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The occurrence of sprouting by fibre systems in the neocortex following lesion is still a controversial issue. In previous studies, we showed a nerve growth factor (NGF)-induced sprouting and hypertrophy of presynaptic terminals in the cholinergic fibres of the rat neocortex following stroke-type lesions, effects that were potentiated by the monosialoganglioside GM1. The present study investigated whether exogenous NGF and/or GM1 treatment could also affect the noradrenergic and somatostinergic systems in the neocortex. Immediately following unilateral vascular decortication, adult rats received, via minipump, a 7-day infusion of vehicle, NGF (12 microg/day) and/or GM1 (1.5 mg/day) into the cerebroventricular space. Thirty days postlesion, the animals were perfused with histological fixatives, the brains were removed, and relevant sections were processed for dopamine beta-hydroxylase and somatostatin immunocytochemistry at the light and electron microscopic levels. A Quantimet 920 image analysis system was used for the quantification of fibre length and size of presynaptic boutons. The lesion caused a reduction in the dopamine beta-hydroxylase-immunoreactive fibre length, which was not attenuated by either NGF or GM1 treatment or both. The somatostatin-immunoreactive network, in contrast, was unaffected by the lesion, and there was no sprouting of somatostatin fibres following trophic factor therapy. We also found no significant differences in the size and number of synapses of both the dopamine beta-hydroxylase-immunoreactive and somatostatin-immunoreactive boutons following lesion and drug treatments. These results indicate that NGF and/or GM1 therapies do not cause regrowth in the noradrenergic and somatostatinergic cortical fibre networks or their presynaptic elements following a cortical devascularizing lesion.

This study examined the behavioral effects of maximal doses of exogenous NGF and/or GM1 when given intracerebroventricularly to adult rats with unilateral cortical lesions. In addition, the long-term effects of these agents on choline acetyltransferase (ChAT), glutamic acid decarboxylase (GAD) activity, and choline uptake, as well as on ChAT and NGF receptor (p75NGFR) immunoreactivity in various brain regions, were also investigated. When retested in passive avoidance and Morris water maze tasks, 30 days postlesion (i.e., 2 weeks after termination of treatment), decorticated vehicle-treated rats showed retention and reacquisition deficits which were equally attenuated by NGF (6 micrograms/day, 14 days) or NGF + GM1 (750 micrograms/day, 14 days) treatment. By contrast, lesioned animals which received GM1 alone only showed improved reacquisition of the two tasks. After behavioral testing (52 days postlesion) lesioned vehicle-treated animals had decreased ChAT activity in the ipsilateral nucleus basalis magnocellularis (NBM) but not in other subcortical brain areas examined. Neuronal loss was observed only in the ventrolateral nucleus of the ipsilateral dorsal thalamus. However, using quantitative image analysis a significant shrinkage of ChAT immunoreactive (IR) and p75NGFR-IR NBM neurons as well as a decrease in their neuritic network was noted, particularly in the mid portion of the NBM. GM1 and NGF equally prevented these deficits in the NBM and, furthermore, enhanced ChAT activity and choline uptake in the remaining cortex ipsilateral to the lesion site. These alterations in NBM and cortical cholinergic markers were even more augmented in rats which received both NGF and GM1 treatment. By contrast, the noted NGF-induced increase in striatal ChAT activity was not further increased by concomitant GM1 treatment. GAD activity in all brain areas examined was unaltered by the lesion or any of the treatments and the apparent thalamic neuronal retrograde degeneration was not prevented by any of the treatments. It is concluded that GM1 or NGF treatment can distinctly affect performance of cortically lesioned rats in passive avoidance and Morris water maze tasks despite their equal ability to serve as long-term neuroprotective agents for the basalo-cortical cholinergic pathway.

