Effects of partial lesion of dorsal hippocampal afferent and GM1 ganglioside treatment on conditioned emotional response and hippocampal afferent markers in rats.

Acquisition of the conditioned emotional response (CER) in 32 male hooded rats previously learned to press a bar for food and divided into four groups was studied. Two groups received electrolytic lesions of the dorsal hippocampal afferent and were thereafter injected either with GM1 ganglioside (30 mg/kg daily) or with buffer. Two remaining groups were sham operated and similarly injected. The partial hippocampal deafferentation evoked immediate enhancement of bar presses rate which persisted during the 2-week period of testing. CER training undertaken 2 days after surgical procedures appeared unsuccessful, whereas similar training with a cue of different modality initiated a week later resulted in acquisition of conditioned suppression of bar presses in all groups. Toward the end of training the conditioned suppression was more pronounced in lesioned than in control rats. The GM1 injections attenuated the conditioned suppression in control rats, presumably due to an antinociceptive role of ganglioside treatment. Behavioural training did not change the normal distribution pattern in cholinergic and serotonergic hippocampal afferent markers showing dorso-ventral gradient along longitudinal axis. The lesion-induced decrease pattern was also not affected. However, in contrast to previous findings in non-trained animals, the GM1 treatment was not effective in protecting against degenerative changes in the hippocampus of trained rats.

In vivo activated brain astrocytes may produce and secrete nerve growth factor-like molecules.

The cellular localization of the nerve growth factor-like immunoreactivity (NGF-LIR) has been studied in the septum and hippocampus of the rat brain 7 days following partial electrolytic lesion (2 mA, 30 s) of the septohippocampal pathways or after single intraventricular administration of 15 U of interleukin-1 beta (IL-1 beta). A double immunostaining technique which allowed a simultaneous localization of NGF-LIR and that of astroglia marker glial fibrillary acidic protein was used. Our data show that after both treatments, apart from neuronal localization of NGF-LIR typical for normal brain, many astrocytes both in the septum and hippocampus became NGF-like immunoreactive. Besides, NGF-LIR often formed a "halo" reaction around astrocytes. These results support the notion that activated in vivo brain astrocytes may, just as astrocytes growing in vitro, synthesize and secrete NGF-like molecules. Our findings may be of importance in considerations concerning trophic support to the cholinergic neurons of the basal forebrain nuclei whose impaired function is essentially responsible for some cognitive deficits in neurodegenerative diseases such as Alzheimer disease.

Derivatives of ganglioside GM1 as neuronotrophic agents: comparison of in vivo and in vitro effects.

Exogenously administered gangliosides have been shown to behave as neuronotrophic/neuritogenic agents in a variety of cell culture systems and animal models, but it is not known whether they operate by the same mechanism in vivo and in vitro. To probe this question we have employed two derivatives of GM1 lacking the negative charge: the methyl ester (GM1-CH3) and the NaBH4 reduction product of the latter (GM1-OH) in which the carboxyl group is replaced by a primary alcohol. Both derivatives proved to be as neuritogenic as GM1 in 3 cell culture systems: neuro-2A cels, PC12 cells and explanted dorsal root ganglia. However, GM1-OH proved ineffective when applied to two animal models involving reduction of cholinergic markers in: (a) hippocampus following lesion of the lateral fimbria and (b) nucleus basalis magnocellularis following cortical lesion; GM1-CH3 showed marginal activity in (a) but more in (b), possibly owing to slow hydrolysis to GM1 which was highly active in both animal models. These results indicate the necessity of a negative change on the ganglioside molecule for in vivo but not in vitro activity and point to different mechanisms for the trophic effects of exogenous gangliosides.

Differential response of subtypes of 5-HT1 recognition sites in the rat hippocampus to partial denervation.

[3H]5-HT uptake and [3H]5-HT binding to 5-HT1 receptor subtypes (5-HT1A and non-5-HT1A sites, having high and low affinity to spiperone, respectively) were studied in the rat hippocampus ten days after two types of electrocoagulative lesions. The lesion of supracallosal area and subtotal lesion of the septum destroy supra- and subcallosal hippocampal afferents, respectively. Both types of afferents carry serotonergic fibers to the hippocampus. A significant decrease of [3H]5-HT uptake (by about one half of the control) was observed after both lesions. [3H]5-HT binding to 5-HT1A sites, comprising ca 60% of the total number of 5-HT1 sites, remained unchanged after both lesions, while the binding to non-5-HT1A sites decreased significantly (by ca 20%) but only after the lesion of the septum. The results point to a postsynaptic localization of 5-HT1A and of the bulk of non-5-HT1A sites; the decrease of the proportion of non-5-HT1A sites after septal lesion may be due to their presynaptic localization on the subcallosal pathway and/or may reflect receptor alterations in consequence of transsynaptic events in the hippocampus caused by septal lesion. Differential response of serotonin receptor subtypes to lesions of supracallosal and septal areas may underlie the differential functional responses to those lesions.

