The age-related increase in galanin binding sites in the rat brain correlates with behavioral impairment

Xenon inhalation attenuates neuronal injury and prevents epilepsy in febrile seizure Sprague-Dawley pups

Background

Febrile seizures (FS) usually occur in childhood and may cause irreversible neuronal damage, cognitive functional defects, and an increase in the risk of epilepsy later in life. Anti-epileptic drugs (AEDs), currently used to treat FS in children, can relieve seizures. However, their effects in preventing the risk of developing epilepsy in later life are unsatisfactory. Moreover, AEDs may damage child brain development. Here, we evaluated the efficiency of xenon in treating prolonged FS (PFS) and preventing epilepsy in Sprague-Dawley pups.

Methods

Prolonged FS was induced by hyperthermic treatment. After 90 min of PFS, the pups in the xenon treatment group were immediately treated with 70% xenon/21% oxygen/9% nitrogen for 60 min. The levels of glutamate, mitochondrial oxidative stress, mitophagy, and neuronal injury, seizures, learning, and memory functions were measured at specific time points.

Results

Neonatal period PFS led to spontaneous seizure, learning and memory dysfunction, accompanied by increased levels of glutamate, mitochondrial oxidative stress, mitophagy, and neuronal injury. Xenon treatment alleviated the changes caused by PFS and reduced the risk of PFS developing into epilepsy later.

Conclusion

Our results suggest that xenon inhalation could be a potential therapeutic strategy to attenuate neuronal injury and prevent epilepsy in patients with FS.

Galanin and Cognition

Since the neuropeptide galanin’s discovery in 1983, information has accumulated that implicates it in a wide range of functions, including pain sensation, stress responses, appetite regulation, and learning and memory. This article reviews the evidence for specific functions of galanin in cognitive processes. Consistencies as well as gaps in the literature are organized around basic questions of methodology and theory. This review shows that although regularities are evident in the observed behavioral effects of galanin across several methods for measuring learning and memory, generalization from these findings is tempered with concerns about confounds and a restricted range of testing conditions. Furthermore, it is revealed that many noncognitive behavioral constructs that are relevant for assessing potential roles for galanin in cognition have not been thoroughly examined. The review concludes by laying out how future theory and experimental work can overcome these concerns and confidently define the nature of the association of galanin with particular cognitive constructs.

Locus coeruleus galanin expression is enhanced after exercise in rats selectively bred for high capacity for aerobic activity

The neuropeptide galanin extensively coexists with norepinephrine in locus coeruleus (LC) neurons. Previous research in this laboratory has demonstrated that unlimited access to activity wheels in the home cage increases mRNA for galanin (GAL) in the LC, and that GAL mediates some of the beneficial effects of exercise on brain function. To assess whether capacity for aerobic exercise modulates this upregulation in galanin mRNA, three heterogeneous rat models were tested: rats selectively bred for (1) high intrinsic (untrained) aerobic capacity (High Capacity Runners, HCR) and (2) low intrinsic aerobic capacity (Low Capacity Runners, LCR) and (3) unselected Sprague-Dawley (SD) rats with and without free access to running wheels for 3 weeks. Following this exercise protocol, mRNA for tyrosine hydroxylase (TH) and GAL was measured in the LC. The wheel running distances between the three models were significantly different, and age contributed as a significant covariate. Both selection and wheel access condition significantly affected GAL mRNA expression, but not TH mRNA expression. GAL was elevated in exercising HCR and SD rats compared to sedentary rats while LCR rats did not differ between conditions. Overall running distance significantly correlated with GAL mRNA expression, but not with TH mRNA expression. No strain differences in GAL or TH gene expression were observed in sedentary rats. Thus, intrinsic aerobic running capacity influences GAL gene expression in the LC only insofar as actual running behavior is concerned; aerobic capacity does not influence GAL expression in addition to changes associated with running.

