Supplementary Materials

Acute nicotine increases both impulsive choice and behavioural disinhibition in rats

Kolokotroni, K.Z. *, Rodgers, R.J.and Harrison, A.A.

Behavioural Neuroscience Laboratory

Institute of Psychological Sciences`

University of Leeds

Leeds LS2 9JT

U.K.

*Address all correspondence to: Dr Zoe Kolokotroni, Department of Psychology, Leeds Metropolitan University, D420 Civic Quarter, Calverley Street, Leeds, LS1 3HE, England.

Phone: +44-(0)113-812-4968

Fax: +44-(0)113-343-5749 (non-confidential)

Email:

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Supplementary Results

Experiment 3: effect of alterations in primary motivation on performance of the Go/No-go and Delayed Reward tasks.

I. Go/No-go Task

For all descriptive data see Table 5.

Phase 1: decrease in primary motivation

During 1hr prefeeding with normal lab chow, animals consumed 12.58 ± 0.74g of food leading to a weight gain of 15.85 ± 1.83g (increase of 3.62 ± 0.28% versus baseline). During 30 minutes prefeeding on sucrose pellets, animals consumed 12.10 ± 1.03g of food leading to a weight gain of 16.63 ± 2.81g (increase of 3.69 ± 0.60% versus baseline). Food consumption did not differ as a function of food type (t = 0.405 df = 5, N.S), nor did weight gain expressed either as an absolute or percentage increase (all t ≤ -0.301, df = 5, N.S.).

Accuracy of Responding: No significant effect on overall performance was observed following pre-feeding with either normal chow (t = -0.575, df = 6, N.S.) or sucrose pellets (t = -1.525, df = 5, N.S). Analysis of the independent accuracy during Go and No-go trials further mirrored the lack of effect on accuracy of performance in the task (normal chow: all t ≤ -1.393, df = 6, N.S.; sucrose pellets: all t ≤ -1.470, df = 5, N.S.).

Anticipatory Responding: Neither form of prefeeding had any significant effect on the frequency of early responding (normal chow: all t ≤ 0.977, df = 6, N.S.; sucrose pellets: all t ≤ 2.127, df = 5, N.S.), or on inappropriate magazine entries (normal chow: all t ≤ 1.208, df = 6, N.S.; sucrose pellets: all t ≤ 2.004, df = 5, N.S.) during Go and No-go trials.

Speed of Responding: No significant effects of prefeeding were observed on correct or incorrect response latencies in the task (normal chow: all t ≤ -1.427, df = 6, N.S.; sucrose pellets: all t ≤ 0.524, df = 5, N.S.). Although incremental trends were observed for magazine latencies during Go and No-Go trials, these failed to reach significance following either feeding manipulation (normal chow: all t ≤ 1.427, df = 6, N.S.; sucrose pellets: all t ≤ -1.689, df = 5, N.S.).

Omissions: Failure to collect reward during No-go trials was found to increase significantly in response to prefeeding with both normal chow (Z= -1.997, p = 0.046) and sucrose pellets (Z = -2.201, p = 0.028).

Phase 2: increase in primary motivation

Restricting food intake to 50% of the normal ration on the day prior to testing led to a loss of 5.85 ± 1.03g bodyweight (a decrease of 1.30 ± 0.22% relative to baseline).

Accuracy of Responding: Food restriction had no effect on overall performance accuracy in comparison to baseline (t = -0.688, df = 6, N.S.). Independent analysis of Go and No-go trials supported further the lack of influence of food restriction on task performance (t = -0.611, df = 6, N.S.; t = -0.894, df = 6, N.S., respectively).

Anticipatory Responding: Early responding during both Go and No-go trials did not differ from baseline following an increase in hunger motivation (t = 0.405, df = 6, N.S.; t = 0.595, df = 6, N.S., respectively). The frequency of magazine entries during Go and No-go trials also remained unchanged (t = -0.930, df = 6, N.S.; t = 1.066, df = 6, N.S., respectively).

Speed of Responding:Restricting food intake resulted in a significant decrease in the latency to incorrectly respond during No-go trials (t = 3.526, df = 6, p = 0.012). In contrast, correct response latency did not differ in comparison to baseline (t = -0.380, df = 6, N.S.) nor did the speed with which reward was collected following either a correct Go or No-go trial (t = 0.516, df = 6, N.S.; t = -1.655, df = 6, N.S., respectively).

