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Hedonic interactions of medial prefrontal cortex and nucleus reticularis gigantocellularis

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Abstract

It has been shown that 'pure reward' and 'reward-escape' sites in the lateral hypothalamus (LH) of rats respectively ameliorate and exacerbate nucleus reticularis gigantocellularis (NGC) stimulation-induced aversion52. Conversely, the present studies found that 'rewarding' medial prefrontal cortex (MPFC) stimulation increased escape from NGC stimulation regardless of whether the MPFC site tested was 'pure reward' or 'reward-escape' in type. This suggested that a simple algebraic summation model of positive and negative affective processes may not adequately describe the NGC-MPFC interaction. In a subsequent study, rats were observed both to barpress less to obtain, and more to escape from, 'rewarding' MPFC stimulation during continuous NGC stimulation, supporting the hypothesis that the observed MPFC stimulation-mediated increase in NGC stimulation escape reflected an exacerbation of aversion. Finally, NGC stimulation was seen to increase barpressing to obtain 'subreward' MPFC current trains, indicating a potentiation of the reward value of such current. Results of this series of studies suggests a hedonic interaction model of NGC and MPFC characterized by reciprocal neuromodulation. The model is conceptualized as a 'neural opponent process' subserving affective 'balance' and 'feature enhancement', and its possible relevance to the putative role of the MPFC in cocaine use is discussed.