Age-related impairments of synaptic plasticity in the lateral perforant path input to the dentate gyrus of galanin overexpressing mice

In the present study, electrophysiological recordings were made from hippocampal slices obtained from mice overexpressing galanin under the promoter for the platelet-derived growth factor-B (GalOE mice). In these mice, a particularly strong galanin expression is seen in the granule cell layer/mossy fibers. Paired-pulse facilitation (PPF) of excitatory postsynaptic field potentials (fEPSPs) at the lateral perforant path (LPP)-dentate gyrus synapses was elicited in the dentate gyrus after stimulation with different interpulse intervals. Slices from young adult wild-type (WT) animals showed significant PPF of the 2nd EPSP evoked with paired-pulse stimuli, while PPF was reduced in slices from young adult GalOE mice, as well as aged WT mice, but were not observed at all in slices from aged GalOE animals. Application of the putative galanin antagonist M35 increased PPF in slices from aged WT mice as well as from adult and aged GalOE mice, but had no effect in slices taken from young adult WT mice. These data indicate that galanin is involved in hippocampal synaptic plasticity, in particular in age-related reduction of synaptic plasticity in the LPP input to the dentate gyrus. Galaninergic mechanisms may therefore represent therapeutic targets for treatment of age-related memory deficits and Alzheimer's disease.

Molecular endocrinology and physiology of the aging central nervous system

Aging is associated with a progressive decline in physical and cognitive functions. The impact of age-dependent endocrine changes regulated by the central nervous system on the dynamics of neuronal behavior, neurodegeneration, cognition, biological rhythms, sexual behavior, and metabolism are reviewed. We also briefly review how functional deficits associated with increases in glucocorticoids and cytokines and declining production of sex steroids, GH, and IGF are likely exacerbated by age-dependent molecular misreading and alterations in components of signal transduction pathways and transcription factors.

Endocrinology of anorexia of ageing

Appetite and food intake decrease with normal ageing, predisposing to the development of under-nutrition. Under-nutrition is common in older people and has been implicated in the development and progression of chronic diseases commonly affecting the elderly, as well as in increasing mortality. An understanding of the factors that contribute to the physiological and pathological declines in food intake in older people is likely to aid in the development of effective forms of prevention and treatment. Ageing affects many of the endocrine factors involved in the control of appetite and feeding but few studies have been performed in humans to clarify these changes. Possible hormonal causes of the anorexia of ageing include increased activity of cholecystokinin, leptin and various cytokines and reduced activity of ghrelin and testosterone.

Presynaptic regulation of neurotransmitter release in the cortex of aged rats with differential memory impairments

Cluster analysis of water-maze reference-memory performances of 25-27-month-old (compared to 3-5-month-old) rats distinguished subpopulations of young adult rats (YOUNG), aged rats with no significant impairment (AU), aged rats with moderate impairment (AMI), and aged rats with severe impairment (ASI). In the frontoparietal cortex, we subsequently assessed the electrically evoked release of tritium in slices preloaded with [3H]choline, [3H]noradrenaline (NA), or [3H]serotonin (5-HT) and the effects of an agonist (oxotremorine, UK 14,304, and CP 93,129) of the respective autoreceptors. Cholinergic and monoaminergic markers were measured in homogenates. Overall, aged rats exhibited reduced accumulation of [3H]choline (-25%) and weaker evoked transmitter release (in % of accumulated tritium: -44%, -20%, and -34%, for [3H]acetylcholine, [3H]NA, and [3H]5-HT, respectively). In all rats, the inhibitory effects of the autoreceptor agonists on the evoked release of [3H] were comparable. Acetylcholinesterase (AChE), not choline acetyltransferase (ChAT), activity was reduced. The results suggest age-related modifications in the cholinergic, noradrenergic, and serotonergic innervation of the frontoparietal cortex, alterations of evoked transmitter release, but no interference with presynaptic autoinhibition of the release. Neither of these alterations seemed to account for the cognitive impairment assessed.

