Levo-Stepholidine as a Potential Cognitive Enhancer: Insights into Executive Function and Memory Improvements

Abstract

Background/objectives: Levo-Stepholidine (l-SPD), a compound extracted from Chinese herbs, has the potential to treat psychotic disorders where cognitive deficits are a critical challenge. L-SPD displays a D1R agonism/D2R antagonism pharmacological profile, and its effect on cognitive function is still vague and lacks comprehensive study. Here, we investigated the impact of l-SPD on two core indexes of executive function, working memory and response inhibition, and learning and memory.

Methods: Using a delayed alternation T-maze task (DAT), we investigated the impact of l-SPD on working memory, evaluated its effect on response inhibition using the stop-signal task (SST), and assessed the impact on learning and memory using trace fear conditioning in Sprague-Dawley rats. We further evaluated its effects on prefrontal glutamate receptor expression using western blot.

Results: Rats receiving l-SPD made fewer errors in the T-maze, exhibited faster stop action in response to the stop signal, and showed longer-lasting memory retention. Molecular mechanism investigations reveal that l-SPD upregulates the expression of prefrontal glutamate receptors. These results demonstrate that l-SPD improves executive function and memory.

Conclusions: Here, we show the enhancement effect of l-SPD on cognitive function, which provides essential implicants for the treatment of cognitive deficits, which is a critical unmet need in psychiatric care.

Keywords: Chinese herb; D1 receptor agonist; D2 receptor antagonist; Sprague-Dawley rats; antipsychotic agents; cognition; executive function; glutamate receptors; memory; prefrontal cortex.

Scheme 1

The diagram for the experiment design.

Figure 1

Effect of l-SPD on spontaneous activity of rats. (A) Scheme of the experimental procedure. (B) The total distance traveled in the open field chamber of animals tested at 0.5 h or 6 h post systemic administrations of l-SPD (5 mg/kg) versus vehicle. *** p < 0.001, n.s. no significance, student’s t-test. n = 6–8. (C) Demo traces traveled in the open field chamber of animals.

Figure 2

l-SPD enhances the working memory of rats in a delayed alternative task in T-maze. (A) Illustration of the delayed alternative T-maze task (DAT task). (B) Performance in DAT task before (baseline), 6 h post, and 30 h post-injection of l-SPD versus vehicle. (C) Schematic diagram of win-shift failure in DAT task. (D) The number of win-shift failures in the DAT task before (baseline), 6 h post, and 30 h post-injection of l-SPD versus vehicle. ** p < 0.01 versus baseline, paired t-test. n = 6–7.

Figure 3

l-SPD enhances stop-signal response inhibition of rats. (A) Configuration of the operant chamber consists of three snout ports and three lights (green circles). A nose poke into any port is detected by breaking the infra beam (left panel). The stop-signal task events in go trials and stop trials show the sequence of animal action (right panel). (B) Dynamic changed stop-signal delay (SSD) in one session. (C,D) Stop-signal reaction times (SSRTs) of animals tested before systemic administrations (pre-treatment), 6 h (6 h post), or 30 h (30 h post) after administrations of l-SPD and vehicle. * p < 0.05, ** p < 0.01, n.s. no significance, versus pre-treatment, paired t-test (C). Normalize SSRTs to pre-treatment of l-SPD (left) and vehicle (right) (D). n = 8–9. (E,F) l-SPD prolongs stop-signal delay (SSD). (E) Cumulative fraction of all SSD in one testing session tested before treatment (pre-treatment), 6 h, and 30 h post-treatment l-SPD (left) versus vehicle (right), respectively. ** p < 0.01, *** p < 0.001, n.s. no significance, Kolmogorov-Smirnov test. (F) Numbers of stop trials with 100–200 ms (dark bar) and 450–600 ms SSD (grey bar) before (pre-treatment), 6 h post, and 30 h post-treatment of l-SPD (left) versus vehicle (right). Dark star symbol,* p < 0.05 for 100–200 ms SSDs, grey # symbol, p < 0.05 for 450–600 ms SSDs, n.s. no significance. (G) Accuracy of stop trial before treatment (baseline), 6 h and 30 h post-treatment of l-SPD versus vehicle. * p < 0.05, ** p < 0.01, n.s. no significance. (H,I) Trial numbers of failed stops following stop trial (H) or go trial (I). Upper panels, diagrams for wrong stop trial following stop trial (H) and following go trial (I). ** p < 0.01.

Figure 4

Effects of l-SPD on go trial in stop-signal task. Effect of administration of l-SPD (left panels in A and B) versus vehicle (right panels in A and B) on go reaction time (GoRT) (A) and the accuracy of Go trial (B). The same data as Figure 3. n.s. no significance.

Figure 5

Effects of l-SPD on the acquisition and storage of trace fear memory. (A) Scheme of the experimental procedure. (B) Freezing behavior of animals treated with l-SPD versus vehicle during trace fear conditioning. (C) Freezing behavior was examined 1 day and 8 days after conditioning. * p < 0.05, student’s t-test; n = 8–9.

Figure 6

Effect of l-SPD on glutamate receptor expression in PFC. Immunoblot (A) and quantification analysis (B) of the expressions of AMPAR GluR1 subunits, NMDAR GluN2A, and GluN2B subunits in PFC from animals treated with l-SPD versus vehicle examined at 0.5 h post- and 6 h post-treatment (* p < 0.05, ** p < 0.01; n = 3–4 for each treatment).