Neurons in the periaqueductal gray are critically involved in the neuronal network for audiogenic seizures during ethanol withdrawal

Abstract

The periaqueductal gray (PAG) is implicated in the network subserving audiogenic seizures (AGS). AGS are seen during ethanol withdrawal (ETX), and the present study examined effects of focal NMDA receptor blockade in PAG during ETX and PAG neuronal firing changes associated with ETX. Bilateral cannulae or microwire electrodes were chronically implanted into PAG. Ethanol was administered intragastrically at 8-h intervals for 4 days, resulting in AGS susceptibility during ETX. Microinjection of a competitive NMDA receptor antagonist, DL-2-amino-7-phosphonoheptanoic acid (AP7) (2 and 5 but not 1 nmol/side), into the PAG suppressed AGS, in part, reversibly. In microwire experiments spontaneous and acoustically evoked PAG neuronal responses in behaving rats were reduced significantly 1 h after initial administration of ethanol. During ETX, when the animals were susceptible to AGS, significant increases in spontaneous and acoustically evoked PAG neuronal firing occurred. PAG neurons exhibited burst firing 2–4 s prior to the tonic–clonic phase of AGS and tonic repetitive firing during this seizure phase, which ceased during post-ictal depression. Increased NMDA receptor function in PAG may be important to the aberrant PAG neuronal firing in AGS, since previous studies observed upregulation of NMDA receptors during ETX, and the present study observed that focal microinjection of a NMDA antagonist into PAG blocked AGS.