Omissions: There was no effect of food restriction on the frequency of failure to collect reward during No-go trials (Z = -0.211, N.S.)

II. Systematic Delayed Reward task

For all descriptive data see Table 6.

Phase 1: Decrease in primary motivation

During 1 hr prefeeding on normal chow, animals consumed 11.72 ± 0.50g of food leading to a weight gain of 12.88 ± 0.71g (increase of 2.54 ± 0.14 % relative to baseline). Similarly, during 30min free access to sucrose pellets, animals consumed 12.49 ± 0.84g food leading to a weight gain of 12.32 ± 1.03g (increase of 2.38 ± 0.21% relative to baseline). Food consumption did not differ as a function of food type (t = -1.100 df = 9, N.S) nor did weight gain expressed either as an absolute or percentage increase (t = 0.550, df = 9, N.S.; t = 0.766, df = 9, N.S., respectively).

Choice Behaviour: Prefeeding on chow or sucrose had no significant effects on overall percentage choice of delayed reward in comparison to baseline (normal chow: t = 1.527, df = 9, N.S; sucrose pellets: t = 2.231, df = 9, N.S.). Analysis of choice by delay also failed to reveal any significant main effects of level of motivation on choice of delayed reward (normal chow: F(1,9) = 0.577, N.S.; sucrose pellets: F(1,9) = 2.289, N.S.). A highly significant main effect of delay was however found following both feeding manipulations (normal chow: F(4,36) = 41.652, p < 0.001; sucrose pellets: F(4,36) = 35.766, p < 0.001), post hoc analysis confirming a reduction in choice of delayed reward at 20, 40 and 60 seconds relative to 0 second delay trials (all p<0.01). No significant motivation x delay interactions were observed (normal chow: F(4,36) = 0.661, N.S.; sucrose pellets: F(4,36) = 0.791, N.S.).

Speed of Responding: Relative to baseline, prefeeding on normal chow significantly increased trial initiation latency (t= -4.471, df = 9, p=0.001) and reduced the speed with which the immediate reward was selected (t =-2.326, df = 9, p= 0.045). However, no changes were observed in delayed response latency (t = -1.892, df = 9, N.S.), or in magazine latencies following either immediate (t = -1.170, df = 9, N.S.) or delayed choices (t = 1.325, df = 9, N.S.). In contrast, while prefeeding with sucrose pellets also significantly increased trial initiation latency (t = -2.998, df = 9, p = 0.015), no significant changes were evident on either immediate and delayed response latencies (t =-1.589, df = 9, N.S.; t = 1.476, df = 9, N.S., respectively). Decreasing the motivation for sucrose pellets did however increase significantly delayed reward magazine latency (t = -3.229, df = 9, p = 0.009), whilst leaving unchanged magazine latency following an immediate choice (t = 0.565, df = 9, N.S.).

Omissions: Prefeeding with either normal chow or sucrose pellets had no significant effects on the failure to initiate trials (normal chow: Z=-1.389, N = 10; N.S.; sucrose pellets: Z = -1.219; N=10, N.S.) or to collect reward following a delayed reward choice (normal chow: Z = -1.122, N = 10; N.S.; sucrose pellets: Z = -1.130, N= 10; N.S.).

Phase 2: increase in primary motivation

The reduction of food allowance by 50% on the day prior to testing led to a loss of an average of 4.52 ± 0.72gof bodyweight (a decrease of 1.01 ± 0.002% relative to baseline).

Choice Behaviour: Food restriction led to a significant increase in overall percentage choice of the delayed larger reward (t = -2.507, df = 9, p = 0.033): overall choice of delayed reward: baseline = 70.06 ± 7.18%; following reduction of daily food intake = 73.06 ± 8.07%. Analysis of choice by delay further supported the increased preference for the delayed reward (F(4,36) = 8.253, p = 0.018). A main effect of delay was also revealed (F(4,36) = 32.826, p < 0.001), again confirming that the choice of the delayed larger reward decreased with increasing delays, reaching significance at the 40 and 60 second delays relative to the 0 second delay condition (all p<0.001). The effect of hunger on choice behaviour was delay-dependent, as indicated by the significant motivation x delay interaction (F(4,36) = 5.688, p = 0.001). To examine this interaction further, a series of repeated measures t-tests compared choice behaviour at each delay. While hunger significantly increased the choice of the delayed reward during the 10 second delay condition versus baseline (t = -5.577, df = 9, p < 0.001) (see Fig. 3), choice of delayed reward across all remaining delay conditions remained comparable to baseline (all t ≥ 0.210, df = 9, N.S.).

