Schizandrin ameliorates ovariectomy-induced memory impairment, potentiates neurotransmission and exhibits antioxidant properties

Abstract

Background and purpose: Schizandrin (SCH) has been reported to prevent or reduce learning and memory defects. However, it is not known whether SCH ameliorates cognitive impairments induced by oestrogen deficiency. In the present study, we investigated the effect of SCH on memory in ovariectomized (OVX) and non-OVX rats.

Experimental approach: A passive avoidance test was used to evaluate the effect of SCH on memory. Field EPSPs were recorded in hippocampal slices using an electrophysiological method. In OVX rats, biochemical parameters in the bilateral hippocampus were measured; these included superoxide dismutase (SOD), malondialdehyde (MDA) and AChE. Also, the number of NADPH-diaphorase (NADPH-d) positive neurons was counted by NADPH-d histochemistry staining technique.

Key results: Oral SCH improved the memory and facilitated the induction of long-term potentiation in non-OVX and OVX rats; this effect was more obvious in OVX rats. Similarly, SCH perfusion enhanced synaptic transmission in hippocampal slices from both non-OVX and OVX rats. However, SCH perfusion reduced the ratio of paired-pulse facilitation only in OVX but not in non-OVX rats. In addition, SCH decreased AChE activity and MDA level and increased SOD activity and the number of NADPH-d-positive neurons in OVX rats.

Conclusions and implications: SCH improves memory in OVX rats and its potential mechanisms may include a reduction in the loss of hippocampal NADPH-d positive neurons, an increase of antioxidant properties and a potentiation of synaptic transmission that possibly involves to enhance cholinergic function. Overall, our findings indicate that SCH has potential as a therapeutic strategy for the cognitive dysfunctions associated with the menopause.

Figure 1

Effects of SCH on the latency time of passive avoidance test at days 28 (A), 29 (B) and 35 (C) in non-OVX rats. The box plots show the median and interquartile range. *P < 0.05. Day 28, the day of behavioural training; Days 29 and 35, the days of behavioural testing. n = 20 for all groups.

Figure 2

SCH 30 mg·kg⁻¹, p.o., facilitates the induction of tetanic LTP in the hippocampal Schaffer-CA1 pathway of non-OVX rats. (A) Representative records of evoked potentials in hippocampal CA1 region. Black, traces before HFS; gray, traces at 15 min after HFS. (B) Noted that the enhancement in the amplitude of the fEPSPs at 15 min after HFS. (C) Effects of SCH on the amplitude of the fEPSPs after HFS during the 75 min recordings. HFS consisted of 10 trains of five pulses at 100 Hz bursts presented at 200 ms intervals. *P < 0.05 and **P < 0.01. Each group n = 10.

Figure 3

Perfusion of SCH enhances the basal synaptic transmission of hippocampal Schaffer-CA1 pathway in non-OVX rats. (A) Dose–response relationship of the effect of SCH (50, 100 and 200 μg·mL⁻¹) on the basal synaptic transmission is shown. (B) Perfusion with 200 μg·mL⁻¹ SCH reversibly enhanced the fEPSPs' amplitude during the 75 min recordings. The intensity of the stimulating test pulses (0.2–1.0 mA, 0.1 ms in duration) was initially adjusted so as to produce about 30 to 50% maximal fEPSPs' amplitude. *P < 0.05 and **P < 0.01. Each group n = 10.

Figure 4

The effect of SCH perfused in vitro on the ratio of PPF in the brain slices from non-OVX rats. (A) Representative records of PPS-evoked potentials after the application of 200 μg·mL⁻¹ SCH. (B) Note that 200 μg·mL⁻¹ SCH slightly decreased the ratio of PPF. (C) Time course of PPR in the hippocampal slice from non-OVX rats after perfusion of SCH during a period of 90 min. PPS at an interval of 50 ms was applied. Recordings were collected after a stable baseline had been established for 15 min and then the effect of SCH on PPF was tested by bath application for 30 min. Each group n = 10.

