Neuroscience
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Comparative Study
Differential responsiveness of dopamine transmission to food-stimuli in nucleus accumbens shell/core compartments.
The nucleus accumbens septi is the major target of mesolimbic dopamine neurons originating in the ventral tegmental area of the mesencephalon. Studies involving experimental manipulation of dopamine transmission by drugs and by lesions, as well as in vivo monitoring of extracellular dopamine concentrations, have provided evidence that the dopamine transmission of the nucleus accumbens plays an important role in behaviour motivated by conventional (e.g., food, sex) and drug reinforcers. Motivated behaviour is distinguished into an appetitive (preparatory/anticipatory) phase consisting of flexible response patterns intended to search and approach the reward itself, and a consummatory phase, consisting of fixed response patterns (eating, drinking, copulating, etc.) finalized to the utilization of the biological resources of the reward (caloric, metabolic, genetic, etc.). ⋯ Unpredicted consumption of Fonzies preferentially stimulated dopamine transmission in the shell as compared to the core. Appetitive food stimuli (perforated Fonzies-filled boxes) phasically stimulated dopamine transmission in the core but not in the shell and sensitized the dopamine response to feeding in the core but inhibited that in the shell. These clear-cut differences between nucleus accumbens shell and core suggest that phasic dopamine transmission in each compartment of the nucleus accumbens subserves different roles in motivated behaviour.
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The modulation of GABA-gated ion channel responses to GABA, pentobarbital and diazepam by muscarine was studied in freshly isolated rat dorsal root ganglion neurons using a whole-cell patch-clamp technique. Muscarine enhanced current activated by 5 microM GABA dose-dependently with an EC50 of 40 +/- 2 microM. This potentiation was not blocked by pirenzepine, gallamine and atropine, the specific and non-specific muscarinic receptor antagonists. ⋯ However, muscarine attenuated the facilitatory effect of saturating concentrations of diazepam (> 100 nM). The potentiating effect of muscarine was blocked by 1 nM ethyl-beta-carboline-3-carboxylate, the inverse agonist of benzodiazepine receptors. These results suggest that GABA-gated ion channel responses to GABA and pentobarbital were potentiated by muscarine and the binding site(s) for muscarine might be related to those for diazepam.
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Streptozotocin-diabetic rats, an animal model for diabetes mellitus, show learning deficits and impaired long-term potentiation in the CA1-field of the hippocampus. The present study aimed to further characterize the effects of streptozotocin-diabetes on N-methyl-D-aspartate receptor-dependent long-term potentiation in the CA1-field, to extend these findings to N-methyl-D-aspartate receptor-dependent and independent long-term potentiation in other regions of the hippocampus and to examine effects on long-term depression. First, the effect of diabetes duration on long-term potentiation in the CA1-field was determined. ⋯ Expression of N-methyl-D-aspartate receptor-dependent long-term potentiation was impaired in the CA1-field and dentate gyrus and expression of N-methyl-D-aspartate receptor-independent long-term potentiation was impaired in the CA3-field. In contrast, expression of long-term depression was facilitated in CA1. It is suggested that this combination of changes in plasticity may reflect alterations in intracellular signalling pathways.
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The effect of the novel GABAc receptor antagonist (1,2,5,6-tetrahydropyridine-4-yl)methyl-phosphinic acid (TPMPA) on synaptic transmission and GABA-mediated responses was investigated with electrophysiological recordings from the in vitro spinal cord preparation of the neonatal rat. Bath-applied TPMPA (10 microM) had no effect on spinal reflexes evoked by dorsal root stimulation, on ventral root polarization level or amplitude of ventral root depolarizations induced by exogenously applied GABA (0.5 mM). TPMPA significantly attenuated the depressant action of GABA on spinal reflexes without changing responses induced by the GABA(A) receptor agonist isoguvacine (50 microM) or the GABA(B) receptor agonist baclofen (0.5-2 microM). ⋯ This bursting pattern, which is generated at the level of the interneuronal network, was significantly slowed down by TPMPA, which also increased the duration of individual bursts and the number of intraburst oscillations. These results suggest that in the neonatal rat spinal cord some functional GABAc receptors exist: their role was clearly unmasked following pharmacological block of GABA(A) (and glycine) receptors. Under these conditions GABAc receptors appeared to contribute to the excitation of spinal interneurons supporting rhythmic bursting activity.
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Comparative Study
Sex and seasonal differences in the rate of cell proliferation in the dentate gyrus of adult wild meadow voles.
In order to study the neurobiological basis of seasonal changes in hippocampal structure and function, the rate of cell proliferation was examined in male and female wild meadow voles captured during different seasons. We found that the number of [3H]thymidine-labeled cells varied across the seasons and across sex in the meadow vole. Non-breeding female meadow voles had a higher rate of cell proliferation and cell death than males captured during either season or breeding females. ⋯ Females captured during the non-breeding season had higher rates of cell proliferation in the granule cell layer than females captured during the breeding season. This seasonal fluctuation was related to hormone levels, with high levels of corticosterone and estradiol being related to lower levels of cell proliferation. These seasonal changes in cell proliferation may be related to known changes in spatial learning in the meadow vole and provide insights into changes in the hippocampus that occur in other species, including primates.