Renin-like effects of NGF evaluated using renin-angiotensin antagonists

Long-term effects of nerve growth factor and neural transplants on behavior of rats with medial septal lesions

The present experiment investigated the interaction between exogenous nerve growth factor (NGF) and intrahippocampal septal grafts on the behavior of rats after a medial septum lesion. Young female rats received a bilateral injection of a fetal septal cell suspension into the dorsal hippocampus either immediately (immediate grafts) or 8 days after the lesion (delayed grafts). For delayed grafts, a higher concentration of endogenous neurotrophic factors can be assumed to be present in the deafferentated host tissue at the time of transplantation. One group of rats with lesions received NGF with the immediate grafts, another group received NGF alone. A sham-operated group and 3 groups with lesions (and given either immediate or delayed intrahippocampal saline injections, or no other treatment) constituted controls. The animals were tested for spontaneous alternation and for performance in a radial 8-arm maze, 1, 5 and 9 months postoperatively. Medial septal lesions reduced spontaneous alternation but, 9 months after surgery, recovery was observed in both lesion-control rats and in rats with delayed grafts (but not with immediate grafts). In the radial maze task, lesions produced a persistent impairment, although both immediate and delayed grafts reduced this deficit several months after surgery (more markedly and rapidly in the case of delayed grafts). NGF, however, increased the maze learning deficit especially 5 months postoperatively. These latter results are in contrast to findings of earlier studies showing transient beneficial effects of NGF administration. It is suggested that the effects of NGF in the present study might be due to an enhanced sprouting of sympathetic fibers into the hippocampal formation.

Behavioural and neurochemical effects of chronic intraventricular injections of nerve growth factor in adult rats with fimbria lesions

Rats received bilateral lesions of the fimbria. These lesions impaired their ability to learn a radial maze. Rats given repeated intraventricular injections of nerve growth factor (NGF, 10 micrograms twice weekly during 4 weeks after the lesion) learned the maze problem more rapidly than rats with the same injury but treated with a control protein (cytochrome c). When retested after a period of 6 weeks without NGF treatment, the performance of NGF-treated and cytochrome c-treated rats with fimbria lesions did not differ. Whereas our previous study showed an increase in choline acetyltransferase (ChAT) activity in the septum and the hippocampus 4 days after the last NGF injection, the present study found that after the retest period (i.e. 10 weeks after the last NGF injection) ChAT activity was increased in the septum but not in the hippocampus. The relationship between the NGF-induced changes in ChAT activity and behaviour is discussed.

Choline acetyltransferase activity in striatum of neonatal rats increased by nerve growth factor

Some neurodegenerative disorders may be caused by abnormal synthesis or utilization of trophic molecules required to support neuronal survival. A test of this hypothesis requires that trophic agents specific for the affected neurons be identified. Cholinergic neurons in the corpus striatum of neonatal rats were found to respond to intracerebroventricular administration of nerve growth factor with prominent, dose-dependent, selective increases in choline acetyltransferase activity. Cholinergic neurons in the basal forebrain also respond to nerve growth factor in this way. These actions of nerve growth factor may indicate its involvement in the normal function of forebrain cholinergic neurons as well as in neurodegenerative disorders involving such cells.

Chronic intraventricular injections of nerve growth factor elevate hippocampal choline acetyltransferase activity in adult rats with partial septo-hippocampal lesions

Nerve growth factor (NGF) was injected intraventricularly during 4 weeks into adult rats with unilateral partial lesions of the cholinergic septo-hippocampal pathway. On the lesioned side, NGF treatment elevated choline acetyltransferase (ChAT) activity up to 60% above the activity measured on the lesioned side of cytochrome c-treated controls. On the unlesioned side, NGF treatment increased ChAT activity only to an insignificant degree. ChAT activity in the septum of NGF-treated animals was increased by 60% as compared to controls. The NGF-induced increases on the lesioned side and in the septum were not accompanied by elevations in acetylcholinesterase (AChE) activity. Furthermore, histochemical analysis revealed no difference in AChE staining pattern or intensity between NGF-treated and control animals. The lack of effect on AChE strongly suggests that the increases in ChAT activity in hippocampus and septum are due to an elevation of ChAT activity within cholinergic neurons surviving the lesion rather than to a promotion of sprouting of cholinergic fibers.

