Neurotransmitter pathways

The pleasure derived from using tobacco is linked to the stimulation of dopamine-dependent neurotransmitter pathways in the brain, particularly in the meso-limbic system. The precise nature of this link remains controversial, but many of the neurophysiological processes underlying nicotine addiction are common to other addictive drugs with diverse pharmacological actions such as opiates, cannabis, alcohol and cocaine. 

The anatomical studies indicate that activation of modality-specific primary and secondary sensory areas and their subcortical connections are involved in different types of hallucinations. The distribution of the neurotransmitter pathways supplying these areas (Figs 2-5, Chapter 1) suggests that many neurotransmitters are involved. This conclusion is supported by the large number and heterogeneity of drugs that can produce hallucinations (Table 2). Thus,... 

Consequently, antipsychotic drugs all share a basic mechanism of action that involves dopamine receptor blockade. It is apparent, however, that they are not all equal in their ability to affect specific sub-types of dopamine receptors, and that their effectiveness and side effects are related to their affinity and preference for certain receptors. As indicated earlier, other neurotransmitters may also be involved in the pathogenesis of psychosis, and differences in specific antipsychotic medications may be related to their ability to directly or indirectly affect these other transmitters as well as block dopamine influence. Future studies will continue to clarify how current antipsychotics exert their beneficial effects and how new agents can be developed to be more selective in their effects on dopamine and other neurotransmitter pathways. 

Figure 9.10. Main brain regions and neurotransmitter pathways thought to be involved in OCD.

In SUMMARY, it is apparent that the biological basis of PTSD remains obscure although there is evidence that the hypothalamic-pituitary-adrenal axis is hypofunctional. So far there is no convincing evidence that any of the classical neurotransmitter pathways are directly involved although there is limited evidence that the opioid system could be hyperactive which might contribute to the suppression of memory recall which is often exhibited by victims of torture and sexual abuse. 

Many AD patients have damage to other neurotransmitter pathways as much as to their cholinergic pathways thus, they would not be helped much by manipulating only ACh levels in their brains. 

The major neurotransmitter pathways—and those most important in... 

These pioneering tissue culture studies clearly documented that certain extracellular factors were capable of re-directing the biochemical choices of neurons previously committed to another neurotransmitter pathway. A comparable role for differentiation factors in vivo is supported by the work of Landis and colleagues (for review see, Landis,... 

Since these radiohistochemical techniques can be used in a quantitative and reproducible way, a great deal of information regarding drug and neurotransmitter receptors has been provided. These radiohistochemical studies can be used as important complements to mapping neurotransmitter pathways. They can also be useful complements to various physiological experiments, and they often provide new hypotheses about the mechanisms of action of various drugs. 

Other models have been described which reproduce learning impairment and memory loss. These models are based on lesioning or pharmacological blockade (scopolamine) of specific neurotransmitter pathways, or as in the Brattleboro strain of rats where vasopressin production is perturbed due to an hereditary disorder. These models will undoubtedly make a contribution, but they are aimed at studying memory and do not necessarily elucidate the characteristic features of Alzheimer s disease. 

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