Introduction

Learning is the ability of an individual to gain new information, whereas memory is defined as the process by which brain encodes and stores the acquired knowledge and recalls the same whenever needed (Sherwood 2015).

Memory can be affected by various pathologies such as neurodegenerative diseases, stroke, tumor, anxiety, head injury, lack of oxygen, heart surgery, undernourishment, attention deficit disorder, depression, harmful effects of drugs, and old age (Joshi et al. 2007; Budson and Price 2005). Prevention and delay in the onset of memory disorders will have a great impact on society by reducing the disease burden and finances (Oliveira et al. 2009).

The process of learning and memory involve long-lasting modifications of the brain, various neurotransmitters are involved in this process such as acetylcholine, dopamine, and serotonin. These neurotransmitters activate the receptor linked enzymes which produce intercellular messengers. Numerous studies have revealed the contribution of the cholinergic system in learning and memory process of the brain (Maurer and Williams 2017; Peter et al. 2016). It has been proved that Alzheimer’s disease is associated with damage to cholinergic neurons in the cerebral cortex and hippocampus areas of the brain and decreased the action of the enzyme choline acetyl transferase. Based on this finding, acetyl cholinesterase (AChE) inhibitors were developed to treat dementia associated with Alzheimer’s disease (Kim et al. 2007).

The Ayurveda system of traditional medicines has gained a lot of popularity in this respect (Oh et al. 2005). Numerous plants, characterized as the “Medhya” are reported to improve the process of cognition (Joshi and Parle 2006). Adams assembled facts on more than 150 plant species for many age-related cognitive disorders. Various phenolic compounds, such as resveratrol obtained from grapes and red wine, curcumin isolated from turmeric and epigallocatechin acquired from green tea revealed neuroprotective effects (Frank and Gupta 2005; Sun et al. 2008). Antiamnesic effects of various plants extracts are well documented in the literature (Hsieh et al. 2010).

Dementia which is a gradual loss of memory is widespread among elderly people. Expenditure estimates go beyond a billion Euros in Europe only. Alzheimer’s disease is responsible for many cases of dementia, followed by vascular, Lewy body type and dementia induced by Parkinson’s disease. The pathogenesis of the disease is of diverse type and indicate various abnormalities such as β-amyloidosis, ischemic damages, α-synucleinopathy, neurotransmitter abnormalities including abnormalities in cholinergic, glutamatergic and serotonergic systems, abnormal tau, inflammation, oxidative stress, cell death and neuroplasticity (Ballard et al. 2007; Muñoz-Torrero 2008).

Medicines available for the treatment of dementia are few and include the acetyl cholinesterase inhibitors, butyrylcholinesterase inhibitors (in few cases) and memantine (a glutamate NMDA receptor antagonist). Additional drugs often advised to some patients include antipsychotics, sedatives, and antidepressants. Cholinesterase inhibitor drugs increase the level of the neurotransmitter acetylcholine in the brain by inactivating the enzyme acetylcholinesterase. Acetylcholinesterase inhibitors include rivastigmine, donepezil, galantamine and tacrine (Orhan et al. 2009).

Scopolamine, a cholinergic antagonist drug can induce impairment of learning and memory in experimental animals (Misane and Ögren 2003; Ballard et al. 2005). It is a widely accepted method to evaluate antiamnesic effects of herbal extracts (Bejar et al. 1999).

Several studies on various plants all over the world have shown the therapeutic effectiveness of herbal medicines on memory because of their neuroprotective effects either by inhibiting acetyl cholinesterase enzyme or antioxidant ability (Rabiei et al. 2014). Plants are more efficacious have less harmful effects and are more cost-effective. Hence studies on plant extracts may offer a basis for the development of novel compounds (Katiyar et al. 2012).

Trigonella foenum-graecum Linn. (Fenugreek) is a famous ancient medicinal plant pertaining to the family Fabaceae, various parts of which are consumed as food component such as leaves and seeds (Nathiya et al. 2014).

This study was accomplished using seeds of T. foenum graecum L. Seeds are small (3–5 mm long, 2 mm thick) having a firm consistency ranging from yellowish brown to brown in color. They are flattened and have a distinctive rhomboid shape. They have a typical peppery odor, bitter and mucilaginous taste (Nasroallah et al. 2013).

