The Induction of Drug Tolerance in Mice
Introduction:
We are aiming to find out whether or not a barbiturate group of drugs has any effects on gamma-aminobutyric acid (GABA) receptors found in the central nervous system of mice, and to compare these results to the effects of exposure to TCPOBOP before exposure to the drug, if any, has on their drug tolerance levels. We will achieve this by, initially, exposing the mice to 3 different doses of pentobarbitone: 50, 60 and 70mg/kg and recording the results. Then we will do the experiment again, but first the mice will be pre-treated with the TCPOBOP, the results will be compared and this will show how quickly the mice have built their tolerance for the drug. | | | | | | | | | |
Expectations for week 1: the mice exposed to the highest dose will lose its “righting reflex” for longer, and will take longer to wake up as it has been newly introduced to the drug therefore has not built up any tolerance.
Expectations for week 2: the mice’s tolerance will increase due to the pre-treatment of TCPOBOP, and will wake up and gain their “righting reflex” quicker than the first time.
Method:
Refer to schedule.

Results:
Week 1: Doses of Pentobarbitone (mg/kg) | MEDIAN | MEAN | SEM | 50 | 1780 | 2618.667 | 497.0424 | 60 | 3255 | 3363.1 | 227.0589 | 70 | 5085 | 5043.3 | 397.5642 | |
Fig.1 – showing mean, median and SEM of loss of righting reflex

Figure 1 shows the mean, median and standard error mean of the results we obtained for the duration of loss of the righting reflex against each dose of pentobarbitone administered. These were established from the collective data from the 10 mice in each dose group. They show the increase in duration as the dosage of the drug also increases. The graph plotted (fig.2), shows the dose curve for these results.

| 50 | 60 | 70 | 10 | 87.11 | 100 | 91.8 | 20 | 88 | 88.8 | 72.8 | 30 | 88 | 88 | 72.8 | 40 | 91 | 93.56 | 70.6 | 50 | 96 | 97.14 | 75.56 | 60 | 88 | 104 | 67.25 | 70 | 112 | 132 | 89 | 80 | 108 | - | 90 | 90 | 88 | - | 107 | 100 | - | - | 132.33 |
Fig. 3 – showing the mean breathing rate at each time against each dose

Figure 3 is a table displaying the average breathing rates once they were calculated using the raw data, for each time (10-90mins) against each dose. The graph (fig.4) shows the erratic breathing rate of the mice at the different doses that were given, and that a correlation cannot be established.

At 50mg/kg | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 0 | 6 | 8 | 3 | 2 | 3 | 1 | 0 | 0 | 0 | W | 2 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 0 | M | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | S | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | Total | 9 | 8 | 4 | 4 | 3 | 3 | 1 | 1 | 1 |

At 60mg/kg | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 0 | 5 | 7 | 6 | 4 | 2 | 0 | 0 | - | - | W | 4 | 3 | 2 | 4 | 1 | 2 | 0 | - | - | M | 1 | 0 | 2 | 0 | 2 | 3 | 0 | - | - | S | 0 | 0 | 0 | 1 | 3 | 0 | 1 | - | - | Total | 10 | 10 | 10 | 9 | 8 | 5 | 1 | - | - |

At 70mg/kg | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 0 | 9 | 9 | 7 | 6 | 6 | 4 | 1 | 1 | 1 | 0 | W | 1 | 1 | 2 | 2 | 1 | 3 | 3 | 2 | 1 | 0 | M | 0 | 0 | 1 | 1 | 2 | 1 | 4 | 1 | 1 | 3 | S | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 3 | 0 | 0 | Total | 10 | 10 | 10 | 9 | 9 | 9 | 9 | 7 | 3 | 3 |
Fig.5 - showing the predominant blink reflex at each dose against each time (W = weak, M = medium, S = strong, 0 = no response)

