PCB Amperometry_NBTS 2012

1
Rats were anesthetized with urethane (1.5 mg/kg IP) and placed into a stereotaxic apparatus (Kopf). A concentric bipolar stimulating electrode was implanted into the left medial forebrain bundle (MFB; coordinates from bregma in mm: AP -4.2, ML -1.8 and DV -7.8 from dura) of each rat. A carbon-fiber microelectrode (250 μm in length by 10 μm o.d.) was implanted into the left NAc core (coordinates from bregma in mm: AP 1.60, ML +1.5, and DV -7.4 from dura) [7]. A Ag/AgCl reference/auxiliary electrode was positioned in contact with contralateral cortical tissue. A fixed positive potential (+0.8 V) was applied via the auxiliary electrode to induce oxidation of DA at the recording electrode. The analog current (e-), constituting DA oxidation, was converted (A/D converter) to a digital signal that was monitored in real time (10K samples/sec) on an electrometer 60 Hz line-filtered and 10 Hz low- pass filtered. Thus, increases in DA oxidation corresponded to proportional increases in DA release in the NAc core as a result of brief electrical stimulation of DA axons in the MFB. Stimulation parameters (15 cathodic monophasic 0.5 msec pulses at 50 Hz and 800 μA intensity every 30 sec) were applied to the MFB to one male and female/litter before and after a single acute administration of cocaine (20 mg/kg, Perinatal exposure to polychlorinated biphenyls in rats alters cocaine-induced dopamine efflux in the nucleus accumbens Jenna R. Fielding, Tiffany D. Rogers, Abby E. Meyer, Mellessa M. Miller, Jenna L. Nelms, Melissa A. Ward, Guy Mittleman, Charles D. Blaha, and Helen J. K. Sable [1] Erickson M. (1986). Analytical chemistry of PCBs. Boston: Butterworth Publishers. [2] Jacobson, J., Fein, G., et al. (1984). Am J Public Health 74: 378-9; Sable, H., Schantz, S. (2006). In Animal Models of Cognitive Impairment (Frontiers in Neuroscience). E. D. Levin and J. J. Buccafusco (eds). New York, CRC Press: 147-67. [3] Angus, W., Contreras, M. L. (1996). Toxicol Lett, 89, 191-9; Bemis, J., Seegal, R. (2004). Toxicol Sci, 80, 288-95; Choksi, N., Kodavanti, P., et al.(1997). Fund Appl Toxicol, 39, 76-80. Seegal R., Brosch, et al. (1989). Neurotoxicol, 10, 757-64. [4] Bemis , J., Seegal, R. (2000), Neurotoxicol, 21, 1123-34. [5] Wise, R. (1984). NIDA Res Monogr, 50, 15-33. [6] Kostyniak, P., Hansen, L. et al. (2005). Toxicol Sci, 88, 400-11. [7] Paxinos, G., Franklin, K. (2001) The Mouse Brain in Stereotaxic Coordinates (2nd ed.). San Diego, CA: Academic Press. Introduction Subjects and Exposure Polychlorinated Biphenyls (PCBs) are a ubiquitous environmental toxin that were widely used in industry for commercial needs until they were banned in the late 1970s [1]. Over time, PCBs have been dispersed into rivers, lakes, air and soil and have bioaccumulated within the ecosystem. A major health concern is that PCBs readily cross the placenta and can accumulate in breastmilk [2] thereby exposing the developing fetus/infant to potentially irreversible neuroteratogenic effects during gestation and lactation. Using a variety of experimental designs, researchers have found that PCB exposure reduces brain dopamine (DA) content [3], resulting in reduced extracellular DA concentrations in medial prefrontal cortex and striatum that lasts into adulthood [4]. These alterations suggest the reinforcing properties of drugs of abuse that act on the dopamine system may be affected by developmental PCB exposure. For example, the reinforcing properties of cocaine have been related to increased extracellular concentrations of dopamine in the nucleus accumbens (NAc) [5]. Thus, the current study was conducted to determine if electrically evoked NAc DA efflux following both acute and chronic daily injections of cocaine (20 mg/kg IP) differed between adult rats exposed to an environmentally relevant mixture of PCBs throughout gestation and lactation and non-exposed controls. Amperometry Testing Results and Conclusions References Female Long-Evans rats were dosed with the Fox River PCB Mixture [6] beginning 28 days prior to breeding and continuing until weaning (n=8 litters/exposure group). At weaning two males and females from each litter were kept for later amperometry testing. Department of Psychology Memphis, TN 38152 USA Gestation 21 days Lactation 21 days PND -57 -29 -21 0 21 60 Pups Born Weaning Breeding Dosing began Fixed Potential Amperometry began Gestation PCB Exposure Developmental PCB Exposure In a Rat Model 0, 3, or 6 mg/kg PCBs dissolved in corn oil and pipetted onto half of a vanilla wafer; volume based on body weight IP). These parameters were repeated in a second male and female/litter who had received six prior daily cocaine injections of the same dose. Changes in stimulation-evoked DA oxidation current were recorded for 60 min post-injection. Peak increases in DA oxidation current evoked by MFB stimulation after cocaine injection were expressed as percentage change with respect to pre-injection baseline responses (100%). Percentage changes were subsequently averaged across animals for each condition. Sixty min post-injection, continuous stimulation (100 Hz) was administered with the intention of depleting presynaptic NAc DA stores. The total current measured was summed across the period beginning 30 sec and terminating 90 sec after the start of continuous stimulation. There was a significant PCB exposure group x injection schedule interaction [F(2,21)=10.76, p=.001]. Exposure dose-dependently increased peak DA release following the acute injection of cocaine ( + p=.055, ***p=.001 from 0 mg/kg group) but attenuated release following chronic injections of cocaine (*p=.019 from 0 mg/kg group). PCB-exposure attenuated the typical DA sensitization seen in non-exposed rats following chronic cocaine exposure (**p=.005). There was a marginally significant main effect of exposure group [F(2,21)=3.10, p=.066]. PCB exposure dose-dependently attenuated DA release following continuous, MFB stimulation (*p=.047). Supported by R00 ES015428 PCB-exposed rats exhibited enhanced stimulated DA release following acute administration of cocaine. Non-exposed rats exhibited typical DA sensitization following the chronic cocaine injections, but this effect was attenuated in PCB-exposed rats. Continuous stimulation suggested a reduction in pre-synaptic DA stores in PCB-exposed animals. No differences in the time-course of peak DA release were found. These results indicate that developmental PCB exposure can modify DA synaptic transmission and pharmacology in the NAc in a manner previously shown to alter the reinforcing properties of cocaine. There were no significant main effects or interactions found on the time course of peak DA release following cocaine administration.

