Neurochemical Changes Correlated With Behavior Maintained Under Fixed‐interval and Fixed‐ratio Schedules of Reinforcement

Abstract

Key pecking of 4 pigeons was maintained under a multiple 3-min fixed-interval, 30-response fixed-ratio schedule of food presentation. Only one schedule was in effect during an experimental session, and each was correlated with a different keylight stimulus and location (left vs. right). The different schedule components alternated across days or weeks. Cerebrospinal fluid was collected from chronically implanted intracerebroventricular cannulae following sessions with the different schedules, as well as following sessions in which reinforcement was withheld (extinction), when response-independent food was delivered, and when the experimental chamber was dark and there were no scheduled events. Metabolites of the neurotransmitters serotonin, norepinephrine, and dopamine were assayed in cerebrospinal fluid using high-performance liquid chromatography with electrochemical detection. Compared to the fixed-ratio condition, responding maintained under the fixed-interval schedule resulted in consistently higher levels of the serotonin metabolite 5-hydroxyindoleacetic acid and of the dopamine metabolite homovanillic acid in all pigeons. Levels of 3-methoxy-4-hydroxyphenylethylene glycol, a metabolite of norepinephrine, and dihydroxyphenylacetic acid, another dopamine metabolite, were also higher in 3 of the 4 pigeons following exposure to the fixed-interval schedules when compared to levels of these metabolites after exposure to the fixed-ratio schedule. Extinction of fixed-ratio responding resulted in large increases in 5-hydroxyindoleacetic acid compared to levels of this metabolite under the fixed-ratio schedule, whereas this serotonin metabolite decreased during extinction of responding under the fixed-interval schedule. Control procedures suggested that the neurochemical changes were not related to the rate of responding but were a function of the specific experimental conditions. Distinctive neurochemical changes that accompany schedule-controlled responding show the sensitivity of the neurochemical environment to behavioral contingencies and demonstrate further the profound impact that such contingencies have on biobehavioral processes.

Functional aspects of dopamine metabolism in the putative prefrontal cortex analogue and striatum of pigeons (Columba livia)

“…This finding is in correspondence with previous neurochemical studies in birds (Juorio and Vogt, 1967;Barrett and Hoffmann, 1991;Gruss and Braun, 1997;Gruss et al, 1999;Kostá l et al, 1999). Remarkably, the HVA/DOPAC ratio in NCL dialysates was more than twice as high as in LPO dialysates.…”

Effects of 5‐HT2A receptor stimulation on economic demand for fentanyl after intermittent and continuous access self‐administration in male rats

“…This waiting period caused the INT group to develop increased anticipation of drug availability, indicated by short latencies to earn injections at the beginning of a session (relative to the CON group), and a pronounced scalloped pattern of non‐reinforced responding during OFF periods. A scalloped response pattern is typical of fixed‐interval schedules, which result in different neurochemical changes than fixed ratio schedules for food 28 . With cocaine, long access conditions lead to tolerance to cocaine's effects on the dopamine transporter, whereas intermittent access leads to sensitization 29 .…”

É possível ser um psiquiatra behaviorista radical? Primeiras reflexões

“…Por questões técnicas, tal experimento ainda não é possível, mas existem alguns estudos que se aproximam disso. Num primeiro exemplo, mais fácil de explicar, observou-se que os níveis cerebrais de neurotransmissores como a serotonina e a noradrenalina, tão apontados como "causas" de depressão e ansiedade 3 , se mostraram dependentes de variáveis ambientais, mudando em função do esquema de reforçamento em vigor (Barrett & Hoffmann, 1991). Num outro exemplo, foi demonstrado que a atividade elétrica basal de neurônios de ratos cultivados in vitro poderia ser captada por eletrodos e transformada em comandos para um simulador de vôo (Wood, 2004).…”