Consciousness cholinergic system

Recent research has indicated select abnormalities in the cholinergic system (Perry et al., 2001). Although previously unexamined neurochemically, there was an indication that the cholinergic system may be involved in autism, with abnormalities reported in neurons in the basal forebrain (Bauman Kemper, 1994). Perry et al. (2001) found extensive loss of high affinity nicotinic receptors from the neocortex (frontal and parietal), and from the cerebellum (Lee, et al., in preparation). Nicotinic receptors are implicated in attention, and also consciousness as many general anaesthetics block the receptor channel (Chapter 9). 

While normal cholinergic activity in the brain is essential for its normal functioning, strong activation of the cholinergic system in the CNS leads to loss of consciousness, to epilepsy-type convulsions, to muscular fasciculations (CNS-caused) and to down-regulation of the breathing center. 

Damsma, G., Westernik, B.H., de Vries, J.B., and Horn, A.S., The effect of systemically applied cholinergic drugs on the striatal release of dopamine and its metabolites, as determined by automated microdialysis in conscious rats, Neurosci. Lett., 89, 349, 1988. 

Accordingly, several of the neurochemical and neuroanatomical systems considered to be involved in arousal and consciousness, i.e. Meynert nucleus, pontine reticular formation, locus coeruleus and raphe nucleus with their cholinergic, noradrenergic and serotonergic afferents (Delacourt, 1995) are affected in PD. In addition, the dopamine system, in particular the mesolim-bocortical system, is involved in cognition and motivation, and possibly in the emergence of positive psychotic symptoms such as hallucinations and delusions. 

Later in this chapter I will assign to them (and their cholinergic colleagues in the laterodorsal tegmental and pedunculopontine nuclei) one of three dimensions in the AIM state space model that I use to integrate the pharmacologically altered states with those that occur naturally. It is of paramount importance to emphasize that the brain uses its own chemical systems to achieve a rich panoply of altered states of consciousness, including some truly psychedelic ones ... 

Some erections are mediated by a sacral nerve reflex arc (e.g., erections can occur while the patient is sleeping). However, in the conscious patient, sensory sexual stimulation mediates erections via the central nervous system. That is, when a patient sees an attractive partner, hears sweet words, smells a particular scent, or tastes or touches a pleasant object, this can result in an erection. In this case, the patient s brain processes this information and the nervous impulse is carried down the spinal cord to peripheral cholinergic nerves that innervate the vascular supply to the corpora, resulting in an erection. 

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