Binding of [H-3]cocaine to membrane preparations from whole fetal rat brain was studied. High-affinity binding (1. nM cocaine) was detected as early as gestational day (GD) 1. and steadily increased across subsequent ...
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Binding of [H-3]cocaine to membrane preparations from whole fetal rat brain was studied. High-affinity binding (1. nM cocaine) was detected as early as gestational day (GD) 1. and steadily increased across subsequent development. Saturation studies comparing [H-3]cocaine binding at GD20 and adulthood yielded similar K-D values, and LIGAND analyses favored a two-site model if an extended range of [H-3]cocaine concentrations was used. Various monoamine uptake inhibitors displaced labeled cocaine with potencies consistent with the idea that [H-3]cocaine labels the dopamine (DA), serotonin (5-HT), and possibly also the norepinephrine (NE) transporters in whole fetal brain preparations. Synaptosomal DA uptake was well developed by GD20, as was the potency of cocaine to inhibit such uptake. The results indicate that functional, monoamine transporter related cocaine binding sites are present in the fetal rat brain. Such sites are likely to play an important role in mediating the direct interactions of prenatally-administered cocaine with developing monoaminergic systems in both animals and humans.
A-currents were studied in acutely dissociated chick autonomic neurons. Switching from salines containing 4 mM Mg2+ to salines containing 4 mM Ca2+ caused a large positive shift in the voltage dependence of steady-sta...
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A-currents were studied in acutely dissociated chick autonomic neurons. Switching from salines containing 4 mM Mg2+ to salines containing 4 mM Ca2+ caused a large positive shift in the voltage dependence of steady-state inactivation, but had no effect on the voltage dependence or kinetics of activation, deactivation, the rate at which channels became inactivated, or the rate at which channels recovered from inactivation. This effect saturated with increasing concentrations of Ca2+. Other group IIA divalent cations were less effective than Ca2+, in the order Ca2+ > Ba2+ > Mg2+ = Sr2+. Application of 4 nM Mg2+ partially antagonized the effects of 4 mM Ca2+. The results suggest that divalent cations selectively alter the voltage dependence of steady-state inactivation by acting at sites accessible from the outside of the cell.
The olfactory bulb of many elasmobranch fishes is morphologically subdivided into distinct units or sub-bulbs immediately adjacent to the olfactory epithelium. We investigated this morphological feature in two species...
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The olfactory bulb of many elasmobranch fishes is morphologically subdivided into distinct units or sub-bulbs immediately adjacent to the olfactory epithelium. We investigated this morphological feature in two species of shark and one species of ray in order to understand its impact on the arrangement of the primary olfactory projections onto the bulb. Using anterograde tracing methods in vitro (biocytin) as well as in fixed tissue (DiI), we observed a direct segregated projection of the olfactory afferents onto the bulb. Application of tracers to the lateral part of the olfactory epithelium resulted in staining restricted to the this region of the bulb, whereas the same tracers applied to the medial part of the epithelium resulted in staining of the medial olfactory bulb. The sub-bulbs appear to be individual anatomical units that each receive input from the olfactory lamellae. Nissl and myelin staining as well as the Golgi method show that the cytoarchitecture of the sub-bulbs is not substantially different from that of other anamniotes. However, we did note the existence of two types of mitral cell, based on the morphology of their dendritic arborization. Type L cells exhibit a loose dendritic arborization, whereas type T cells are characterized by a dense, bush-like dendritic arborization. Both types of mitral cells lack basal dendrites.
The peptidase system in Drosophila melanogaster (dipeptidase-A, -B, and -C and leucine aminopeptidases G and P) was used as a model to study the effects of modifier genes on activity of enzymes with similar functions....
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The peptidase system in Drosophila melanogaster (dipeptidase-A, -B, and -C and leucine aminopeptidases G and P) was used as a model to study the effects of modifier genes on activity of enzymes with similar functions. A screen of X, second, and third chromosome substitution isogenic lines revealed the presence of activity modifiers for peptidases on all three chromosomes. Correlation analyses indicated that covariation between some of the peptidase activities is independent of genetic background, while others are associated with variable second chromosomes. Chromosome-specific effects on K(m), V(max), and specific activity of partially purified peptidases were also detected. Moreover, a repeatable technique using anion-exchange column chromatography allowed the characterization of possibly two putative peptidic enzymes, glycyl-L-isoleucine-ase and L-leucyl-L-proline-ase, whose kinetic properties differ from the dipeptidases and the leucine aminopeptidases. These findings confirm the existence of activity modifiers for peptidases, much like other enzymes in Drosophila melanogaster.
The passive electrical cable properties of CA3 pyramidal neurons from guinea pig hippocampal slices were investigated by applying current steps and recording the voltage transient from 25 CA3 neurons, using a single i...
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The passive electrical cable properties of CA3 pyramidal neurons from guinea pig hippocampal slices were investigated by applying current steps and recording the voltage transient from 25 CA3 neurons, using a single intracellular microelectrode and a 3-kHz time-share system. Two independent methods were used for estimating the equivalent electrotonic length of the dendrites, L, and the dendritic to somatic conductance ratio, .rho.. The first method is similar to that used by Gorman and Mirolli and gave an average L of 0.96;the average .rho. was 2.44. The 2nd method, derived for the 1.t time, assumes a finite-length cable with lumped soma. It is an exact solution for L and .rho., using the slopes and intercepts of the first 2 peeled exponentials. The average L was 0.94;the average .rho. was 1.51. The results, using both methods, are in close agreement. The average membrane time constant for all 25 CA3 neurons was 23.6 ms, suggesting a large (23,600 .***2) average membrane resistivity. CA3 neurons are electronically short.
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