Chronic Intermittent Cold Stressand Serotonin Depletion Induce

Deficits of Reversal Learning in an Attentional Set-shifting Task in Rats

M. Danet S. Lapiz-Bluhm, Alexandra E. Soto-Piña,

Julie G. Hensler,David A. Morilak

Brain Jargon• Primarily concerned with

the Prefrontal Cortex (PFC)in the main paper, specifically the Orbitofrontal Cortex (OFC).

• PFC – implicated in cognitive flexibility, ability to attend tochanges in the environment, and adapt behavioral response strategies accordingly– mPFC involved in shifting

attention b/n perceptual features of complex stimuli.

Brain Jargon (cont.)

• Output of decision making processes influenced/determined by interaction b/n two forebrain loops.– Limbic (affective/motivational)

loop• OFC, amygdala, and ventral

striatum– Cognitive (executive/motor)

loop• Dorso-lateral prefrontal cortex

and dorsal striatus

Cold Stress

• CIC leads to an increase in Hypothalamic-Pituitary-Adrenal response.– Hypersensitizes the individual to respond to acute

stress, specifically increases noradrenergic receptor activity.

• Dysregulation of both the HPA axis and noradrenergic system leads to anxiety like behaviors

Cold Stress

Serotonin Depletion

• Tryptophan -> 5-HT– Depleted through pharmacological (main paper)

or dietary means (background paper)

• Low 5-HT levels linked to poor decision making and gambling proneness– Assesed through the rIGT and rodent Probabilistic

Delivery Test (rPDT)

Serotonin Depletion

• rIGT– Istead of four

choices, onlytwo this time• Advantageous• Disadvantageous

Serotonin Depletion

• rPDT– 10 days – 2 choices• Large Luck Linked• Small Sure

– 6 vs. 2 pellets

– Indifferent point• LLL and SS choice

equally wise.

Serotonin Depletion

• The authors believe that– 5-HT depletion leads to a lower sensitivity to

punishment– 5-HT depleted rats (T-) show only slight reduction

in LLL preference. Indicative of a tolerance of reward uncertainty

– (T-) rats also exhibit motor impulsivity. Not hitting the button long enough

– (T-) rats stuck on short term focus

The Paper Proper

• Objectives– To assess the effects of chronic intermittent cold

(CIC) stress on performance of rats in an attentional set-shifting task (AST)

– Assess a possible role for serotonin in CIC-induced deficits and test the effects of acute serotonin reuptake blockade

• Model organism– Sprague-Dawley rats

Attentional Set-shifting Task (AST)• …subjects must learn a series of reward contingencies,

using cues that vary along multiple stimulus dimensions (e.g., odor and texture, shape and color, etc). Extra Dimensional set shifting involves the acquisition of a new contingency requiring a shift in attention (and responding) away from the stimulus dimension that had been established previously as the relevant or informative dimension (i.e., formation of a cognitive set) to a previously irrelevant stimulus dimension…

• …reversal learning, another form of cognitive flexibility in which a previously positive cue becomes negative and a previously negative cue becomes positive, but within the same stimulus dimension.

AST

Rem

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Terracota pots

Divider

Hypothetical “no-mans land”

Rat

-Various digging media-Various scents-¼ cheerio as reward

Procedure

• Immediately following 14 day CIC treatment (or control housing)

• Day 15 – Habituation. Train rat to dig for food.• Day 16 – Training. Train to a series of SD. First

odor, then medium• Day 17 – Testing. Increasingly difficult

discriminations.– Trials to criterion• 6 correct choices in a row.

Testing

• 1st stage – Simple Discrimination (SD)– Discriminate b/n two odors or two types of

medium.

• 2nd stage – Compound Discrimination (CD)– Same as above but also included a second

irrelevant stimulus (medium or odor)

• 3rd stage – Reversal 1 (R1)– Same as above, but the (-) stimulus is now (+)

Testing (cont.)

• 4th stage – Intradimensional shift (ID)– Same setup as CD except all new odor and

medium. Relevant stimulus still the same as 2nd stage.

• 5th stage – Reversal (R2)– Same setup as above except (-) stimulus now (+)

Testing (cont.)

• 6th stage – Extradimensional shift (ED)– All new mediums and odor introduced, relevent

stimulus now switched. If odor was relevant cue originally, now medium is the relevant cue.

• 7th stage – Reversal 3 (R3)– Same as above but (-) stimulus now (+)

Protocol

Experiments

• Experiment 1– Effect of CIC stress on rAST• 24 rats. 12 control - 12 CIC

– Note – CIC protocol was 14 days not 7 as in previous papers– 7 days prior to testing food was restricted to 14g/day

(promote reward seeking)

Results – Exp. 1

Experiment 2

• Effect of 5-HT depletion on rAST performance– 20 rats randomly assigned to two groups, vehicle

(control) or PCPA (4-chloro-DL-phenylalanine methyl ester hydrochloride) delivered intraperitonealy.

– PCPA – tryptophan hydroxylase inhibitor. Depletes serotonin levels (96.6%)• Note: 5-HT depletion isn’t localized, whole body.

Results – Exp. 2

Experiment 3

• Effects of acute citalopram administration on CIC rats in the rAST– Citalopram – SSRI, not sure of exact mechanism– 43 rats randomly assigned to two groups. • Control

– Citalopram– Vehicle Control

• CIC– Citalopram – Vehicle Control

Results – Exp. 3

Citalopram = 5-HT reuptake inhibitor.

Experiment 4

• Effects of CIC on 5-HT release in Orbitofrontal cortex– 24 rats randomly assigned to two groups• CIC • Control

– All had microdialysis probes implanted into the Orbitofrontal Cortex to monitor 5-T release.

Results – Exp 4

Reversal Learning

Effective reversal learning involves a number of specific and distinct operations, including:

1.Detection of the shift in contingency (i.e. “error detection”)

2.Inhibition of the prepotent, previously learned positive response

3.Overcoming learned avoidance of the previously negative stimulus

4.Acquisition of the new association.

Conclusions

• Apparent dysregulation of serotonergic function in the OFC of rats exposed to CIC stress.

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