Seeds are traditionally used as a spice in food. Ancient people used it customarily for various medicinal uses. It is a rich source of various bioactive constituents such as saponins (fenugreekine, diosgenin), alkaloids (trigonelline, gentianine, carpaine), amino acids (4-Hydroxy isoleucin, arginine) polyphenols and flavonoids (Wani and Kumar 2016; He et al. 2015; Dande and Patil 2012; Mandegary et al. 2012). Literature review showed various scientifically appraised activities such as hypoglycemic (Raju et al. 2001), hypolipidemic (Ribes et al. 1987), antioxidant (Rababah et al. 2004), anticancer (Shabbeer et al. 2009) and antiulcer activities (Kaur et al. 2011). Transfer latency is the parameter used to measure acquisition and retention process of memory (Pellow et al. 1985).

The present study was specially designed to evaluate the effect of T. foenum graecum L. seeds methanol extract (TFGS-ME) on learning and memory process in mice.

Materials and methods

Formulation of extract

The cold extraction method was executed to formulate crude extract of methanol (Hossain et al. 2010). Seeds (5 kg) purchased from the local herbal store were purified from all scums manually and crushed to obtain a fine powder, which was immersed in 80% 1000 ml methanol for 10 days in airtight jars with their caps tightly closed. Jars were shaken frequently every 2 days until the solvent turn out to be medium brown in color. The acquired solvent was sieved first through cotton and then by What-Mann No.1 filter paper. Subsequently, the obtained filtrate was vaporized under reduced pressure by means of a rotary evaporator at 45°C, followed by freeze- drying at −30 °C of temperature. The crude extract of methanol so developed was preserved in Petri dishes and kept at −20°C temperature for further use. The yield of extract obtained was 1120 mg of dry weight.

Animals

This study was conducted at Department of Pharmacology, Faculty of Pharmacy and Pharmaceutical Sciences, the University of Karachi after the approval of Board of Advanced Study and Research (BASR) of University of Karachi. The albino mice of either gender weighing 18–24 g were procured from Hussain Ebrahim Jamal (HEJ) Research Institute of Chemistry, University of Karachi. All the animals were retained in plastic cages placed at the animal house of Department of Pharmacology, University of Karachi, under strict conditions of temperature (22 ± 2°C) and humidity (50–60%) in an alternating 12-h light/dark cycle. Animals were fed with standard food and water regularly. Guidelines of National Institute of Health (NIH) were followed for handling and experimentation on animals (National Research Council 1996).

Grouping and dosing

35 Swiss albino mice were randomly distributed into 5 different groups, each comprised of 7 animals. One group was tagged as the control group and received distilled water 1 ml/kg orally once a day. The second group was labeled as the standard drug group and was administered Piracetam (GlaxoSmithKline) at 200 mg/kg body weight through intraperitoneal route. Three test groups received TFGS-ME in three varying dosages (50, 100 and 200 mg/kg body weight respectively) orally once a day. All the treatments were continued for 8 days. Transfer latency (TL) was measured 90 min after the last dose on acquisition day (Day 8). Memory was noted on retention day (Day 9) 24 h after the first day’s test.

Testing

Elevated plus maze test was employed to assess the effect on learning and memory as an exteroceptive behavioral test. Scopolamine-induced amnesia was performed to assess the effect on learning and memory as interoceptive behavior test.

Elevated plus maze

The elevated plus maze functioned as the exteroceptive behavioral test (in which provocation is present exterior to the body) to assess learning and cognition function (Joshi and Parle 2006). The tool is comprised of two open arms (16 cm × 5 cm) and two covered arms (16 cm × 5 cm × 12 cm), spreading from a platform (5 cm × 5 cm) positioned in the center. The maze is situated 5 cm above the floor. On day 1, each mouse was positioned at the termination corner of an open arm, located away from the central platform and transfer latency was recorded. Transfer latency is defined as the time spent by the mouse to reach into one of the covered arms by using all four legs. If the mouse could not reach into one of the covered arms within 90 s, it is transferred into one of the two covered arms and the transfer latency was marked as 90 s. The mouse was permitted to search the maze for further 10 s and then sent back to its residing cage. Cognition was tested on the day 2, 24 h after the first day’s test. Significant reduction in transfer latency signifies improved learning and memory (Dhingra et al. 2004; Parle et al. 2004).

Scopolamine-induced amnesia

Scopolamine hydrobromide (Sigma-Aldrich Inc., St. Louis, MO, USA) was used to induce amnesia in experimental animals. Scopolamine hydrobromide was administered to animals of all groups at 0.4 mg/kg body weight through intraperitoneal route 90 min after the last treatment on acquisition day (Day 8) except to the standard drug group which received the injection 60 min after the last treatment, after 8 continuous days of treatment. Transfer latency was measured 45 min after the administration of scopolamine hydrobromide. Memory was observed on retention day (Day 9), 24 h after the first day’s test (Saini et al. 2011).

