The objective of this study was to elucidate the effect of chronic stress (CS) on dopamine (DA) level and synaptic efficiency in the hippocampal dentate gyrus (DG) during spatial learning and memory. Sprague Dawley (SD) male rats were randomly divided into control group and CS group (n = 10). CS group was treated with chronic mild unpredictable stress, and control group did not receive any treatments. The levels of epinephrine and corticosterone (CORT) in serum were measured by using enzyme-linked immunosorbent assay (ELISA); the spatial learning and memory abilities of rats were measured by Morris water maze (MWM) test. Meanwhile, the amplitude of field excitatory postsynaptic potential (fEPSP) and concentration of DA in the DG region were determined by in vivo electrophysiology, microdialysis and HPLC techniques during MWM test in rats. After that, the DA D1 receptor (D1R) and its key downstream members in DG were examined by immunohistochemistry or Western blot assay. The results showed that the levels of epinephrine and CORT in the serum of the rats in CS group were significantly increased compared with those in the control group (P < 0.05). In CS group rats, the escape latency was significantly prolonged and the number of platform crossing was markedly decreased during MWM test, compared with those in control group (P < 0.05). Furthermore, the amplitude of fEPSP in the DG was not changed during MWM test in CS rats, while it was significantly increased on the 3rd day of MWM test in control group (P < 0.05). Compared with baseline or control group, CS group showed significantly increased DA level from the 1st to 3rd days of MWM test in the DG (P < 0.05). In addition, the protein expression of D1R was markedly up-regulated in the DG in CS group, while the protein expression levels of p-PKA, p-CREB and BDNF were significantly reduced, compared with those in control group. These results suggest that CS may impair spatial learning and memory abilities in rats through the enhancement of the DA levels in the hippocampal DG.
Animals ; Dentate Gyrus ; Dopamine ; Hippocampus ; Male ; Maze Learning ; Rats ; Rats, Sprague-Dawley ; Spatial Learning ; Spatial Memory

The present study aimed at investigating the effects of chronic multiple stress on learning and memory functions of rats. Adult male Wistar rats were randomly divided into stressed and control groups. Rats in the stressed group were irregularly and alternately exposed to the situation of vertical revolution, sleep deprivation, noise stimulation, and night illumination 6 h per day for 6 weeks to prepare a chronic multiple stressed model. Learning and memory performance of rats was measured by using Morris water maze first and Y-maze afterwards. Neurons in the dentate gyrus(DG), CA3 and CA1 regions of the hippocampus were stained by using Cresyl violet method and counted. The results showed that: (1) After chronic multiple stress, compared with the control rats, the escape latency to the hidden platform in Morris water maze was significantly shortened in stressed rats. In stressed and control groups, the escape latency periods were (15.89+/-9.15) s and (27.30+/-12.51) s, respectively, indicating that spatial memory of the stressed rats was stronger than that of the control ones. In brightness-darkness discrimination learning in the Y- maze, the correct trials and correct percentage of entering safe arm was remarkably increased in the stressed rats, the correct rates of stressed and control groups were (79.01+/-1.23)% and (66.12+/-1.61)%, respectively, indicating that brightness-darkness discrimination learning ability of the stressed rats was better than that of the control ones. (2) After chronic multiple stress, nerve cell density in DG, CA1 and CA3 of the hippocampus in stressed rats was higher than that of the control group, the cell densities in DG, CA1 and CA3 of the stressed and the control group were (223.78+/-26.52), (112.07+/-14.23) and (105.55+/-18.12) as well as (199.13+/-15.36), (92.89+/-13.69), and (89.02+/-15.77) respectively. These results suggest that the chronic multiple stress may enhance the capability of spatial memory and brightness-darkness discrimination learning of rats. Possible reasons for the chronic multiple stress-induced learning and memory enhancement of rats were also discussed.
Animals ; Hippocampus ; physiology ; Learning ; physiology ; Male ; Maze Learning ; Memory ; physiology ; Neuronal Plasticity ; physiology ; Rats ; Rats, Sprague-Dawley ; Spatial Behavior ; physiology ; Stress, Physiological ; physiopathology

OBJECTIVETo explore the changes in spatial learning performance and long-term potentiation (LTP) which is recognized as a component of the cellular basis of learning and memory in normal and lead-exposed rats after administration of melatonin (MT) for two months.