Perinatal distribution of galanin and galanin receptor-1 mRNA in the rat hindbrain

In situ hybridisation was used to determine the distribution and levels of mRNA for galanin precursor preprogalanin (ppGAL) and galanin receptor-1 (GAL-R1) in the rat hindbrain before and after birth. Quantification of mRNA levels was performed from E21. Also, immunohistochemistry was used to study GAL-like immunoreactivity (GAL-LI) prenatally. On E16, no expression of ppGAL mRNA could be detected in any areas examined, whereas on E19 low transcript levels were observed. GAL-LI, however, was seen at relatively high levels in nerve fibres already on E16, mainly in the areas receiving primary afferents. Also, GAL-R1 mRNA was expressed at high levels in discrete areas of the hindbrain on E16. On E21 ppGAL mRNA was found in the locus coeruleus (LC), the nucleus of the solitary tract, the dorsal motor nucleus of the vagus (nX), the lateral reticular nucleus (LRn) and superficially along the ventral medullary surface. Expression increased postnatally in all these areas except in nX and LRn. GAL-R1 mRNA, on the other hand, was found to be expressed at high levels on E21 in the LC, where levels then decreased on P1. Expression of GAL-R1 mRNA was also found in other areas of the brainstem, but here no changes were detected around birth. These findings demonstrate that ppGAL and GAL-R1 mRNAs, as well as GAL-LI, are present in the brainstem in the rat fetus and that the changes in expression after birth could be of importance for the newborn in the transition from pre- to postnatal life.

Galanin receptors in the hippocampus and entorhinal cortex of aged Fischer 344 male rats

Galanin (GAL) has been proposed to be an inhibitory modulator of cholinergic memory pathways because it acts within the hippocampus to inhibit the release and antagonize the postsynaptic actions of acetylcholine. Here we have used: 1) slice binding and quantitative autoradiography to assess the density and occupancy of GAL receptors; and 2) in situ hybridization histochemistry to assess expression of the GALR1 receptor subtype in the ventral hippocampus of 3-month-old and 21-month-old Fischer 344 male rats. We detected a small but significant (p < or = 0.0003) age-related reduction in 125I-GAL binding-site density in the ventral hippocampus and entorhinal cortex under standard binding conditions. Post-hoc analysis indicated that this reduction with age persisted in the CA1 radiatum and entorhinal cortex following GTP-induced desaturation to unmask pre-existent GAL receptors occupied by endogenous ligand. It was not associated with a significant change in peak GALR1 gene expression in the hippocampus. Because a portion of GAL receptors in this region have been postulated to function as presynaptic auto-receptors on cholinergic fiber terminals, the reduction in GAL binding sites with age may be a consequence of age-related alterations in GAL receptor expression by basal forebrain cholinergic neurons which project to the ventral hippocampus.

Ionotropic glutamate receptor subtypes in the aged memory-impaired and unimpaired Long-Evans rat

The comparative quantitative autoradiographic distribution of ionotropic glutamate receptor subtypes were investigated in young adults (six months) and aged (24-25 months) cognitively impaired and unimpaired male Long-Evans rats. Aged rats were behaviorally characterized as either cognitively impaired or unimpaired based upon their performances in the Morris water maze task compared to the young adult controls. The status of the N-methyl-D-aspartate, [125I]dizocilpine maleate, [3H]kainate and amino-3-hydroxy-5-methylisoxasole-4-propionate (AMPA, [3H]AMPA) receptor binding sites were then established in these three subgroups of animals as a function of their cognitive performance in the Morris water maze task. The apparent densities of both N-methyl-D-aspartate/[125I]dizocilpine maleate and kainate binding sites were significantly decreased in various regions of the aged rat brain. Marked losses in [125I]dizocilpine maleate binding sites were observed in outer laminae of the frontal, parietal and temporal cortices, and the stratum radiatum of the CA3 subfield of the hippocampus. Interestingly, losses in [125I]dizocilpine maleate binding sites were generally most evident in the cognitively unimpaired aged subgroup, suggesting a possible inverse relationship between losses of this receptor subtype and cognitive performances in the Morris water maze task. The levels of [3H]kainate binding were most significantly diminished in various cortical and hippocampal areas as well as the striatum and septal nuclei of both groups of aged rats. In contrast, the apparent density of [3H]AMPA binding was increased in most hippocampal subfields and the superficial laminae of the occipital cortex of the cognitively impaired vs young adult rats. Changes in [3H]AMPA labeling failed to reach significance in the unimpaired cohort. Taken together, these results show that while losses in [3H]kainate binding were similar in both subgroups of aged rats, differences were seen with respect to cognitive status for both [125I]dizocilpine maleate/N-methyl-D-aspartate and [3H]AMPA binding sites. Decreases in [125I]dizocilpine maleate binding sites were mostly restricted to cortical areas of cognitively unimpaired rats, while increases in the AMPA binding subtype were seen in the memory-impaired subgroup. It would thus appear that changes in N-methyl-D-aspartate and AMPA receptor subtypes may be more critical than alterations in kainate binding sites for the emergence of the functional deficits seen in the aged cognitively impaired rat.