Nerve growth factor induces a dose-dependent and long-lasting increase of choline acetyltransferase activity in the septal area and hippocampus of uninjured rats.

The effect of nerve growth factor (NGF) on the intact septohippocampal cholinergic system of adult rats was studied. Nerve growth factor was continuously infused at different doses (5-100 micrograms) for two weeks into the lateral ventricle of adult rats. Controls received intracerebroventricular infusion of equal amounts of cytochrome c. Nerve growth factor treatment was capable of inducing a dose-dependent increase of choline acetyltransferase activity (ChAT) in septal area and ventral hippocampus. In both areas, the NGF-induced rise of ChAT activity was sustained for at least one week after infusion, then it progressively declined towards control values. By three and five weeks, using NGF at 25 and 100 micrograms respectively, ChAT increase was still significant in both septum and ventral hippocampus. The present findings corroborate a role for NGF in adult septohippocampal cholinergic system and indicate that the "pharmacological" modulation of these neurons by NGF may last several weeks following withdrawal of this trophic factor.

Early changes in ornithine decarboxylase activity in a partially denervated hippocampus of rats untreated and treated with GM1 ganglioside.

Bilateral transection of the lateral fimbria, which disrupts partially the septo-hippocampal projections and results in partial hippocampal denervation, produced a significant increase in the ornithine decarboxylase (ODC) activity in the hippocampus. An increase occurred already 0.5 h after the operation and the activity remained intensified for at least 22 h after injury. The enzyme response was enhanced by a single dose of GM1 monosialoganglioside (30 mg/kg) administered directly after the operation. This enhancement, detected 2 h after the injury, persisted for at least 22 h after the operation. Lack of influence of GM1 ganglioside on ODC activity in the hippocampus of unlesioned animals allows us to ascribe the observed effect to the processes induced by the lesion. This study confirms the involvement of ODC in GM1 ganglioside neurotrophic effects produced in an injured brain.

Nerve growth factor affects uninjured, adult rat septohippocampal cholinergic neurons.

The effect of nerve growth factor on the intact versus injured septohippocampal cholinergic system of adult rats was studied. Nerve growth factor was continuously infused into the lateral ventricle of adult uninjured rats or rats that had received unilateral partial transection of the fimbria. Controls (operated and unoperated) received intraventricular infusion of cytochrome c. After 2 weeks of nerve growth factor or cytochrome c treatments, choline acetyltransferase and acetylcholinesterase activities were measured in the septal area and in the hippocampus (divided into dorsal, medial and ventral parts). The continuous infusion of nerve growth factor resulted in a marked dose-dependent increase of choline acetyltransferase activity in both septum and hippocampus of adult unlesioned rats. In lesioned rats the nerve growth factor treatment was capable of inducing choline acetyltransferase activity in the hippocampus of not only the lesioned but also the unlesioned side, as well as in the septal area. In addition, nerve growth factor affected choline acetyltransferase activity differently in the hippocampus of the operated side with respect to the contralateral side or in unoperated animals. The chronic infusion of nerve growth factor did not affect acetylcholinesterase activity in the septum or in the hippocampus of either lesioned or unlesioned rats. The present findings indicate that nerve growth factor is capable of modulating the function of not only damaged but also normal adult forebrain cholinergic neurons. This suggests that nerve growth factor may modulate the function of these neurons in adulthood.

Analysis of the time course of GM1 ganglioside effect on changes in choline acetyltransferase activity in partially denervated rat hippocampus.

The effect of chronic GMl ganglioside administration (30 mg/kg, daily) for 6, 21, 42 and 90 days on the activity of choline acetyltransferase was investigated in the hippocampus of rats with partial electrolytic lesions of the dorsal hippocampal afferents and in unoperated rats. No influence of GM1 administration on ChAT activity was noted in unoperated animals. The lesions caused denervation in the hippocampus, which occurred with varying intensity along its dorsoventral axis, as shown by the gradual pattern of decrease in ChAT activity. GM1 counteracted the decline in enzyme activity, however the intensity of this influence diminished with the time after surgery. A positive correlation between the GM1 effectiveness and the degree of denervation at early postsurgical stages (6, 21 days) was found, which may be ascribed to the appearance of neuronotrophic factors at this period, proportional to the severity of damage. We suggest that the decline of the GM1 effectiveness is due to a decrease in trophic activity, and/or the development of spontaneous recovery

Differential response of hippocampal muscarinic cholinergic receptors to various deafferentations of the hippocampus in the rat.