METHODSExperiment was performed in adult male Wistar rats (12 controls, 12 exposed to melatonin treatment, 10 exposed to lead and 10 exposed to lead and melatonin treatment). The lead-exposed rats received 0.2% lead acetate solution from their birth day while the control rats drank tap water. Melatonin (3 mg/kg) or vehicle was administered to the control and lead-exposed rats from the time of their weaning by gastric gavage each day for 60 days, depending on their groups. At the age of 81-90 days, all the animals were subjected to Morris water maze test and then used for extracellular recording of LTP in the dentate gyrus (DG) area of the hippocampus in vivo.

RESULTSLow dose of melatonin given from weaning for two months impaired LTP in the DG area of hippocampus and induced learning and memory deficit in the control rats. When melatonin was administered over a prolonged period to the lead-exposed rats, it exacerbated LTP impairment, learning and memory deficit induced by lead.

CONCLUSIONMelatonin is not suitable for normal and lead-exposed children.

Animals ; Female ; Lead ; toxicity ; Learning ; drug effects ; Long-Term Potentiation ; drug effects ; Male ; Maze Learning ; drug effects ; Melatonin ; administration & dosage ; toxicity ; Rats ; Spatial Behavior ; drug effects

To investigate the effect of treadmill running on the ability of learning in young rats, male Sprague-Dawley rats (5 weeks of age) were used for the experiment. Animals were randomly divided into the control and running groups (n=15 in each group). The rats in running group were made run on a motor-driven treadmill for 1 week at a speed of 2 m/min for the first 5 min, at a speed of 5 m/min for the next 5 min, then at a speed of 8 m/min for the last 20 min. Then the Morris water maze was used to observe learning and memory ability of rats in both groups. The tests consisted of place navigation and spatial probe test. We found that, in place navigation training, the latency of rats in running group was less than that in control group (P<0.05); and from the third training session on, there was significant difference between the rats in control and running groups in swimming velocity (P<0.01); furthermore, it was observed that the rats in running group had stronger motivation and more exact orientation in searching for platform, which could be indicated by the index of turn angle and angular velocity. In spatial probe test, there was no significant difference between the two groups in swimming velocity, percentage of swimming distance and frequency of crossing platform in D quadrant, where the platform situated (P>0.05). These findings suggest that low speed treadmill running can enhance the ability of learning in young rats.
Age Factors ; Animals ; Male ; Maze Learning ; physiology ; Memory ; physiology ; Physical Conditioning, Animal ; physiology ; Rats ; Rats, Sprague-Dawley ; Spatial Behavior ; physiology ; Swimming ; physiology

Learning/memory impairment is one of the most serious problems induced by stress, and the underlying mechanisms remain unclear. Opiates and opioid receptors are implicated in multiple physiological functions including learning and memory. However, there is no clear evidence whether the endogenous opioid system is involved in the formation of the stress-induced spatial reference memory impairment. The aim of the present study was to evaluate the role of μ opioid receptor in the stress-induced spatial reference memory impairment by means of Morris water maze (MWM) test in a mouse elevated platform stress model. The mice were trained in the MWM for four trials a session for 4 consecutive days after receiving the elevated platform stress, and intracerebroventricular injection of μ opioid receptor agonist DAMGO, antagonist CTAP or saline. Retention of the spatial training was assessed 24 h after the last training session with a 60-s free-swim probe trial using a new starting position. The results showed that intracerebroventricular injection of μ opioid receptor agonist DAMGO but not antagonist CTAP before MWM training impaired the memory retrieval of mice. Elevated platform stress before MWM training also impaired memory retrieval, which could be reversed by pre-injection of CTAP, and aggravated by DAMGO. These results suggest that endogenous opioid system may play a crucial role in the formation of the stress-induced memory impairment.
Animals ; Enkephalin, Ala(2)-MePhe(4)-Gly(5)- ; pharmacology ; Maze Learning ; Memory Disorders ; Mice ; Receptors, Opioid, mu ; physiology ; Spatial Memory ; Stress, Physiological

OBJECTIVEFebrile seizure is a very common emergency in children. Although researchers home and abroad constantly pay close attention to studies on brain damage and lesion possibly caused by febrile seizure, studies of effects on motor, behavior, spatial learning and memory are relatively seldom. In our study, Sprague-Dawley rats were utilized for the purpose of the exploration of effects of febrile seizures on their motor, behavior, spatial learning and memory.

METHODSSixty 21-day-old male Sprague-Dawley rats, weighing (50 +/- 5) g were divided randomly and equally into febrile seizure group (FS), febrile control group (FG) and normal control group (NG). Febrile seizure animal model was induced by hyperthermal bath with 45 degrees C water. Febrile seizure was induced twice a day, thus ten times within five days in FS group. Rats of FG group were immersed in the same hyperthermal water for 2 minutes. Nothing special was performed on NG group. The abilities of motor and behavior of every rat in these 3 groups were tested in inclined plane test (IPT), overhanging test (OHT) and open field test (OFT) to show their varieties. Furthermore, Morris water maze was applied to evaluate the effects by febrile seizure on spatial learning and memory in rats during the place navigation test and spatial probe test.

