Epigenetic inheritance of a cocaine-resistance phenotype

Abstract

We delineated a heritable phenotype resulting from the self-administration of cocaine in rats. We observed delayed acquisition and reduced maintenance of cocaine self-administration in male, but not female, offspring of sires that self-administered cocaine. Brain-derived neurotrophic factor (Bdnf) mRNA and BDNF protein were increased in the medial prefrontal cortex (mPFC), and there was an increased association of acetylated histone H3 with Bdnf promoters in only the male offspring of cocaine-experienced sires. Administration of a BDNF receptor antagonist (the TrkB receptor antagonist ANA-12) reversed the diminished cocaine self-administration in male cocaine-sired rats. In addition, the association of acetylated histone H3 with Bdnf promoters was increased in the sperm of sires that self-administered cocaine. Collectively, these findings indicate that voluntary paternal ingestion of cocaine results in epigenetic reprogramming of the germline, having profound effects on mPFC gene expression and resistance to cocaine reinforcement in male offspring.

Figure 1

Cocaine self-administration by the F0 sires. The data are expressed as mean±s.e.m. mg cocaine consumed on each of the 60 days of self-administration. Note that the behavior stabilizes in the second week and subsequently escalates after approximately 45 days of self-administration

Figure 2

There were no differences in the acquisition and maintenance of 0.5 mg/kg (a) or 1.0 mg/kg (b) cocaine self-administration between the female saline-sired (♀SalSired) and cocaine-sired (♀CocSired) groups. With female progeny there also was no difference between groups when cocaine was self-administered under a progressive ratio schedule (c). In contrast, there was delayed acquisition of 0.5 (d) and 1.0 (e) mg/kg cocaine self-administration and reduced asymptotic intake of 1.0 mg/kg cocaine (e) in the male offspring of cocaine-experienced sires. Data are expressed as the mean (±s.e.m.) cocaine infusions per daily two-hour session. The asterisks represent significant differences between the SalSired and CocSired groups (p<0.05). 15 male and 11 female rats per treatment were tested at the low cocaine dose and 11 male and 9 female subjects per treatment were exposed to the higher dose of cocaine.

Figure 3

When cocaine was self-administered under a progressive ratio schedule, there were no differences between the breakpoints of female CocSired and SalSired rats at either cocaine dose (a). The breakpoint for 1.0 mg/kg cocaine was significantly reduced in male cocaine-sired relative to saline-sired (♂SalSired) rats (b). Data are expressed as the mean (±s.e.m.) lever presses per session. The asterisks represent significant differences between the SalSired and CocSired groups (p<0.05).

Figure 4

a, BDNF protein was increased in the mPFC of male, but not female, CocSired relative to SalSired rats. The inset includes representative Western bots from the two male offspring groups. b, No change in BDNF mRNA expression in female CocSired relative to SalSired rats. c, Increased expression of BDNF exon IV-containing transcript in the mPFC of male CocSired rats. d, Increased association of AcH3 with BDNF promoter IV in the mPFC of male CocSired rats. All data are expressed as mean (±s.e.m.). The asterisks indicate significant differences (p<0.05) between the SalSired and CocSired groups.

Figure 5

Pretreatment with the TrkB antagonist ANA-12 normalized the decreased acquisition of cocaine self-administration in CocSired rats. The data are expressed as the mean (±s.e.m.) lever presses summed across the 10 days of cocaine self-administration. The asterisk represents a significant difference from both other groups (Fisher’s LSD, p<0.05). The number of rats per treatment was as follows: SaSired=16, CocSired=21, CocSired+ANA-12=8.

Figure 6

Representative sections of testes from saline- (a) and cocaine- (b) exposed rats showing clear qualitative increases in AcH3 (a,b) in the tubules as measured by immunohistochemistry. Staining of To-Pro DNA dye (c,d) and the overlay of To-Pro and AcH3 (e,f) in saline- and cocaine-experienced rats, respectively, shows co-expression as expected (scale bars=100 µM). g, Quantitative assessment of the percent of total cell counts (±s.e.m.) showed a significant increase in AcH3 staining (intensity/cell) in the testicular tubules of cocaine relative to saline rats (p<0.05). h, Increased association of AcH3 with BDNF promoters I, IV and VI among cocaine exposed sires, expressed as % input ±s.e.m. The asterisks denote a significant main effect of treatment (p<0.05).