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PubMed1986

Electrophysiological characteristics of neurons in forebrain regions implicated in self-stimulation of the medial forebrain bundle in the rat.

In an attempt to identify neurons likely to play a role in self-stimulation of the medial forebrain bundle (MFB), action potentials of single neurons in the septum and basal forebrain of anesthetized rats were recorded by means of extracellular electrodes. Refractory period estimates were obtained from cells antidromically activated by stimulation of the lateral hypothalamus or ventral tegmental area, and estimates of interelectrode conduction time were obtained from cells that were driven by stimulation of both sites. The results show that some descending MFB axons arising in the medial septum, diagonal band of Broca and neighboring forebrain structures have characteristics comparable to properties of MFB reward neurons inferred from behavioral experiments.

Animals↗
PubMed2003

Exposure of mice to a predator odor increases acoustic startle but does not disrupt the rewarding properties of VTA intracranial self-stimulation.

The present investigation assessed the propensity of an acute psychogenic stressor exposure to induce behavioral change in paradigms assessing fear/anxiety (acoustic startle) and motivation/anhedonia (intracranial self-stimulation) in CD-1 mice. In the acoustic startle paradigm, a 10-min exposure of 2-4 month old mice (young adult mice) to fox odor (2,5-dihydro-2,4,5-trimethylthiazoline; TMT) was associated with decreased acoustic startle relative to mice exposed to the control odor, butyric acid (BA), immediately and relative to both saline and BA exposure 24 h following odor exposure in the home cage. In contrast, a 2-min exposure of young adult mice to TMT was associated with an increase in startle relative to saline and BA during the immediate post-odor test session only. In young adult mice a 2-min and a 10-min exposure to BA resulted in a startle profile of mice reminiscent of saline-treated mice. In comparison to young adult mice, a 2-min exposure of mature adult mice (5-7 months old) to TMT enhanced startle for up to 48 h relative to both saline and BA, while a 10-min exposure of mature adult mice to TMT enhanced startle for 168 h post-odor exposure relative to saline-exposed mice only. However, the greatest increase in startle amplitude (i.e. 48 h) was acquired following the 2-min exposure of mature mice to TMT. Among mature adult mice, a 10-min exposure to BA in the home cage eventuated in enhanced startle relative to saline-exposed animals 168 h following odor exposure. In comparison, exposure of mice to 10 min of TMT depressed responding for VTA brain stimulation at the initial 80 Hz frequency, but was ineffective in elevating reward thresholds relative to mice merely exposed to saline. Mice assessed in the ICSS paradigm were approximately 2-4 months old at the time of surgery and 5-7 months old at the completion of testing. These data suggest that acute odor exposure may induce a fear gradient dependent upon the perceived stressor severity and that the resultant anxiety-like effects are dependent on the duration of odor exposure, age of the animals and the temporal interval between odor presentation and behavioral testing. Moreover, the anxiogenic properties of psychogenic stressors can be separated from their anhedonic effects. The implications of these data for clinical psychopathology are discussed.

Acoustic Stimulation↗
PubMed1998

Involvement of the parafascicular nucleus in the facilitative effect of intracranial self-stimulation on active avoidance in rats.

To evaluate whether parafascicular nucleus (PF) is involved in the facilitative effect of lateral hypothalamic intracranial self-stimulation (LH-ICSS) on two-way active avoidance acquisition (5 sessions, 10 trials each, one daily) and long-term retention (10 days), rats were lesioned bilaterally at the PF and implanted with an electrode aimed at the LH to obtain ICSS behavior. After each acquisition session rats were allowed to self-administer 2500 trains of LH-ICSS. The main results were: (1) LH-ICSS facilitated the acquisition and retention of conditioning; (2) PF lesions impaired both acquisition and retention of two-way active avoidance; (3) there was a positive relationship between PF lesions size and learning disruption, and (4) LH-ICSS failed to facilitate learning when PF was lesioned. We concluded that the lesion size is a critical variable to evaluate the effects of PF lesions on learning and memory, and that LH-ICSS treatment may exert their effects through the PF nucleus or, at least, the integrity of PF is required for LH-ICSS to improve clearly the task.

Animals↗
PubMed1986

Acquisition of intracranial self-stimulation in medial prefrontal cortex of rats facilitated by amphetamine.

Two groups of rats were trained to lever press for intracranial self-stimulation (ICSS) in the medial prefrontal cortex (mPFC) using a uniform amount of stimulation for all animals. One group acquired the lever pressing task very gradually during saline pretreatment but dramatically improved its rate of acquisition during the third week of training when pretreated with d-amphetamine (0.5 mg/kg). Administration of amphetamine to the other group of rats before each of the first five training sessions greatly facilitated acquisition of the ICSS task, and a significant improvement in performance over the saline control group appeared on the third day of training. After ICSS performance had stabilized, testing the animals revealed a significant amphetamine-induced increase in rate over the dose range of 0.25 to 1.0 mg/kg. These effects of amphetamine suggest that ICSS in mPFC is sensitive to changes in catecholamine neurotransmission during both the acquisition and maintenance of this behavior.