RESULTSIn the present experiments, febrile seizures were altogether induced 192 times with the mean latency being (4.25 +/- 0.98) minutes and the mean duration being (1.06 +/- 0.59) minutes. The experiments confirmed that multiple febrile seizures could lead to decreases of abilities in all tests in which analysis of variance indicated that there were significant differences between febrile seizure group and the other two (P < 0.01). In inclined plane test, the turning ability of the rats was weakened. The mean turning time was (9.1 +/- 2.6) seconds for FS, (5.3 +/- 2.1) seconds for FG and (5.3 +/- 2.0) seconds for NG. In overhanging test, the overhanging time was shortened: (33.4 +/- 18.1) seconds for FS, (50.1 +/- 20.3) seconds for FG and (59.0 +/- 20.7) seconds for NG. In the open field test, the rats became less active with the scores (5.1 +/- 2.0) for FS, (10.4 +/- 3.0) for FG and (13.2 +/- 2.3) for NG. Meanwhile, the authors discovered the decreases of the abilities of spatial learning and memory in rats caused by febrile seizures many times. In the place navigation test, the mean escape latency for the rats' looking for hidden platform was prolonged; the efficiency of their search strategy decreased; the swimming time the animals spent in platform region decreased [(44.02 +/- 5.25) seconds for FS, (51.75 +/- 5.28) seconds for FG and (57.07 +/- 5.36) seconds for NG; analysis of variance, P < 0.01.]; the number of times they crossed the platform area decreased [(6.07 +/- 1.77) times for FS, (9.25 +/- 2.07) times for FG and (11.34 +/- 2.37) times for NG; analysis of variance, P < 0.01]; the percentage of their swimming time fell (36.68% for FS, 43.13% for FG and 47.56% for NG).

CONCLUSIONThe experiments confirmed that multiple febrile seizures could result in damage and lesion of motor, behavior, spatial learning and memory in rats.

Animals ; Male ; Maze Learning ; physiology ; Memory ; physiology ; Motor Activity ; physiology ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Seizures, Febrile ; physiopathology ; Spatial Behavior ; physiology

OBJECTIVETo investigate the neuroprotective effect of leptin by observing its effect on spatial memory of rats with white matter damage in developing brain.

METHODSA total of 80 neonatal rats were randomly divided into 3 groups: sham-operation (n=27), model (n=27) and leptin intervention (n=27). The rats in the model and leptin intervention groups were used to prepare a model of white matter damage in developing brain, and the rats in the leptin intervention group were given leptin (100 μg/kg) diluted with normal saline immediately after modelling for 4 consecutive days. The survival rate of the rats was observed and the change in body weight was monitored. When the rats reached the age of 21 days, the Morris water maze test was used to evaluate spatial memory.

RESULTSThere was no significant difference in the survival rate of rats between the three groups (P>0.05). Within 10 days after birth, the leptin intervention group had similar body weight as the sham-operation group and significantly lower body weight than the model group (P<0.05); more than 10 days after birth, the leptin intervention group had rapid growth with higher body weight than the model and sham-operation groups (P>0.05). The results of place navigation showed that from the second day of experiment, there was a significant difference in the latency period between the three groups (P<0.05); from the fourth day of experiment, the leptin intervention group had a similar latency period as the sham-operation and a significantly shorter latency period than the model group (P<0.05). The results of space search experiment showed that compared with the sham-operation group, the model group had a significant reduction in the number of platform crossings and a significantly longer latency period (P<0.05); compared with the model group, the leptin intervention group had a significantly increased number of platform crossings and a significantly shortened latency period (P<0.05), while there was no significant difference between the leptin intervention and sham-operation groups.

CONCLUSIONSLeptin can alleviate spatial memory impairment of rats with white matter damage in developing brain. It thus exerts a neuroprotective effect, and is worthy of further research.

