The effects of beta-endorphin: state change modification

Jan G Veening, Henk P Barendregt, Jan G Veening, Henk P Barendregt

Abstract

Beta-endorphin (β-END) is an opioid neuropeptide which has an important role in the development of hypotheses concerning the non-synaptic or paracrine communication of brain messages. This kind of communication between neurons has been designated volume transmission (VT) to differentiate it clearly from synaptic communication. VT occurs over short as well as long distances via the extracellular space in the brain, as well as via the cerebrospinal fluid (CSF) flowing through the ventricular spaces inside the brain and the arachnoid space surrounding the central nervous system (CNS). To understand how β-END can have specific behavioral effects, we use the notion behavioral state, inspired by the concept of machine state, coming from Turing (Proc London Math Soc, Series 2,42:230-265, 1937). In section 1.4 the sequential organization of male rat behavior is explained showing that an animal is not free to switch into another state at any given moment. Funneling-constraints restrict the number of possible behavioral transitions in specific phases while at other moments in the sequence the transition to other behavioral states is almost completely open. The effects of β-END on behaviors like food intake and sexual behavior, and the mechanisms involved in reward, meditation and pain control are discussed in detail. The effects on the sequential organization of behavior and on state transitions dominate the description of these effects.

Figures

Figure 1
Figure 1
The Funnel-Model of the sequential organization of the male rat behavior. The model is based on a transition analysis of the behavioral elements of the male rat occurring during a series of experiments, which included feeding behavior, sexual behavior and territorial aggression, combined with the effects of electrical stimulation of the ventromedial hypothalamic nucleus (VMH). Explanation: see text. We have coined this model the ‘Funnel-Model’, because it illustrates clearly that in phase 1 of the behavioral sequence the animal is relatively free to make choices leading to any possible ‘consummatory act’, or in a wider view, to any behavioral state. Phase 1 can be characterized as a transitional situation, from where any behavioral sequence leading to a specific consummatory act can be performed or from where any possible behavioral state can be reached. At the end of phase 2 the situation is completely different: the male is ‘bound to’ perform the consummatory act, (mostly consisting of a series of physiological reflexes) and the opportunity to select other behavioral transitions is temporarily blocked. Only after completing the consummatory behavior, the ‘freedom’ of phase 1 is available again. The ‘Funnel-model’ illustrates on the one hand that physiological and brain mechanisms are working to support behavioral perseverance and to keep behavior directed to a specific goal, while on the other hand, especially in phase 1, the opportunity is raised to choose another strategy, or to pursue another goal or to reach another state.

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