The effect of monosialoganglioside GM1 and/or nerve growth factor treatment on the cholinergic innervation of the rat cortex was studied using both light- and electron-microscopic techniques assisted by image analysis. Adult male Wistar rats were unilaterally decorticated and received continuous infusions, via minipump, of vehicle, GM1 (1.5 mg/day) and/or nerve growth factor (12 micrograms/day) into the cerebroventricular space. Treatments were initiated immediately post-lesion and ended after seven days. Thirty days post-lesion (i.e. 23 days after the end of drug administration) brains were processed for choline acetyltransferase immunocytochemistry for either light- or electron-microscopic analysis. At this time-point choline acetyltransferase-immunoreactive neurons in the ipsilateral nucleus basalis magnocellularis were significantly reduced in size especially in the mid portion of this nucleus, in lesion vehicle-treated rats. Moreover, decreases in choline acetyltransferase immunoreactive fibre length (ranging from 31 to 50%) and varicosity number (ranging from 26 to 39%) occurred in all cortical layers within a portion of the remaining cortex of these animals. Monosialoganglioside GM1 or nerve growth factor treatment equally attenuated deficits in nucleus basalis magnocellularis cell size and cortical choline acetyltransferase immunoreactive fibre length. However, nerve growth factor, but not monosialoganglioside GM1 treatment also increased choline acetyltransferase-immunoreactive varicosity number above control levels. In lesioned rats which received both nerve growth factor and the monosialoganglioside GM1, the mean cross-sectional area of nucleus basalis magnocellularis cholinergic neurons did not differ significantly from control values. By contrast, cortical choline acetyltransferase-immunoreactive fibre length and varicosity number were significantly increased above control values and that induced by nerve growth factor treatment alone. Quantitative electron-microscopic analysis showed that cholinergic boutons in cortical layer V were considerably shrunken in lesioned vehicle-treated rats and that GM1 treatment failed to significantly attenuate this deficit. However, exogenous nerve growth factor provoked a significant increase (35% above control values) in cortical cholinergic presynaptic terminal size which was even further augmented by concurrent GM1 treatment (69% above control values). This trophic factor-induced increase in bouton size was confirmed using serial electron microscopy and computer-assisted three-dimensional reconstruction of the cholinergic varicosities. The number of synaptic contacts in cortical layer V was also found to be significantly reduced (45% of control values) in lesioned vehicle-treated rats but was maintained at control levels by exogenous GM1 treatment. In addition, a significant increase (95% above control levels) in the number of choline acetyltransferase-immunoreactive boutons with synaptic differentiations was noted in lesioned nerve growth factor-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

The cholinergic pathway ascending from the nucleus basalis magnocellularis (NBM) to the cortex has been implicated in several important higher brain functions such as learning and memory. Following infarction of the frontoparietal cortical area in the rat, a retrograde atrophy of cholinergic cell bodies and fiber networks occurs in the basalocortical cholinergic system. We have observed that neuronal atrophy in the NBM induced by this lesion can be prevented by intracerebroventricular administration of exogenous nerve growth factor (NGF) or the monosialoganglioside GM1. In addition, these agents can upregulate levels of cortical choline acetyltransferase (ChAT) activity in the remaining cortex adjacent to the lesion site. Furthermore, an enhancement in cortical high-affinity 3H-choline uptake and a sustained in vivo release of cortical acetylcholine (ACh) after K+ stimulation are also observed after the application of neurotrophic agents. Moreover, these biochemical changes in the cortex are accompanied by an anatomical remodeling of cortical ChAT-immunoreactive fibers and their synaptic boutons.

This study examined the performance of cortically lesioned rats and their response to cholinomimetic agents in passive avoidance and water maze tasks. Lesions encompassing mainly the frontal and parietal cortices produce a deficit in a 5-day passive avoidance retention test. This deficit was attenuated by the intraperitoneal (IP) administration of muscarinic agonists or an anticholinesterase. In the Morris water maze task, lesioned vehicle-treated animals showed greater escape latency times when compared to their sham counterparts. Cholinomimetics, injected daily during acquisition, improved mean escape latency time on days 3 and 4 of testing. The performance of the various groups in a cued version of the water task did not differ. This work demonstrates that performance deficits arising from neocortical loss can be attenuated by cholinergic drugs.

