antipsychotics which are routinely used in the management of schizophrenia and other affiliated disorders are often associated with distressing extra - pyramidal side effects . the phenomenon of cataleptic immobility - induced in animals by typical neuroleptics ( e.g. haloperidol ) is a robust behavioral model to study the nigrostriatal function and its modulation by cholinergic , dopaminergic and other neurotransmitter systems ( 1 ) . haloperidol - induced catalepsy occurs due to the blockade of dopamine ( d2 ) receptors and reduced dopaminergic transmission . enhanced stimulation of the intrinsic central cholinergic system has also been implicated in haloperidol - induced catalepsy as it has been reported to be enhanced and antagonized by pilocarpine and the cholinergic blocker , atropine , respectively ( 1 ) . interesting evidences suggest the important roles of inflammatory reactions accompanied with the pathological processes caused by cyclooxygenase-2 ( cox-2 ) seen in many neurodegenerative disorders , including parkinson s disease ( pd ) ( 2 , 3 ) . furthermore , the inhibition of cox-2 or cox-2 gene expression as we previously showed can improve the movement disorders of pd in animal model ( 4 - 6 ) . also previous reports suggest that cox-2 can cause an increase in the level of acetylcholine in the brain through producing the prostaglandin e2 and increasing the expression of cholinergic markers , such as choline acetyltransferase and vesicular acetylcholine transporter protein . it has been mentioned that prostaglandins have modulatory effects on adrenergic , noradrenergic and glutaminergic transmissions ( 7 , 8) . in addition , some of the investigations have shown that cox-2 inhibitor impairs the spatial memory through the reduction of acetylcholine level in the brain ( 9 , 10 ) . the compound 11b [ 1-(phenyl)-5-(4-methylsulfonylphenyl)-2-ethylthioimidazole ] ( as we reported ( 11 ) its synthesis and biological potencies as the most potent and selective cox-2 inhibitor ( cox-2 ic50 = 0.58 m with no inhibition of cox-1 up to 25 m ) relative to the reference drug celecoxib ( cox-2 ic50 = 0.21 m with no inhibition of cox-1 up to 25 m ) ) was selected to investigate its effects on the haloperidol - induced catatonia as a different pd animal model and also neuroleptic overdose animal model . furthermore , simultaneous to the catalepsy measurement , the in - vivo assay of dopamine concentration changes in the striatum as the affecting area in the cataleptic disorders after the administration of selective cox-2 inhibitor , was the latter interest of this research . adult male albino rats ( weighing 250 - 300 g ) were selected for the study . the animals were purchased from pasteur institute of iran and housed in stainless steel cages , handled daily , and provided with food and water ad libitum . a 12 h light/12 h dark cycle was maintained and animals were tested during the light cycle . these animals experiments were carried out in accordance with the recommendations from the declaration of helsinki and the internationally accepted principles in the use of experimental animals . compound 11b and haloperidol were freely dissolved in distilled water and scopolamine was dissolved - suspended in 1% gum acacia solution . in acute study , all injections were ip and in chronic , all injections were p.o except the haloperidol ip . surgery and microdialysis procedure 
  after anesthetizing [ 75 mg / kg ketamine combined with 8 mg / kg xylazin ip ] and placing the rats in the stereotaxic apparatus , a sagittal incision was made in the scalp with sterile blade . subsequently , the skin and inferior tissue layers covering the skull were retracted and then , the skull was exposed and a hole was drilled through it in the area overlying the right striatum , using the following coordinates with respect to the bregma : a / p + 1 mm ; m / l + 3 mm , d / v + 6 mm according to the atlas ( 12 ) . a guide - cannula lowered into the brain for inserting the microdialysis probe which delivered a modified ringer solution through the probe , was fixed to the cranium and the incision was closed . rats were allowed to recover from the surgery for 7 - 10 days . on the experimental day , a microdialysis probe was inserted into the cannula , and the inputs of the probes were connected to a microperfusion pump , cma/102 infusion pump ( cma / microdialysis , sweden ) , which delivered a modified ringer solution ( 147 mm nacl , 1.2 mm cacl2 , 2.7 mm kcl , 1.0 mm mgcl2 and 0.04 mm ascorbic acid ) through the probe at a flow rate of 2 l / min . ringer solution was then infused for 3 - 3.5 h before the baseline samples being collected to obtain stable basal extracellular levels of dopamine . the microdialysate samples ( 20 l ) were collected every 20 min . when a stable outflow was shown by four consecutive samples of neurotransmitters , rats were given orally compound 11b ( 2 , 4 and 8 mg / kg ) and scopolamine ( 1 mg / kg ) and dimethyl sulfoxide ( dmso ) as vehicle . control rats received a saline injection ( 1 ml / kg ) . the stress caused by the ip vehicle injection and handling of the rats was not found to alter the extracellular glutamate - dopamine levels . in part of experiments , when the rats were given drugs or vehicle after four stable consecutive samples , the dialysates were collected for 2.5 h after the injection . after the experiments , the location of the probe was determined histologically on serial coronal sections . animals were individually housed for the duration of the experiment in a cma/120 system ( cma / microdialysis , sweden ) . dopamine samples were analyzed by the reverse - phase , high performance liquid chromatography ( hplc ) with the electrochemical detection ( 13 ) . 
