Noradrenaline depletion protects cholinergic neurons in rat hippocampus against AF64A-induced damage

Serotonergic lesion of median raphe nucleus alters nerve growth factor content and vulnerability of cholinergic septohippocampal neurons in rat

About 45% of the serotonergic raphe neurons are reported to express nerve growth factor (NGF) receptors. We therefore investigated whether selective serotonergic lesions of the median or dorsal raphe nuclei are associated with changes in NGF protein levels of the brain and whether the loss of serotonergic function alters the vulnerability of cholinergic septohippocampal neurons. In adult rats the hippocampal NGF content changed in a biphasic way after lesion of the median raphe nucleus by 5,7-dihydroxytryptamine (5,7-DHT), with a significant increase after 2-3 weeks of up to 35%, followed by a significant reduction of 22% below control levels after 7 weeks, and a return to control levels within the following 4 weeks. By contrast, the decrease in hippocampal serotonin and 5-hydroxyindoleacetic acid remained throughout the observation period of 11 weeks, being still reduced to 15 and 30% of the control levels, respectively. In the frontal cortex the partial loss of the serotonergic innervation projecting from the median raphe was associated 5 weeks after 5,7-DHT injection with an increase in NGF protein of 39.7+/-9.6% (P<0.05), which remained elevated up to 11 weeks. At 9 weeks after 5,7-DHT, the lesion of the septohippocampal cholinergic neurons induced by the cholinotoxin ethylcholine aziridinium (AF64A) was exaggerated (P<0.05) as compared to AF64A-treated rats with intact serotonergic innervation. The present data indicate that a serotonergic lesion of the median raphe nucleus results in biphasic changes of NGF protein content and in a delayed increase in the vulnerability of septohippocampal cholinergic neurons.

The AF64A model of cholinergic hypofunction: an update

Based on numerous reports in the literature since 1980, one can now conclude that ethylcholine aziridinium (AF64A) is selective for the cholinergic system in vivo, and that the effect is both dose- and site-dependent. Thus, AF64A treatment, under the correct conditions of dose and time will result in selective reductions in levels of ACh, AChE, ChAT, HAChT, and K(+)- and ouabain-stimulated release of ACh. While other neurotransmitters may also be affected in brains of AF64A treated rats, the effect is only transient and is most probably secondary to the initial cholinergic deficit-induced by AF64A, reflecting an adaptive reaction of these neurotransmitter systems, which are normally integrated with cholinergic interconnections, to the cholinergic deficiency induced by AF64A. This paper provides a historical perspective for the development of AF64A as a selective cholinotoxin, and surveys its potential mechanisms of action at the neurochemical and molecular levels. Moreover, the availability of an animal model such as the AF64A-treated rat, in which the cholinergic system has been compromised selectively for an extended period of time, has allowed investigators to study a wide variety of questions that relate to factors controlling cholinergic function in vivo. Several key illustrations are presented at the end of this paper.

Treatment of pregnant alcohol-consuming rats with buspirone: effects on serotonin and 5-hydroxyindoleacetic acid content in offspring

This laboratory previously demonstrated that in utero ethanol exposure markedly impairs the development of the serotonergic system in rat brain. Developmental abnormalities could be detected as early as G15 in the brainstem and G19 in the cortex. Because of the importance of fetal serotonin (5-HT) and 5-HT1A receptors for the normal development of 5-HT containing neurons, we initiated studies to determine whether administration of a 5-HT1A agonist, buspirone, to pregnant rats could overcome the adverse effects of in utero ethanol exposure on the developing serotonergic system in offspring. Female, Sprague-Dawley rats were given daily subcutaneous injections of buspirone (4.5 mg/kg) from gestational day 13 (G13) to G20. 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) content were determined in the cortex and cortical regions. These experiments demonstrated that the ethanol-associated abnormalities in the development of the serotonergic system can be partially overcome by in utero exposure to buspirone. Specifically, whereas untreated ethanol rats had a deficiency of 5-HT and/or 5-HIAA in whole cortex on PN5, and in the motor cortex on PN19 and 35, no significant differences were detected in these regions of the age-matched offspring of buspirone-treated, ethanol-fed rats. In contrast, the 5-HT and 5-HIAA deficiency in the somatosensory cortex of 19-day-old offspring of ethanol-fed rats was not corrected by in utero buspirone treatment. These results suggest that the abnormal development of cortical projections of serotonergic neurons may be due in part to the low fetal 5-HT content in ethanol-exposed rats and may potentially be overcome by in utero treatment with a 5-HT1A agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of chronic ethanol consumption on the mesolimbic and nigrostriatal dopamine systems