Transcript of PCB Amperometry_NBTS 2012

Rats were anesthetized with urethane (1.5 mg/kg IP) and placed into a stereotaxic apparatus (Kopf). A concentric bipolar stimulating electrode was implanted into the left medial forebrain bundle (MFB; coordinates from bregma in mm: AP -4.2, ML -1.8 and DV -7.8 from dura) of each rat. A carbon-fiber microelectrode (250 μm in length by 10 µm o.d.) was implanted into the left NAc core (coordinates from bregma in mm: AP 1.60, ML +1.5, and DV -7.4 from dura) [7]. A Ag/AgCl reference/auxiliary electrode was positioned in contact with contralateral cortical tissue. A fixed positive potential (+0.8 V) was applied via the auxiliary electrode to induce oxidation of DA at the recording electrode. The analog current (e-), constituting DA oxidation, was converted (A/D converter) to a digital signal that was monitored in real time (10K samples/sec) on an electrometer 60 Hz line-filtered and 10 Hz low-pass filtered.

Thus, increases in DA oxidation corresponded to proportional increases in DA release in the NAc core as a result of brief electrical stimulation of DA axons in the MFB. Stimulation parameters (15 cathodic monophasic 0.5 msec pulses at 50 Hz and 800 µA intensity every 30 sec) were applied to the MFB to one male and female/litter before and after a single acute administration of cocaine (20 mg/kg,

Perinatal exposure to polychlorinated biphenyls in rats alters cocaine-induced dopamine efflux in the nucleus accumbens Jenna R. Fielding, Tiffany D. Rogers, Abby E. Meyer, Mellessa M. Miller, Jenna L. Nelms, Melissa A. Ward, Guy Mittleman, Charles D. Blaha, and Helen J. K. Sable