Animals ; Female ; Leptin ; pharmacology ; Maze Learning ; drug effects ; Neuroprotective Agents ; pharmacology ; Pregnancy ; Rats ; Rats, Sprague-Dawley ; Reaction Time ; Spatial Memory ; drug effects ; White Matter ; pathology

Hippocampal neuronal network oscillation is closely related to the memory, anxiety and behavioral inhibition of mammalian. The cognitive decline and behavioral disinhibition in the patients with Alzheimer's disease (AD) may be relevant to amyloid β protein (Aβ)-induced impairment in hippocampal neuronal cooperative activity. However, it is not well known whether intrahippocampal injection of Aβ could induce behavioral disinhibition and neuronal network disorder, as well as cognition decline in animals. In the present study, we observed the effects of intracerebral injection of Aβ(1-42) on the spatial memory and behavioral inhibition of rats by using Morris water maze and elevated plus-maze tests. Further, we analyzed hippocampal theta rhythm by recording hippocampal local field potential. The results showed that: (1) bilateral hippocampal injection of Aβ(1-42) reduced the anxious behavior of rats, with a significant behavioral disinhibition in the elevated plus-maze test, representing as an increase in the mean entering times and mean residence time in the open arm; (2) Aβ(1-42) injection resulted in a significant impairment of spatial memory in rats, with significantly increased mean escape latencies in hidden platform test; (3) Aβ(1-42) disrupted the induction of theta rhythm induced by tail pinch, with a significant reduction in the peak power, not the peak power frequency of the theta rhythm. These experimental results indicate that intrahippocampal injection of Aβ(1-42) can induce behavioral disinhibition and theta rhythm suppression, as well as spatial memory impairment in rats, which suggests that the cognition deficits and behavior impairments in AD are probably associated with the Aβ-induced disruption of hippocampal theta rhythm and consequent down-regulation of synaptic plasticity.
Amyloid beta-Peptides ; adverse effects ; Animals ; Down-Regulation ; Hippocampus ; physiopathology ; Maze Learning ; Neuronal Plasticity ; Peptide Fragments ; adverse effects ; Rats ; Spatial Memory ; Theta Rhythm

The present study was aimed to explore the effect of sodium nitrite on cytoskeletal protein phosphorylation and spatial learning and memory in rats. Rats were served with drinking water containing sodium nitrite (100 mg/kg) for 60 days, then, the ability of spatial learning and memory of the rats was measured by Morris water maze. Phosphorylation level of tau and neurofilament, and the expression of protein phosphatase 2A (PP2A) catalytic subunit in the hippocampus were detected by immunohistochemistry and Western blot. In comparison with the rats served with normal tap water, the rats served with sodium nitrite water showed significantly longer latency to find the hidden platform in Morris water maze (P < 0.05), elevated phosphorylation level of tau and neurofilament, and decreased expression of PP2A catalytic subunit (P < 0.05). These results indicated that administration of sodium nitrite could impair the spatial learning and memory of the rats, and the hyperphosphorylation of cytoskeletal proteins and the down-regulation of PP2A might be underlying mechanisms for the impairment.
Animals ; Cytoskeletal Proteins ; metabolism ; Down-Regulation ; Hippocampus ; metabolism ; Maze Learning ; Memory ; drug effects ; Neurofilament Proteins ; metabolism ; Phosphorylation ; Protein Phosphatase 2 ; metabolism ; Rats ; Rats, Sprague-Dawley ; Sodium Nitrite ; pharmacology ; Spatial Learning ; drug effects ; tau Proteins ; metabolism

OBJECTIVETo study the effect of nano-SiO2 on spatial learning and memory.

METHODSTwenty-four male rats were randomly divided into 3 groups: control group (C group), low dose group (L group) and high dose group (H group). The rats were intragastrically administrated with nanometer particles at 25 and 100 mg/kg body weight every day for 4 weeks. After exposure, the ability of learning and memory of rats was tested by Morris water maze, and electrophysiological brain stereotactic method was used to test long-tear potentiation (LTP) in dentate gyrus (DG) of the rats.

RESULTSThe increase rate of body weight in H group was reduced significantly compared with C group ( P < 0.05). In the space exploration experiment of Morris water maze test, the escape latency of H group was longer than that of C group (P < 0.05). The rats of H group spent less time in finding the target quadrant (P < 0.05) . The rate of LP induction of H group was significantly lower than that of C group (P < 0.05). After high fre quency stimulation (HFS), The changes of amplitude of population spike (PS) of L group and H group were lower than those of C group significantly (P < 0.05, P < 0.01).

CONCLUSIONNano-SiO₂may result in impairment of spatial learning and memory ability by reducing the rate of LTP induction and the increase of PS in hippocampus.

Animals ; Dentate Gyrus ; drug effects ; Long-Term Potentiation ; drug effects ; Male ; Maze Learning ; drug effects ; Memory ; drug effects ; Nanoparticles ; adverse effects ; Rats ; Silicon Dioxide ; adverse effects ; Spatial Learning ; drug effects