Changes in the acetylcholine content in the rat brain after lesions of the septum, fimbria and hippocampus

Nerve growth factor rapidly increases muscarinic tone in mouse medial septum/diagonal band of Broca

Nerve growth factor (NGF) has been implicated in maintaining and regulating normal functioning of the septohippocampal pathway. However, many aspects of its physiological actions and the underlying mechanisms await elucidation. In this study, we investigated the effect of acute NGF exposure on neurons in the mouse medial septum/diagonal band of Broca (MS/DB), focusing on the cholinergic neurons and the subpopulation of noncholinergic neurons that were identified to be putatively GABAergic. We report that MS/DB neurons in a thin slice preparation, when exposed to NGF via bath perfusion, rapidly and indiscriminately increased the rate of spontaneous firing in all MS/DB neurons. However, focal application of NGF to individual MS/DB neurons increased spontaneous firing in cholinergic, but not in the noncholinergic, subpopulation. The NGF-induced effect on cholinergic neurons was direct, requiring activation and signaling via TrkA receptors, which were immunohistochemically localized to the cholinergic neurons in the MS/DB. TrkA receptors were absent in putative GABAergic MS/DB neurons, and blockade of TrkA signaling in these and other noncholinergic neurons had no effect on their firing activity after exposure to NGF. Conversely, methyl scopolamine, blocked the increased firing activity of noncholinergic neurons during bath perfusion of NGF. We propose a cell type-specific mode of action for NGF in the MS/DB. The neurotrophin directly enhances cholinergic neuronal activity in the MS/DB through TrkA-mediated signaling, increasing acetylcholine release and, thus, muscarinic tone. This increase in muscarinic tone, in turn, results in heightened firing activity in noncholinergic MS/DB neurons.

Excitatory amino acid receptors in brains of rats with methylazoxymethanol-induced microencephaly

We used methylazoxymethanol-acetate (MAM), a potent alkylating agent, to produce microencephaly in offspring by injecting it into pregnant rats on day 15 of gestation. Binding activities of central excitatory amino acid receptors were examined in Triton-treated membranes prepared from brains of adult offspring with MAM-induced microencephaly (MAM rats). MAM rats exhibited approximately 40-50% reductions of the wet weights of the cerebral cortex, hippocampus and striatum compared to those in controls. In the cortex and hippocampus of MAM-rats, total bindings of [3H]glutamate (Glu) (which is sensitive to N-methyl-D-aspartate (NMDA) receptor), and strychnine-insensitive [3H]glycine (Gly) and (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801; a noncompetitive antagonist of NMDA receptor), were reduced to approximately 40% of those in controls. Similarly, in both regions of MAM rats, total bindings of [3H]kainate and DL-alpha-amino-3-[3H]hydroxy-5-methylisoxazole-4-propionic acid (an agonist of quisqualate receptors), were reduced to approximately 35-50% of those in controls. However, total bindings of these radioligands in the striatum of MAM rats were more than 65% of those in controls, despite the significant loss of striatum mass. However, specific bindings of radioligands in the striatum of MAM rats were elevated by more than 60% of those in controls, and Scatchard analysis revealed that elevations of [3H]Glu, [3H]Gly and [3H]MK-801 bindings were due to a significant increase in the densities of binding sites, with their affinities remaining unaltered. Spatial recognition ability examined by an 8-armed radial maze task was markedly impaired compared to those in controls. These results suggest that the proliferation of neurons bearing excitatory amino acid receptors (EAA) in the striatum is less affected by MAM treatment on day 15 of gestation than that in the cortex and hippocampus in spite of drastic weight loss in these brain regions. The significant reduction of EAA receptors in the cortex and hippocampus may be involved in the impairment of spatial memory observed in MAM-treated rats.

Effects of fetal treatment with methylazoxymethanol acetate on radial maze performance in rats

Pregnant rats (Wistar-Imamichi strain) were treated with 15 mg/kg/d of methylazoxymethanol acetate (MAM) on days 13-15 of gestation. Nine male rats, which were randomly selected from the MAM-treated offspring (MAM rats), were examined for their spatial recognition ability by the radial maze technique and compared with control offspring. Although the performances of MAM rats were inferior to the control, they could reach the predetermined criterion within 15 trials. Subsequent retention tests revealed the drastic impairment of performance in MAM rats when the retention interval was over 15 min. The total activity of choline acetyltransferase showed a significant decrease in the hippocampus and cerebral cortex of MAM rats. These results suggest that working memory disorders of MAM rats on radial maze tasks may be due to the lowering of cholinergic functions in their hippocampus and cerebral cortex.

