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Practical report: PSY236
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PSY236 (Biopsychology and Learning), Practical 1 The effect of methamphetamine on aggressive
behaviour in crickets
Abstract
Our experiment aims to examine the potential of methamphetamine to elicit aggressive behaviour in crickets. It seems to be reasonable to assume that methamphetamine makes crickets more aggressive, because it has been shown that methamphetamine increases aggression in various species, including humans (Sekine et al., 2006). Methamphetamine is known to reverse the dopamine (Kuczenski, Segal, Cho, & Melega, 1995) and serotonine transporters (Kokoshka et al., 1998), resulting in an increase of neurotransmitters in the synaptic cleft. Since in particular dopamine is said to be involved in aggressive behaviour (Louilot et al., 1986), it seems justified to assume that methamphetamine increases the level of aggression in crickets, too. It will turn out that our experiment is not able to provide Introduction
Neurotransmitters play a substantial role in behaviour. All types of behaviour are linked to a characteristic chemical profile in the brain. Even minor changes in the composition of neurotransmitters can lead to a variety of behavioural changes. One of the fundamental types of neurotransmitters are monoamines, such as dopamine, serotonin, noradrenaline, adrenaline, histamine and octopamine. Since monoamines are involved in many processes of neurotransmission, they are highly influential with In this paper, we will examine the role of specific neurotransmitters in the behaviour of crickets (acheta domestica). In the nervous system of crickets, the monoamines octopamine, serotonine and dopamine are essentially important (Nagao & Tanimura, 1988). Hence, it is necessary to bring these chemicals into sharper More specifical y, we want to investigate the effects of metamphetamine on cricket behaviour. For other species, it has been shown that methamphetamine promotes aggressive behaviour. Studies have provided evidence in the case of, for example, humans (Sekine et al., 2006; Pinhey & Wel s, 2007) and mice (Sokolov, Schindler, & Cadet, 2004; Sokolov & Cadet, 2006). This phenomenon can be explained from the neurochemical perspective of neurotransmitters: Methamphetamine is able to reverse the dopamine transporters at the presynaptic terminals (Kuczenski, Segal, Cho, & Melega, 1995; Fumagal i, Gainetdinov, Valenzano, & Caron, 1998). Usually, after an action potential has caused dopamine neurotransmission and a postsynaptic potential has been created, the dopamine transporter takes up dopamine from the synaptic cleft. This is necessary due to various various: First, the dopamine has finished its task, namely creating a single EPSP. Hence, it has to be removed from the synaptic cleft, away from the receptors at the postsynapses. Second, the dopamine transporter moves dopamine into the presynaptic terminals so that it can be metabolised or repackaged into vesicles again. This is much more economic and efficient compared to the creation of new dopamine for each process of neurotransmission. But when methamphetamine reverses the dopamine transporter, these tasks can not be executed – the dopamine reuptake is blocked. Thus, dopamine stays in the synaptic cleft. Furthermore, since the dopamine transporter is reversed and not only blocked, it also moves stored dopamine from the presynaptic terminal to the synaptic cleft. These processes directly lead to a greater postsynaptic effect. There is also evidence that methamphetamine reverses the serotonin transporter (Kokoshka et al., 1998; Haughey, Fleckenstein, Metzger, & Hanson, 2000; Sekine at al., 2006), resulting in an increase of the postsynaptic effect of serotonin, respectively.
The next step is to tie this neurochemical modification to a change in behaviour. It has been shown that an increase in dopamine causes a higher level of aggression in many species (Louilot et al., 1986; Glazer & Dickson, 1998; Fitzgerald, 1999). However, there are contradictory studies with respect to serotonin. Some research suggests that serotonin plays a role in aggressive behaviour for various species (Unis et al., 1997, Chiavegatto & Nelson, 2003; Donly & Caveney, 2005), including crickets (Murakami & Itoh, 2003). But other studies indicate evidence that the opposite is the case (Yodyingyuad et al., 1985; Volavka et al., 1990).