The influence of bilateral electrolytic lesions of different parts of the septum on muscarinic receptor binding in the hippocampus was studied within 14-21 days after operation. The effect of total septal lesion upon receptor binding was also investigated separately in the dorsal and ventral hippocampus and in five consecutive hippocampal parts along the septotemporal axis of the structure. The data indicate that: (i) differential response of muscarinic receptors, as revealed by a decrease, increase or lack of changes in the [3H]QNB binding depends on the site and extent of the lesion, (ii) lack of changes in muscarinic receptor binding can be spurious when the investigation is performed on the whole hippocampus, and masked by regional response differences, (iii) differential response of [3H]QNB binding sites in distinct parts of the hippocampus to total septal lesion may depend on the preexisting differences in the density of cholinergic innervation and of muscarinic receptors.

The effect of GM1 ganglioside on cholinergic and serotoninergic systems in the rat hippocampus following partial denervation is dependent on the degree of fiber degeneration.

The partial lesion paradigm of the dorsal hippocampal afferents in the rat was used as a model to study the effect of GM1 ganglioside treatment on recovery of neurotransmitter markers of the cholinergic and serotoninergic activity in various hippocampal regions. It was found that the enhancement of recovery of acetylcholinesterase, choline acetyltransferase and serotonin uptake by GM1 treatment (30 mg/kg i.m., daily), as studied on the 6th and 21st postlesion day, was dependent on the degree of fiber degeneration. The results may be interpreted in terms of the relationship between the action of GM1 and that of neuronotrophic factors whose release also depends on the extent of the fiber degeneration. These data indicate that GM1 elicits the recovery of biochemical parameters, or fails to, depending on the specificity of the trauma. The result may explain why, after certain brain lesions, GM1 does not promote functional recovery.

Bilateral changes in glutamate uptake, muscarinic receptor binding and acetylcholinesterase level in the rat hippocampus after unilateral entorhinal cortex lesions.

This report examines the effects of unilateral electrolytic and knife-cut lesions of entorhinal cortex on glutamate uptake, the muscarinic receptor [(3)H]QNB binding and acetylcholinesterase (AChE) activity in the dorsal and ventral parts of the ipsi- and contralateral hippocampus of the rat. We found that (1) in unoperated, control rats there are no pre-existing differences in the level of the investigated markers between the right and left hippocampus, (2) both electrolytic and knife-cut lesions of the entorhinal cortex evoke bilateral changes in the investigated markers and (3) the character of the response is dependent on the survival time and on the hippocampal part involved. Four days after operation a substantial reduction in glutamate uptake was found in both the dorsal and ventral parts of the ipsi- and contralateral hippocampus. At the same time there was a drop in muscarinic receptor binding, while AChE activity was not affected. The decrease in glutamate uptake persisted on the 21st postoperative day, whereas muscarinic receptor binding was enhanced, in comparison with the control level, in the ventral part of both the ipsi- and contralateral hippocampus. This overshoot was not so evident on the 30th postoperative day; glutamate uptake at that time reached or even surpassed the control level. Enhancement of AChE activity on the ipsi- and contralateral sides was noted on both the 21st and 30th day after operation. We suggest the following interpretation of these results: (1) glutamatergic projections from the entorhinal cortex to the hippocampus are bilateral, (2) some transneuronal changes probably contribute to the decline in glutamate uptake, particularly on the contralateral side, (3) neuronal depolarization does not seem to be the only mechanism responsible for the decrease in muscarinic receptor binding and (4) some compensatory mechanisms occur in the hippocampus at a later time after the lesion. Moreover, we believe that the use of the contralateral side as a control should be considered with caution in studies with unilaterally lesioned animals.

Effect of GM1 ganglioside treatment on postlesion responses of cholinergic enzymes in rat hippocampus after various partial deafferentations.

The effect of intramuscular administration of monosialoganglioside (GM1) on postlesion responses of choline acetyltransferase and acetylcholinesterase activity in partially deafferented rat hippocampus was studied at various survival times. Lesions partially destroying the medioventral, septal area, or lesions performed in supracallosal stria including corpus callosum and cingulum evoked cholinergic denervation of the hippocampus, while those made in entorhinal cortex resulted in partial glutamatergic deafferentation. GM1 treatment potentiates the responses of both cholinergic enzymes, independently of whether the partial deafferentation was homo- or heterotypical. These data indicate that GM1 may facilitate the regrowth of new cholinergic nerve terminals. However, an effect on other compensatory processes, especially in the first postoperative period, is also possible.