA-Rac1-C450A under the control of the mouse glial fibrillary acidic protein (mGFAP) promoter to manipulate Rac1 activity in astrocytes by optical stimulation. Primary culture of hippocampal astrocytes was infected with the recombinant AAV-PA-Rac1 or AAV-PA-Rac1-C450A. Real-time fluorescence imaging showed that the cell membrane of the astrocyte expressing PA-Rac1 protruded near the light spot, while the astrocyte expressing PA-Rac1-C450A did not. We injected AAV-PA-Rac1 and AAV-PA-Rac1-C450A into dorsal hippocampus to investigate the role of the activation of Rac1 in regulating the associative learning. With optical stimulation, the PA-Rac1 group, rather than the PA-Rac1-C450A group, showed slower learning curve during the fear conditioning compared with the control group, indicating that activating astrocytic Rac1 blocks the formation of contextual memory. Our data suggest that the activation of Rac1 in dorsal hippocampal astrocyte plays an important role in the associative learning.
Animals ; Astrocytes ; physiology ; Cell Membrane ; Cell Movement ; Conditioning, Classical ; Cytoskeleton ; Dependovirus ; Fear ; Hippocampus ; physiology ; Memory ; Mice ; Mice, Inbred C57BL ; Neuropeptides ; genetics ; physiology ; Optogenetics ; rac1 GTP-Binding Protein ; genetics ; physiology

OBJECTIVETry to observe the plasticity of neuron in primary cortex of rat evoked by conditioned stimulus of different sound level.

METHODSApplying conventional electrophysiological technique of extracellular recording to investigate the plasticity of characteristic frequency (CF) and frequency turning curve (FIC) of neurons in rat auditory cortex (AC) by determining CF shifts of neurons caused by sound stimulus of different sound level.

RESULTSWhen the frequency difference between conditioned stimulus (CS) frequency and the CF of neuron was in 1.0 kHz, the plasticity of CF induced by CS was associated with sound level. The probability of the plasticity of CF evoked by CS of higher sound lever was more than the lower. And the probability was dependent on frequency turning curve (FTC) and almost independent on the sound level of conditioned signal.

CONCLUSIONSound level of conditioned stimulus differs the plasticity of characteristic frequency of neurons in rat auditory cortex.

Acoustic Stimulation ; Animals ; Auditory Cortex ; cytology ; Auditory Perception ; physiology ; Conditioning, Classical ; physiology ; Female ; Male ; Neuronal Plasticity ; physiology ; Neurons ; physiology ; Perceptual Masking ; Rats ; Rats, Sprague-Dawley ; Sound

AIMTo inquire a new credible animal model in studies of startle conditioned reflex.

METHODSThrough the trials of combining a conditioned stimulus (a tone) with an unconditioned stimulus(a foot shock), the startle responses were established in animals by conditioned stimulus. Arterial blood pressure were measured before and after blocking basolateral and lateral amygdala with lidocaine.

RESULTSThe blood pressure was increased by the conditioned stimulus after four days training. When the basolateral amygdala was blocked by lidocaine, the blood pressure was not increased by the conditioned stimulus.

CONCLUSIONThe animal model used and verified in this experiment is a new credible chronic animal model in startle conditioned reflex by measuring arterial blood pressure.

Animals ; Arteries ; physiology ; Blood Pressure ; Conditioning, Classical ; physiology ; Female ; Male ; Models, Animal ; Rats ; Rats, Wistar ; Reflex, Startle ; physiology