Peptide nucleic acids (PNAs) form stable and tight complexes with complementary DNA and/or RNA and would be promising antisense reagents if their cellular delivery could be improved. We show that a 21-mer PNA, complementary to the human galanin receptor type 1 mRNA, coupled to the cellular transporter peptides, transportan or pAntennapedia(43-58), is efficiently taken up into Bowes cells where they block the expression of galanin receptors. In rat, the intrathecal administration of the peptide-PNA construct results in a decrease in galanin binding in the dorsal horn. The decrease in binding results in the inability of galanin to inhibit the C fibers stimulation-induced facilitation of the rat flexor reflex, demonstrating that peptide-PNA constructs act in vivo to suppress expression of functional galanin receptors.
The neuropeptide galanin has been shown to suppress epileptic seizures. In cortical and hippocampal areas, galanin is normally mainly expressed in noradrenergic afferents. We have generated a mouse overexpressing galanin in neurons under the plateletderived growth factor B promoter. RIA and HPLC analysis revealed up to 8-fold higher levels of galanin in transgenic as compared with wild-type mice. Ectopic galanin overexpression was detected especially in dentate granule cells and hippocampal and cortical pyramidal neurons. Galanin-overexpressing mice showed retardation of seizure generalization during hippocampal kindling, a model for human complex partial epilepsy. The high levels of galanin in mossy fibers found in the transgenic mice were further increased after seizures. Frequency facilitation of field excitatory postsynaptic potentials, a form of short-term synaptic plasticity assessed in hippocampal slices, was reduced in mossy fiber-CA3 cell synapses of galanin-overexpressing mice, indicating suppressed glutamate release. This effect was reversed by application of the putative galanin receptor antagonist M35. These data provide evidence that ectopically overexpressed galanin can be released and dampen the development of epilepsy by means of receptor-mediated action, at least partly by reducing glutamate release from mossy fibers.G alanin, a 29-aa neuropeptide (1), is widely distributed throughout the rat brain (2, 3) and coexists with classic transmitters in several systems (4), with particularly high levels in noradrenergic locus coeruleus neurons (5, 6). Galanin-binding sites have been mapped (7,8), and three receptor subtypes, GalR1 (9-11), 49), and GalR3 (15), have been cloned. There is evidence for involvement of galanin in multiple neuronal functions (16,17), as also revealed in recent studies on transgenic mice (18)(19)(20).Many studies support an important role of neuropeptides in seizure activity (21)(22)(23). This role is true also for galanin. Thus, intrahippocampal injection of galanin during status epilepticus (SE) in rats has powerful anticonvulsant effects (24). In accordance with these data, mice overexpressing the galanin gene under the dopamine--hydroxylase promoter, presumably in noradrenergic fibers, show increased resistance to SE and kainate-and pentylenetetrazol-evoked seizures (25). Conversely, administration of galanin antagonists, such as M35 (26), and targeted disruption of the galanin gene increase seizure susceptibility in these models (24,25). Taken together, available data indicate that galanin released from noradrenergic fibers (3, 5, 27) can suppress epileptic seizures. Although the underlying mechanisms are not known, it has been shown that galanin can inhibit glutamate release by means of activation of presynaptic ATP-dependent K ϩ channels (28).We speculated that galanin release from neurons not normally containing this neuropeptide, e.g., in the epileptic focus, might be necessary to optimize the seizure-suppressant action of galanin. To explore the functional conseque...
The neuropeptide galanin colocalizes with choline acetyltransferase, the synthetic enzyme for acetylcholine, in a subset of cholinergic neurons in the basal forebrain of rodents. Chronic intracerebroventricular infusion of nerve growth factor induces a 3-to 4-fold increase in galanin gene expression in these neurons. Here we report the loss of a third of cholinergic neurons in the medial septum and vertical limb diagonal band of the basal forebrain of adult mice carrying a targeted loss-of-function mutation in the galanin gene. These deficits are associated with a 2-fold increase in the number of apoptotic cells in the forebrain at postnatal day seven. This loss is associated with marked agedependent deficits in stimulated acetylcholine release, performance in the Morris water maze, and induction of long-term potentiation in the CA1 region of the hippocampus. These data provide unexpected evidence that galanin plays a trophic role to regulate the development and function of a subset of septohippocampal cholinergic neurons.T he 29 amino acid peptide galanin (1) colocalizes with choline acetyltransferase (ChAT) in 30-35% of cholinergic neurons in the medial septum and vertical limb diagonal band (VLDB) of the basal forebrain in the rat (2, 3). Most, if not all, of these galaninpositive cholinergic neurons project to the hippocampus (2, 4). These findings have led to a number of functional studies addressing the role played by galanin in the basal forebrain cholinergic system, including its effects on acetylcholine (ACh) release as well as learning and memory. Acute administration of galanin into the hippocampus or third ventricle of rodents inhibits scopolamineinduced ACh release in a dose-dependent manner and is reversed by the coadministration of the chimeric-peptide galanin receptor antagonists M15 and M40 (5, 6). Centrally administered galanin also has inhibitory effects on several tests of learning and memory (7,8). In contrast to these inhibitory actions, exogenous galanin has no effect on the increased release of ACh that occurs when a rodent is exposed to a novel environment (9). Neither of the galanin antagonists has an effect on ACh release or on cognition in the absence of exogenously administered galanin (5, 6). Similarly, whereas exogenous galanin inhibits long-term potentiation (LTP) in hippocampal CA1 slices that is reversed by the M40 galanin antagonist, M40 has no effect on LTP when applied alone (10). In addition, there is increasing evidence that the M15 and M40 ligands may act as partial agonists in the hippocampus (11, 12) and as full agonists in vitro to the cloned galanin receptor subtypes (13). These somewhat conflicting data emphasize the limitations of the pharmacological tools that are currently available and cast some doubt on the role played by endogenously secreted galanin in the modulation of steady-state ACh release.We have recently generated mice carrying a loss-of-function mutation in the galanin gene (14) and have demonstrated that galanin is (i) essential for the developmental s...
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