Classical conditioning in the rat fetus. III. Retention, extinction, and re‐activation of the conditioned response (CR)

Abstract

A single paired presentation of an artificial nipple (conditioned stimulus, CS) and milk (unconditioned stimulus, US) resulted in classical conditioning. When re-exposed to the artificial nipple CS after conditioning, fetuses showed fewer oral grasp responses compared to control fetuses exposed to the milk (US) and artificial nipple (CS) in an unpaired fashion. The reduction in oral grasping was evident when the test of oral grasping was administered 18 min after conditioning but not 21 to 30 min after conditioning (Experiments 1a and 1b). Experiments 2a and 2b confirmed that nine or more exposures to the CS after conditioning, without a milk infusion, resulted in experimental extinction of the conditioned reduction in oral grasping. One re-exposure to milk during the period after classical conditioning was sufficient to re-activate memory for the association between artificial nipple CS and milk US (Experiment 3a). Fetuses exposed to one or two re-activation treatments that comprised an intraoral infusion of milk showed evidence of the conditioned reduction in oral grasping when tested after a delay sufficient to produce forgetting. Experiment 3b showed that the orosensory properties of milk were sufficient to re-activate fetal memory for the association between artificial nipple and milk. Experiment 3c indicated that central injection of 10 ng of dynorphin A 1-13 re-activated fetal memory for the classically conditioned association. Experiments 3b and 3c suggested that the orosensory properties of milk activated a kappa opioid system in the fetal brain that reduced oral grasping of the artificial nipple during the test for oral grasping.

Maternal anesthesia via isoflurane or ether differentially affects pre‐and postnatal behavior in rat offspring

“…It is important to note, however, that behavioral suppression induced by ether is not so pronounced that meaningful analyses have been obscured. A wealth of published literature relying on chemomyelotomy and/or cesarean delivery under brief maternal ether exposure has revealed astounding capabilities of the rat fetus (Becker & Smotherman, 1996;Browne et al, 1994;Brumley & Robinson, 2005;Chotro & Molina, 1992;Dominguez et al, 1993;Kleven et al, 2004;Kozlov et al, 2006;Petrov et al, 2006;Robertson & Smotherman, 1990;Robinson, 2005;Robinson et al, 1992;Ronca & Alberts, 1990;Shen et al, 1991;Smotherman & Robinson, 1985, 1989Smotherman, 2002Smotherman, , 2003. The results of this study indicate a powerful need for careful comparison of anesthetic agents when preparing rat dams for behavioral studies of prenatal and newborn offspring.…”

“…Essentially all pharmacological agents undergo transplacental drug transfer (Benitz & Druzin, 2005;Nau & Plonait, 1998), including general anesthetics that can induce varying degrees of fetal anesthesia and behavioral depression (Ostheimer, 1984). Ether is relatively inexpensive, readily available, and easy to administer, and therefore continues to be the most commonly used maternal anesthetic in psychobiological investigations of perinatal rats (Brumley & Robinson, 2005;Kleven, Lane, & Robinson, 2004;Kozlov, Petrov, Varlinskaya, & Spear, 2006;Petrov, Nizhnikov, Varlinskaya, & Spear, 2006;Robinson, 2005;Smotherman, 2002Smotherman, , 2003. Ether, however, is characterized by high blood solubility that can be associated with accumulation in the fetal blood and tissues, and altered neurobehavioral function (Hodgkinson, Marx, Kim, & Miclat, 1977;Palahniuk, Scatliff, Biehl, Wiebe, & Sankaran, 1977).…”

“…(1) spontaneous movements that are both coordinated intrinsically and shaped by the proximal environment (Robertson & Smotherman, 1990;Robinson & Kleven, 2005;Ronca, Kamm, Thelen, & Alberts, 1994;, (2) responses to sensory cues typical of intrauterine stimuli , 1995aSmotherman & Robinson, 1985;Smotherman, Robinson, Ronca, Alberts, & Hepper, 1991), including those that are characteristic of intrauterine stimuli, (3) habituation and classical conditioning (Mickley et al, 2004;Smotherman, 2002Smotherman, , 2003Smotherman & Robinson, 1998), (4) species-typical action patterns (Smotherman & Robinson, 1987, 1989, and (5) oral grasping of an artificial nipple (Browne, Robinson, & Smotherman, 1994;Robinson et al, 1992). Clearly, the mammalian fetus is capable of a rich and varied repertoire of behaviors that are organized, regulated, and under sensory control.…”

Appearance of fetal pain could be associated with maturation of the mesodiencephalic structures

“…Also for classical conditioning, the myelination of the CNS is not a necessary condition. Rat fetuses could undergo classical conditioning, while myelination process starts postnataly 67,68…”

Reflexões sobre o estudo do desenvolvimento na perspectiva da análise do comportamento

“…Ou ainda, um estímulo que seria naturalmente evitado nos pós-natal, tem sua aversividade diminuída com uma história de exposição pré-natal a ele (Sneddon et al, 1998). O fenômeno já foi observado em diferentes animais, como coelhos, frangos e ratos, evidenciando possivelmente a generalidade entre espécies (Gehm, 2011 Smotherman, 2002aSmotherman, , 2002bSmotherman, , 2003. O método normalmente empregado por ele envolve na abertura do abdome de ratas prenhas, de forma que os fetos possam ser observados e os procedimentos possam ser realizados diretamente com eles.…”