Cholinergic basis of memory improving effect of Ocimum tenuiflorum linn

Corresponding Author:

H. Joshi
Department of Pharmacognosy, SET’s College of Pharmacy, S. R. Nagar, Dharwad-580002, India.
E-mail: amanjoshi17@yahoo.com

Abstract

Dementia is one of the age-related mental problems and a characteristic symptom of Alzheimer's disease. Nootropic agents are used in situations where there is organic disorder in learning abilities. The present work was undertaken to assess the potential of Ocimum tenuiflorum Linn. as a nootropic and anticholinesterase agent in mice. Ethanol extract of dried whole plant of O. tenuiflorum Linn. ameliorated the amnesic effect of scopolamine (0.4 mg/kg) and aging-induced memory deficits in mice. Passive avoidance paradigm served as the exteroceptive behavioural model. O. tenuiflorum extract increased step-down latency and acetyl cholinesterase inhibition significantly. Hence, O. tenuiflorum can be employed in the treatment of cognitive disorders such as dementia and Alzheimer's disease.

In Ayurveda, Ocimum tenuiflorum Linn. (O. sanctum –Lamiaceae) is popularly known as the sacred tulsi (holy basil) and has been in clinical use for centuries; leaves possess anthelmintic, expectorant, diaphoretic, stimulant effects; infusion of the plant is given in arthritis, toothache, ringworm infections, and piles; decoction of the root is given in genitourinary disorders and malaria [1]. It is reported to possess chemo preventive [2], antistress [3], anticonvulslant [4], antiulcer [5], antidiabetic [6], analgesic [7], antioxidant [8], anticancer [9], immunomodulatory [10], and antiinflammatory [11] activity. The present study was undertaken to assess the potential of ethanol extract of Ocimum tenuiflorum Linn. as a memory strengthening and anti cholinesterase agent.

The whole plant of Ocimum tenuiflorum Linn. was collected from the local areas of Bangalore, identified and authenticated at Department of Pharmacognosy, M. S. Ramaiah College of Pharmacy, Bangalore. A voucher specimen (OT/HS-235) has been deposited in the department. One kilogram powder of O. tenuiflorum was extracted by Soxhlet method using ethanol (90%). The crude extract was filtered and concentrated by rotavapour flash evaporator. The yield of the extract from crude powder of O. tenuiflorum was 17%. A suspension was prepared using Tween 80.

Swiss mice of either sex weighing around 18 g (younger ones, aged 3 months) and around 25 g (older ones, aged 7 months) were used in the present study. Institutional Animals Ethics Committee (IAEC) approved the experimental protocol, and care of animals was taken as per guidelines of CPCSEA (Reg. No. 220/CPCSEA).

Exteroceptive behavioural model (passive avoidance paradigm) and Interoceptive behavioural models (scopolamine-induced amnesia and ageing-induced amnesia) were employed [12]. Passive avoidance behaviour is based on negative reinforcement and is used to examine the long-term memory. Step-down latencies (SDL) were recorded. The whole brain acetyl cholinesterase (AChE) activity was measured using the method reported by Ellman et al [13]. The data were expressed as mean±SEM. The normally distributed data were subjected to one-way ANOVA, followed by unpaired ‘t’ test using SPSS-computer software. Kruskal Wallis [14] one-way ANOVA, followed by multiple range tests, was used for the analysis of non-normally distributed data. P <0.05 was considered significant.

Normal ageing is known to deteriorate memory in human beings [15]. O. tenuiflorum increased SDL in both young and aged mice when subjected to passive avoidance paradigm, indicating its potent antiamnesic activity (Table 1). Central cholinergic system plays an important role in learning and memory [16]. Phenytoin is known to reduce hippocampal ACh concentration [17]. In our study, phenytoin per se (12 mg/kg, p.o.) significantly elevated brain AChE activity, whereas piracetam (250 mg/kg, p.o.) and O. tenuiflorum (50, 100, and 200 mg/kg, p.o.) lowered this activity significantly (P <0.05) (Table 2). Hence O. tenuiflorum may be useful as a nootropic agent in the early management of various cognitive disorders.

Table 1: effect of O. Tenuiflorum linn. on Step-down latency

Table 2: Effect of O. Tenuiflorum linn. and Piracetam on Ache Activity in Aged Mice.

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