The Effects of 5-Hydroxytryptophan on Pain Following Formalin Administration

 

Aduema W.¹*, Amah A. K¹, Wariso A.C²

¹Department of Human Physiology, Gregory University, Uturu, Abia State, Nigeria.

²Department of Human Physiology, Abia State University, Uturu, Abia State, Nigeria

 

ABSTRACT

The aim of the study was to investigate the effect of repeated administration of 5-Hydroxytryptophan (5-HTP) on pain sensation. The quantity of 5-HTP reaching the Central Nervous System (CNS) is affected by the extent to which 5-HTP is converted to serotonin in the periphery. The formalin test  was used to access pain perception using two groups of mice weighing 22g-32g (n=10 each).The control group received (15g) normal rodent chow, while the test group received (15g w/w) 5-HTP diet. Daily food intake, water intake and body weight change were measured.  The results in the formalin test, showed that the frequency and duration of paw attention and paw lick in both phases of the test was significantly lower (P< 0.05) in the 5-Hydroxytryptophan group (5-HTP) compared to the control. Therefore, repeated administration of 5-Hydroxytryptophan diet decreases pain perception in mice.

 

 

 

INTRODUCTION:

5-Hydroxytryptophan is an aromatic amino acid naturally produced from L-tryptophan (LT). It is obtained commercially by the extraction from the seeds of the plant Griffonia simplicifolia.5-Hydroxytryptophan (5-HTP) has been used clinically for over 30 years (Timothy and Birdsall, 1998). The clinical efficacy of 5-Hydroxytryptophan is its ability to increase production of serotonin. There are some research to support the use of 5-HTP in treating cerebellar ataxia, headache, depression, psychiatric disorders or aid panic disorder, but studies in people with schizophrenia has shown different results(Bagdy et al., 2007) and as an appetite suppressant etc. (Harford et al., 2007.)

 

Troullas et al, 1988. Bono et al, 1984). 5-HTP may cause Git disturbances, mood disturbance, seizure etc. It has also been reported that side effects might result from contaminants in 5-HTP products. However, most of the studies involving the use of 5-HTP were for depression which were done many years ago. At that time, there was a high level of interest in serotonin hypothesis on depression (Shawk,et al.,2002). It is possible that this series of events may have led to the loss of interest in 5-HTP in respect to neurobehaviour. It may be worthwhile to find out whether repeated administration of 5-Hydroxytryptophan diet can affect behaviour. This was of particular interest when we consider the challenges that confront human behaviour and how behavioural disorders still remain a global concern (Messman, 2005).

 

 

 

EXPERIMENTAL ANIMALS/GROUPING:

Twenty (20) Swiss mice weighing between 22g and 32g were randomly assigned into two groups A, and B of 10 mice each. Group A was the control and groups B (Test). Animals in group A received normal rodent chow, while group B animals were administered 15g of 5-Hydroxytryptophan diet, daily for a period of 30 days.

 

EXPERIMENTAL DESIGN:

The formalin test was used to assess pain as developed by (Abbot et al., 1981) .Each mouse was picked at the base of its tail and 0.2ml of formalin 2.5% concentration was injected into the right hind paw of the mouse using a needle and syringe and observed for 5minutes and again observed after 30 minutes for 5minutes.The observations of the sensitivity of mice to pain were recorded. Behaviour scored during the test included the following;

·        Frequency and duration of Right hind paw lick

·        Frequency and duration of Right hind paw attention.

 

STATISTICAL ANALYSIS:

Data collected were expressed a Mean ± SEM (standard error of mean), analysis of variance (ANOVA) and the student‘t’ test were used for analysis. “P” value less than 0.05, was considered statistically significant.

 

RESULTS:

Figure 1.0 compares the frequency of right hind paw attention injected formalin in the early phase of the test in the two groups of animals (mice) within five minutes. These values are, 24.43± 3.60 (control) and 6.43± 2.00(5-Hydroxytryptophan). In the late phase, the values are 1.20 ± 0.47/5 min for control and 0.43±0.30/5min (5-htp). Figure 1, shows that in both phases of the test, frequencies of 5-Hydroxytryptophan fed mice was statistically lower (P<0.05) compared to control.