Behavioral effects of intracerebral injections of renin and captopril in intact and brain-damaged rats

Rats with, or without, bilateral lesions of the caudate nucleus received intracaudate injection of either renin or renin plus Captopril (SQ 14225). Following such treatment, animals were impaired on a spatial reversal task compared to controls. We concluded that the putative renin contaminant of nerve growth factor (NGF) does not contribute to behavioral recovery from brain damage observed after NGF injections in other studies. Furthermore, angiotensin II might play a possible role in mediating footshock learning and spatial reversal performance.

Renin-induced sodium appetite: effects on sodium balance and mediation by angiotensin in the rat

1. Injection of pig renin or purified renin from the mouse submaxillary gland into the preoptic region or third ventricle of the rat caused thirst within a minute or so of injection followed shortly afterwards by increased sodium appetite. Renin from two widely different sources produced identical responses.2. The stimulating effect of renin on intake of water and hypertonic (2.7%) NaCl was continuous and persisted for at least a week after the largest (265 ng) dose of purified renin.3. The stimulating effect was also very large. A single preoptic injection of less than 0.75 pmol (26.5 ng) purified mouse renin caused mean intakes of 250.4 +/- 26.2 ml water and 44.8 +/- 12.5 ml 2.7% NaCl by five naive rats in 24 h. After the largest dose (265 ng) intakes of water and 2.7% NaCl reached about 80% and 20% body weight respectively.4. Weekly injections of renin resulted in progressively larger intakes of NaCl and water in response to the injections.5. Even after repeated injections, carbachol did not stimulate sodium appetite. The stimulating effect on water intake was quickly over and showed no progressive increase with repeated injections. Overnight intake of water was generally depressed after carbachol.6. Preoptic injection of renin caused some increase in sodium excretion but this was small compared with the stimulating effect on sodium appetite.7. Detailed temporal analysis of fluid and sodium balance shows that the increased intakes of water and 2.7% NaCl were not secondary to renin-induced urinary losses. Increased intakes of water and 2.7% NaCl caused by renin resulted in the rats going into and remaining in positive fluid and sodium balance throughout the 24 h experiment.8. Renin-induced sodium appetite and thirst were inhibited by the converting enzyme inhibitors teprotide or captopril, or by the angiotensin antagonist saralasin. Inhibition was longer lasting after captopril. Carbachol-induced thirst was unaffected.9. In conclusion, renin injected into the preoptic region or third ventricle is a potent stimulus to sodium appetite as well as thirst. The effect is mediated by local generation of angiotensin II and it is not secondary to increased urinary loss.

An effect of nerve growth factor on parasympathetic neurite outgrowth

Addition of nerve growth factor (NGF) to dissociated parasympathetic ciliary ganglion neurons resulted, within 60 min of its addition, in a 2-fold increase in average neurite length and an accompanying enlargement and spreading of neuronal growth cones. These effects occurred over a concentration range of NGF of 0.1-10 ng/ml and were blocked by affinity-purified antibody to NGF. Epidermal growth factor, fibroblast growth factor, and angiotensin did not have these effects, although insulin at high concentrations was able to induce a response similar to that of NGF. Dissociated sympathetic chain neurons also responded to NGF with increased neurite lengths, and, in addition, NGF considerably extended the survival time of these neurons in culture. However, the effect of NGF on ciliary ganglion neurons was limited to neurite outgrowth, and NGF did not promote the survival of these parasympathetic neurons.