Both the mesolimbic dopamine system, which is involved with the rewarding properties of several drugs of abuse, and the nigrostriatal dopamine system, which is involved with motor function, appear to be sensitive to the effects of ethanol. In order to determine which components of the mesolimbic and nigrostriatal dopamine systems are adversely affected by chronic ethanol consumption, we assessed dopamine and DOPAC (3,4-dihydroxyphenylacetic acid) concentration and D1 and D2 receptors in several dopaminergic brain areas. These studies demonstrated that consumption of a 6.6% (v/v) ethanol-containing lipid diet for 1 month affected several components of the mesolimbic dopamine system in 3-month-old Fisher 344 rats and fewer components of the nigrostriatal dopamine system. Specifically, there was a 1.6- to 2.6-fold increase in the concentration of DOPAC in the nucleus accumbens (NA), frontal cortex (FCX), ventral tegmental area (VTA), and substantia nigra (SN). While the increase in DOPAC in the FCX and VTA was paralleled by a similar increase in dopamine, there was a significant deficiency of dopamine in the SN. These results suggest that there is an increase in dopamine turnover in the FCX, VTA, NA, and SN, which is accompanied by increased dopamine synthesis in the former two regions. Studies of dopamine receptors in control and ethanol-fed rats demonstrated a 25% loss of D1 receptors in the NA. No significant differences were found in D1 receptors in the striatum or globus pallidus. In addition, there were no differences in the number of total D2 receptors or in the conversion of the high to low affinity state of D2 receptors in the nucleus accumbens and striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of in utero ethanol exposure on the developing serotonergic system

Previous work in this laboratory demonstrated that the 19- and 35-day-old offspring of ethanol-fed rats have a significant deficiency of cortical serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), as well as a decrease in the number of total 5-HT1 receptors in the motor and somatosensory cortex. The present studies extend our previous reports by demonstrating that there is also a deficit of 5-HT and 5-HIAA in the motor cortex but not in the somatosensory cortex. In addition, we have shown that a deficit of 5-HT1A receptors in the motor and somatosensory cortices contributes to the deficit of total 5-HT1 receptors. In contrast, we did not observe any changes in the binding to 5-HT1B receptors in these cortical regions from the 19-day-old offspring of ethanol-fed rats. The present studies also examined the effects of in utero ethanol exposure on the early development of the serotonergic system. The results of these studies demonstrated a deficit of 5-HT and/or 5-HIAA in the brain stem as early as the 15th day of gestation (G15) and in the cortex as early as G19. In addition, we demonstrated a delay in both the normal developmental decline of 5-HT1A receptors in the brain stem and in the acquisition of cortical 5-HT1A receptors. No changes were found in the binding of [125I]cyanopindolol to 5-HT1B receptors in either region of fetal or neonatal rats exposed to ethanol in utero.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral impairments after lesions of the nucleus basalis by ibotenic acid and quisqualic acid

Ibotenic acid (IBO) or quisqualic acid (QUIS) was infused into the region of the nucleus basalis magnocellularis (NBm) in F344 rats in order to behaviorally and biochemically characterize the effects of these two neurotoxins. QUIS infusion resulted in a slightly higher depletion of choline acetyltransferase (ChAT) activity in both anterior and posterior regions of cortex than did lesions caused by infusion of IBO. Both QUIS- and IBO-treated rats demonstrated significantly longer latencies than controls to find a hidden platform in a Morris water maze task. In addition, QUIS-treated rats performed significantly better than IBO-treated rats in the water maze. Analysis of swim speed and open field behavior did not show significant differences in general motor activity. Passive avoidance retention was unaffected by either neurotoxin. Cortical amino acid levels, [3H]neurotensin binding, dopamine, norepinephrine, and serotonin levels were unaffected by either neurotoxin. The levels of HVA and 5-HIAA in the IBO and QUIS groups were significantly reduced compared to controls, but were not significantly different from each other. Histological examination showed greater damage to non-NBm structures with IBO than with QUIS, including the basolateral nucleus of the amygdala and the reticular formation of the thalamus. The greater behavioral deficit seen after IBO lesions may be due to damage to other areas rather than differences in the extent of depletion of corticai ChAT, amino acids, catecholamines or indolamines.

Effects of in utero ethanol exposure on the developing dopaminergic system in rats

Previous studies from this and other laboratories suggest that dopamine is decreased in selected brain regions of postnatal rats exposed to ethanol in utero. The present study expands previous work by examining the effects of in utero ethanol exposure on dopamine D1 and D2 binding sites and dopamine uptake in postnatal rats. In addition, dopamine content in the brain stem and frontal cortex of fetal and neonatal rats was examined. The experimental results indicate that in utero ethanol exposure markedly affects the postnatal development of the dopaminergic system in the striatum and frontal cortex. We observed a marked, transient deficiency of striatal dopamine (greater than 40% decrease at 19 days) and dopamine uptake sites (approximately 25% decrease in Vmax at 35 days). The Bmax for striatal dopamine D1 binding sites was decreased by greater than 20% at both 19 and 35 days. Cortical D1 sites were markedly decreased at 19 days (greater than 40%). In contrast, the number of striatal D2 receptors was unaffected by in utero ethanol exposure at both ages. Analysis of tissue from neonatal rats demonstrated a marked dopamine deficiency in ethanol-exposed rats on postnatal day 5. In light of the proposed morphogenic actions of dopamine early in development, it is possible that the early dopamine deficiency contributes to the abnormal postnatal development of the dopaminergic system.