hypermotility induced by LPS, 3 and 7 days after surgery (Figure 1), could be a
compensatory reaction of dopaminergic neurons that survived the lesion.
It is well know that COX-1 is constitutively expressed in nearly all tissues
including the brain, in neurons and astrocytes [17]. COX-2, although an inducible
protein, is constitutively expressed in only a few tissues including the brain,
particularly in neuronal soma, but not in astrocytes, of different regions including
the cortex, amygdale, hippocampal formation, and the dorsal horn of the spinal
cord [4]. It becomes up-regulated briefly – 1 – 8 h after seizure, trauma,
intracerebral hemorrhage, ischemia, or other neurodegenerative diseases
[3,38,23,21,12]. Microglial activation can be triggered by pathogenically-
modified activation of Central Nervous System (CNS) proteins, antigens from
infection agents (such as the gram-negative bacterial cell wall component LPS),
prion proteins, or by a complex combination of molecules including ATP, cAMP,
interleukin (IL)-1
β
, IL-6, and IL-10 [15,36]. In this line, there is an increase in
reactive microglia in the striatum and SN of patients with idiopathic PD [31,33].
Thus, the brain area that encompasses the SN has the highest density of microglia
in the brain [22].
In postmortem, investigations of humans exposed to MPTP, activated
microglia have been detected 16 years after the last drug exposure [27]. Activated
microglia and dopaminergic cell loss are also found in the SN of primates years
after they were treated with MPTP [32]. Moreover, a transient microglial reaction
was verified from the 1
st
until the 14
th
day in the SN and striatum in mice that
received intraperitoneal MPTP injection [24]. These findings suggest that the
microglia play an active role in the pathology of PD and may indeed perpetuate the
degeneration of dopaminergic neurons once activated [14].
The MPTP-induced model can be considered a good animal model to study
the impairment of motor activity associated with Parkinson’s disease. This
established model has been reproduced in our group with a significant reduction of
striatal dopamine levels verified in MPTP-lesioned rats [7,11,34,41]. Our behavioral
results corroborate that data, the MPTP group showed motor impairment indicated
by a decrease in locomotion and rearing frequency 24 h after surgery (Figures 1