 experimental procedure 
  simultaneously to the microdialysis haloperidol - induced , catatonia was induced with haloperidol ( 1 mg / kg ) and assessed at 30 min intervals until 120 min and at the end of 240 min by means of standard bar test ( 14 , 15 ) . haloperidol ( 1 mg / kg ip ) was chosen so that it could elicit a moderate degree of catalepsy and thus enable the detection of either attenuation or potentiation of phenomenon ( 16 , 17 ) . catalepsy was assessed in terms of the times for which the rat maintained an imposed position with both front limbs extended and resting on a 10 cm high wooden bar ( 1.25 cm diameter ) . the end point of catalepsy was considered to occur when the both front paws were removed from the bar or if the animal moved its head in an exploratory manner . scoring method : if the animal maintained the imposed posture for at least 20 sec , it was considered to be cataleptic and given one point . for every additional 20 sec that the cataleptic posture was maintained , one extra point was given . the animals were tested twice at 30 min intervals and only the greater duration of immobility was considered . in the acute study , compound 11b ( 2 , 4 and 8 mg / kg ) and scopolamine ( 1.0 mg / kg ) were administered only 30 min prior to the haloperidol administration . in the sub - chronic study , these agents were administered once daily 30 min prior to the haloperidol administration for seven days . catalepsy was determined 30 min after the haloperidol administration on the 1 and 7 day of the treatment . statistical analysis 
  for each group , mean  sem was considered and the data was analyzed by one way anova followed by dunnett s multiple comparison test . the average concentration of four stable samples before the administration of drugs or vehicle [ dmso ] was considered as the basal glutamate - dopamine concentration . statistical evaluation of the results was performed by means of one - way analysis of variance ( anova ) and student - newman - keuls multiple range test , considering the following significant differences : p < 0.05 . acute study ( 
 figure 1 
 ) 
  acute administration of compound11b as a new selective cox-2 inhibitor can significantly attenuate the haloperidol - induced catalepsy as well as scopolamine in the acute study , the administration of standard drug ( scopolamine ) and all doses of the test drug gave cataleptic scores similar to the vehicles - treated groups . however , from 60 min onwards after the haloperidol administration , scopolamine ( 1.0 mg / kg ) resulted in significantly lower cataleptic scores than the vehicle - treated rat . on the other hand , the median dose and the lower dose of compound 11b resulted in lower cataleptic scores as compared to the vehicle - group , 60 and 90 min after the haloperidol administration , respectively . however , from 120 min onwards until 240 min after the haloperidol administration , the higher dose of compound 11b significantly lowered the cataleptic scores compared to the vehicle group . in fact , 90 min post - haloperidol - induced all doses of compound 11b were actually more protective against catalepsy than even the standard drug scopolamine . surprisingly , the higher dose of compound 11b was observed to be less effective in catalepsy improvement , comparing to other doses of compound . 
