Cerebral cortex dendrite alterations

Currently, there is a commonly expressed view that decreased cortical volume in schizophrenia is the result of a reduction of cortical neuropil, presumably due to an atrophy of neural dendrites and axons (e.g., (Selemon and Goldman-Rakic, 1999)). A direct prediction of this model is that neuron density should be increased in proportion to the decrease in cortical volume. While there is some evidence for increased density in the prefrontal cortex (Selemon et al., 1995, 2003), there are also a number of negative findings (Akbarian et al., 1995 Cotter et al., 2002 Cullen et al., 2006 Thune et al., 2001). In auditory areas, the available studies have not shown an altered neuron density, even with hemispheric comparisons (Beasley et al., 2005 Cotter et al., 2004 Smiley et al., 2002). An alternative hypothesis is that reduced cortical volume is accompanied by a loss of neuron number, but this issue remains to be addressed in the auditory cortex. In other brain areas, there is some evidence for decreased neuron number, although the differences are often subtle and statistically nonsignificant (Benes et al., 1986 Dorph-Petersen et al., 2007 Stark et al., 2004 Thune et al., 2001). Changes in total cell number in the cerebral cortex have been difficult to determine, because these measurements require a clearly identified reference volume. 

Altered migration and differentiation of neurons Cell migration - cerebellum Cerebral cortex and hippocampus Stunted dendritic and axonal growth and maturation Purkinje cells Dendritic spine number Delayed and poor deposition of myelin Reduced axonal number Thyroid hormone receptors... 

Bernal (2005) reviewed the morphological aspects in the brain of the hypothyroid rat and found (1) altered cell migration, particularly in the cerebellum and cerebral cortex (2) increments in cell density, caused by a reduction in the neuropil (3) markedly reduced dendritic arborization in the Purkinje cells of the cerebellum, and decreased and altered distribution of the pyramidal dendritic spines in the cortex layer V and finally (4) delayed myelination and poor myelin deposit in the white matter and fewer myelinated axons. This study further showed that hypothyroidism produces changes in the colossally projecting neurons, which may be due to the maintenance of juvenile patterns of projections. In addition, a recent report (Lavado-Autric et al., 2003) indicates that focusing on maternal hypothyroidism can produce migration defects in the fetal cortex, when... 

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