The role of glutamatergic (NMDA), cholinergic and purinergic neurotransmission in the pedunculopontine nucleus, red nucleus, ventrolateral thalamic nucleus, entopeduncular nucleus, and the substantia nigra in the development of the high pressure neurological syndrome (HPNS) was investigated in the rat. Focal injection of d-2-amino-7-phosphonoheptanoate (D-APH, 5 nmol per side) into the red nucleus or the pedunculopontine nucleus was protective against HPNS-induced convulsions. Carbachol (10 nmol), injected into the red nucleus, did not influence the severity of the symptoms of HPNS. Injection of carbachol into the pedunculopontine nucleus, significantly lowered the threshold pressure for convulsions and increased the threshold pressure for tremor. 2-Chloroadenosine (5 nmol), injected into the red nucleus, produced a potent antitremorgenic effect and a similar but less pronounced effect when injected into the pedunculopontine nucleus. 2-Chloroadenosine, injected into the substantia nigra (12.5 nmol) or the ventrolateral thalamic nucleus (25 nmol), facilitated the development of tremor and, in the entopeduncular nucleus (25 nmol), facilitated the occurrence of convulsions. These results show the complexity of neurotransmitter interactions in different regions of the brain, under high pressure. They also indicate that the biochemical and anatomical substrates, involved in the convulsions produced by HPNS, differ substantially from those in other experimental models of epilepsy. © 1991.
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