Feeds:
Posts
Comments

Posts Tagged ‘drugs/ lab animals; drugs/wild animals;Goodman and Gilman’s Pharmacological Basis of Therapeutics (1985) Goodman and Gilman’s Pharmacological Basis of Therapeutics (1985)’

As the prehistoric period begins to close up everywhere—even in the isolated crannies and corners of the world—millennia of prehistoric drug use have left us with no understanding at all of why people use psychoactive dugs. Human beings eat and drink only those substances which nourish their bodies, drugs excepted. They don’t eat soil or grasses  except under bizarre conditions. A half answer might be that we use drugs because drugs satisfy us just as food does. But this begs the question, why should feelings of reward attach to drugs when those same feelings do not attach to any substance accept those that our bodies need ?

In a reversal of natural sequencing, the answer to ‘why do individuals use drugs?’ became clear  following research into ‘why do some individuals overuse drugs?’

 This research began in the USA in the 1960s, following the influx of what seemed excessive student drug use and multiple drug use on US campuses. At the time, the current explanatory paradigm emphasized the causal relationship between drug seeking behaviour and physical dependence, a physiological state which could be empirically verified. Accordingly, early experiments used as subjects already drug dependent animals; it being both unethical and difficult to use people in this type of investigation.

Laboratory animals quickly learn to self administer most of the drugs commonly used by individuals for non‑ medical, recreational purposes. These included  opoids, barbiturates, alcohol, anesthetic gases, local anesthetics, volatile solvents, and central nervous system stimulants like  phencyclidine, nicotine and caffeine. However, animals avoided using substances ignored by humans. This indicated, at first thought, a causal relationship between physical  dependence and drug‑seeking behaviour.

 But logic and  empirical observation led to further investigation.  It revealed that some drugs which do not produce physical  dependence nevertheless produce drug‑seeking behaviour in  experimental animals.  Moreover, it was realized that, even with drugs that produce physical  dependence, the initial drug‑seeking behaviour could not be  attributed to physical dependence since this takes time to  become established.  The general text book Goodman and  Gilman’s Pharmacological Basis of Therapeutics (1985) describes  this research thus:

 

Such observations suggest that pre‑existing psychopathology is not a requisite for initial or even continued drug taking, and that drugs themselves are powerful reinforcers, even in the absence of physical dependence (Gilman et al. 1985:534).

  Although  wild animals do not have comparable access to drugs, there  are numerous examples of them ingesting psychoactive  substances.  There is a close association between reindeer and the psychoactive fly‑agaric mushroom in Siberia (Furst  1972:101).  It is commonly accepted that grazing animals  prefer fermented fallen fruit and that birds sometimes select nectars which intoxicate.  Altogether, there is  increasing evidence that animals seek out psychoactive  experiences.  Researchers from the University of California  claim knowledge of more than 2,000 cases of animals  consuming psychoactive substances, of which 310 were  investigated and their use found to be ‘intentional and  addictive’ (Greenberg 1983:300).

**********

Simultaneous with the above research, a rush of interest began in the newly unfolding science of neurobiology. Instead of electricity firing the brain as formerly thought, scientists discovered that central nervous system activity depended upon least fifty chemical compounds named neurotransmitters. The latter controlled and coordinated flows of information between the  neurons within the brain, including data about  emotions, memories and pleasures.

 The main chemical transmitters  include dopamine, acetylcholine, nor epinephrine, serotonin,  gamma‑amino butyric acid, and the recently discovered opoid  peptides. Each possesses a specific molecular and spatial  arrangement which enables it to ‘plug’ into a receptor in a  target neuron, rather like a key into a lock.  The neuron is thus activated, information passes from one neuron to the  next, and the neurotransmitter, its function accomplished, decays.

 This may seem far distant from  packing a cone or sipping gin and tonic.  Here is the connection. Humans and non- human animals are not the only natural phenomena containing neurotransmitters. Some plants contain (almost) identical chemicals.  A unique situation results. The nicotine in  tobacco, for example, fits receptors designed for  the acetylcholine receptor and, once plugged into the receptor, nicotine  activates the same processes that acetylcholine can activate. Similarly, morphine from opium poppies fits receptors  for the body’s endogenous opiates… and so on. 

However, one difference exists  between plant chemicals and the mammal neurotransmitters of  which they are analogues. Plant neurotransmitters are  much more resistant to inactivation by biotransformation  processes. Therefore plant neurotransmitters often become potent neurotoxic  agents (Kosterlitz and Hughes 1978:412).  Thus, the effect of  psychoactive drugs is to potentiate or inhibit  neurotransmitters, or alter their synthesis, storage or  release.  By this means drug use modifies memory, learning,  emotions, mood, and perceptions of self and others (Levine  1978:344). 

That leaves unanswered the question, “why do drugs make us feel good?”

 Bibliography

Furst, P. (1972). Flesh of the gods: The ritual use of hallucinogens.London. George Allen & Unwin.

Greenberg, M. (1983). Natural highs in natural habitats. Science News, 124, 300-301.

Gilman, A.G., Goodman, L.S., Rall, T.W, & Murad, F. (1985). Goodman and Gilman’s pharmacological basis of therapeutics. New York. MacMillan.

Kosterlitz, H.W., and Hughes, J. (1978). Endogenous opoid peptides. In J. Fishman (Ed) The bases of addiction: Report of the Dahlem Workshop on the bases of addiction. Abakon. Verlagagesellschaft.

Levine, R.R. (1978). Drug actions and reactions. Boston. Little Brown and company.

Schuster, C. (197) Drugs as reinforcers in monkey and man. Pharmacological Reviews 27:511-251

Read Full Post »