 sub - chronic study ( 
 figure 2 
 ) 
  sub - chronic administration of compound11b as a new selective cox-2 inhibitor can significantly attenuate the haloperidol - induced catalepsy as well as scopolamine in the sub - chronic study , the administration of standard drug and all doses of the test drug 30 min after the last haloperidol dose on the 7 day , gave cataleptic scores similar to the vehicles - treated groups . however , from 60 min onwards after the haloperidol administration , scopolamine ( 1.0 mg / kg ) and compound 11b ( 2 , 4 and 8 mg / kg ) resulted in significantly lower cataleptic scores than the vehicle - treated rat . the sub - chronic results of the study showed that the highest dose of compound 11b was as protective as the 1 mg / kg dose of scopolamine . our statistical analysis showed that the protective effect of compound 11b against haloperidol - induced - catatonia was both dose - and time - dependent . acute microdialysis study ( 
 figure 3 
 ) 
  acute administration of compound11b as a new selective cox-2 inhibitor can significantly enhance the striatum dopaminergic neurotransmission as well as scopolamine the striatal extraneuronal ( i.e. microdialysate ) concentration of dopamine in rats of all examined groups before the drug - vehicle injection ( baseline ) was 2.1  0.33 pg/20 l respectively . cox-2 inhibitor and their doses as well as scopolamine were observed to modify dopaminergic neurotransmission in the striatum of rats during the observation period . additionally , the changes were seen to be significant ( p < 0.05 ) for dopamine concentrations on or after 40 min throughout the process until 180 min . sub - chronic microdialysis study ( 
 figure 4 
 ) 
  sub - chronic administration of compound11b as a new selective cox-2 inhibitor can significantly enhance the striatum dopaminergic neurotransmission as well as scopolamine the striatal extraneuronal ( i.e. microdialysate ) concentration of dopamine in rats of all examined groups were 2.9  0.41 pg/20 l respectively before the drug - vehicle injection ( baseline ) . this observation shows that sub - chronic administration of selective cox-2 inhibitor compound 11b can elevate the basal level of striatum dopamine from 2.1  0.33 pg/20 l to 2.8  0.41 pg/20 l . the day 7 , results of the microdialysis experiment showed the significant increasing level of striatal dopaminergic neurotransmission with regard to the 7 day basal level after the administration of selective cox-2 inhibitor but just with its high dose 8 mg / kg as well as scopolamine 1 mg / kg within 40 - 120 min observation period . this study was intended to explore the more important role of cox-2 in dopaminergic neurotransmission in striatum of rats . also this study shows that acute and sub - chronic cox-2 selective inhibitor compound 11b administration had an important role in haloperidol - induced catalepsy improvement by enhancing the dopaminergic neurotransmission . it seems that cox-2 and its metabolites , prostaglandins ( pgs ) , have an important role in neurotransmitter release and pd affiliated rigidity as noted in previous reports ) 4 , 5 , 18 ) suggesting that cox-2 causes increased levels of acetylcholine in the brain via production of pge2 and increases in expression of cholinergic markers , such as choline acetyl transferase and vesicular acetylcholine transporter protein . it was also noted that prostaglandins have modulatory effects on adrenergic , noradrenergic and glutaminergic transmission , specially pge2 , and prostaglandin synthesis inhibitors induced increases in the blood pressure via increases in the release of the catecholamine ; for example using large doses of glucocorticoids in humans may cause insomnia , euphoria and increase the intracranial pressure . additionally , an in - vitro study evaluated the effects of some nsaids on cultured primary rat embryonic neurons from rat embryos mesencephalon also containing glial cells , an experimental preparation that reflected the cellular composition of the brain , useful in the study of neuroinflammation . the study considered as indices the reduction of the decrease in dopaminergic uptake caused by glutamate , and the attenuation of the tyrosine hydroxylase positive cells loss . among the tested nsaids , ibuprofen was the most effective one and surprisingly increased the number of dopaminergic cells in the basal condition , most likely protecting them from the excitotoxicity associated with culture medium change . in the present research , we showed in subchronic study that only high doses of compound 11b were able to modify the dopamine levels . it has been shown that normally , cox-2 is expressed in low levels in nigral dopaminergic neurons , but it becomes up - regulated in both patients and experimental pd models ( 19 ) . these suggest that different levels of cox-2 in normal and suprachiasmatic nuclei - lesioned ( scn - lesioned ) rats may explain the aforementioned observations . due to a lot of difficulties such as lack of technical and financial supports , we could not investigate the effect of compound 11b on other related neurotransmitter systems such as cholinergic - glutaminergic neurotransmissions and these should be further investigated in the future experiments .
the aim of this research was to investigate the cyclooxygenase-2 ( cox-2 ) selective inhibition effect on haloperidol - induced catatonia . in this study , 
 the effect of orally , acutely and sub - chronically administrations of compound 11b [ 1-(phenyl)-5-(4-methylsulfonylphenyl)-2-ethylthioimidazole ] ( 2 , 4 and 8 mg / kg ) , a newly selective cox-2 inhibitor , was investigated against the haloperidol - induced catatonia phenomenon comparing to the standard drug scopolamine ( 1 mg / kg ) followed by microdialysis analysis of striatum dopaminergic neurotransmission . 
 the results showed a great potency for compound 11b in improvement of catalepsy followed by enhancing the dopaminergic neurotransmission p < 0.05 . 
 in addition , our statistical analysis showed that the protective effect of compound 11b against haloperidol - induced catatonia was both dose- and time - dependent . 
 these findings are additional pharmacological data that suggest the effectiveness of compound 11b in treatment of schizophrenic drug overdoses and also parkinson s disease ( pd ) affiliated rigidity .