Nerve growth factor (NGF) stimulation of cholinergic telencephalic neurons in aggregating cell cultures

The addition of nerve growth factor (2.5S NGF) to serum-free aggregating cell cultures of fetal rat telencephalon greatly stimulated the developmental increase in choline acetyltransferase activity. Two other neuronal enzymes, acetylcholinesterase and glutamic acid decarboxylase, showed only slightly increased activities after NGF treatment whereas the total protein content of the cultures and the activity of 2',3'- cyclic nucleotide phosphodiesterase remained unchanged. The stimulation of choline acetyltransferase was dependent on the NGF media concentrations, showing a 50% maximum effect (120% increase) at approximately 3 ng/ml (10-10 M 2.5S NGF). NGF treatments during different culture periods showed that the cholinergic neurons remained responsive for at least 19 days. The continued treatment was the most effective; however, an initial treatment for only 5 days still caused a significant stimulation of choline acetyltransferase on day 19. The observed stimulation appeared to be specific to NGF. Univalent antibody fragments (Fab) against 2.5S NGF completely abolished the NGF-dependent increase in choline acetyltransferase activity, whereas Fab fragments of control IgG were ineffective. Furthermore, angiotensin II, added in high amounts to the cultures, showed no stimulatory effect. The present results suggest that certain populations of rat brain neurons are responsive to nerve growth factor.

The stimulation of inositol lipid metabolism that accompanies calcium mobilization in stimulated cells: defined characteristics and unanswered questions

It now appears to be generally agreed that the 'phosphatidylinositol response', discovered in 1953 by Hokin & Hokin, occurs universally when cells are stimulated by ligands that cause an elevation of the ionized calcium concentration of the cytosol. The initiating reaction is almost certainly hydrolysis of an inositol lipid by a phosphodiesterase. Phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate all break down rapidly under such circumstances. However, we do not yet know which of these individual reactions is most closely coupled to receptor stimulation, nor do we know where in the cell it occurs. With many stimuli, inositol phospholipid breakdown is closely coupled to occupation of receptors and appears not to be a response to changes in cytosol [Ca2+]: this provoked the suggestion that it may be a reaction essential to the coupling between activation of receptors and the mobilization of Ca2+ within the cell. In a few situations, however, it appears probable that inositol lipid breakdown can occur as a result of the rise in cytosol [Ca2+] that follows receptor activation: such observations gave rise to the alternative opinion that inositol lipid breakdown cannot be related to stimulus-response coupling at calcium-mobilizing receptors. It now seems likely that these two views are too rigidly polarized and that some cells probably display both receptor-linked and Ca2+-controlled breakdown of inositol lipids. Both may sometimes occur simultaneously or sequentially in the same cell.

Sodium appetite in sheep induced by cerebral ventricular infusion of angiotensin: comparison with sodium deficiency

Intraventricular administration of supraphysiological amounts of renin, nerve growth factor preparation, or angiotensin II greatly increased the consumption of water and hypertonic sodium bicarbonate solution by sheep. These effects were antagonized by intraventricular administration of drugs that prevent the formation of angiotensin II or block its receptors. The fact that these angiotensin-blocking drugs did not change the sodium intake of sodium-deficient sheep challenges the idea that central angiotensin action is involved in sodium appetite due to a deficiency.

Stimulation of the pituitary-adrenocortical axis and induction of tyrosine hydroxylase by nerve growth factor are not dependent on mouse submaxillary gland isorenin

A biologically active 2.5S NGF preparation free of renin-activity was prepared. Stimulation of the hypothalamo-pituitary-adrenocortical axis as well as induction of tyrosine hydroxylase in sympathetic ganglia are characteristic NGF effects and are not mediated by renin. These findings are confirmed by observations showing that captopril, an angiotensin converting enzyme inhibitor, failed to block these responses.

The isolation and characterisation of nerve growth factor from the prostate gland of the guinea-pig

Nerve growth factor from the guinea-pig prostate gland has been completely purified and characterised. Its chemical and biological properties in vitro are compared with those of nerve growth factor from other sources.

Induction of ornithine decarboxylase by renin-free nerve growth factor

Renin-free nerve growth factor causes the induction of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in superior cervical ganglia from neonatal rats but not in the brain of mature rats. Less pure preparations of nerve growth factor induce the enzyme in both brain and ganglia. The induction of ornithine decarboxylase in the central nervous system appears to be due to renin, not to nerve growth factor itself.