Experiments were conducted in accordance with UK Home Office regulations (Animals (Scientific Procedures) Act, 1986). A total of 51 Wistar-Kyoto rats (Harlan, UK; 3–4 weeks old) were used in this study and ARRIVE guidelines complied with. Animals were group housed in cages of five with water and food supplied ad libitum . Temperature and humidity were maintained at 21°C and 55 ± 10% respectively.

Seizures were induced using PTZ (Sigma, Poole, United Kingdom). After overnight fasting, rats received either vehicle (20% solutol (Sigma) in 0.9% w / v NaCl) or CBDV (400 mg kg −1 ; GW Pharmaceuticals Ltd., Salisbury, UK) in vehicle by oral gavage. Three and a half hours after vehicle or CBDV administration, rats were challenged (i.p.) with saline or PTZ (95 mg kg −1 ) and behaviour monitored for 1 h. Animals were euthanised by CO 2 overdose and brains immediately removed. Whole hippocampi, neocortices and prefrontal cortices were isolated, snap-frozen in liquid nitrogen and stored at −80°C until RNA extraction.

Seizure behaviour was video recorded and responses coded exactly as described previously ( Hill et al., 2012a ). Responses were coded using the following modified Racine seizure severity scale: 0, normal behaviour; 1, isolated myoclonic jerks; 2, atypical clonic seizure; 3, fully developed bilateral forelimb clonus; 3.5, forelimb clonus with tonic component and body twist; 4, tonic–clonic seizure with suppressed tonic phase; 5, fully developed tonic–clonic seizure. Latency to the first sign of seizure was also recorded.

Gene expression analysis

Gene expression was quantified in rat hippocampus, prefrontal cortex and neocortex for four experimental groups: vehicle + saline treated (n = 5), vehicle + PTZ treated (n = 7), CBDV + saline treated (n = 5) and CBDV + PTZ treated (n = 7). Total RNA was extracted using an miRNeasy Mini kit (Qiagen, West Sussex, UK), following the manufacturer’s protocol. RNA purity was assessed spectrometrically at 260/280 nm. RNA integrity was determined by gel electrophoresis. A 28S:18S rRNA ratio of ∼2:1 was taken to indicate intact RNA.

Total RNA (0.5 µg) was reverse-transcribed into cDNA using High Capacity cDNA Reverse Transcription Kits (Applied Biosystems). qPCR assays were carried out in a volume of 14 µl, containing 5 µl cDNA, 2 µl 2.5 µM primer mix (forward and reverse primers) and 7 µl QuantiTect SYBR Green QPCR 2× Master Mix (Qiagen, West Sussex, UK). Samples were processed for 40 cycles on a StepOnePlus™ (Applied Biosystems, Foster City, CA, USA) as follows: denaturation at 95°C for 15 min (one cycle), 40 cycles of denaturation at 95°C for 15 s and annealing at 60°C for 1 min. All samples were analysed in the same plate in a single PCR run and quantification was based on the standard curve method. Standard curves were constructed using cDNA solution diluted fivefold in series for a total of five dilutions and consisted of a mixture of cDNA equally from hippocampus, prefrontal cortex and neocortex of all animals. Sample cDNA concentrations were expressed relative to the concentration of the standard curves. Normalisation of quantitative data was based on a housekeeping gene, β-actin. Values are expressed as a percentage of control (mean of the vehicle + saline group). The following primers were used (parenthesised values are forward and reverse sequence and amplicon length respectively): Ccl3 (5′-TGCCCTTGCTGTTCTTCTCTGC-3′, 5′-TAGGAGAAGCAGCAGGCAGTCG-3′, 96), Ccl4 (5′-CGCCTTCTGCGATTCAGTGC-3′, 5′-AAGGCTGCTGGTCTCATAGTAATCC-3′, 127), Npy (5′-TCGTGTGTTTGGGCATTCTGGC-3′, 5′-TGTAGTGTCGCAGAGCGGAGTAG-3′, 111), Arc (5′-AGGCACTCACGCCTGCTCTTAC-3′, 5′-TCAGCCCCAGCTCAATCAAGTCC-3′, 146), Bdnf (5′-AGCCTCCTCTGCTCTTTCTGCTG-3′, 5′-TATCTGCCGCTGTGACCCACTC-3′, 150), Egr1 (5′-AGCCTTCGCTCACTCCACTATCC-3′, 5′-GCGGCTGGGTTTGATGAGTTGG-3′, 113), Penk (5′-CCAACTCCTCCGACCTGCTGAAAG-3′, 5′-AAGCCCCCATACCTCTTGCTCGTG-3′, 121) and Camk2a (5′-TGAGAGCACCAACACCACCATCG-3′, 5′-TGTCATTCCAGGGTCGCACATCTTC-3′, 142), Fos (5′-TGCGTTGCAGACCGAGATTGC-3′, 5′-AGCCCAGGTCATTGGGGATCTTG-3′, 104), Casp3 (5′-TTGCGCCATGCTGAAACTGTACG-3′, 5′-AAAGTGGCGTCCAGGGAGAAGG-3′,111) and β-Actin (5′-CTCTATCCTGGCCTCACTGTCCACC-3′, 5′-AAACGCAGCTCAGTAACAGTCCGC-3′, 124). Primers were designed using NCBI/Primer-BLAST (http://www.ncbi.nlm.nih.gov/tools/primer-blast/).