Figure 5 shows the most predominant blink reflexes established when the eyes of the mice was lightly touched by a moistened tissue and the results then recorded by judging the strength of the blink as strong, medium or weak, or whether or not there was a response at all. The graph (fig.6) shows the data from these tables for each dose and how they compare.
At 50mg/kg | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 0 | 8 | 6 | 8 | 4 | 1 | 2 | 1 | 0 | 0 | W | 1 | 2 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | M | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | S | 0 | 0 | 0 | 1 | 2 | 1 | 0 | 1 | 0 | Total | 9 | 8 | 9 | 6 | 3 | 3 | 1 | 1 | 1 |

At 60mg/kg | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 0 | 7 | 8 | 8 | 8 | 7 | 0 | 0 | - | - | W | 2 | 2 | 1 | 0 | 0 | 1 | 0 | - | - | M | 1 | 0 | 1 | 0 | 0 | 4 | 0 | - | - | S | 0 | 0 | 0 | 1 | 1 | 0 | 1 | - | - | Total | 10 | 10 | 10 | 9 | 8 | 5 | 1 | - | - |

At 70mg/kg | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 0 | 8 | 7 | 9 | 8 | 8 | 6 | 8 | 2 | 4 | 2 | W | 1 | 3 | 0 | 0 | 0 | 2 | 0 | 3 | 0 | 0 | M | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | S | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 2 | 0 | 3 | Total | 10 | 10 | 10 | 9 | 9 | 9 | 9 | 7 | 4 | 6 |
Fig.7 – showing the toe response at each dose against each time (W = weak, M = medium, S = strong, 0 = no response)

Figure 7 is a table that shows the toe responses when each mice was tested for their withdrawal reflexes while under the drugs influence, by lightly squeezing the toes on one of the hind paws and recording the results. The most frequent strength that occurred for each time was recorded in the table above and a total was calculated. The graph (fig.8) shows the plotted figures for each dose at each time (10-90mins).
Week 2:

Doses of Pentobarbitone (mg/kg) | MEDIAN | MEAN | SEM | 60 | 942 | 1006.22 | 179.31 | 70 | 1365 | 1451.40 | 181.18 | 80 | 2075.50 | 2050.80 | 84.85 |
Fig.9 – showing mean, median and SEM of loss of righting reflex after TCPOBOP is given

Figure 9 shows the mean, median and standard error mean for the raw data results we obtained for the duration of loss of righting reflex after TCPOBOP was registered to each of the mice before administering the drug and the separate doses. It shows how pre-treating the mice with the TCPOBOP affected the length of the period in which the righting reflex was lost. The graph (fig.10) shows the mean values plotted once they were calculated creating a curve and showing a positive correlation. | 60 | 70 | 80 | 10 | 194 | 113.33 | 104 | 20 | 90 | 113.75 | 92.4 | 30 | - | 136 | 106.5 | 40 | - | - | 138 |
Fig. 11– showing the mean breathing rate at each time against each dose after TCPOBOP is given

Figure 11 is a table showing the average breathing rates once they were calculated using the raw data obtained once the mice were pre-treated and then given the pentobarbitone dose by counting the number of breaths in 15 seconds and then multiplying that value by 4. The graph (fig.12) shows the erratic breathing for each dose against each time (10-40mins).
At 60mg/kg | 10 | 20 | 30 | 40 | 0 | 5 | 0 | - | - | W | 1 | 1 | - | - | M | 0 | 1 | - | - | S | 1 | 0 | - | - | Total | 7 | 2 | - | - |

At 70mg/kg | 10 | 20 | 30 | 40 | 0 | 5 | 3 | 0 | - | W | 4 | 1 | 1 | - | M | 0 | 2 | 1 | - | S | 1 | 2 | 0 | - | Total | 10 | 8 | 2 | - |

At 80mg/kg | 10 | 20 | 30 | 40 | 0 | 6 | 6 | 2 | 0 | W | 4 | 4 | 5 | 1 | M | 0 | 0 | 0 | 0 | S | 0 | 0 | 1 | 1 | Total | 10 | 10 | 8 | 2 |
Fig.13 - showing the predominant blink reflex at each dose against each time (W = weak, M = medium, S = strong, 0 = no response)

Figure 13 displays the most predominant blink reflex values that were established in the experiment after the mice were treated with the TCPOBOP, the graph (fig.14) shows the values plotted with each dose against the times and the strengths of the blink (w, m, s, nr) in order to aid us comparing the graph with the graph for blink reflex in week 1.