Figure 5

Effects of SCH on the latency time of passive avoidance test at days 70 (A), 71 (B) and 77 (C) in OVX rats. The box plots show the median and interquartile range. *P < 0.05 and **P < 0.01. Day 70, the day of behavioural training; days 71 and 77, the days of behavioural testing. OVX, ovariectomized group; EB, OVX plus 20 μg·kg⁻¹ EB treatment; 10 and 30 mg·kg⁻¹ SCH, OVX plus 10 or 30 mg·kg⁻¹ SCH treatments respectively. n = 20 for all groups.

Figure 6

SCH 30 mg·kg⁻¹, p.o., facilitates the induction of tetanic LTP in the hippocampal Schaffer-CA1 pathway of OVX rats. (A) Representative records of the potentials evoked in the hippocampal CA1 region from baseline, in sham, OVX, OVX + EB and OVX + SCH groups. Black, traces before tetanic stimulation; gray, traces 15 min after HFS. (B) Note that ovariectomy obviously lowered the fEPSPs' amplitude at 15 min after HFS, while 30 mg·kg⁻¹ SCH markedly improved the fEPSPs' amplitude after HFS in OXV rats. *P < 0.05 and **P < 0.01. (C) Effects of 30 mg·kg⁻¹ SCH on the fEPSPs' amplitude after HFS in the hippocampal Schaffer-CA1 pathway of OVX rats. HFS consisted of 10 trains of five pulses at 100 Hz, bursts presented at 200 ms intervals. Each group n = 10.

Figure 7

A perfusion of SCH enhances the basal synaptic transmission in the hippocampal Schaffer-CA1 pathway of OVX rats. (A) The dose–response relationship for the effect of SCH (50, 100 and 200 μg·mL⁻¹) on the fEPSPs' amplitude. (B) SCH 100 μg·mL⁻¹ reversibly enhanced the fEPSPs' amplitude in the hippocampal slices from OVX rats during a period of 75 min recordings. The intensity of the stimulating test pulses (0.2–1.0 mA, 0.1 ms in duration) was initially adjusted so as to produce about 30 to 50% maximal fEPSPs' amplitude. **P < 0.01. Each group n = 10.

Figure 8

Perfusion of 100 μg·mL⁻¹ SCH in vitro reduces the ratio of PPF in OVX rats. (A) Representative records of PPS-evoked potentials with 100 μg·mL⁻¹ SCH applied for 30 min. (B) Note that 100 μg·mL⁻¹ SCH obviously decreased the ratio of PPF. (C) Time course of the ratio of PPF in the hippocampal slices from OVX rats treated with SCH during a period of 90 min. PPS was applied at intervals of 50 ms. *P < 0.05 and **P < 0.01. Each group n = 10.

Figure 9

Effects of oral SCH on the level of MDA (A) and activities of SOD (B) and AChE (C) in the hippocampus of OVX rats. *P < 0.05 and **P < 0.01. OVX, ovariectomized group; EB, OVX plus 20 μg·kg⁻¹ EB; 10 and 30 mg·kg⁻¹ SCH, OVX plus 10 or 30 mg·kg⁻¹ SCH respectively. n = 12 for all groups.

Figure 10

Oral SCH decreases the loss of NADPH-d positive neurons in the hippocampal CA1 region of OVX rats. (A) Photographs showing the distribution of NADPH-d positive neurons in the hippocampal CA1 area (×400, bar = 100 μm). The black arrows indicate the NADPH-d positive neurons. (B) Number of NADPH-d positive neurons in the hippocampal CA1 area. Sham, sham surgery; OVX, ovariectomized group; EB, OVX plus 20 μg·kg⁻¹ EB; 10 and 30 mg·kg⁻¹ SCH, OVX plus 10 or 30 mg·kg⁻¹ SCH respectively. *P < 0.05 and **P < 0.01. n = 40 for all groups.