Cerebellar cortex appearance

Of all the neurotransmitters in the central nervous system, y-aminobutyric acid (GABA) 12.91) has lent itself most readily to investigation and hence is the best understood. GABA mediates transmission of impulses in local inhibitory neurons in parts of the brain that lie near to the spinal cord, and it also mediates presynaptic inhibition within the spinal cord. At least, half a dozen other centres in the brain, including the major output cells of the cerebellar cortex, appear to depend on GABA as a neurotransmitter of inhibitory impulses. GABA mediation is usually detected with the convulsant alkaloids picrotoxin and bicu-culline, neither of which is used in medicine (Curtis etal., 1971). 

In the cerebellar cortex, the most frequently noted pathology is a decreased number of Purkinje cells (Kemper and Bauman, 1998 Palmen et al., 2004 Bauman and Kemper, 2005 Whitney et al., 2008). This pathology is most marked in the posterior lateral part of the cerebellar hemispheres and the adjacent archicerebellar cortex and occurs without evidence of loss of neurons in the inferior olive in the brain stem (Kemper and Bauman, 1998 Bauman and Kemper, 2005). The Purkinje cells have an intimate relationship with the axons of the inferior olivary neurons in the brain stem, such that loss of Purkinje cells at any time after birth leads to loss of neurons in the inferior olive (Holmes and Stewart, 1908 Norman, 1940 Sakai et al., 1994). Since this intimate relationship between the Purkinje cell and the inferior olive is established in the human brain sometime after 29-30 weeks of gestation (Rakic and Sidman, 1970), it is likely that the decrease in number of Purkinje cells occurred before this time. In those brains with a marked decrease in the number of Purkinje cells, there appears to be a concomitant decrease in the number of granule cells (Bauman and Kemper, 2005). The relationship between the number of granule cells and the number of Purkinje cells noted in the autistic brain has been elucidated in rat studies. With prenatal loss of Purkinje cells the number of granule cells is adjusted such that the ratio of Purkinje cells to the number of granule cells is maintained (Chen and Hilman, 1989). 

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