**Abstract**

*Capsicum annum*, an extensively cultivated vegetable, is commonly used to spice many dishes prepared in several parts of the world. It contains capsaicinoids, which give it a characteristic pungency. The most active and well known amongst these capsaicinoids is capsaicin (8-methyl-N-vanillyl-6-nonenamide), which is neurogenic and may affect neuronal functions. Therefore, our study investigated the effects of consumption of chilli pepper and capsaicin diets on neurobehaviour of CD-1 mice. The neurobehavioural parameters assessed were anxiety, motor coordination, pain, social behaviour, learning and memory. The animals were randomly assigned into three groups of 10 mice each, namely, control, pepper-diet (20% w/w), and capsaicin-diet (10% w/w) groups. Their learning and memory abilities were assessed through their ability to locate the hidden platform model of Morris water maze apparatus. The elevated plus maze and light-dark transition box were used to assess anxiety-related behaviour, while the beam walking test and nesting behaviour were used to determine motor coordination and social behaviour, respectively. Tail immersion, hot plate, and formalin tests were conducted to assess pain perception. Consumption of the chilli pepper and capsaicin diets decreased pain perception, increased anxiety, and impaired learning and memory but enhanced social behaviour and motor coordination in mice.

**Keywords:** *Capsicum annum*, capsaicin, pain, social behaviour, anxiety, motor coordination, learning and memory

### **1. Introduction**

Spices are used all over the world not only for their flavours but also for their medicinal properties [1]. One of such spices is chilli pepper. Chilli pepper or chillies are vegetables used world over for culinary purposes and belong to the family Solanaceae [2].

These peppers are widely used as spices in food industry and in a broad variety of medicinal applications worldwide [3]. These spices are remarkable sources of antioxidant compounds including phenolic compounds and flavonoids, of which their consumption has potential health benefits due to their activity as free radical scavengers and may also help prevent inflammatory diseases and pathologies associated with oxidative damage such as atherosclerosis and Alzheimer's disease [3].

Chilli peppers are called *Ntokon* in Efik, *Osé* in Ibo and *Brukunu* in Hausa languages in Nigeria. They are usually red or green in colour. It is the most commonly consumed pepper in Nigeria.

The substances that give chillies their hot sensation and intensity when ingested or contacted are pungent chemical compounds collectively known as Capsaicinoids with Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) as the most abundant [4]. Exposure to the skin causes intense burning sensation while exposure to the eyes leads to intense tearing, conjunctivitis and blepharospasm [5].

The burning sensations associated with Capsaicin ingestion result from the activation of transient receptor potential, vanilloid 1 (TRPV1) located in the gut and other organs [6]. The stimulation of these TRPV1 receptors brings about the influx of sodium and calcium ions which results in the depolarization of nociceptive neurons, leading to the firing of action potentials and finally the sensation of spiciness [7]. Capsaicin is an alkaloid which is highly volatile, odourless, colourless and hydrophobic [8]. It structurally, belongs to a group of chemicals known as vanilloids, having a vanillyl (methylcatechol) head group (A-region) and an aliphatic tail (hydrophobic— C-region) linked by a central amide bond (B-region). This combination of these regions is accountable for the pharmacological activities of capsaicin [8].

Numerous health benefits are believed to emanate from Chilli pepper consumption [7]. Kempaiah et al. [9] reported that Capsaicin demonstrated protective effects against obesity and cholesterol by speeding up metabolism through stress hormone release. It is used as a topical agent in formulations against arthritis [10] and also in preparation of defensive sprays because of its irritant properties and ability to cause neurogenic inflammation (stinging sensation of hands, eyes and mouth) [11, 12].

*Capsicum annum* contains capsaicin which is neurogenic [11] and therefore, can affect neuronal activities in the body [13]. It is therefore conceivable that it may affect some nervous function parameters such as pain, social behaviour, anxiety, motor coordination, learning and memory. Hence, we present the report of our study that investigated the comparative effects of long-term consumption of capsaicin and chillies on the aforementioned neurobehavioural parameters using mice as experimental models to ascertain whether the effects obtained with pepper-diet consumption can be attributed to capsaicin.
