Epileptiform activity in the nucleus accumbens induced by GABAA receptor antagonists in rat forebrain slices is of cortical origin

• Published in: Experimental brain research 2001-11, Vol.141 (2), p.146-152
• Main Authors: BUCKBY, L. E, LACEY, M. G
• Format: Article
• Language: English
• Subjects: Bicuculline; Biological and medical sciences; Brain slice preparation; Central nervous system; Cortex (frontal); Cortex (piriform); Electrophysiology; Epilepsy; Excitatory postsynaptic potentials; Forebrain; Fundamental and applied biological sciences. Psychology; Glutamic acid receptors; Nucleus accumbens; Picrotoxin; Tetrodotoxin; Vertebrates: nervous system and sense organs; α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid; γ-Aminobutyric acid A receptors; γ-Aminobutyric acid receptors
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s002210100841

Extracellularly recorded field potentials, evoked by stimulation of cortico-nucleus accumbens border, were recorded in the nucleus accumbens (NAcc) in horizontal slices of rat ventral forebrain. The field excitatory postsynaptic potential (EPSP) event (N2) was calcium dependent, blocked by tetrodotoxin (1 µM), and reduced by over 70% by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 µM), the antagonist of AMPA-type glutamate receptors. The EPSP amplitude was enhanced by either of the GABAA receptor antagonists, picrotoxin (10 µM; by 252±33%, n=18) and bicuculline methiodide (20 µM; by 216±34%, n=4). Additionally, picrotoxin (3–50 µM) and bicuculline methiodide (20 µM) promoted epileptiform activity within the NAcc, manifest as the emergence of additional late components, N3, N4 and N5, in the evoked synaptic waveform. In slices with the frontal cortex removed, picrotoxin (10–50 µM) and bicuculline methiodide (20 µM) were unable to promote epileptiform activity within the NAcc, although a smaller increase in the peak amplitude of the field EPSP (163±18%, n=6) was observed at the highest concentrations of picrotoxin (50 µM). Histological examination of the slice demonstrated that in such decorticated slices, the piriform cortex (PC) had been removed. We propose that stimulation of the cortico-NAcc border not only evokes an orthodromic EPSP in the NAcc, but also causes antidromic activation of cortical tissue. Disinhibition by GABAA antagonists of circuits intrinsic to the cortex, possibly the piriform cortex, is the principal cause of the facilitation of the EPSP and of regenerative epileptiform activity in NAcc evoked by stimulation of cortical input.