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The effects of naloxone on the rewarding and aversive properties of brain stimulation derived from the ventral tegmental area and the nucleus reticularis gigantocellularis, respectively, were assessed in rats, based on the following measures-the current threshold for latency to escape aversive nucleus reticularis gigantocellularis stimulation, the frequency threshold for rewarding ventral tegmental area stimulation, and the frequency threshold for self-stimulation obtained from delivery of concurrent ventral tegmental area and nucleus reticularis gigantocellularis stimulation, before and after three systemic doses of naloxone (0, 10, and 20mg/kg); in the latter case, the stimulation trains were interdigitated with an interpulse interval of 2 ms. Initially, thresholds for concurrent stimulation were elevated relative to the values obtained for ventral tegmental area stimulation alone, returning to baseline values only when the nucleus reticularis gigantocellularis stimulation no longer induced escape. After each pairing of the two sites, the current threshold for escape gradually increased until the maximum value administered, 700 microA, at which point aversive responses were no longer observed. This required very few pairings, between one and five trials across animals. Drug tests were then begun and produced a significant dose-response threshold increase across animals, without reinstating the latency to escape nucleus reticularis gigantocellularis stimulation. These findings are discussed in terms of a dissociation between the analgesic and rewarding properties of ventral tegmental area stimulation.
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Article
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Article
Describes a new theory of motivation and its applications to addiction and aversion. It assumes that many hedonic, affective, or emotional states are automatically opposed by CNS mechanisms which reduce the intensity of hedonic feelings, both pleasant and aversive. Opponent processes for most hedonic states are strengthened by use and weakened by disuse. These assumptions lead to deductions of many known facts about acquired motivation. The theory also suggests several new lines of research on motivation. It argues that the establishment of some types of acquired motivation does not depend on conditioning and is nonassociative in nature. Relationships between conditioning processes and postulated opponent processes are discussed. It is argued that the data on several types of acquired motivation, arising from either pleasurable or aversive stimulation, can be fruitfully reorganized and understood within the framework provided by the opponent-process model. (34 ref)
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A critical review supplementing previous articles upon the role of hedonic processes in motivation and learning. Special emphasis is placed upon the organizing and regulatory functions of affective processes. Recent experiments from the author's laboratory are reviewed and their theoretical significance considered. These experiments deal with hedonic processes as related to gustatory stimulation, food preference and intake, regulation of ingestive behavior, development of incentive values, and related matters. The main topics considered are: basic concepts and definitions; psychophysical studies of hedonic processes; studies of thresholds, preference, and the regulation of food intake; physiology of affective processes; the role of affective processes in motivation and learning; general conclusions. (2 p. ref.)
Article
Rats were allowed to self-stimulate while their responses were being recorded on tape. Subsequently, prerecorded patterns of their brain stimulation were "played back" to them. All subjects learned to escape brain stimulation delivered in exactly the same manner as they had previously elected to receive it.
Article
A theory of learning concerning approach behavior in the rat is applied to the phenomena of electrical self-stimulation of the brain. First, the theory is outlined and its application to learning in the intact animal is shown. Examples of subsequently verified predictions are then given. The theory is then applied to the phenomena of intracranial self-stimulation. Here learning is induced by the direct stimulation of parts of the central nervous system. However, such learning differs in many important respects from normal learning. It is shown that its anomalies are to be predicted from the theory. Further experimental verifications to test the theory in its application to intracranial self-stimulation are also described. The reason why a theory based on behavioral evidence can be used to predict at a more physiological level is that it is a hypothesis about what type of system it is which produces observed behavior.
Article
The projections of the rostal medulla were studied using retrograde and orthograde transport techniques in the rat. The present horseradish peroxidase (HRP) studies indicate that the ventral portion of nucleus reticularis (NGC) and nucleus reticularis magnocellularis (NMC) project to both rostral and caudal levels of the spinal cord, while dorsal NGC projects only to the rostral cord. A differential density distribution of labeled cells was observed, with the greatest density of NGC-spinal neurons located rostral to the level of the inferior olive; and the greatest density of NMC-spinal neurons located caudally.
Article
Neuronal systems involved in the initiation of cocaine reinforcement were investigated by identifying brain sites where direct application of the drug was reinforcing. This was accomplished by allowing rats to self-administer picomolar concentrations of cocaine into discrete brain regions. The medial prefrontal cortex supported self-administration, while the nucleus accumbens and ventral tegmental area did not. Self-administration could be attenuated by including equimolar concentrations of the dopaminergic D2-receptor antagonist sulpiride in the microinjection system. These results imply that cocaine reinforcement is mediated in part through a direct action on mesocortical dopaminergic receptors.
Article
The purpose of this experiment was to determine whether self-stimulation and stimulation-escape are mediated by one or two populations of directly stimulated neurons. Using paired-pulse, two electrode stimulation, we attempted to find out whether the substrate for stimulation-escape includes a direct axonal link between the lateral hypothalamus and the ventral tegmental area. Concurrent stimulation at two sites that are so linked will result in collision provided that the phase difference between stimulations at the two sites does not exceed the sum of the inter-electrode conduction time and the neuronal refractory period. Such phase effects in neurons mediating stimulation-produced behaviors can be measured behaviorally using the frequency scaling method [11] and hence, collision and anatomical linkage can be inferred. In a previous experiment [8] collision-like effects were obtained in three of four self-stimulating subjects suggesting that reward-related fibers directly link the lateral hypothalamus and ventral tegmental area. We now report that two of these three subjects showed no evidence of such a linkage when tested for stimulation-escape. Since the same electrodes and current intensities were used for the self-stimulation and stimulation-escape tests, different populations of directly stimulated fibers must have been responsible for the ON- and OFF-response.
Article
Hypothalamic stimulation in rats both reduces escape from noxious hindbrain stimulation and sustains self-administration only when hindbrain stimulation is inescapable. Self-administration reflects an aversion-ameliorative action of brain stimulation and not a positive reinforcement process. The psychophysical testing used is offered as a model for establishing the analgesic properties of brain stimulation.
Article
Prior electrical stimulation of the medial prefrontal cortex MFC facilitated the subsequent acquisition of intracranial self-stimulation (ICSS) from the same MFC electrode site. Stimulations that were spaced over a period of six days were more effective in producing this facilitation than the same number of stimulations delivered over a two day period. These data suggest that the rewarding effects of MFC stimulation may involve some process akin to the kindling phenomenon and as such may provide insights in the neuronal modifications thought to underlie learning and memory.