Results from animal studies and from human tissue removed from epileptics show that certain subgroups of hippocampal neurons are more vulnerable to seizure activity than others. It is possible that neurons which contain
calcium-binding proteins, such as
parvalbumin, may be protected from the high
calcium overload that results from seizure activity. In the present study,
seizures were induced by an injection of
tetanus toxin into the rat hippocampus. A morphological and quantitative analysis was made of the
parvalbumin-containing neurons and of those which co-localized
somatostatin and
neuropeptide Y. At 2 weeks there was a generalized increase in immunoreactivity in both groups of neurons. From 1 month through to 3 months after injection, the up-regulation in immunoreactivity was sustained in the surviving hilar neurons which co-localized
somatostatin and
neuropeptide Y but there was a marked reduction in immunoreactivity of the
parvalbumin neurons. Although there was no evidence for a loss of
parvalbumin neurons there was a small and significant reduction in the number of
somatostatin +
neuropeptide Y double-labelled neurons in the contralateral hilus at 3 and 4 months after a
tetanus injection. The vulnerability of the
somatostatin +
neuropeptide Y double-labelled hilar neurons but not of the
parvalbumin-containing, presumed, basket cells are considered in terms of their connectivity.