Animals↗
PubMed2003

Posttraining intracranial self-stimulation ameliorates the detrimental effects of parafascicular thalamic lesions on active avoidance in young and aged rats.

To evaluate whether intracranial self-stimulation (SS) ameliorates conditioning deficits induced by parafascicular nucleus (PF) damage in young and aged rats, the authors gave rats a daily session of 2-way active avoidance until a fixed criterion was achieved. Four experimental groups were established in both young and aged rats: SS treatment after every conditioning session (SS groups), pretraining PF lesions (lesion groups), PF lesions and SS treatment (L + SS groups), and controls. SS treatment not only canceled the detrimental effects of PF lesions, but also improved conditioning in lesioned rats (L + SS groups). This effect was more powerful in aged rats. SS treatment compensated for memory deficits generated by hypofunctionality of arousal systems such as that involving the PF.

Age Factors↗
PubMed1976

Evidence that self-stimulation of the region of the locus coeruleus in rats does not depend upon noradrenergic projections to telencephalon.

Rats with intracranial self-stimulation (ICSS) electrodes in the locus coeruleus and adjacent pontine tegmental structures received stereotaxically placed bilateral injections of 6-hydroxydopamine (4 mug/2 mul) into the mesencephalic trajectory of the dorsal tegmental noradrenergic bundle. The consequent depletions of norepinephrine in the cerebral cortices and hippocampi (96.7%) did not result in significant changes in ICSS. Thus, diencephalic and telencephalic noradrenergic projections of the locus coeruleus do not appear to be critical for the occurrence of ICSS from that nucleus or its surrounding region. Nor do these projections appear to be crucially involved in the enhancement of this ICSS by D-amphetamine. Rats in this study showed two-fold increases in responding following injections of D-amphetamine sulfate (0.5 mg/kg) both before and after the lesions of the dorsal tegmental bundle. These results suggest that the ascending projections of the locus coeruleus are not critically involved in ICSS of the dorsal pontine tegmentum.

Animals↗
PubMed1986

Effects of agonists and antagonists of cholinergic receptors on self-stimulation of the medial prefrontal cortex of the rat.

The effects of agonists and antagonists of muscarinic and nicotinic receptors on self-stimulation (SS) of the medial prefrontal cortex (MPC) were investigated. Rats, implanted chronically with monopolar electrodes in the MPC, received subcutaneous injections of nicotine (0.2, 0.4 and 0.8 mg/kg), mecamylamine (2.0, 4.0 and 8.0 mg/kg), pilocarpine (0.5, 1.0, 2.0 and 4.0 mg/kg), scopolamine (0.05, 0.1, 0.2, 0.4 and 0.8 mg/kg) and physostigmine (0.1, 0.2 and 0.4 mg/kg). In order to assess the possible non-specific effects of drugs such as sedation or motor dysfunction, spontaneous locomotor activity (SLA) was used as control. In those groups of rats in which the drugs produced an effect on SS, an operant behaviour for drinking (DB) on an FR-10 schedule was also used as control. Nicotine and mecamylamine had no effect on SS. Both pilocarpine and physostigmine produced a decrease in SS, SLA and DB. Scopolamine, on the contrary, produced a dose-related decrease on SS rate, which was accompanied by a facilitatory effect on SLA and DB. These results suggest that only muscarinic receptors could play a specific role on SS of the MPC.

Acetylcholine↗
PubMed1978

Tolerance to amphetamine's facilitation of self-stimulation responding: anatomical specificity.

Further work on the phenomenon reported by Leith and Barrett, wherein tolerance was shown to develop to the well-known D-amphetamine-induced facilitation of self-stimulation, clearly indicates that the development of such tolerance is dependent on the location of the stimulating electrode. Thirty-seven Fisher or Harlan rats were trained to bar press for hypothalamic stimulation (60 Hz, AC). Following several sessions during which small doses of D-amphetamine were administered to demonstrate facilitation, the subjects were placed on a 4-day D-amphetamine regimen. During this time they were given three daily injections of continuously increasing doses of D-amphetamine (total 78 mg/kg). Subsequent tolerance was shown for electrodes stimulating dorsal or medial hypothalamic structures (H2 field of Forel, dorsal medial forebrain bundle, medial hypothalamic nuclei), but did not develop with ventral or lateral hypothalamic stimulation sites (fornix, ventral medial forebrain bundle).

Animals↗
PubMed1990

Diazepam's impact on self-stimulation but not stimulation-escape suggests hedonic modulation.

