Sex, Drugs, and Neurobiology

It’s that feeling when your favorite song comes on the radio, the ping in your heart once that cute stranger returns your smile, it may even be that first bite of your favorite sandwich –it’s the feeling of pleasure. Although we each have our own unique definition of what is pleasurable, the biochemistry that conjures up these feelings is surprisingly forthright. Interestingly, these biological processes explain why recreational drugs have had such a strong influence on our society. Rather than stimulate a context-dependent signal, some drugs can simply  flip on the pleasure switch. And it all begins in the neuron.

At any given second, a plethora of chemical interactions are being carried out by every cell in the body and neurons are no exception. One of the most distinctive features of a neuron is its ability to use chemical molecules, called neurotransmitters, to potentiate information. These neurotransmitters literally act as the cell’s voice – carrying messages to other neurons.  These messages are processed by protein receptors which act as ‘ears’ and allow the receiving neuron to process and pass along what it has heard. There are an assortment of receptors and neurotransmitters used by the brain; each of which defines the role of the neuron they are expressed in.

Most of the billions of chattering neurons which make up the brain are anatomically segregated into different regions based on their function. For example, the neurons in the prefrontal cortex are responsible for personality traits, decision making, and cognitive behavior. This region is fairly unique in primates.  On the other hand, one of the oldest and most primitive regions in the brain comprises the limbic system. The anatomy of the limbic region in the human brain is quite similar to that of most animals with backbones. This anatomical similarity is responsible for our more primitive instincts (i.e. the limbic system is responsible for behaviors such as aggression, appetite, sexual desire, and pleasure).  Quite aptly, neuroscientist Paul D. MacLean referred to these regions as the ‘Reptilian Brain’.

So what happens when pleasure is felt? From the moment a stimulus is seen, felt, touched, tasted, or smelt, the body, in an attempt to put this new information in context, elicits electrical and chemical signals that bounce around numerous regions of the brain until a thought is complete. For example, when a picture is viewed that conjures up a happy childhood memory, the image is first processed, then the memory associated with that image is referenced, then the feeling is recalled, and finally the region of the brain associated with that feeling is stimulated. It is a heavily-involved computational task that only the most advanced and efficient computers in existence, our brains, can perform.

A better understanding about how these neurons send and receive signals has led to successful diagnosis and treatment of many personality disorders and other psychological impairments. It also provides us with insights into the use of pleasure-inducing recreational drugs.

Almost all the recreational drugs that have been studied manipulate the interaction between a neurotransmitter and a receptor. Cannabinoids activate C1 and C2 receptors, alcohol stimulates GABA receptors, ecstasy affects NMDA receptors, and Cocaine/amphetamines (e.g. recreational use of Adderall) increase dopamine levels. In the short term these drugs change the balance of signaling molecule and receptor response, but in the long run they can actually change the very anatomy and chemistry of your brain.

Some of the most popular recreational drugs used today affect dopamine levels in the limbic system. Dopamine is one of the major neurotransmitters which targets cells associated with the ‘pleasure regions’ of the brain. Cocaine exerts its stimulatory effect by preventing the degradation of dopamine, this maintains a longer lasting signal to the neurons in that region (the voice carries on longer). Adderall increases the amount of dopamine released, creating a more intense signal (a louder voice). Although these drugs induce a euphoric sensation which makes the user feel confident and joyous, it is ephemeral, and inevitably the body will return to homeostasis and the feeling will be lost. With the continual use of a substance, neurons will become accustomed to the artificial levels of the neurotransmitter the drug induces, and dependencies of one form or another will occur.

Another drug commonly used today is alcohol (ethanol). In fact, if alcohol was just discovered today, it would be classed as a schedule II drug (drugs such as morphine and Ritalin) for which a prescription would be needed. Ethanol molecules bind to GABA receptors, aberrantly increasing their activity. GABA receptors actually inhibit the transmission of information through the neuron. Predictably, the GABA receptors most affected by ethanol are those present in our prefrontal cortex. With the correct amount of alcohol, the regions of our brain responsible for rational thought shuts down, reducing the alcohol consumer to a creatures akin to lizards, in both logic ( reducing the user’s thoughts to fight, eat, sex, happy) and grace. [share_this_post]

It is very apparent that the utilization of drugs which modify cognition or induce artificial pleasure have embedded themselves into human culture. The underlying biochemical mechanisms of recreational drugs tap into regions of the brain that were established to reward breeding and survival, ensuring evolutionary success.  It is therefore not surprising that despite the high risks of dependency and toxicity, that the irresponsible use of these drugs will always be prevalent.

Image: A characteristic night out and a few drinks. Cartoon by Kenric Hoegler  © 2014

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