The functional status and columnar organization of single cells responding to cutaneous stimulation in neonatal rat somatosensory cortex S1.

Abstract

SUMMIARY1. An investigation was carried out on single cells in 7 day old rat primary somatosensory cortex, which responded to cutaneous stimulation using mechanical pulses. 3 % of cells encountered showed stable spontaneous activity, whereas 88 % were silent in the absence of intentional stimulation. The remainder showed unstable spontaneous activity. In contrast, the great majority of adult cells were spontaneously active in the absence of stimulation, under similar conditions of urethane anaesthesia.2. The distribution within cortical layers of cutaneously driven cells was similar in adult and 7 day old rats, and similar to that found in adult mammalian cortex by other workers.3. 7 day old cells showed diminished excitability to cutaneous stimulation with stimuli at intervals below 10-15 sec, whereas adult cells could be successfully repetitively driven with stimuli at intervals of 500 msec. The low ability of the immature cells to follow repetitive cutaneous stimulation is not due to an overall depression of these cells excitability per se. Latencies of unitary responses in these immature cells were about sixfold those found in equivalent cells at maturity.4. Columnar organization at seven days of age was similar in outline to that of the adult, but much less discrete. Receptive fields were considerably larger at 7 days and evidence is given that this may be due to inadequate surround inhibition. Immature vibrissae-driven units were directionally selective.5. At 7 days of age, long inter-spike intervals were rare in spontaneously active cells with the result that inter-spike interval histogram distributions (i.h.s.) were approximately normal. Corresponding i.h.s. of adult cells invariably showed skew distributions.6. Tactile stimulation of centre receptive fields produced an increase in 21 -2 5M. ARMSTRONG-JAMES short and long intervals from spontaneously active cells at each age. In contrast to adult cells, the immature cells commonly responded cyclically, with alternating phases of increased and decreased firing rate for periods of up to 3 sec following punctate stimulation.7. Decrease in spontaneous firing rate, following the first phase of excitation, was profound in 7 day old cells, and implied that inhibitory mechanisms operate at an early age in the rat somatosensory system. These mechanisms also appear to contribute to cyclical activity of 7 day old cells when driven by punctate cutaneous stimulation.

Shifts in Developmental Timing, and Not Increased Levels of Experience-Dependent Neuronal Activity, Promote Barrel Expansion in the Primary Somatosensory Cortex of Rats Enucleated at Birth

“…Although previous work suggests that incremental increases in neuronal activity associated with enhanced somatosensory experience lead to S1 expansion in birth-enucleated rodents [9], [10], the present results weaken this notion. The observations that support our conclusions are: 1) The size and growth rate of whiskers in birth-enucleated rats are similar to those observed in control sighted rats; 2) The magnitude of barrel expansion was similar between young and adult rats enucleated at birth; 3) Unilateral dewhiskering at 168 h did not prevent barrel expansion in the deprived hemisphere nor did it produce barrel overgrowth in non-deprived hemispheres of birth-enucleated adult rats; 4) Neither enucleation after the period of barrel formation nor raising rats in complete darkness promoted barrel expansion; 5) Metabolic markers of neuronal activity (CyOx and 2DG) were comparable in the trigeminal ganglion and/or in non-expanded and expanded PMBSF barrels of control and birth-enucleated rats, respectively, at different ages; and 6) Barrel expansion in birth-enucleated rats took place before the onset of active whisking (PD12)[55]–[59], and before cortical-evoked activity [60]–[62].…”

The Emergence of Somatotopic Maps of the Body in S1 in Rats: The Correspondence Between Functional and Anatomical Organization

“…Despite this, there have been very few studies that have explicitly examined the development of whisker receptive fields for neurons within the barrels of the cortex [14], [15], [55], [83]. Further, we are aware of no studies that have tightly correlated the developmental time-course of the formation of anatomical parcellations with the emergence of full maps of the whiskers.…”

“…In 1975, Armstrong-James recorded from single cells in S1 of P7 rats [14]. He identified large receptive fields on multiple body parts, and determined that these receptive fields changed their size, shape, and orientation as he recorded from different cortical layers.…”

The Functional Microarchitecture of the Mouse Barrel Cortex

“…Trial durations were either 3,200 ms (50 frames) (Figure 2A) or 768 ms (12 frames) (all figures other than Figure 2A). To minimize use-dependent depression, intertrial intervals were long (20–30 s) [93]. Whiskers were stimulated in an interleaved fashion.…”