Statistics

Data analysis was done utilizing Superior Performance Statistical Software (SPSS)-23 and is presented as mean ± SEM. Anova followed by post hoc Tukey test was performed for comparisons of values with control. Values of P < 0.05 were considered as significant and P < 0.01 as highly significant.

Results

Table 1 demonstrates the effect of TFGS-ME and piracetam on transfer latency in mice in Elevated plus maze test after 8 days of uninterrupted administration. Animals received TFGS-ME at doses of 50 and 100 mg/kg body weight showed a decrease in transfer latency on both acquisition and retention day but the decrease was statistically inconsequential as compared to control animals. However, animals received TFGS-ME extract at 200 mg/kg body weight showed a highly noteworthy decrease in transfer latency on both acquisition and retention day i.e. 15.34 ± 1.7 s and 9.67 ± 1.3 s in contrast to control animals. These effects were similar to animals which received standard drug piracetam at 200 mg/kg body weight.

Table 1 Effect of TFGS-ME and piracetam on transfer latency in elevated plus maze
Full size table

Table 2 demonstrates the effect of TFGS-ME and piracetam on transfer latency in mice on scopolamine-induced amnesia after 8 days of uninterrupted administration.

Table 2 Effect of TFGS-ME and piracetam on transfer latency in scopolamine-induced amnesia
Full size table

Animals received TFGS-ME at doses of 50 and 100 mg/kg body weight showed decrease in transfer latency on both acquisition and retention day but the decrease was statistically inconsequential as compared to control animals, however animals received TFGS-ME extract at 200 mg/kg body weight showed highly noteworthy decrease in transfer latency at both acquisition and retention day i.e. 20.03 ± 1.2 s, 13.12 ± 1.6 s respectively in contrast to control animals. These effects were comparable to the effects of animals received standard drug piracetam at 200 mg/kg body weight.

Discussion

In this study, the effect of TFGS-ME was also evaluated on learning and memory by both exteroceptive and interoceptive behavioral models. In both tests, it was found that animals receiving extract at 200 mg/kg of dose exhibited a highly noteworthy decline in transfer latency on both acquisition and retention day in contrast to control animals. Results were equivalent to the standard drug Piracetam at a similar dose.

Diet and lifestyle perform a crucial role in slowing the onset as well as the development of neurodegenerative ailments and considerably enhancing memory function (Spencer 2008; Nurk et al. 2009). It has been found that diet rich in polyphenols have revealed favorable influences on learning and memory process and are linked with a decreased chance of dementia (Beking and Vieira 2010). Polyphenols and their metabolites have modulatory actions on protein and lipid kinase signaling pathways (Williams et al. 2004). These may even protect the neurons against the harms induced by inflammation and oxidative stress (Calabrese et al. 2012). These have the ability to reverse the age-related neuronal changes (Chan et al. 2006; Ashok et al. 2010). T. foenum graecum L. seeds are a rich source of polyphenols (Rayyan et al. 2010). Thus learning and memory enhancing activities are might be due to the presence of these polyphenols.

It has been found that the flavonol rutin increased the levels of noradrenaline and dopamine neurotransmitters in the brain, thus improving spatial memory in aged rats (Pyrzanowska et al. 2012). Improvement in learning and memory can be due to flavonol rutin present in T. foenum graecum L. seeds (Rayyan et al. 2010).

Alkaloids have also shown antiamnesic effect in scopolamine induced memory impairment in mice (Chuong et al. 2014). Trigonelline, an important alkaloid of T. foenum graecum L. seeds has shown neuroprotective and memory boosting effect in animals (Zhou et al. 2012). Saponins also have favorable effect on learning and memory (Jiang et al. 2007). Diosgenin, an important saponin content of T. foenum graecum L. seeds considerably upgraded learning and memory in mice, it was suggested that memory boosting effects of diosgenin may be facilitated by increasing antioxidant enzymatic activities (Chiu et al. 2011). Improvement in learning and memory can be due to the presence of alkaloids and saponins content of T. foenum graecum L. seeds.

Present study indicates that T. foenum graecum L. improves learning and memory and has significant potential as antiamnesic agent. Hence there is extreme need to isolate the dietary constituents which may play a dynamic role in future invention of novel drugs.