Drug effects: Heroin, UTC for healthcare professionals

Opiates like heroin inhibit the neurons. Although this resembles CNS depressants, substances of this distinct pharmacological class have different mechanisms of action.

Drugs such as morphine or heroin produce their effects interacting with the endogenous opioid system, which has receptors distributed in the periaqueductal gray matter of the brain, spinal cord, myenteric digestive plexuses, and joints (Gutstein, 2001). There are four different subtypes of opioid receptors in humans (Álvarez, 2005): mu (μ), delta (δ), kappa (κ), and nociceptin (nociceptin/orphanin).

Opiates produce their reinforcing effects in the dopaminergic neurons of the ventral tegmental area (VTA), activating μ receptors (Miñarro, 2006), and decreasing the activity of inhibitory (GABAergic) neurons (Koob,2004). These neurochemical interactions favor the unregulated release of dopamine in the nucleus accumbens of the reward circuit and its areas of projection. Opiates act as ligands in metabotropic receptors of the postsynaptic neurons, where they trigger long-term reactions that, unlike endogenous opioids, are long-lasting and difficult to reverse (Cruz, 2006).

The chronic use of high-affinity opiate agonists, such as morphine and heroin, leads to tolerance and physical dependence. It is essential to understand that tolerance develops in a deferred way, both in time and intensity. It begins with the loss of efficacy to induce nausea and euphoria, then the analgesic effect disappears, and finally there is partial tolerance to constipation and respiratory depression. This process explains the risk of dying from respiratory arrest, even for experienced chronic users (Cruz, 2008).

References

- Álvarez, Y. & Farré, M. (2005).Farmacología de los opioides. Monografía opiáceos. Adicciones, 17, 21 – 40.

- Cruz, M. C. S. (2006). El cerebro y el consumo de drogas. Boletín CINVESTAV, Abril-Junio: 36 – 45.

- Cruz, M. C. S., & Granados-Soto, V. (2008). Opioids and opiates: Ligands, receptors and effects, En M. Méndez & R. Mondragon. (Eds), Neural Mechanisms of Action of Drugs of Abuse and Natural Reinforcers (pp. 1-24). Ontario, Canada: Research Signpost.

- Gutstein, H. B. & Akil, H. (2001). Opioid Analgesics. En: J. G.,Hardman, L. E.Limbird, A. G., & Gilman., (Eds), The pharmacological basis of therapeutics (pp. 569 – 619). New York: McGraw-Hill.

- Koob, G. F., Ahmed, S. H., Boutrel, B., Chen, S. A., Kenny, P. J., Markou, A., O’Dell, L. E., Parsons, L. H., Sanna, P. P. (2004). Neurobiological mechanisms in the transition from drug use to drug dependence. Neuroscience & Biobehavioral Reviews, 27, 39 – 49.

- Miñarro, J., & Manzanedo, C. (2006). Efectos conductuales del consumo de opiáceos. En Tratado SET de Trastornos Adictivos. Sociedad Española de Toxicomanías (pp. 296 – 300). Madrid, España: Colegio Iberoamericano de Trastornos Adictivos.

Related topics

UTC for healthcare professionals

• Neurobiology of Addiction: https://www.issup.net/node/7342
• Classification of Drugs: https://www.issup.net/node/7521