In this study light and EM quantitative analysis were used to examine whether exogenous nerve growth factor (NGF) could affect terminal fields and synaptic connections in the adult rat brain in vivo. Adult rats received, immediately after unilateral decortication, 2.5S NGF (12 micrograms/day) or vehicle intracerebroventricularly for 7 days. Thirty days after the lesion cholinergic fiber length was quantified, using image analysis, in the remaining cortical area adjacent to the lesion site in each animal. Rats that had received vehicle showed a significantly reduced cortical choline acetyl-transferase-immunoreactive fiber network in the remaining cortex when compared with control animals. By contrast, the network in lesioned rats that had received 2.5S NGF was not different from control animals. Furthermore, the number of cortical choline acetyltransferase-immunoreactive varicosities, which decreased in vehicle-treated lesioned rats, significantly increased above control in lesioned rats that had received 2.5S NGF. At the ultrastructural level, 30 days after the lesion, animals that had received vehicle showed shrunken cholinergic boutons in cortical layer V and fewer synapses compared with control animals. Exogenous NGF, administered to lesioned rats, increased to supernormal levels both size of cholinergic boutons and number of synaptic contacts. These parameters were unaltered in unlesioned rats treated with NGF. This study demonstrates that exogenous NGF can cause significant compensatory changes in terminal fields and synaptic connections in the adult fully differentiated central nervous system.

Cholinergic neurons of the forebrain respond trophically to nerve growth factor (NGF) in some experimental circumstances. The cholinergic cell system of the nucleus basalis magnocellularis (NBM) which projects to the cortex shows signs of cellular degeneration following limited devascularizing cortical lesions, while no apparent damage is observed in the remaining ipsilateral cortex. These cholinergic cells possess receptors for NGF and the administration of this peptide into the cerebroventricular space prevents cell shrinkage and loss of activity of the biosynthetic enzyme for acetylcholine, choline acetyltransferase (ChAT). Analogous trophic responses can be elicited in this system with the application of the sialoganglioside GM1. In addition, GM1 can increase the effects of NGF on ChAT activity in lesioned neurons of the NBM-to-cortex model system described above. This cooperative interaction is observed even when ineffective doses of GM1 are administered. Furthermore, an interaction between these two putative neurotrophic substances has been noted over other cholinergic parameters such as cortical high affinity choline uptake (HACU). These studies confirm the idea that trophic factors can be utilized to rescue degenerating neurons of the CNS and, in addition, lend support to the concept that gangliosides can facilitate actions of endogenously produced trophic factors.

Striatal and cortical extracellular acetylcholine (ACh) and choline (Ch) levels were determined in samples collected under in vivo conditions using microdialysis in normal (naive) and decorticated rats treated with saline or the monoganglioside GM1. ACh and Ch were assayed using a sensitive high performance liquid chromatography technique coupled to a postcolumn reactor with immobilized enzymes. Picomole amounts of ACh could be measured in the presence of an acetylcholinesterase inhibitor (neostigmine) in the microdialysis perfusion medium (striatal ACh = 0.2-0.4 microM; cortical ACh = 0.03-0.04 microM). Ch was detected both in the presence and in the absence of neostigmine (striatal Ch = 0.5-0.6 microM; cortical Ch = 0.6-2 microM). ACh, but not Ch, was strongly stimulated by 100 mM of KCl included in the perfusion medium. Decortication produced by devascularization did not significantly modify the cortical or striatal basal levels of ACh. However, in the cortex, KCl produced a higher ACh stimulation in the GM1-treated than in the saline-treated decorticated or naive rats. The present results indicate that GM1-treatment increases the ability of cortical cholinergic terminals to release ACh and support the idea that trophic factors such as monoganglioside GM1 can promote recovery following injuries of the central nervous system.

Unilateral devascularizing lesions of neocortex of the rat altered the responsiveness to the direct and indirect dopaminergic agonists, apomorphine and methamphetamine, respectively. These lesions produced subcortical damage manifesting itself as (1) decreased responsiveness to drug-induced locomotor activity, (2) the development of drug-induced rotational activity and (3) loss of body weight. Administration of the monosialoganglioside GM1 (i.c.v.; 5 mg/kg/day; 7 days) reversed these effects when the subjects were tested 10 and 30 days after surgery. The data are interpreted as resulting from damage to dopaminergic systems in the striatum.