 

The duration of paw attention for control mice was 89.33 ± 0.94 and 39.57 ± 0.48/seconds (5-Hydroxytryptophan) respectively in the early phase while in the late phase of the test, there values were and 2.60 ± 0.60secs (control) and 0.55±0.39 seconds (5htp fed diet). The graph in figure 2 shows that the duration of attention fed with the 5- Hydroxytryptophan diet was significantly lower (P<0.05) when compared with the control.

 

Figure 3.0 compares the frequency of right hind paw licks in the two experimental groups. The values are: 14.09± 0.09(control) and 5.39± 0.09(5-htp) in the early phase and 6.87 ± 0.22/5 min (control) and 0.14±0.14/5min (5-htp fed diet) in the late phase. The right hind paw lick frequency 5-Hydroxytryptophan fed mice was shorter (p<0.05) compared to the control in both phases.

 

 

The duration of right hind paw lick between the two experimental groups is in figure 4. The values are: 27.60±2.72 (control) and 12.57 ± 2.38(5-Hydroxytryptophan). The duration of paw lick of the 5-Hydroxytrytophan fed mice in the late phase was also significantly different (P<0.05) compared to control. The values were 13.30 ± 0.52secs (control) and 4.16±0.16 seconds respectively for 5-htp diet fed group.

 

 

Fig 1: Frequencies of right hind paw attention of the different experimental groups after two trials during the assessment of pains using formalin. Values are expressed as mean, ± SEM, n = 10,*p<0.05 vs. control.

 

 

Fig 2: Right hind paw duration of the different experimental groups after two trials during the formalin test for pain assessment of pains. Values are expressed as are expressed as mean ± SEM, n = 10,*p<0.05 vs. control.

 

Fig 3: Right hind paw lick frequency of the different experimental groups after two trials during the formalin test assessment for pains. Values are expressed as are expressed as mean ± SEM, n = 10,*p<0.05 vs. control.

 

Fig 4: right hind paw lick duration of the different experimental groups after two trials during the assessment of pain using formalin. Values are expressed as are expressed as mean ± SEM, n = 10,*p<0.05 vs. control.

 

DISCUSSION:

In this study, the animal model of physiological pain assessment used was the formalin test (Ito et al., 2001). This test was in two phases. The response within the first 30 seconds following formalin injection is the perception of acute pain, while the later period shows chronic pain perception. Frequency of hind paw attention and hind paw-licking following injection with formalin was defined as the number of times the mice lick or shake their hind paw after injection with formalin. Lower frequencies of hind paw attention and hind paw licking indicate analgesic effect while higher frequencies indicate hyperalgesia. Our finding showed that during acute and chronic phases of pain, the 5-Hydroxytryptophan fed mice had significantly less pain perception compared to control, since the frequencies and durations of hind paw lick and hind paw attention following formalin injection was significantly lower in the 5-HTP diet- fed mice when compared to the control. It is therefore interesting to note that 5-HTP diet can be beneficial in the reduction of chronic pain if the results in mice can be extrapolated to man.Similarly, 5-Hydroxytryptophan diet mice showed less sensitive to pain, when compared to those fed with the control diet. This may be so because 5-HTP (serotonin precursor) plays a positive role in the brain analgesia system (Osim, 2008, Sembulingam K and Sembulingam P, 2010).

 

CONCLUSION:

Our results suggest that repeated administration of 5-Hydroxytryptophan (5-HTP) may have an inhibitory influence on pain.

 

ACKNOWLEDGEMENT:

We acknowledged Mr. and Mrs. B.A.Aduema,                    Dr. Nmaju, and Associate Prof. A. A. Nwankwo for their support.

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Accepted on 11.02.2018            © A&V Publications All right reserved