Rapid acquisition of operant conditioning in 5‐day‐old rat pups: A new technique articulating suckling‐related motor activity and milk reinforcement

Abstract

Newborn rats are capable of obtaining milk by attaching to a surrogate nipple. During this procedure pups show a gradual increase in head and forelimb movements oriented towards the artificial device that are similar to those observed during nipple attachment. In the present study the probability of execution of these behaviors was analyzed as a function of their contingency with intraoral milk infusion using brief training procedures (15 min). Five-day-old pups were positioned in a smooth surface having access to a touch-sensitive sensor. Physical contact with the sensor activated an infusion pump which served to deliver intraoral milk reinforcement (Paired group). Yoked controls received the reinforcer when Paired neonates touched the sensor. Paired pups trained under a continuous reinforcement schedule emitted significantly more responses than Yoked controls following two (Experiment 1) or one training session (Experiment 2). These differences were also observed during an extinction session conducted immediately after training. The level of maternal deprivation before training (3 or 6 hr) or the volume of milk delivered (1.0 or 1.5 microl per pulse) did not affect acquisition or extinction performances. In addition, it was observed that the rate of responding of Paired pups during the early phase of the extinction session significantly predicted subsequent levels of acceptance of the reinforcer. These results indicate that the frequency of suckling-related behaviors can be rapidly modified by means of associative operant processes. The operant procedure here described represents an alternative tool for the ontogenetic analysis of self-administration or behavior processes of seeking.

Amniotic Fluid as an Extended Milieu Intérieur

“…Infusion of milk into the mouth also can serve as a positive reinforcer to support operant conditioning in the infant rat. Rat pups 1-5 days old can learn to press their head or forelimbs against a paddle or touch-sensor to deliver a small infusion of milk reinforcement (Arias, Spear, Molina, & Molina, 2007;Dom ınguez, Bocco, Chotro, Spear, & Molina, 1993;Johanson & Hall, 1979), and can learn to discriminate between a paddle that provides milk and one that does not (Johanson & Terry, 1988).…”

Brain Acetaldehyde Exposure Impacts upon Neonatal Respiratory Plasticity and Ethanol-Related Learning in Rodents

“…At PD5, and following breathing evaluations, pups were removed from their maternal cages and were intraorally implanted with a cannula (PE-10) that allowed liquid infusions (Hall, 1979; Dominguez et al, 1996; Abate et al, 2001; Cheslock et al, 2001; Arias et al, 2007; Bordner et al, 2008; Miranda-Morales et al, 2014). They remained pair-housed in holding cages for 3 h until operant procedures took place.…”

“…Before commencement of the evaluation, animals were anogenitally stimulated with a cotton swab to promote urination and defecation, weighed to the nearest 0.01 g. They were then fastened inside a disposable respirator mask (3M dust, fume and mist respirator 8801 P2) through a restrictor vest, expandable enough, to allow free movements of the head and limbs. The respiration mask was tilted at 40 degrees from the floor surface supported with a cardboard box (see Arias et al, 2007 for further procedural details).…”

“…The number of sensor contacts of each Paired subject and its corresponding Yoked control were recorded. Similar procedures have been employed when analyzing early operant leaning regulated by positive reinforcers such as milk, sucrose and ethanol (Arias et al, 2007; Bordner et al, 2008; March et al, 2009; Miranda-Morales et al, 2014). …”

“…To address these phenomena in perinatal rats, it was decided to employ similar central ethanol (100 mg%) and ACD (0.35 μmol) doses that have been observed to exert analogous motivational effects (Nizhnikov et al, 2007; March et al, 2013a,b). A second goal was to further analyze if central pre-exposure to the drug or its metabolite modulate subsequent seeking behavior of ethanol as a reinforcer in an operant task specifically developed for perinatal or infant rats (Arias et al, 2007; Bordner et al, 2008; March et al, 2009; Miranda-Morales et al, 2014). These goals were sequentially examined.…”