Although the role of serotonin is not yet clear-cut, there is converging evidence in the case of dopamine. Since both serotonin and dopamine are present in the nervous system of crickets, we assume that methamphetamine encourages aggressive behaviour in crickets. The aim of this paper is to test this hypothesis.
Materials and Methods
In our experiment, we examined adult male crickets (acheta domestica). They were obtained from Biosupplies NSW and housed in a plastic tube with 24 other crickets. The crickets were supplied by means of soaked carrots and a damp sponge.
The experimental procedure was the following: First of al , a cricket (“resident”) was put into a 2 litre round glass container. After 20 minutes, another cricket (“intruder”) was injected with either 20 µl of saline (0.9%, control group) or 1 mg/ml of methamphetamine (dissolved in saline) into the abdomen of the cricket by means of a 29 Ga hypodermic needle and 1 ml syringe. Saline was purchased from the Clifford Hallam Pharmaceuticals NSW and Methamphetamine from the Australian Government Analytical Laboratories NSW. 10 minutes after the treatment, the intruder was put into the contrainer to the resident. Thereafter, we observed their behaviour for 15 minutes, namely the horizontal locomotor activity. Since we intended to measure the aggressive behaviour, we focussed on 3 features, each measured by a different person: First, we measured the total time of aggressive behaviour with the use of a digital stopwatch. We defined aggressive behaviour by antennal fencing, unilateral and bilateral mandible spreading, mandible engagement, grappling, chirping and kicking. Second, we counted the number of chirrups. The last feature we measured was the number of kicks. For each of these features, we did not only measure the overal results, but also the data for each minute.
Our data contained 34 cricket pairs for the control group and 37 cricket pairs for the methamphetamine treatment. Al crickets were naïve to this experiment and the resident and intruder have never interacted with each other before. The lighting was at a moderate level and we tried to lower noise. For the statistical analysis, we applied an unpaired t-test for each feature using the software SPSS.
The results turned out to be not significant. This holds for aggression time (p=0,895), chirrups (p=0,139) and kicks (p=0,115). The mean of the aggression time was 100 seconds for saline, with a standard error of 15,419s, and 97,46s for methamphetamine, with a standard error of 11,705s. For chirrups, the means were 183,62s for saline (SEM=41,294s) and 112,86s for methamphetamine (SEM=24,699s), for kicks it was 23,38s for saline (SEM=6,026s) and 13,32s for Discussion
The results show that our treatment with methamphetamine did not change the aggressive disposition of crickets, which is contrary to our initial hypothesis. There are various reasons which could have played a role in this outcome.
One reason could be that the experiment was simply not properly executed, since the data was measured mostly by unexperienced students. In addition to that, some unintended factors could have influenced the result. For example, some crickets were missing a leg and some cricket pairs differed considerably in size.
But there are also many conceivable neurological reasons. Our hypothesis was mainly driven by the effect of methamphetamine on the dopamine transporter. However, it has been shown that dopamine is present to a lesser extent than octopamine and serotonin in the cricket nervous system (Nagao & Tanimura, 1988). Hence, dopamine is possibly not very influential on cricket behaviour. Studies suggest that octopamine is more important than dopamine when it comes to aggressive behaviour in crickets (Stevenson, Dyakonova, Ril ich, & Schildberger, 2005; Adamo, Linn, & Hoy, 1995). The higher the level of octopamine, the higher the level of aggression. This relationship has also been shown for other insects (Zhou, Rao, & Rao, 2008). But there is, at least to my knowledge, no clear evidence that methamphetamine significantly increases the level of octopamine in crickets. Octopamine is often called the noradrenaline for invertebrates. For vertebrates, it has been shown that methamphetamine increases noradrenaline (Ferrucci et al., 2007), which is involved in aggressive dispositions – but evidence for an analogous increase of octopamine in invertebrates seems to be lacking. Hence, the role of octopamine could be the crucial factor for the results of our experiment.
