Enhancement of auditory fear conditioning after housing in a complex environment is attenuated by prior treatment with amphetamine Lisa A. Briand, Terry E. Robinson and Stephen Maren

Background Living in a complex environment increases: cerebral volume Dendritic spine density and number LTP Resistance to neural insult Synaptic connectivity Living in a complex environment increases: cerebral volume Dendritic spine density and number LTP Resistance to neural insult Synaptic connectivity

Background Hippocampal-dependent learning tasks affected by complex housing Morris water maze Hebb-Williams Maze Pavlovian fear conditioning in mice Hippocampal-dependent learning tasks affected by complex housing Morris water maze Hebb-Williams Maze Pavlovian fear conditioning in mice

Background Traditionally, cued fear is thought to be purely amygdala dependent and contextual fear, hippocampal and amygdala dependent. Recently, the ventral hippocampus has been implicated in auditory fear conditioning. Traditionally, cued fear is thought to be purely amygdala dependent and contextual fear, hippocampal and amygdala dependent. Recently, the ventral hippocampus has been implicated in auditory fear conditioning.

Background Psychostimulants Increase dendritic branching and spine density Regions implicated in behavioral sensitization Block dendritic changes induced by complex environment Those changes that may be responsible for learning and memory Psychostimulants Increase dendritic branching and spine density Regions implicated in behavioral sensitization Block dendritic changes induced by complex environment Those changes that may be responsible for learning and memory

Psychostimulants Amphetamine increases dopamine in the synaptic cleft by acting as a false substrate for DAT VTA NAc DA GABA VTA interneuron Amphetamine & Cocaine Nicotine + Opiates - Ethanol (?) -

Questions Does a complex environment modulate learning in a Pavlovian fear-conditioning paradigm? Does prior treatment with amphetamine modulate environmental effects on learning? Does a complex environment modulate learning in a Pavlovian fear-conditioning paradigm? Does prior treatment with amphetamine modulate environmental effects on learning?

Details Sprague Dawley rats Housed for 3 months in Individual plastic hanging cages (isolated) 20 x 23 x 20 cm Groups of 3 rectangular plastic cages (social) 20 x 43 x 20 cm Groups of 12 stainless-steel monkey cages (complex) 61 x 61 x 72 cm Sprague Dawley rats Housed for 3 months in Individual plastic hanging cages (isolated) 20 x 23 x 20 cm Groups of 3 rectangular plastic cages (social) 20 x 43 x 20 cm Groups of 12 stainless-steel monkey cages (complex) 61 x 61 x 72 cm

General Methods Animals housed for 3 months in respective environments then housed in social/standard cages during tests Day1 - Fear conditioning paradigm Day2 - Contextual test Day3 - CS test (auditory cue) Animals housed for 3 months in respective environments then housed in social/standard cages during tests Day1 - Fear conditioning paradigm Day2 - Contextual test Day3 - CS test (auditory cue)

Experiment 1 4 Pairings of tone (CS) with shock (US) 30 sec; 80 dB; 2 kHz 2 sec; 1 mA Measured freezing (CR) No statistical differences 4 Pairings of tone (CS) with shock (US) 30 sec; 80 dB; 2 kHz 2 sec; 1 mA Measured freezing (CR) No statistical differences

Experiment 1 CS alone elicits long- term fear memory 6 min of tone (Black line) Complex group shows prolonged freezing response Difference due to complex environment rather than social housing CS alone elicits long- term fear memory 6 min of tone (Black line) Complex group shows prolonged freezing response Difference due to complex environment rather than social housing

Experiment 1 Context alone does not elicit significant differences Trend toward significance Complex group may freeze more to context at later time points Context alone does not elicit significant differences Trend toward significance Complex group may freeze more to context at later time points

Conclusions Housing in a complex environment facilitated Pavlovian fear conditioning Effect of environment on conditioned fear was much stronger for auditory fear than contextual fear Housing in a complex environment facilitated Pavlovian fear conditioning Effect of environment on conditioned fear was much stronger for auditory fear than contextual fear

Discussion Inconsistent with previous studies in mice (Duffy et al. 01; Tang et al. 01) Found equal effects of enrichment on contextual and auditory fear Used single pairing of shock and tone Species difference or methodological Inconsistent with previous studies in mice (Duffy et al. 01; Tang et al. 01) Found equal effects of enrichment on contextual and auditory fear Used single pairing of shock and tone Species difference or methodological

Discussion The isolated and socially housed animals may use additional time in the conditioning context to consolidate contextual fear memory Whereas complex-housed animals may exhibit a ceiling effect The isolated and socially housed animals may use additional time in the conditioning context to consolidate contextual fear memory Whereas complex-housed animals may exhibit a ceiling effect

Discussion Environmental complexity could modify the ventral hippocampus in a way that allows for the enhancement of cued fear while having only a slight effect on contextual fear.

