Neuroscience
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Comparative Study
Kinetics of synaptic transfer from rods and cones to horizontal cells in the salamander retina.
We examined synaptic transmission between rods or cones and horizontal cells, using perforated patch recording techniques in salamander retinal slices. Experimental conditions were established under which horizontal cells received nearly pure rod or pure cone input. The response-intensity relation for both photoreceptors and horizontal cells was described by a Michaelis-Menten function with an exponent close to 1. ⋯ The good fit to the model confirms that these are the key features of synaptic transmission from rods and cones. The model accommodated changes in kinetics induced by the glutamate uptake blocker, dihydrokainate. The match between model and response was not improved by including an estimate of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor desensitization or by making glutamate uptake voltage dependent.
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Comparative Study
The mouse nac1 gene, encoding a cocaine-regulated Bric-a-brac Tramtrac Broad complex/Pox virus and Zinc finger protein, is regulated by AP1.
NAC1 cDNA was identified as a novel transcript induced in the nucleus accumbens from rats chronically treated with cocaine. NAC1 is a member of the Bric-a-brac Tramtrac Broad complex/Pox virus and Zinc finger family of transcription factors and has been shown by overexpression studies to prevent the development of behavioral sensitization resulting from repeated cocaine treatment. This paper reports the cloning and characterization of the corresponding gene. ⋯ Activation of immediate early genes such as c-fos and c-jun following chronic drug treatments has been well characterized. The present data describe one potential regulatory cascade involving these transcription factors and activation of NAC1. Identification of drug induced alterations in gene expression is key to understanding the types of molecular adaptations underlying addiction.
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Comparative Study
Brainstem prolactin-releasing peptide neurons are sensitive to stress and lactation.
Prolactin-releasing peptide (PrRP) was originally thought to participate in the control of adenohypophyseal prolactin secretion, but its predominant expression in a subset of medullary noradrenergic neurons is more in line with roles in interoceptive and/or somatosensory information processing. To better define functional contexts for this peptide system, immuno- and hybridization histochemical methods were used to monitor the capacity of PrRP neurons to display activational responses to lactation, suckling, acute footshock or hypotensive hemorrhage. PrRP mRNA signal was reduced in the medulla of lactating dams, relative to both male and diestrus female controls, with cell counts revealing 42% and 43% reductions in the number of positively hybridized cells in the nucleus of the solitary tract (NTS) and ventrolateral medulla, respectively. ⋯ A substantially greater fraction of the total medullary PrRP population exhibited sensitivity to footshock than hemorrhage (71 versus 39%, respectively). These results suggest that medullary PrRP neurons are negatively regulated by (presumably hormonal) changes in lactation, and are not recruited to activation by suckling stimuli. These populations exhibit differential sensitivity to distinct acute stressors, and may participate in the modulation of adaptive neuroendocrine and autonomic responses to each.
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Comparative Study
Learning deficits in forebrain-restricted brain-derived neurotrophic factor mutant mice.
Brain-derived neurotrophic factor (BDNF) participates in synaptic plasticity and the adaptive changes in the strength of communication between neurons thought to underlie aspects of behavioral adaptation. By selectively deleting BDNF from the forebrain of mice using the Cre site-specific DNA recombinase, we were able to study the requirements for BDNF in behaviors such as learning and anxiety. Early-onset forebrain-restricted BDNF mutant mice (Emx-BDNF(KO)) that develop in the absence of BDNF in the dorsal cortex, hippocampus, and parts of the ventral cortex and amygdala failed to learn the Morris Water Maze task, a hippocampal-dependent visuo-spatial learning task. ⋯ Emx-BDNF(KO) mice did not exhibit altered sensory processing and gating, as measured by the acoustic startle response or prepulse inhibition of the startle response. Although they were less active in an open-field arena, they did not show alterations in anxiety, as measured in the elevated-plus maze, black-white chamber or mirrored chamber tasks. Combined, these data indicate that although an absence of forebrain BDNF does not disrupt acoustic sensory processing or alter baseline anxiety, specific forms of learning are severely impaired.
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We have assessed the expression and kinetics of voltage-gated K(+) currents in cardiac dorsal root ganglion (DRG) neurons in rats. The neurons were labelled by prior injection of a fluorescent tracer into the pericardial sack. Ninety-nine neurons were labelled: 24% small (diameter<30 microm), 66% medium-sized (diameter 30 microm>.48 microm) and 10% large (>48 microm) neurons. ⋯ All three K(+) current components (I(As), I(Af) and I(K)) were present in every small and medium-sized cardiac DRG neuron. We suggest that at hyperpolarized membrane potentials the fast reactivating I(As) current limits the action potential firing rate of cardiac DRG neurons. At depolarised membrane potentials the I(Af) K(+) current, the reactivation of which is very slow, does not oppose the firing rate of cardiac DRG neurons.