At 60mg/kg | 10 | 20 | 30 | 40 | 0 | 3 | 2 | - | - | W | 4 | 0 | - | - | M | 0 | 0 | - | - | S | 0 | 0 | - | - | Total | 7 | 2 | - | - |

At 70mg/kg | 10 | 20 | 30 | 40 | 0 | 7 | 2 | 2 | - | W | 1 | 2 | 2 | - | M | 0 | 2 | 0 | - | S | 2 | 2 | 1 | - | Total | 10 | 8 | 5 | - |

At 80mg/kg | 10 | 20 | 30 | 40 | 0 | 10 | 8 | 6 | 0 | W | 0 | 1 | 1 | 1 | M | 0 | 1 | 0 | 0 | S | 0 | 0 | 1 | 1 | Total | 10 | 10 | 8 | 2 |
Fig.15 - showing the toe responses at each dose against each time (W = weak, M = medium, S = strong, 0 = no response)
Figure 15 is of a table showing the toe responses for the mice after they were treated and administered with the drug, the most frequent strength of the withdrawal reflex from the raw data was acquired and displayed in the table above. It was then plotted onto a graph (fig.16) and used to compare data.
Week 3:
Hypothesis: Comparative to the liver taken from the normal mice, the one treated with TCPOBOP will produce less formaldehyde as the metabolic enzyme activity, used to demethylate the aminopyrine, is induced. | Absorbance | 1 | 0.170 | 2 | 0.123 | 3 | 0.070 | 4 | 0.125 | 5 | 0.032 | 6 | 0.108 | 7 | 0.222 | 8 | 0.396 | 9 (blank) | 0.000 |

Fig.17 – showing the absorbance values (412nm) found for the enzyme assay liver

Figure 17 shows the absorbance values obtained at wavelength of 412nm, from the enzyme assay done on the liver and formaldehyde dilutions. The 9th one was used as a blank and the others were looked at via a spectrophotometer and the results were then recorded in the table above. A standard calibration curve was then plotted using these values (fig.18) showing us how the absorbance varies with the different concentrations.
Discussion:
The results we obtained are what we expected. When a drug is taken only once, the effect it has on the neurotransmitters in the CNS is different to the effects it has if that drug is then, subsequently taken a hundred times more, because by then a tolerance will have built up [1].
The positive correlation found between the duration of loss of righting reflex and the increasing dosage of pentobarbitone administered from week 1 to week 2 confirms the mice had developed a tolerance for the drug and therefore reacted differently and regained their reflexes quicker than the first time, showing how the neurotransmitters in the brain reacted to the already exposed drug. This is a result of the induction of the microsomal enzymes that are responsible for metabolising the barbiturate group of drugs that were administered [2].
The varying findings from the breathing rates show that it may not be comparable to other studies. Also the methods used to record the reflexes were qualitative, making the results harder to comprehend. But once a way was found to quantify these results, it was clear that they were in line with the expectations. Similarly, the results found for the measurement of metabolic tolerance using aminopyrine also displayed that the mice had ascertained a drug tolerance.
Conclusion:
From my results, it is clear that a drug tolerance between these mice did develop. It showed a positive correlation between the pentobarbitone dose and the duration of loss of righting reflexes, and showed us that by simply pre-treating the mice with TCPOBOP, the tolerance to the drug increased, cutting time from 100mins to just 40mins.
References:
[1] - Parrott, Andrew. (2004). psychoactive drugs: introduction and overview. In: Understanding drugs and behaviour. Chichester, West Sussex: J. Wiley. 7-8.
[2] - Philip B Bradley. (1989). Anaesthetics, hypnotics and sedatives. In: Introduction of Neuropharmacology. London: Butterworth and co. LTD. 187-188