An experiment was conducted at the University of British Columbia to examine the correlation of psychostimulants, dopamine, and sexual behavior. The hypothesis that “behavioral sensitization caused by repeated psychostimulant administration can ‘cross-sensitize’ to a natural behavior, such as sex, and that increased NAC[nucleus accumbens] DA[dopamine] release may contribute to the facilitation of appetitive and consummatory aspects of this behavior” was supported by results of the study (Fiorino 1999). Simply put, giving an organism a drug (like cocaine) over a period of time can cause the drug to have a stronger affect then it originally did, as referred to in the previous sentence as behavioral sensitization. Scientists set out to prove that behavioral sensitivity due to repetitive drug use can influence the sensitivity of other behaviors, and that increased dopamine release in the nucleus accumbens can account for an increase in the desire for gratification by way of sexual intercourse.
The researchers used several of the techniques discussed in Physiology of Behavior to prove their hypothesis. Male and female rats were kept in separate plastic cages when they were not being observed. The ovaries of the female rats were removed, and they were given estradil benzoate (the most powerful hormone secreted by the ovaries) and progesterone (produced by the body to prepare for implantation) (Fiorino 1999).
Stereotaxic surgery, which is most often used for lesion production, was performed on the male rats. In this case, the surgery was done so that the scientists could insert microdialysis probe guide cannulas into the NAC. The cannulas, or small metal tubes, function by carrying a solution into a certain area of the brain (in this case the NAC) so that it can collect molecules from the extracellular fluid; after the molecules are collected, the fluid comes out through another tube. The cannulas were secured to the skull with dental acrylic and jeweler’s screws, and a wire “training post” was cemented to the top of the skull behind the cannula (Carlson & Fiorino, 2004, 1999).
Chambers were used to join the male and female rates together. For twenty consecutive days, the male rats were placed into its appropriate chamber and attached to a liquid swivel by way of a steel coil that was secured to his training post. The rats waited half an hour before D-amphetamine sulfate or the saline control was administered, and two hours more after the injection was given. This way, the rats were able to get accustomed to the probe and their surroundings before testing began. Samples were taken by microdialysis every ten minutes during this two-hour period (Fiorino 1999).
All the male rats were sexually inexperienced, whereas the female rats were not. On the twenty-first day, the female and male rats were joined for sixty minutes, while interaction was allowed for thirty. Sexual behavior was videotaped and recorded by computers. Many statistics were available, including, but not limited to, ejaculation frequency and latency, mount frequency, and intromission (insertion) frequency. Microdialysis was used to determine the amount and alterations of dopamine in the NAC (Fiorino 1999).
After the test was completed, the mice were given a fatal dose of chloral hydrate and underwent perfusion via saline and formalin injection (used to harden the brain). The brains were sliced and sections were stained with cresyl violet to determine if the probes were placed in NAC. Only the mice with correct placement of the probes were included in the study (Fiorino 1999).
Stereotaxic surgery was used to pinpoint the correct area of the brain for probe insertion. Histological methods (such as fixation, sectioning, and staining) were used to ensure the results were valid by verifying what area of the brain was tested. Microdialysis was used to view the extracellular changes, along with video and computer monitoring of physical activity. All these techniques were used to ensure the validity of the test, to make the relationship between psychological and physical functions clear, and to have a deeper understanding then the naked eye can provide (Carlson & Fiorino, 2004, 1999).
In conclusion, the results confirmed that the male rats who were given D-amphetamine displayed a much higher dopamine increase during the first thirty minutes of female-exposure opposed to the control group. They also had an increased number of mounts, ejaculations, and intromissions. A higher dopamine increase occurred for two-hours after drug injection opposed to normal readings, and a noteworthy increase occurred between the first and tenth injection. Scientists can conclude from this study that using a drug over a period of time can cause an increase in the amount of dopamine release, which in turn raises an organism’s sexual drive and triggers behavioral sensitivity (Fiorino 1999). .
References:
1. Carlson, Neil R. (2004). Neurotransmitters and Neuromodulators. In Physiology of Behavior, 8, 112-130.
2. Fiorino, D. & Phillips, A. (1999). Facilitation of Sexual Behavior and Enhanced Dopamine Efflux in the Nucleus Accumbens of Male Rats after D-Amphetamine-Induced Behavioral Sensitization [electronic media]. The Journal of Neuroscience, 19(1), 456-463.