[1] Erickson M. (1986). Analytical chemistry of PCBs. Boston: Butterworth Publishers. [2] Jacobson, J., Fein, G., et al. (1984). Am J Public Health 74: 378-9; Sable, H., Schantz, S. (2006). In Animal Models of Cognitive Impairment (Frontiers in Neuroscience). E. D. Levin and J. J. Buccafusco (eds). New York, CRC Press: 147-67. [3] Angus, W., Contreras, M. L. (1996). Toxicol Lett, 89, 191-9; Bemis, J., Seegal, R. (2004). Toxicol Sci, 80, 288-95; Choksi, N., Kodavanti, P., et al.(1997). Fund Appl Toxicol, 39, 76-80. Seegal R., Brosch, et al. (1989). Neurotoxicol, 10, 757-64. [4] Bemis , J., Seegal, R. (2000), Neurotoxicol, 21, 1123-34. [5] Wise, R. (1984). NIDA Res Monogr, 50, 15-33. [6] Kostyniak, P., Hansen, L. et al. (2005). Toxicol Sci, 88, 400-11. [7] Paxinos, G., Franklin, K. (2001) The Mouse Brain in Stereotaxic Coordinates (2nd ed.). San Diego, CA: Academic Press.

Introduction

Subjects and Exposure

Polychlorinated Biphenyls (PCBs) are a ubiquitous environmental toxin that were widely used in industry for commercial needs until they were banned in the late 1970s [1]. Over time, PCBs have been dispersed into rivers, lakes, air and soil and have bioaccumulated within the ecosystem. A major health concern is that PCBs readily cross the placenta and can accumulate in breastmilk [2] thereby exposing the developing fetus/infant to potentially irreversible neuroteratogenic effects during gestation and lactation.

Using a variety of experimental designs, researchers have found that PCB exposure reduces brain dopamine (DA) content [3], resulting in reduced extracellular DA concentrations in medial prefrontal cortex and striatum that lasts into adulthood [4]. These alterations suggest the reinforcing properties of drugs of abuse that act on the dopamine system may be affected by developmental PCB exposure. For example, the reinforcing properties of cocaine have been related to increased extracellular concentrations of dopamine in the nucleus accumbens (NAc) [5]. Thus, the current study was conducted to determine if electrically evoked NAc DA efflux following both acute and chronic daily injections of cocaine (20 mg/kg IP) differed between adult rats exposed to an environmentally relevant mixture of PCBs throughout gestation and lactation and non-exposed controls.

Amperometry Testing

Results and Conclusions

References Female Long-Evans rats were dosed with the Fox River PCB Mixture [6] beginning 28 days prior to breeding and continuing until weaning (n=8 litters/exposure group). At weaning two males and females from each litter were kept for later amperometry testing.

Department of Psychology

Memphis, TN 38152 USA

Gestation

21 days

Lactation

21 days

PND -57 -29 -21 0 21 60

Pups

Born

Weaning

Breeding

Dosing began Fixed

Potential

Amperometry

began

Gestation

PCB Exposure

Developmental PCB Exposure

In a Rat Model

0, 3, or 6 mg/kg PCBs dissolved in corn oil and pipetted onto half of a vanilla wafer; volume based on body weight

IP). These parameters were repeated in a second male and female/litter who had received six prior daily cocaine injections of the same dose. Changes in stimulation-evoked DA oxidation current were recorded for 60 min post-injection. Peak increases in DA oxidation current evoked by MFB stimulation after cocaine injection were expressed as percentage change with respect to pre-injection baseline responses (100%). Percentage changes were subsequently averaged across animals for each condition. Sixty min post-injection, continuous stimulation (100 Hz) was administered with the intention of depleting presynaptic NAc DA stores. The total current measured was summed across the period beginning 30 sec and terminating 90 sec after the start of continuous stimulation.

There was a significant PCB exposure group x injection schedule interaction [F(2,21)=10.76, p=.001]. Exposure dose-dependently increased peak DA release following the acute injection of cocaine (+p=.055, ***p=.001 from 0 mg/kg group) but attenuated release following chronic injections of cocaine (*p=.019 from 0 mg/kg group). PCB-exposure attenuated the typical DA sensitization seen in non-exposed rats following chronic cocaine exposure (**p=.005).

There was a marginally significant main effect of exposure group [F(2,21)=3.10, p=.066]. PCB exposure dose-dependently attenuated

DA release following continuous, MFB stimulation (*p=.047).

Supported by R00 ES015428

PCB-exposed rats exhibited enhanced stimulated DA release following acute administration of cocaine. Non-exposed rats exhibited typical DA sensitization following the chronic cocaine injections, but this effect was attenuated in PCB-exposed rats. Continuous stimulation suggested a reduction in pre-synaptic DA stores in PCB-exposed animals. No differences in the time-course of peak DA release were found. These results indicate that developmental PCB exposure can modify DA synaptic transmission and pharmacology in the NAc in a manner previously shown to alter the reinforcing properties of cocaine.

There were no significant main effects or interactions found on the time course of peak DA release following cocaine administration.