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To follow on prior studies of the cerebral cortex, we examined the acetylcholine innervation in the developing hippocampus of rat, by means of light and electron microscopic immunocytochemistry with a highly sensitive antibody against choline acetyltransferease. As in neocortex, the growth of this innervation mostly occurred within the first two weeks after birth. A preliminary ultrastructural survey indicated that a vast majority of these ChAT-immunostained axon varicosities were asynaptic during development as in the adult. In parallel, we quantified the cholinergic innervations of cerebral cortex and hippocampus in transgenic mice overexpressing human ß-amyloid peptide (hAPPSW,IND). A selective, widespread, plaque independent cholinergic denervation was thus demonstrated, first in hippocampus and then neocortex, in addition to a non-selective, plaque-dependent, local neurotoxic effect of aggregated ß-amyloid on ACh and 5-HT axons. [ABSTRACT FROM AUTHOR]

5-HT[sub 1A] knockout (KO) mice display an anxious-like phenotype, whereas 5-HT[sub 1B] KOs are over-aggressive. To identify serotoninergic correlates of these altered behaviors, autoradiographic measurements of 5-HT[sub 1A] and 5-HT[sub 1B] serotonin (5-HT) receptors and transporter (5-HTT) were obtained using the radioligands [[sup 3]H]8-OH-DPAT, [[sup 125]I]cyanopindolol and [[sup 3]H]citalopram, respectively. By comparison to wild-type, density of 5-HT[sub 1B] receptors was unchanged throughout brain in 5-HT[sub 1A] KOs, and that of 5-HT[sub 1A] receptors in 5-HT[sub 1B] KOs. In contrast, decreases in density of 5-HTT binding were measured in several brain regions of both genotypes. Moreover, 5-HTT binding density was significantly increased in the amygdalo-hippocampal nucleus and ventral hippocampus of the 5-HT[sub 1B] KOs. Measurements of 5-HT axon length and number of axon varicosities by quantitative 5-HT immunocytochemistry revealed proportional increases in the density of 5-HT innervation in these two regions of 5-HT[sub 1B] KOs, whereas none of the decreases in 5-HTT binding sites were associated with any such changes. Several conclusions could be drawn from these results: (i) 5-HT[sub 1B] receptors do not adapt in 5-HT[sub 1A] KOs, nor do 5-HT[sub 1A] receptors in 5-HT[sub 1B] KOs. (ii) 5-HTT is down-regulated in several brain regions of 5-HT[sub 1A] and 5-HT[sub 1B] KO mice. (iii) This down-regulation could contribute to the anxious-like phenotype of the 5-HT[sub 1A] KOs, by reducing 5-HT clearance in several territories of 5-HT innervation. (iv) The 5-HT hyperinnervation in the amygdalo-hippocampal nucleus and ventral hippocampus of 5-HT[sub 1B] KOs could play a role in their increased aggressiveness, and might also explain their better performance in some cognitive tests. (v) These increases in density of 5-HT innervation provide the first evidence for a negative control of 5-HT neuron growth mediated by 5-HT[sub 1B] receptors. [ABSTRACT FROM AUTHOR]

Abstract Numerous features of its primary structure demonstrate that the orphan transporter Rxt1 belongs to the Na+/Cl–-dependent neurotransmitter plasma membrane transporter superfamily, which includes the dopamine, norepinephrine, serotonin and γ-aminobutyric acid (GABA) transporters. Initial immunocytochemical investigations with affinity-purified antibodies have established that Rxt1 is localized, almost exclusively, in axon terminals of glutamatergic neurons and subsets of GABAergic neurons in the CNS. Further studies were carried out to determine its subcellular distribution. In a first series of experiments, PC-12 cells were transfected with plasmids encoding either the dopamine transporter or Rxt1. Immunofluorescence experiments showed that the dopamine transporter was expressed in these cells, and, as expected, addressed to their plasma membrane. Surprisingly, this was never the case with Rxt1, which was targeted to the same subcellular compartment as synaptophysin, a vesicular protein. In a second set of experiments, subcellular fractionation of rat striatum showed that Rxt1, but not the dopamine transporter, was relatively abundant in the purified synaptic vesicle fraction. Finally, electron microscopic immunocytochemistry with anti-Rxt1 antibodies showed peroxidase as well as pre- and post-embedding immunogold labelling confined to the intracellular compartment in various brain regions. Moreover, quantitative analysis of post-embedding experiments demonstrated that the immunogold particles corresponding to Rxt1 immunoreactivity were mostly localized to small synaptic vesicles. These data indicate that, in contrast with the other members of the Na+/Cl–-dependent neurotransmitter transporter superfamily, which are targeted to the plasma membrane, Rxt1 is distributed as a vesicular protein in the CNS. [ABSTRACT FROM AUTHOR]