Dynamic quantitative monitoring of cerebrospinal fluid monoamine neurotransmitter markers during the modeling process of chronic stress-induced depression in monkeys (Macaca mulatta)

Abstract

Background: Depression is known as the "mental cold" and is also considered a major cause of disability worldwide. It is estimated that over 300 million people worldwide suffer from severe depression, equivalent to 4.4% of the world's population. The monoamine hypothesis of depression predicts the underlying pathophysiological mechanisms of depression, but in-depth research has failed to find convincing evidence.

Method: In this study, we will dynamically and strictly quantitatively monitor the concentration changes of monoamine transmitters in the cerebrospinal fluid (CSF) of macaques, based on our previous work. In the experiment, timed and quantitative collection of CSF samples from macaques was performed and the concentration of monoamine transmitters was determined.

Result: The results showed that after 2 months of chronic stress, the concentrations of high vanillin acid (HVA) and 3,4-dihydroxy-phenylacetic acid were significantly higher in the maternal separation (MS) group, whereas there was no significant difference in dopamine and 5-hydroxyindoleacetic acid.

Conclusion: This study is the first to observe the long-term dynamic relationship between early adversity, chronic stress, adolescent depression, and CSF monoamine concentrations. The research suggests that MS and chronic stress play an undeniable role in the pathogenesis of depression and that concentrations of HVA and dihydroxyphenylacetic acid are likely to serve as early markers of depressive-like symptoms in macaques.

Keywords: chronic stress; depression; early adversity; monoamine transmitters.

FIGURE 1

This figure shows the process of collecting cerebrospinal fluid (CSF) samples. Collect CSF samples from eight macaques (Macaca mulatta), mix them evenly with 0.1 mol/L perchloric acid solution in a 1:1 ratio, centrifuge at a speed of 16,000 g for 15 min in a high‐speed centrifuge, store them in a −80°C refrigerator, and finally perform electrochemical detection of the concentration changes of high vanillin acid (HVA), 5‐hydroxyindoleacetic acid (5‐HIAA), dopamine (DA), and 3,4‐dihydroxy‐phenylacetic acid (DOPAC) in the CSF using high‐performance liquid chromatograph (HPLC).

FIGURE 2

Flowchart for the determination of monoamines transmitters in cerebrospinal fluid (CSF) by high‐performance liquid chromatograph (HPLC). The concentration of four substances, high vanillin acid (HVA), 5‐hydroxyindoleacetic acid (5‐HIAA), dopamine (DA), and 3,4‐dihydroxy‐phenylacetic acid (DOPAC), in CSF was detected by HPLC electrochemical detection. Overall, 20% and 80% methanol water were used for detoxification, needle washing, and pump head cleaning. Subsequently, mobile phases of long and short columns were prepared separately, and parameters were set for monitoring and analysis.

FIGURE 3

The concentration changes of dopamine (DA), 5‐hydroxyindoleacetic acid (5‐HIAA), high vanillin acid (HVA), and 3,4‐dihydroxy‐phenylacetic acid (DOPAC) in the cerebrospinal fluid (CSF) of macaques after experiencing maternal separation (MS) (before introducing chronic stress). (a) After experiencing MS, it was found that there was no significant change in the concentration of DA in the CSF of macaques in the MS group compared to the MR group (unpaired t test, t = .2415, p = .8172). (b) After experiencing MS, it was found that the concentration of 5‐HIAA in the CSF of macaques in the MS group was significantly higher than that in the MR group (unpaired t test, t = 3.116, ^* p = .0357). (c) After experiencing MS, it was found that the concentration of HVA in the CSF of macaques in the MS group was significantly higher than that in the MR group (unpaired t test, t = 7.118, ^** p = .0021). (d) After experiencing MS, it was found that there was no significant change in the concentration of DOPAC in the CSF of macaques in the MS group compared to the MR group (unpaired t test, t = 1.997, p = .1165).

FIGURE 4

After 2 months of chronic stress, continuously monitor the concentration changes of dopamine (DA), 5‐hydroxyindoleacetic acid (5‐HIAA), high vanillin acid (HVA), and 3,4‐dihydroxy‐phenylacetic acid (DOPAC). (a) After 2 months of chronic stress, there was no significant change in DA concentration in the maternal separation (MS) group of macaques compared to before experiencing chronic stress (Tukey's multiple comparisons test, LSR = −3.455, p > .9999). (b) After 2 months of chronic stress, there was no significant change in the concentration of 5‐HIAA in the MS group of macaques compared to before experiencing chronic stress (Tukey's multiple comparisons test, LSR = 21.19, p = .9974). (c) After experiencing 1 month of chronic stress, the concentration of HVA in the MS group macaques significantly increased compared to the MR group macaques (Tukey's multiple comparisons test, LSR = −141.6, ^* p = .0166), after 2 months of chronic stress, the concentration of HVA in the MS group macaques significantly increased compared to the MR group macaques (Tukey's multiple comparisons test, LSR = −98.41, ^* p = .0429). (d) Introducing 2 months of chronic stress, it was found that the concentration of DOPAC in the MS group showed a significant upward trend. After the end of 2 months of chronic stress (Tukey's multiple comparisons test, LS = −1.482, ^* p = .0469; LSR = −1.931, and ^* p = .0136), the concentration of DOPAC decreased (Tukey's multiple comparisons test, LSR = 1.789, ^* p = .0198).