Experiment 2 Robust behavioral sensitization pretreatment 21 consecutive days of amphetamine 4.0 mg/kg with intermittent doses of 0.5 mg/kg to measure extent of psychomotor sensitization Robust behavioral sensitization pretreatment 21 consecutive days of amphetamine 4.0 mg/kg with intermittent doses of 0.5 mg/kg to measure extent of psychomotor sensitization

Experiment 2 Significantly more locomotion on day 21 than day 1 in response to amphetamine dose of 0.5 mg/kg No difference in saline group Significantly more locomotion on day 21 than day 1 in response to amphetamine dose of 0.5 mg/kg No difference in saline group

Experiment 2 Divided into complex and standard cages (groups of 3) for 3 months after amphetamine N=12 for Complex Saline N=12 for Complex Amphetamine N=12 for Social Saline N=12 for Social Amphetamine Divided into complex and standard cages (groups of 3) for 3 months after amphetamine N=12 for Complex Saline N=12 for Complex Amphetamine N=12 for Social Saline N=12 for Social Amphetamine

Experiment 2 CS alone elicits long-term fear conditioning Complex/Saline group shows more robust freezing than all other groups CS alone elicits long-term fear conditioning Complex/Saline group shows more robust freezing than all other groups

Experiment 2 Contextual freezing No differences between groups Contextual freezing No differences between groups

Experiment 3 Animals were moved to social housing (groups of 3) during the fear conditioning and testing in experiments 1 & 2 Experiment 3 simply left the complex housed animals in the same cage during testing Animals were moved to social housing (groups of 3) during the fear conditioning and testing in experiments 1 & 2 Experiment 3 simply left the complex housed animals in the same cage during testing

Experiment 3 CS alone elicits long- term fear memory Complex/saline group still shows more robust freezing response CS alone elicits long- term fear memory Complex/saline group still shows more robust freezing response

Experiment 3 Contextual Freezing No difference Contextual Freezing No difference

Conclusion Amphetamine attenuates cued fear conditioning in animals housed in a complex environment

Discussion Some research has shown that prior exposure to stimulants limits structural plasticity associated with living in complex environment Possibly, exposure to amphetamine blocked effect of complex environment to facilitate fear learning by limiting structural plasticity associated with living in complex environment Some research has shown that prior exposure to stimulants limits structural plasticity associated with living in complex environment Possibly, exposure to amphetamine blocked effect of complex environment to facilitate fear learning by limiting structural plasticity associated with living in complex environment

Discussion An experiment with low doses methamphetamine prior to exposure to a complex environment showed more cortical weight than those without AMP Low doses of amphetamine also improve recovery from brain injury and in conjunction with speech therapy, greater recovery from aphasia An experiment with low doses methamphetamine prior to exposure to a complex environment showed more cortical weight than those without AMP Low doses of amphetamine also improve recovery from brain injury and in conjunction with speech therapy, greater recovery from aphasia

Discussion There are synaptic connections between the nucleus accumbens and both amygdala (fear; emotions) and ventral hippocampus (stress; anxiety)

Discussion Studies that show drugs of abuse limit future experience-dependent plasticity implicate the nucleus accumbens & parietal cortex Complex environment affects plasticity in nucleus accumbens, caudate- putamen, and hippocampus Studies that show drugs of abuse limit future experience-dependent plasticity implicate the nucleus accumbens & parietal cortex Complex environment affects plasticity in nucleus accumbens, caudate- putamen, and hippocampus

Conclusions Dendritic morphology in the hippocampus and the amygdala may also be altered by environmental enrichment and potentially modulated by drug exposure Exposure to drugs of abuse may limit future experience dependent plasticity Dendritic morphology in the hippocampus and the amygdala may also be altered by environmental enrichment and potentially modulated by drug exposure Exposure to drugs of abuse may limit future experience dependent plasticity