Effect of Mentone® on depression- and anxiety-like profiles and regional brain neurochemistry in the adolescent Wistar Kyoto rat, a putative model of endogenous depression

Antidepressants, when prescribed to treat adolescent depression tend to induce adverse effects, including suicidal tendencies. This is because the adolescent brain circuitry is still maturing and is therefore extremely vulnerable. As such, the search is on for compounds for use in complementary/alternative medicine. Polyherbal formulations are widely used as therapeutic alternatives for the treatment of depression. Such formulations and plant extracts are being studied in adult rodent models using standard pharmacological parameters, but not much emphasis has been given to testing the same in adolescents and endogenous animal models of depression. Therefore, the present study was focused on testing out the effect of the polyherbal formulation Mentone® on depression- and anxiety-like profiles and brain neurochemistry in the adolescent Wistar Kyoto rat (WKY), a putative model of endogenous and treatment-resistant depression (TRD). Mentone®, a polyherbal formulation comprising of four different plant species: Centella asiatica (Brahmi), Evolvulus alsinoides (Shankapushpi), Tinospora cordifolia (Guduchi), and Glycyrrhiza glabra (Yashtimadhu) was tested at two (18 and 36 mg/kg body weight) doses from the post-natal day (pnd) 25 to pnd 42 using standard neurobehavioral paradigms. Vehicular controls were intubated with saline and positive controls with 10 mg/kg body weight of conventional antidepressant, Fluoxetine. From pnd 35 onwards, animals were tested on a battery of tests, including sucrose preference, novel open field, elevated plus maze, and forced swim or Porsolt’s learned helplessness test. On pnd 42, animals were sacrificed and brain regional tissues such as the Prefrontal cortex (PFC), Striatum (Str), Nucleus Accumbens (NAc), and Hippocampus were microdissected out and subjected to reverse phase HPLC for the separation and quantification of monoamines: Norepinephrine (NE), dopamine (DA), serotonin (5-HT) and their metabolites, 3,4-Dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in reference to external standards. Mentone® reversed anhedonia by increasing sucrose consumption in Mentone®-treated as compared to Fluoxetine-treated groups. However, there was no effect on anxiety-related parameters in the novel open field or elevated plus-maze. Mentone® exhibited significant anti-depressant-like effects as indicated by its ability to reduce swim stress-induced immobility in Porsolt’s behavioural despair test with a concomitant increase in climbing or struggling behaviour, signifying reversal of depressive-like symptomatology. HPLC-based separation and quantification of brain regional levels of monoamines and their metabolites revealed increased DA levels in NAc and Str in treated groups with decreased levels of metabolite DOPAC in Mentone®-treated groups indicating increased DA tone. Significantly reduced 5-HT metabolite 5-HIAA levels in both PFC and Str is indicative of increased 5-HT tone in both Mentone®- and Fluoxetine-treated groups. NE was variably affected. While no anxiolytic effects and differential neurochemical effects were observed in brain regional areas in relation to Mentone® and Fluoxetine treatment, anhedonia and forced swim test, which are gold-standard tests for assessing depressive-like profiles indicated an effect of Mentone® that was on par with Fluoxetine. Thus, studies on such Ayurvedic formulations would enable a teasing out or differentiation between anxiolytic-like and depressive-like symptomatology and could constitute a source that holds promise in the development of complementary/alternative therapies for the treatment of depression in general and TRD in particular.