36 Greater creatine concentration was also noted39 in patients, perhaps reflecting a greater metabolic demand in the medial thalamus. Amygdala volume decreased with effective SSRI treatment in pediatric OCD patients.40 Interestingly, the change in amygdala volume was not related to a change in OCD symptom severity, but correlated with SSRI dosage. Pituitary gland volume was significantly smaller in pediatric OCD patients as compared to matched controls.41

This was especially apparent in males, highlighting a possible sex difference in OCD. Glutamate and pediatric OCD proton magnetic resonance spectroscopy studies (1H-MRS) The core excitatory neurotransmitter Inhibitors,research,lifescience,medical of this corticalstriatal-thalamic circuit mentioned earlier is glutamate. It was in 1998 that Rosenberg and Keshavan33 Inhibitors,research,lifescience,medical first hypothesized a role for glutamate in pediatric OCD, and evidence of glutamate abnormalities in OCD has been mounting since. In the first report on glutamate in OCD, Rosenberg et al,42 using proton

magnetic resonance spectroscopy (1H-MRS), observed above-normal striatal glutamate + glutamine (Glx) concentrations in psychotropic-naive pediatric OCD patients as compared with controls, which normalized after effective treatment with an Inhibitors,research,lifescience,medical SSRI. This decrease in striatal Glx may endure after SSRI discontinuation.43 Interestingly, the other treatment considered effective for OCD, CBT, did not alter caudate Glx concentrations in pediatric OCD patients despite a reduction Inhibitors,research,lifescience,medical in symptoms.44 Conversely, in the anterior cingulate, a single-voxel 1H-MRS study found lower Glx concentrations in pediatric OCD patients than in healthy controls.45 This was replicated in adults with OCD, where below normal anterior cingulate Glx was observed in female patients.46 Lower anterior cingulate glutamate correlated with symptom severity in this sample. Again in adult OCD patients, Whiteside et al47 observed Inhibitors,research,lifescience,medical elevated Glx/PCr+Cr (creatine) levels in the orbital frontal

white matter in patients as compared with controls. These effects appear to be regionally specific, with no effect noted in the occipital cortex, an area not typically implicated in the pathophysiology of OCD.42 In conclusion, in vivo studies of the cortical-striatal-thalamic circuit in OCD have implicated glutamate directly. It is important whatever to note, however, that correlation does not indicate find more causation and the overall weight of the evidence implicating glutamate should be considered. Animal models and peripheral marker studies These neuroimaging findings have been bolstered by studies using other methods and models. Chakrabarty et al48 studied cerebral spinal fluid (CSF) concentration of glutamate in 21 psychotropic-naïve adults with OCD and 18 healthy controls. CSF glutamate concentration was significantly greater in OCD patients as compared with control subjects.