Speed of Responding:Food restriction had no significant effect on the latency to initiate trials (t = -1.327, df = 9, N.S.), or the speed with which animals selected an immediate or delayed reward (t = -0.260, df = 9, N.S., t = -0.740, df = 9, N.S., respectively). Although magazine latency following an immediate reward choice furthermore did not differ from baseline (t = -1.189, df = 9, N.S.), the speed with which reward was collected following a delayed reward choice became significantly faster (t = 1.905, df = 9, p = 0.045)

Omissions: Food restriction significantly decreased the frequency of failures to initiate trials during the task (Z = -2.060, N = 10, p= 0.039), whereas magazine omissions following a delayed reward choice did not differ significantly from baseline (Z = 0.001, N= 10, N.S.)

Table 5:Experiment 3- The effects of acute alterations in motivation for food reward on performance in the Symmetrically Reinforced Go/no-go task

Behavioural Measure / Average BL Prior to
Prefeeding of
Rat Chow / Sated Following
Prefeeding of
Rat Chow / Average BL Prior to
Prefeeding of
Sucrose Pellets / Sated Following
Prefeeding of
Sucrose Pellets / Average BL Prior to
Reduction of Daily
Food Intake / Increased Deprivation
Following Reduction
of Daily Food Intake
Percentage Total Correct trials
Percentage Correct Go trials
Percentage Correct No-go trials
Go Trials with
Early Responses
No-go Trials with
Early Responses
Go Inappropriate
Magazine Entries
No-go Inappropriate Magazine Entries
Correct Response
Latency (s)
Incorrect Response
Latency (s)
Go Magazine
Latency (s)
No-go Magazine
Latency (s)
No-go Trial Magazine
Omission / 87.75 ± 1.42
97.00 ± 1.09
78.71 ± 2.78
16.06 ± 1.78
5.09 ± 1.02
2.00 ± 1.14
12.11 ± 2.78
1.01 ± 0.18
2.49 ± 0.26
0.27 ± 0.03
0.61 ± 0.07
0.36 ± 0.14 / 88.75 ± 1.28
94.64 ± 2.58
82.86 ± 2.21
14.00 ± 2.58
4.29 ± 0.52
2.00 ± 0.72
10.57 ± 3.17
1.26 ± 0.21
2.31 ± 0.41
0.30 ± 0.03
0.65 ± 0.08
1.33 ± 0.14* / 91.04 ± 1.75
92.92 ± 3.90
89.17 ± 2.30
15.07 ± 1.80
4.73 ± 1.57
1.60 ± 0.48
11.50 ± 3.46
1.11 ± 0.19
2.55 ± 0.42
0.28 ± 0.03
0.65 ± 0.13
1.07 ± 0.58 / 90.83 ± 1.47
94.58 ± 3.12
87.08 ± 2.27
10.83 ± 1.30
3.17 ± 1.11
1.50 ± 0.56
7.83 ± 2.52
1.20 ± 0.23
2.36 ± 0.58
0.29 ± 0.03
0.79 ± 0.09
3.00 ± 0.51* / 88.82 ± 1.61
96.29 ± 1.48
81.36 ± 2.68
14.68 ± 1.73
4.14 ± 0.93
2.29 ± 0.65
12.17 ± 3.18
1.22 ± 0.23
2.49 ± 0.32
0.27 ± 0.03
0.64 ± 0.11
0.60 ± 0.14 / 89.82 ± 2.03
95.71 ± 2.48
83.93 ± 3.44
14.14 ± 2.02
3.86 ± 0.96
3.57 ± 1.65
9.86 ± 3.54
1.29 ± 0.29
1.54 ± 0.29*
0.26 ± 0.03
0.75 ± 0.13
0.57 ± 0.30

Each value represents the mean ± SEM. *, p<0.05versusbaseline. Baseline (BL) = 5 day average baseline performance prior to feeding manipulation.

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