In vivo synaptic transmission in the zebra finch high vocal center and robust nucleus of the arcopallium after different stimulus patterns

BACKGROUND： Electrophysiological studies using brain slices have revealed that the developmental regulation of synaptic plasticity in vocal learning pathway is essential for song learning in zebra finches. Publications reporting in vivo electrophysiological investigation are scarce. Many aspects of neural mechanisms underlying song learning and production still remain uncertain. OBJECTIVE： To observe the efficacy of paired pulses and the effect on synaptic transmission induced by low-frequency stimulations, high-frequency stimulations, and theta-burst stimulations. DESIGN, TIME AND SETTING： A comparative observation. The experiment was conducted from October 2006 to October 2007 in the Neurophysiology Laboratory of South-China Normal University. MATERIALS： Twenty-four adult male zebra finches were supplied by the Department of Animal Experiment of College of Life Sciences, South China Normal University. A SEN-7203 stimulator （NIHON KOHDEN）, as well as a DSJ-731WF microelectrode amplifier and DSJ-F amplifier （provided by South-China Normal University）, were used to stimulate and record, respectively. METHODS： Animals were randomly divided into low-frequency, high-frequency, and theta-burst frequency stimulation groups. After recording evoked potentials, an input-output curve was evaluated. Subsequently, the efficacy of paired pulses with different stimulus intensity （1/3, 1/2, 2/3, or 3/4 of the value that induced the largest synaptic response）, as well as interpulse intervals （50, 75, and 100 ms）, was measured in each group. The test stimulus intensity was set to a level that evoked 1/2 or 1/3 amplitude of the maximum response. MAIN OUTCOME MEASURES： Changes in amplitude, slope, and area of evoked potentials elicited by different stimulus patterns. RESULTS： （1） Efficacy of paired pulses： there was significant paired-pulse facilitation in the high vocal center and robust nucleus of the arcopallium （HVC-RA） synapse. Efficacy decreased when paired-pulse intervals or stimulus intensities were increased. （2） Low-frequency stimulations at 1 Hz had a negligible effect on efficacy of synaptic transmission, while 5 Hz depressed synaptic transmission for only 5 minutes. （3） High-frequency stimulations at 50 Hz or 100 Hz induced synaptic depression that lasted for up to 30 minutes. （4） Theta-burst stimulation depressed synaptic transmission efficiency significantly for about 10 minutes. However, in contrast to low-frequency or high-frequency stimulations, theta-burst stimulations also induced slight potentiation of synaptic transmission for up to 60 minutes following depression phase, although the slope or area did not change. CONCLUSION： Paired pulses induced a remarkable efficacy of paired pulses in the high vocal center and robust nucleus of the arcopallium pathway. Low-frequency, high-frequency, or theta-burst frequency stimulation did not induce long-lasting changes in synaptic transmission.

Effects of subconvulsive electrical stimulation to the hippocampus on emotionality and spatial learning and memory in rats

Objective To observe the effects of repeated subconvulsive electrical stimuli to the hippocampus on the emotional behavior and spatial learning and memory ability in rats.Methods One hundred and eight male Wistar rats were randomized into 3 groups. Animals in group SE (n = 42) were given subconvulsive electrical stimulation to the hippocampus through a constant pulsating current of 100 μA with an intratrain frequency of 25 Hz, pulse duration of 1 millisecond, train duration of 10 seconds and interstimulus interval of 7 minutes, 8 times a day, for 5 days. In the electrode control group or CE group (n = 33), animals were implanted with an electrode in the hippocampus, but were not stimulated. Group NC (n =33) animals received no electrode or any stimulation. The emotional behavior of experimental rats was examined by activity in an unfamiliar open field and resistance to capture from the open field, while the spatial learning and memory ability was measured during training in a Morris water maze.Results The stimulated rats tested 1 month after the last round of stimulation displayed substantial decreases in open field activity (scale: 10. 4±2. 3, P<0. 05) and increases in resistance to capture (scale: 2. 85±0. 56, P < 0. 01 ). The amount of time for rats in group SE to find the platform (latency) as a measurement for spatial bias was prolonged (29±7) seconds after 15 trials in the water maze, P<0. 05). The experimental rats swam aimlessly in all four pool quadrants during the probe trial in the Morris water maze.Conclusions Following repeated subconvulsive electrical stimuli to the hippocampus, rats displayed long-lasting significant abnormalities in emotional behavior, increased anxiety and defensiveness, enhanced ease to and delayed habituation to startlement, transitory spatial learning and memory disorder, which parallels many of the symptoms in posttraumatic stress disorder patients.

Response of Bi-disperse Polyelectrolyte Brushes to External Electric Fields A Numerical Self-consistent Field Theory Study

The self-consistent field theory has been employed to numerically study the response of bi-disperse flexible polyelectrolyte （PE） brushes grafted on an electrode to electric fields generated by opposite surface charges on the PE-grafted electrode and a second parallel electrode. The numerical study reveals that, under a positive external electric field, the shorter and negatively charged PE chains are more responsive than the longer PE chains in terms of the relative changes in their respective brush heights. Whereas under a negative external electric field, the opposite was observed. The total electric force on the grafted PE chains was calculated and it was found that, under a positive external electric field, the magnitude of the total electric force acting on one shorter PE chain is larger than that on one longer PE chain, or vice versa. The underlying mechanism was unraveled through analyzing the total electric field across the two oppositely charged electrodes.