Caffeine and Nutrition: an Overview - Caffeine: Chemistry, Analysis, Function and Effects - page 9

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Figure 1.2

The 5-day sequence of latent inhibition (LI). Left, the experimental
chamber to run the latent inhibition (LI) procedure, in a conditioned
taste-aversion paradigm. Right, the sequence of the three phases of the
LI experiment, described as follows: in phase 1 (pre-exposure to sucrose,
days 1 to 3), animals were placed in this chamber and had access to either
a 5% sucrose solution (sucrose pre-exposed group, PE) or tap water
(non-pre-exposed group, NPE) for 30 min. On phase 2 (''conditioning'';
day 4), all animals were given access to the sucrose solution for 30 min,
immediately followed by an intraperitoneal injection of LiCl (50 mg kg -1 )
as an aversive stimulus to produce the conditioned taste aversion.
Finally, on phase 3 (''testing''; day 5), each animal had simultaneous
access to both sucrose and water for 30 min. LI, expressed as the
''sucrose suppression ratio'' (SSR), was assessed by comparing the
amount of sucrose versus water consumed on day 5, according to the
following formula: SSR 5 [mL sucrose consumed/(mL sucrose consumed
+ mL water consumed)] (unpublished picture from the authors' lab).

In well-nourished rats, previous experiments by others showed that the
administration of 10 mg kg -1 caffeine could not modify selective attention, as
evaluated with the LI model (Bakshi et al 1995). We recently performed a dose-
response curve analysis for caffeine and showed that the caffeine effect depends
on the dose employed. A dose of 30 mg kg -1 , but not treatment with 15 mg kg -1
caffeine, was effective in modulating LI (Aguiar et al 2011; see also our
unpublished data in Figure 1.3). The results can be explained by the central
action of caffeine particularly on the adenosine A 2A and dopamine D 2
receptors (Fredholm 1999; McKim 1996). The effects of caffeine on selective
attention are suggested to depend on the increased dopamine D 2 transmission
following the inhibition of adenosine A 2A receptors by caffeine (Aguiar et al
2011). Other studies also support the involvement of dopaminergic activity in
the mechanisms of attention. D 2 -antagonistic drugs that are effective in the
treatment of psychotic illnesses like schizophrenia also improve selective
attention, which is impaired in this disease, and have been tested in the LI
model (Weiner and Arad 2009). It is worth mentioning that the biological basis
of schizophrenia involves selective attention impairment (Moser et al 2000),
but no one knows if, and how, nutritional disturbances would modulate it.
According to these authors, because of its characteristics, LI is a sensitive and
reliable

model for the study of selective attention and is considered an