Early development of the SI cortical barrel field representation in neonatal rats follows a lateral-to-medial gradient: an electrophysiological study

Abstract

Development of the barrel field in layer IV of SI cortex of neonatal rats was studied in vivo using electrophysiological recording techniques. This study was designed to determine (a) the earliest time SI cortex is responsive to peripheral mechanical and/or electrical stimulation and (b) whether the development of the SI cortical barrel field map of the body surface follows a differential pattern of development similar to the pattern previously demonstrated using peanut agglutinin (PNA) binding (McCandlish et al. 1989). Carbon fiber microelectrodes were used to record evoked responses from within the depth of the cortex in neonatal rats between postnatal day 1. (PND-1), defined as the day of birth, and PND-14. Evoked responses were first recorded approximately 12 h after birth. These responses in the youngest animals were of low amplitude, monophasic waveshape, and long latency, with long interstimulus intervals necessary to drive the cortex. Increases in amplitude and complexity of waveshape and decreases in latency were observed over subsequent postnatal days. The earliest responses recorded on middle PND-1 were evoked by stimulation of the face and/or mystacial vibrissae. The next responses were evoked approximately 24 h after birth (late PND-1) by stimulation of the forelimb. The last responses were evoked approximately 36 h after birth (middle PND-2), by stimulation of the hindlimb. The physiological map of the representation of the body surface follows a developmental gradient similar to the gradient observed using PNA histochemistry; however, the lectin-generated morphological map lagged approximately 48 h behind the physiological map.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional Development of Large-Scale Sensorimotor Cortical Networks in the Brain

“…After the second week, cortical processing between distant networks is established with evoked responses invading several cortical networks downstream of S1 in the frontal motor region and in the sensory and motor regions of the other hemisphere. Sensory evoked responses can be elicited in the rat S1 cortex as early as P1 (Armstrong-James, 1975;McCandlish et al, 1993); however, as in newborns of other mammals comprising humans, cortical responses are weaker and slower than in adults (Pihko and Lauronen, 2004;Borgdorff et al, 2007). In agreement, we observed strong reinforcement and drastic acceleration of cortical responses during the postnatal period.…”

Expression of two forms of glutamic acid decarboxylase (GAD67 and GAD65) during postnatal development of rat somatosensory barrel cortex

“…This finding agrees with the late development of functional GABA inhibition (Miles and Wong, 1987;Luhman and Prince, 1991;Agmon et al, 1996). Additionally, evoked electrical responses in barrel cortex are minimal at birth and change markedly in intensity, latency, and complexity during the second and third postnatal weeks (McCandlish et al, 1993;SeoHiraiwa et al, 1995). Electrophysiological studies have also indicated that physiological plasticity persists for several weeks after the barrel field is anatomically immutable (Fox, 1992).…”

Three-Dimensional Topography of Corticopontine Projections from Rat Barrel Cortex: Correlations with Corticostriatal Organization

“…In the cerebral cortex, the neurogenetic gradient extends from anterolateral toward posterior and medial, in parallel with the rows of barrels in SI (Hicks and D'Amato, 1968;Smart, 1984;Bayer and Altman, 1991;Erzurumlu and Jhaveri, 1992;Bishop et al, 2000). A similar gradient was reported for the development of electrophysiological specificity (McCandlish et al, 1993). Thus, anterolaterally located barrels (high numbers) are developed before the more medially and posteriorly located barrels (low numbers).…”