Characterizing the functional significance of the neonatal rat vibrissae prior to the onset of whisking

Abstract

The present series of experiments assessed how information from the whiskers controls and modulates infant rat behavior during early learning and attachment. Passive vibrissal stimulation can elicit behavioral activity in pups throughout the first two postnatal weeks, although orienting to the source of stimulation is evident only after ontogenetic emergence of whisking. In addition, while pups were capable of demonstrating learning in a classical conditioning paradigm pairing vibrissa stimulation with electric shock, no corresponding changes were detected in the anatomy of the barrel cortex as determined by cytochrome oxidase (CO) staining. Finally, the role of whiskers in a more naturalistic setting was determined in postnatal day (PN)3-5 and PN11-12 pups. Our results showed that both nipple attachment and huddling were disrupted in whisker-clipped PN3-5 pups but only marginally altered in PN11-12 pups. Together, these results suggest that the neonatal whisker system is behaviorally functional and relevant for normal mother-infant interactions, though it lacks the sophistication of a mature whisker system that evokes very specific and directed responses.

Spontaneous activations follow a common developmental course across primary sensory areas in mouse neocortex

“…The ubiquity and generality of this trajectory suggest a strong, internally mediated mechanism for patterning spontaneous activity during the development of primary sensory neocortical areas, regardless of the sensory experience of the cortical area during this developmental period. So while sensory input clearly refines cortical circuitry (Trachtenberg et al 2002), the primary drivers of the changes we observed are most likely internal. Because our recordings were performed in the absence of neuromodulators we can reject the hypothesis that the mechanism is primarily neuromodulatory, suggesting a role for changes of synaptic connectivity and neuronal integration in the progression of circuit dynamics.…”

“…These two areas were selected because they have markedly different developmental timelines: auditory cortex does not receive peripheral input until the cochlea becomes spontaneously active after PND 7 (Sadanaga and Morimitsu 1995), and auditory brain stem responses to external stimuli do not begin until PND 12 (Song et al 2006), while even neonatal pups are capable of using whisker stimulation for a simple classical avoidance conditioning task (Sullivan et al 2003), although active sensation does not occur until the second postnatal week (Mosconi et al 2010). Similarities would suggest a common developmental trajectory that is independent of sensory experience, while differences could be due to outside sensory input or to intrinsic genetic factors.…”

The development of whisker control in rats in relation to locomotion

“…The precocial development of vibrissal touch suggests that it may therefore constitute an important source of sensory information for newborn animals. Sullivan et al (2003) found that, from as early as P3, stimulating the whiskers causes heightened activity in young pups. They respond to passive whisker contacts with head raising, mouthing, and turning towards or away from the stimulus, behaviors that are particularly associated with nipple search and attachment.…”

“…They respond to passive whisker contacts with head raising, mouthing, and turning towards or away from the stimulus, behaviors that are particularly associated with nipple search and attachment. Vibrissal cues have been found to play an important role in nipple attachment (Kenyon, Keeble, & Cronin, 1982;Sullivan et al, 2003), indeed, whisker clipping will cause pups to ''miss'' a nipple more often, particularly in younger pups (P4-6) (Sullivan et al, 2003). In the first post-natal week pups also tend to spend most of their time in litter aggregates, or ''huddles'', as a means of regulating their body temperature (Schank & Alberts, 1997).…”

Behavioral verification of associative learning in whisker-related fear conditioning in mice

“…The behavior of pups was recorded prior to stimulation as a baseline and during training using a motor activity scale designed by Hall (Hall 1979). This scale assigns a score for the number of major body parts or regions that moved for at least 2 s. Specific movements such as crawling, head turning toward and away from the stimulation, and mouthing were counted (Sullivan et al 2003). The motor activity scale measures changes in general motor activity as a response of motorically immature rat pups to stimulus presentation (Hall 1979).…”