Brain research. Developmental brain research
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Brain Res. Dev. Brain Res. · Feb 2000
Endogenously generated spontaneous spiking activities recorded from postnatal spiral ganglion neurons in vitro.
Spontaneous spiking activities in the nervous system play an important role in the neuronal development and the coding of sensory information. Such firings could be initiated by transmitter leaked from the first-order sensory receptors or as a result of the internal operation of voltage-dependent ion channels intrinsic to the neuron. We recorded endogenously-generated spontaneous action potentials (APs) from postnatal spiral ganglion (SG) neurons of mouse in vitro. ⋯ In contrast, matured SG neurons did not display any spontaneous APs, probably due to a large increase in the expression of the whole-cell potassium currents in comparison to their postnatal counterparts. This study provided the first direct evidence that postnatal SG neurons were capable of generating spontaneous APs independent of inputs from hair cells. Intracellular mechanisms for generating the spontaneous random spikes and the possible roles of such spontaneous activities in the postnatal development of SG neurons are discussed.
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Brain Res. Dev. Brain Res. · May 1999
Experience-dependent alteration of zinc-containing circuits in somatosensory cortex of the mouse.
Histochemical staining was used to localize zinc-sequestering terminals in somatosensory barrel cortex of normal mice and mice subjected to tactile deprivation by simple whisker trimming from birth. In normal mice, density of synaptic zinc was highest in laminae I, II and V, intermediate in laminae III and VI, and lowest in lamina IV barrel hollows. Whisker trimming from birth led to increased density of synaptic zinc specifically within deprived barrel hollows.
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Brain Res. Dev. Brain Res. · May 1999
Retrograde transynaptic pseudorabies virus infection of central autonomic circuits in neonatal rats.
Pseudorabies virus (PRV) is widely used to map synaptically-linked neural circuits in adult animals. The present study sought to determine whether PRV has similar utility in neonatal rats, and whether central PRV infection in neonates elicits astrocytic and microglia/macrophage responses similar to those that contribute to specific transynaptic neuronal infection in adult rats. Retrograde transneuronal infection of autonomic circuits was examined 24-64 h after injection of an attenuated strain of PRV (PRV-Bartha) into the ventral stomach wall of 1-day-old rats. ⋯ At the longest post-inoculation intervals, infected neurons also were observed in the area postrema and in certain autonomic-related regions of the rostral brainstem, hypothalamus, and amygdala. Quantitative analysis of immunolabeling in the dorsal vagal complex demonstrated that regions containing neurons at early stages of viral infection displayed increased astrocytic GFAP immunostaining; conversely, areas containing neurons at later stages of infection were characterized by a significant loss of GFAP staining and a parallel increase of OX42 microglia/macrophage immunolabeling. We conclude that PRV is effectively transported through synaptically-linked CNS circuits in neonatal rats, and that spatiotemporally-ordered responses by non-neuronal cells may contribute to the synaptic specificity of transneuronal viral transport.
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Brain Res. Dev. Brain Res. · Feb 1999
Effect of pre- and postnatal nicotine exposure on vasopressinergic system in rats.
Timed pregnant Sprague-Dawley rats were infused subcutaneously either with nicotine (NIC, 6 mg kg-1 day-1; n=17) or saline (control, n=15) on the 3rd day of gestation, via Alzet osmotic pumps, for 28 days. After the parturition, the pups of both, control and NIC infused dams, were each randomly divided into 2 groups and placed to be nursed as following: (1) control dams nursing pups born to control mother (control group); (2) control dams nursing pups born to NIC-infused mother (prenatal NIC group); (3) NIC-infused dams nursing pups born to control mother (postnatal NIC group); (4) NIC-infused dams nursing pups born to NIC-infused mother (pre- and postnatal NIC group). Vasopressin (VP) was measured by RIA in plasma, neurointermediate lobe (NIL) and hypothalamus (HT) in the pups of both sexes, at the following age: 0 (within 24 h after birth); 1, 2, 3, 4 and 6 weeks. ⋯ A marked suppression in the activity of VP-ergic system was observed in both sexes of offspring exposed to NIC prenatally, being first detectable at the age of 3 weeks, when the HT-NIL system becomes fully developed. However, the significant changes were observed at the age of 6 weeks: decreased serum VP concentration, lower VP contents in the HT and NIL, and suppressed VP release, basal and stimulated, from the isolated NIL. Postnatal exposure to nicotine was ineffective.
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Brain Res. Dev. Brain Res. · Sep 1998
Effects of preweanling chronic naltrindole administration on stress-induced antinociceptive responses in rats.
The effect of a daily injection of the delta-selective opioid antagonist naltrindole (1 mg/kg), from birth to postnatal day 19, on the development of stress-induced-antinociception (SIA) and on the antinociceptive response to the mu-selective agonist alfentanil (65 microg/kg) in female rats was investigated. Functional blockade of the delta-receptor during the preweanling period markedly reduced the antinociceptive response to swim-stress in 25-day-old rats, and SIA was only mediated by delta-receptors at this age. ⋯ The lack of interference with mu-receptor function was confirmed as alfentanil responses were unaffected by preweanling naltrindole treatment. The data show independence of mu- and delta-receptors in the control of SIA during development and an impairment of delta- but not mu-mediated SIA after chronic delta-antagonist treatment.