CLINICS 2011;66(4):663-671 BASIC RESEARCH DOI:10.1590/S1807-59322011000400023 Enhancement of basolateral amygdaloid neuronal dendritic arborization following Bacopa monniera extract treatment in adult rats Venkata Ramana Vollala,I Subramanya Upadhya,II Satheesha NayakIII I Department of Anatomy, Rajiv Gandhi Institute of Medical Sciences (RIMS), Adilabad, India. II Department of Physiology, St. George’s University School of Medicine, Grenada, West Indies. III Department of Anatomy, Melaka Manipal Medical College (Manipal Campus), Manipal University, India. OBJECTIVE: In the ancient Indian system of medicine, Ayurveda, Bacopa monniera is classified as Medhya rasayana, which includes medicinal plants that rejuvenate intellect and memory. Here, we investigated the effect of a standardized extract of Bacopa monniera on the dendritic morphology of neurons in the basolateral amygdala, a region that is concerned with learning and memory. METHODS: The present study was conducted on 2K-month-old Wistar rats. The rats were divided into 2-, 4- and 6- week treatment groups. Rats in each of these groups were further divided into 20 mg/kg, 40 mg/kg and 80 mg/kg dose groups (n = 8 for each dose). After the treatment period, treated rats and age-matched control rats were subjected to spatial learning (T-maze) and passive avoidance tests. Subsequently, these rats were killed by decapitation, the brains were removed, and the amygdaloid neurons were impregnated with silver nitrate (Golgi staining). Basolateral amygdaloid neurons were traced using camera lucida, and dendritic branching points (a measure of dendritic arborization) and dendritic intersections (a measure of dendritic length) were quantified. These data were compared with the data from the age-matched control rats. RESULTS: The results showed an improvement in spatial learning performance and enhanced memory retention in rats treated with Bacopa monniera extract. Furthermore, a significant increase in dendritic length and the number of dendritic branching points was observed along the length of the dendrites of the basolateral amygdaloid neurons of rats treated with 40 mg/kg and 80 mg/kg of Bacopa monniera (BM) for longer periods of time (i.e., 4 and 6 weeks). CONCLUSION: We conclude that constituents present in Bacopa monniera extract have neuronal dendritic growth- stimulating properties. KEYWORDS: Bacopa monniera; spatial learning; passive avoidance; amygdaloid neurons; dendritic arborization; memory. Vollala VR, Upadhya S, Nayak S. Enhancement of basolateral amygdaloid neuronal dendritic arborization following Bacopa monniera extract treatment in adult rats. Clinics. 2011;66(4):663-671. Received for publication on November 16, 2010; First review completed on December 8, 2010; Accepted for publication on December 29, 2010 E-mail: ramana.anat@gmail.com Tel.: 91 9494306083 INTRODUCTION Bacopa monniera (BM), a traditional ayurvedic medicine, is reported to improve learning and memory behaviors in animals and humans.1-3 The plant and plant extracts have been extensively investigated for their neuropharmacologi- cal effects, and studies have confirmed their nootropic action.1-6 The active constituents of the plant facilitate learning and memory in normal rats and inhibit the amnesic effects of scopolamine, electroshock and immobilization stress.7,8 BM extracts have been reported to be non-toxic, non-teratogenic and non-mutagenic in rats and monkeys; Copyright 2011 CLINICS – This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non- commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. single and multiple dosing studies in healthy human volunteers have not elicited adverse effects.9 In addition to its claimed memory-enhancing properties, BM has other potential benefits, such as a facilitatory effect on the capacity for mental retention.10,11 BM has been used in ayurvedic medicine and in traditional treatments for a number of disorders, particularly disorders that involve anxiety, intellect and poor memory.3 Significant antidepressant activity comparable to that of imipramine has been observed with the Brahmi extract after five days of oral administration, using a rodent model of depression.12 Additionally, anticholinesterase activity has been demon- strated.13 The amygdala is located deep within the medial temporal lobe, anterior to the hippocampus, close to the tail of the caudate nucleus. The amygdala is structurally diverse and comprises many nuclei. These nuclei are further divided into three major groups: 1) the deep or basolateral group; 2) 663