In rats that self-administered lateral hypothalamic (LH) stimulation through chronically implanted electrodes, ip diazepam (DZ) increased rates and decreased thresholds of self-stimulation (SS) in a dose-related manner. Stimulation-escape (SE), however, was refractory to the drug. There was a complete dichotomy in electrode placements along the anterior/posterior plane. Every pure-reward electrode location was posterior to every reward-escape electrode. DZ-sensitive SS appears to be mediated by a reward substrate common to both pure-reward and reward-escape rats, whereas SE is supported by an aversive system unaffected by DZ and stimulated only in those rats with anterior placements. The lack of control over SE suggests that the drug's effect on stimulation-induced conduct is to increase reward rather than to decrease aversion. This hypothesis is discussed in the context of DZ's interactions with drugs of abuse.

Animals↗
PubMed1995

Curve-shift analysis of self-stimulation in food-restricted rats: relationship between daily meal, plasma corticosterone and reward sensitization.

Chronic food restriction lowers the threshold for lateral hypothalamic electrical self-stimulation (LHSS). This effect has previously been interpreted to reflect a sensitization of reward. In the present study a curve-shift method was used to explicitly differentiate effects of food restriction on brain stimulation rewarding efficacy and performance. Food restriction consistently shifted rate-frequency curves to the left, lowering the M-50 and Theta-0 parameters of rewarding efficacy. Asymptotic rates of reinforcement and slopes of rate-frequency functions were unaffected, confirming that food restriction does not facilitate LHSS by enhancing performance. In this and previous studies, LHSS in food-restricted rats was measured in the period immediately preceding the daily meal when hunger (i.e., period since last meal) and plasma corticosterone are at peak levels. In the light of evidence that corticosterone may regulate sensitivity of the mesolimbic dopamine pathway and account for the sensitizing effect of stress on psychomotor effects of opiates and stimulants, LHSS and corticosterone were measured in the immediate pre-and post-meal periods. While all food-restricted rats displayed elevated corticosterone levels in the pre-meal period and generally displayed a decline to control levels in the post-meal period, the sensitization of reward was not reversed in the post-meal period. These results indicate that chronic food restriction produces a sensitization of reward that does not depend upon the acute state of hunger that precedes the daily meal and does not vary with dynamic changes in plasma corticosterone level.

Animals↗
PubMed1997

Differential effects of immunologic challenge on self-stimulation from the nucleus accumbens and the substantia nigra.

Paralleling the effects of uncontrollable stressors, systemic administration of sheep red blood cells (SRBC) provokes brain neurotransmitter alterations, including DA variations within mesocorticolimbic regions, coinciding with or slightly preceding the peak immune response. Inasmuch as stressors disrupt responding for brain stimulation from the nucleus accumbens, possibly reflecting the anhedonic consequences of stressors, the present investigation assessed whether antigenic challenge would also influence responding for brain stimulation. Sheep red blood cell administration was found to reduce responding for brain stimulation from the nucleus accumbens, without affecting performance from the substantia nigra. The alterations of self-stimulation from the nucleus accumbens occurred at times that approximated the peak immune response. These data suggest that antigenic challenge may induce anhedonic-like effects that may be secondary to central neurochemical alterations engendered by the treatment. The possibility is also entertained that antigenic challenge may be interpreted as a stressor and contribute to alterations of affect.

Animals↗
PubMedDate not supplied

[The effect of new ACTH fragments on the behaviors of self-stimulation, avoidance and grooming in rabbits].

We studied the influence of new cyclic analogues of ACTH fragments EHFRWGKPVG-NH2 and KHFRVG-NH2 on self-stimulation (SS) and active avoidance (AA) behaviour. Intraventricular injection of EHFRWGKPVG-NH2 in low doses (0.5-2.5 mcg) was shown to increase, that in higher doses (4-5 mcg) to decrease SS frequency. Injection of KHFRWG-NH2 in doses of 0.1-5 mcg resulted in 25-30% decrease of SS frequency during the first 15 min, its subsequent return to the background level and repeated decrease. In 24-48 h SS was 5-8% higher than the background level and practically was unchanged in the course of 2 h of experiment. When testing AA behaviour EHFRWGKPVG-NH2 in doses of 0.5-2 mcg induced twice shorter "anxiety time" and longer latency of AA. Both fragments (0.1-5 mcg) evoked excessive grooming. These effects persisted for 24-72 h. The role of the cyclic analogues of ACTH fragments in the mechanisms of positive and negative reinforcement is discussed.

Adrenocorticotropic Hormone↗
PubMed1968

Lateral hypothalamus: food current intensity in maintaining self-stimulation of hunger.