Furthermore, some research indicates that serotonine transporters have a lower sensitivity for trycyclic antagonists in some insects (Donly & Caveney, 2005). Maybe this phenomenon also applies to crickets. In that case, the influence of serotonin would be decreased. Moreover, it has been shown that GABA and glutamate are involved in aggressive behaviour of vertebrates as well (Puglisi-Allegra et al., 1979; Miczek et al. 2004). It is possible that the effects of these chemicals affected the results of our experiment, in a way which we did not expect.
Another good reason for the outcome of our experiment could be the fact that we only measured a singular treatment with methamphetamine. It is reasonable to assume that the results of a long-term treatment with methamphetamine would have been different. In mice (Landa, Slais, & Culcova, 2006) and monkeys (Melega et al., 2008), a singular treatment with methamphetamine increases aggressive behaviour and long-term treatment with methamphetamine decreases the level of aggression. Maybe the opposite is true for invertebrates like crickets. A change in the number of transporters due to an adaptation could play a role.
Apart from that, it may be the case that the applied dosage of methamphetamine was not appropriate. There is evidence that a low dosage and a high dosage can have contrary effects with respect to aggressive dispositions (Kuczenski, Segal, Cho, Melega, 1995). There is evidence for this phenomenon in the case of rats (Silverman, 1966a) and cats (Hoffmeister & Wuttke, 1969).
We can conclude that there is a broad spectrum of conceivable explanations for the results of our experiment. Experiments with locusts or cockroaches may offer further insights, since their neurochemical profile is similar to the cricket (Nagao & Tanimura, 1988). It has to be the object of further research to determine the precise effects of methamphetamine on the cricket nervous system.
References
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This graph shows the mean of the total aggression time (for 15 minutes of experimental procedure) in seconds for both the saline and the methamphetamine )
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One can see that both the mean of the total aggression time as well as the standard error of the mean are slightly higher for saline than for mehtamphetamine. However, this result has turned out to be not significant. This graph shows the mean of the aggression time in seconds for each minute of the experiment (non-cumulative) for both the saline and the methamphetamine s/m
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One can see that the values for both treatments are varying, with neither of them being constantly higher than the other. Both the minimum as well as the maximum aggression time per minute can be found in the results for the methamphetamine treatment: 4s at minute 6 and 9s at minute 5. The SEM results do not seem to show This graph shows the mean of the total number of chirrups (for 15 minutes of experimental procedure) for both the saline and the methamphetamine treatment.
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One can see that both the mean of the total number of chirrups as well as the SEM are higher for saline than for mehtamphetamine. However, this result has turned out This graph shows the mean of the number of chirrups for each minute (non- cumulative) for both the saline and the methamphetamine treatment.
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One can see that both the means of the number of chirrups per minute and the SEM- values are always higher for saline than for methamphetamine. In addition to that, the means of the number of chirrups per minute seem to be constantly increasing, although there are some breaks (mostly for saline at minutes 7 and 13). Saline takes the maximum of 17 at minute 11 and methamphetamine takes the minimum of 5 at This graph shows the mean of the total number of kicks (for 15 minutes of experimental procedure) for both the saline and the methamphetamine treatment.
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One can see that both the mean of the total number of kicks as well as the SEM are higher for saline than for mehtamphetamine. However, this result has turned out to This graph shows the mean of the number of kicks for each minute (non-cumulative) for both the saline and the methamphetamine treatment.
Time (min)
One can see that both the means of the number of kicks per minute are similar for both treatments until minute 7. However, from that minute on, the values for saline are clearly increasing whereas the values for methamphetamine are decreasing. This gap gets balanced again at the end of the experiment. The SEM-results are mostly higher for saline than for methamphetamine. Saline takes the maximum of 2 kicks per minute and methamphetamine the minimum of 0 kicks per minute – this holds for This table shows the results of the independent samples t-test from the statistics software SPSS. The tested for the variables total aggression time, total number of Group Statistics
Independent Samples Test

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