The curve-shift paradigm in self-stimulation

doi:10.1016/0031-9384(86)90388-4

Physiology & Behavior

Volume 37, Issue 1, 1986, Pages 85-91

https://doi.org/10.1016/0031-9384(86)90388-4 Get rights and content

Abstract

Eleven rats were trained to press a lever in an operant chamber in order to earn rewarding trains of cathodal rectangular pulses of fixed intensity and variable frequency. The rate-frequency functions were examined under administration of two neuroleptics (pimozide and chlorpromazine) and three manipulations that interfered with bar pressing (muscular relaxation with methocarbamol, increased lever weight, and limitation of maximum response rates by an FI reinforcement schedule). Chlorpromazine, and pimozide at low dosages produced a near parallel shift of the rate-frequency functions on the logarithmic axis of pulses, suggesting that these drugs decreased the reinforcing efficacy of the stimulation. The three conditions that interfered with bar-pressing decreased the asymptotic rates and produced small or moderate lateral shifts. Changes in the reinforcing efficacy of the stimulation following the above manipulations were inferred from the shift in the number of pulses required at zero and half-maximal performance (θ₀ and M₅₀ indices, respectively). In the cases of the manipulations that interfered with bar-pressing, M₅₀ indicated a larger artifactual change in the efficacy of the stimulation, compared to θ₀. This phenomenon was mainly due to the fact that the asymptote of the altered functions was shifted towards higher pulse numbers.

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The rostromedial tegmental nucleus also referred to as the tail of the ventral tegmental area (tVTA) contains a cluster of gamma-aminobutyric acid (GABA)ergic neurons that receive dense glutamatergic afferents from the lateral habenula (LHb), and project to dopamine (DA) neurons of the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). In light of previous evidence implicating glutamate transmission in the regulation of midbrain DA neuronal activity, we first assessed the impact of intra-tVTA microinjection of NBQX (0.8 nmol/side) and PPPA (0.825 nmol/side), respectively AMPA and NMDA receptor antagonists, on reward induced by intracranial self-stimulation (ICSS) and on locomotor activity. Since the tVTA contains a large concentration of mu opioid receptors, additional measures were obtained following microinjection of endomorphin-1 (EM-1, 1 nmol/side) to confirm tVTA placements. Then, using small interfering RNAs (siRNAs), we tested the effect of tVTA downregulation of the GluN1 subunit of the NMDA receptor on reward and locomotor activity. Results show that NBQX, PPPA and EM-1 all enhance reward and locomotor activity, effects that were of different magnitude in rostral and intermediate parts of the tVTA. On the other hand, a reduction in GluN1 subunits used a marked decrease in operant responding for ICSS, but failed to alter ICSS reward and the reward-enhancing effect of PPPA. Our results support a role for the tVTA as a main inhibitory component of DA-dependent behavioral measures, and suggest that tVTA NMDA receptors that modulate reward are most likely expressed on tVTA afferent terminals.
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Citation Excerpt :
Leptin delivery resulted in a leftward shift in the rate-frequency ICSS curve, lowering the frequency threshold for which rats will work for BSR. This leftward shift in the response rate-frequency curve suggests that BSR is more rewarding as a result of leptin treatment (Bauer et al., 2013; Carlezon and Chartoff, 2007; Miliaressis et al., 1986). Our finding that leptin enhances VTA ICSS complements data from Fulton and colleagues (Fulton et al., 2000) that examined the effects of leptin on lateral hypothalamus (LH) ICSS.
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The insular cortex has been associated with various aversive and rewarding sensory, regulatory, and learning processes. The objective of this study was to examine the characteristics of the reinforcement induced by electrical stimulation of this brain area in rats. Results obtained confirm that electrical stimulation of the insular cortex may induce conditioned place and flavor preferences but the learning acquired is not transferred in a reversal test. Unexpectedly, they also demonstrate that this rewarding effect diminishes after repeated tests. In follow-up experiments, locomotor activity tests revealed an increased number of rearings (a sensitization index) in stimulated animals. Furthermore, in these same animals, administration of low doses of naloxone, an opiate antagonist, developed place aversion toward the maze compartment for which the animals had previously shown preference. These results are interpreted in relation to the effects induced by the repeated administration of natural and artificial rewarding stimuli.
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^☆: Supported by grant No. A8625 from NSERC of Canada.

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ArticleThe curve-shift paradigm in self-stimulation☆

Abstract

Pharmacol Biochem Behav

Brain Res Bull

Brain Res Bull

Physiol Behav

Pharmacol Biochem Behav

Fitting intracranial self-stimulation data with growth models

Behav Neurosci

Article
The curve-shift paradigm in self-stimulation☆