Minireview. Galanin-acetylcholine interactions: relevance to memory and Alzheimer's disease

The neuropeptide, galanin, and its receptors are localized in the cholinergic basal forebrain and its projection areas in mammalian brain. Centrally administered galanin inhibits acetylcholine release in the rat ventral hippocampus, and produces deficits in learning and memory tasks. In Alzheimer's disease, galanin is overexpressed in terminals innervating the nucleus basalis of Meynert cell bodies. Selective galanin receptor antagonists provide a novel approach for increasing cholinergic function, as a potential adjunct to the clinical treatment of dementias.

Neuropeptide modulation of learning and memory processes

The ubiquitous nature of neuropeptides and their respective receptors in the central and peripheral nervous systems suggests that peptides play a key role in controlling physiological processes. Investigations on a cellular level have demonstrated that neuropeptides exert powerful modulatory effects on neurons and neuronal circuits; however, despite these compelling considerations, investigators have rarely been able to assign discrete functional roles to individual neuropeptides. Numerous studies have addressed the influence of neuropeptides on learning and memory processes. Workers have primarily utilized peripheral or central injection of neuropeptides to suggest a facilitatory, or less commonly inhibitory, role in acquisition, retention, or retrieval of memories. Although highly suggestive, critical concerns regarding the specificity of the observed effects have often remained. Recently, the neurogenetic approach has demonstrated the role of a novel neuropeptide in a specific memory phase, high affinity antagonists have confirmed the importance of some endogenous neuropeptides, and evidence of neuropeptide dysfunction in disease states, particularly Alzheimer's disease, has emerged. Continued refinement of traditional techniques, combined with information from alternative approaches, promises to consolidate the role of neuropeptides in learning and memory.

Correlations between water maze performance and cortical somatostatin mRNA and high-affinity binding sites during ageing in rats

Somatostatin levels and high-affinity (somatostatin-1) binding sites are decreased in post-mortem cortical samples of Alzheimer's disease patients but the relationships between such modifications and the cognitive deficits remain to be established. We investigated these relationships in the ageing rat. Three age groups (3-4, 14-15 and 26-27 months) were tested in a modified version of the Morris water maze. Somatostatin mRNA levels were quantified by in situ hybridization and somatostatin binding sites by radioautography using the selective agonist octreotide (SMS 201995) as a competing drug to evaluate high-affinity (somatostatin-1) and low-affinity (somatostatin-2) binding sites. The number of somatostatin mRNA-containing cells was not modified with age or memory performance in cortical, hippocampal and hypothalamic regions, but somatostatin mRNA densities were significantly decreased with age and with memory performance in the frontal and parietal cortex. In the frontal cortex somatostatin mRNA densities were already decreased in 14- to 15-month-old rats, whereas the decrease was observed only in 26- to 27-month-old rats in the parietal cortex. A decrease in somatostatin-1 binding was observed with memory performance, independently of age, in the basolateral amygdala only, while somatostatin-2 binding sites were not affected. In the frontal and parietal cortex, a significant correlation occurred between the latency to find the invisible platform in the water maze and somatostatin mRNA (r = -0.54 and 0.59 respectively, P < 0.02). These results indicate that ageing rats with memory impairments display some of the features of the somatostatinergic deficits observed in Alzheimer's disease.