Rats displaying stimulus-bound eating will press bars for currents slightly above eating threshold only when food is near the bar. At higher currents self-stimulation is maintained without food. Such currents may spread to activate consummatory feedback appropriate to the drive elicited; or, for more intensely stimulated drive mechanisms, wider ranges of sensory feedback may be reinforcing.

Animals↗
PubMed1984

Opioid peptides and self-stimulation of the medial prefrontal cortex in the rat.

The possible involvement of opioid peptides as part of the neurochemical substrates of self-stimulation (SS) in the medial prefrontal cortex (MPC) of the rat was investigated in two different groups of rats bilaterally implanted with monopolar electrodes in the MPC. In the first group, morphine (5, 10, and 20 micrograms) and an enkephalin analogue (BW 180) (5, 10, 20 and 40 micrograms) were injected through cannulae implanted into the lateral ventricles (IV). In the second group, naloxone (0.04, 0.4, and 1.6 micrograms) and morphine (5, 10 and 20 micrograms) were injected through cannulae implanted into the MPC, 1.5 mm above the tip of the stimulating electrodes. In the first group, spontaneous motor activity (SMA) was measured as a control for non-specific effects (sedation or motor dysfunction). In the second group SS, contralateral to the microinjected side, served as control. SS and SMA were were measured 1 and 2 h postinjection. One hour after IV injection of morphine SS was not affected, although SMA was decreased. Two hours postinjection, on the contrary, SS was increased while SMA remained decreased. Similar effects were found with IV microinjections of BW 180. Naloxone, intraperitoneally injected, reversed all these effects. Naloxone or morphine injected intracerebrally (MPC) produced no changes in SS either in the injected or in the contralateral side, which served as control. The present results suggest that the effects found with IV injections of opioids on SS of the MPC are indirect (through activation of other brain areas) and not mediated by a direct action on the neurochemical substrates underlying this behaviour in the MPC.

Animals↗
PubMed1997

Effect of adrenalectomy on cocaine facilitation of lateral hypothalamic self-stimulation.

An emerging body of evidence indicates that the adrenal hormone corticosterone modulates behavioral effects of abused drugs. Recently, it was reported that the self-administration and locomotor stimulatory effect of cocaine are blocked by adrenalectomy (ADX). In order to evaluate the effect of ADX on the brain reward system in general, and cocaine reward in particular, the effect of ADX on lateral hypothalamic self-stimulation (LHSS) and its facilitation by cocaine were investigated. Using curve-shift methodology, effects of cocaine (1.0, 3.0 and 10.0 mg/kg, i.p.) on the rewarding efficacy of brain stimulation were determined in ADX rats, with and without corticosterone supplementation, and compared with sham-operated controls. Results indicate that ADX does not affect LHSS or the facilitatory effect of cocaine. The divergence between these results and the results of cocaine self-administration studies is discussed in terms of the neuroanatomical and psychological processing of reward.

Adrenal Glands↗
PubMed1988

The effects of long-term administration of antidepressant drugs on intracranial self-stimulation responding in rats.

A discrimination procedure employing a two hole nose-poke technique was used to evaluate the effects of chronic administration of desipramine, amitriptyline, bupropion, nomifensine and zimelidine on intracranial self-stimulation (ICSS). Analysis of ICSS as a function of descending and ascending current presentation revealed that long-term exposure to desipramine significantly facilitated rates of responding from the medial forebrain bundle, and resulted in a shift to the left of the rate-intensity functions. The use of a discrimination paradigm allowed for the assessment of incorrect responses which proved to be a sensitive measure of the motor activating properties associated with electrical brain stimulation. These data indicated that the positive reinforcing effects of desipramine were not accompanied by concomitant increases in motor arousal. No changes in ICSS responding were evident after long-term treatment with amitriptyline, or the atypical antidepressants, bupropion, nomifensine and zimelidine. The implications of these findings were discussed in terms of the effects of these drugs on reward processes and the role of dopamine in the therapeutic efficacy of antidepressant drugs.

Animals↗
PubMed1998

Facilitation of acquisition and performance of operant and spatial learning tasks in self-stimulation experienced rats.

Adult male Wistar rats were implanted bilateraly with bipolar electrodes in substantia nigra-ventral tegmental area (SN-VTA) to experience intracranial self-stimulation (ICSS) for 15 min per day over a period of 10 days. These rats were then assessed for the acquisition and performance of the operant and the spatial learning tasks. ICSS experienced rats showed rapid acquisition of both the operant and the spatial learning tasks. Both the lever press performance for 7 sessions in the operant learning task and mean number of alternations per session in the spatial learning task were significantly higher (p < .001) in ICSS experienced rats compared with controls. The results suggest that prior ICSS experience facilitates the acquisition and performance in both the operant and the spatial learning tasks, which may be due to the structural and neurochemical alterations in the hippocampus induced by ICSS experience.

Analysis of Variance↗