GABAergic agents in the medial septal nucleus affect hippocampal theta rhythm and acetylcholine utilization

Neurons of the medial septal nucleus are important in regulating the physiological activity of the hippocampus. If intraseptal injection of putative neurotransmitter substances affects the turnover rate of hippocampal acetylcholine, then concomitant changes would be expected in the electrophysiologic activity of the hippocampus. A GABA agonist, muscimol, was injected into the medial septum of rats and the effects on hippocampal electrical activity and acetylcholine utilization were studied. The intraseptally injected muscimol (100 ng) resulted in hippocampal electrographic records containing low amplitude asynchronous waves and significantly less rhythmic slow activity (RSA, 6-9 Hz), compared to control injections of saline. This effect was antagonized by prior intraseptal injection of bicuculline (3 micrograms). The hippocampal electrical activity returned to normal within 100 min. The utilization of acetylcholine was significantly reduced by intraseptal muscimol at times after administration when electrographic activity was also altered, and spontaneous behavioral movement was increased. These results suggest a physiological connection between hippocampal RSA generation and GABAergic mechanisms in the septum.

Effects of cholinergic and monoaminergic antagonists and tranquilizers upon spatial memory in rats

To explore the pharmacological mechanisms of the spatial memory, performance on the radial arm maze was tested in rats under the following drugs, using a within-subject design; scopolamine (0.25 and 0.5 mg/kg), methylscopolamine (0.5 and 1 mg/kg), phentolamine (5 and 10 mg/kg), propranolol (10 and 20 mg/kg), chlorpromazine (1 and 2 mg/kg), and chlordiazepoxide (5 and 10 mg/kg). The number of correct choices was significantly decreased by scopolamine, while the other drugs, including methylscopolamine, showed no effects on the correct choices. Almost all drugs affected the running time. These findings indicate that the brain cholinergic system is involved in the spatial memory.

Septal lesions enhance hyperactivity induced either by amphetamine or lesions of the nucleus accumbens septi

Spontaneous locomotor activity was measured in 4 groups of rats subjected to either septal, accumbens, combined septal-accumbens or sham operations. Accumbens but not septal lesions increased activity above control levels and the combined septal-accumbens lesion markedly increased activity levels above that produced by the accumbens lesion. Thus, septal lesions appeared to exaggerate the activity changes produced by the accumbens lesions. Furthermore, both septal and combined septal-accumbens lesions enhanced the hyperactivity induced by 0.25, 0.5 and 1.0 mg/kg D-amphetamine-HCl but attenuated the hyperactivity induced by 0.25, 0.5 and 1.0 mg/kg scopolamine-HCl. Rats with accumbens lesions did not differ from controls in their response to amphetamine or scopolamine. Thus, septal lesions modified both lesion and drug-induced changes in locomotor activity.

Simultaneous measurement of acetylcholine and choline in brain by pyrolysis-gas chromatography-mass spectrometry

Pyrolysis-gas chromatography and chemical ionization mass fragmentography were combined to develop a specific, simple and rapid method for simultaneously measuring endogenous and stable isotopic variants of acetylcholine and choline with a detection limit of approximately 10(-12) mol. The recovery and reproducibility of the method are excellent, and the method is suitable for measuring acetylcholine and choline in discrete regions of rat brain and to measure incorporation of choline into acetylcholine, both of which uses are demonstrated. This method affords easy analysis of 40 samples in a working day. The new technique used to extract compounds from tissues and the modified gas flow arrangement may be useful to measure other compounds as well.

Kernicterus: enzymatic evidence for difference between the development of cholinergic and GABAergic innervations in the brain of the Gunn rat

The activities of choline acetyltransferase (CAT) and glutamic acid decarboxylase (GAD), markers of cholinergic and GABAergic terminals, were measured in growing and adult Gunn rats, which possess an autosomal recessive gene for jaundice or kernicterus. In the olfactory tubercle, hippocampus, neostriatum, thalamus, and hypothalamus of the animals with kernicterus, the development of the cholinergic pathways was delayed, but by the adult stage it was normal, while there was practically no action on the innervation by GABAergic neurons, at least as indicated by the chemically measured parameters.

Mediation of footshock sensitivity by serotonergic projection to hippocampus

The present experiments assessed the effects of changes in serotonergic function on footshock sensitivity, as determined by a quantified version of the flinch-jump assessment method. In Experiment 1, depletion of telencephalic serotonin by PCPA injection, medial forebrain bundle lesion, or septal lesion, produced increases in reactivity which were correlated with reductions in telencephalic serotonin levels. In all cases, this increased sensitivity was reversed by injections of d, 1-5-hydroxytryptophan (5-HTP) which restored telencephalic serotonin levels to normal. This effect of 5-HTP had not previously been demonstrated in septal lesioned animals, and overall levels of reactivity of septal animals to other stimuli were also reduced by 5-HTP. Experiment 2 tested the effects of hippocampal lesion on the 5-HTP effect in animals when serotonin depletion produced by either PCPA or septal lesion. Hippocampal lesion, while not increasing footshock sensitivity further, significantly attenuated the effectiveness of 5-HTP in restoring sensitivity to normal. The results suggest that hippocampus may be an important site of action of serotonin in modulating reactivity to footshock, and that failure of raphe lesions to increase reactivity may be due to failure to adequately deplete hippocampal serotonin.

Scopolamine does not affect footshock sensitivity in the rat

To test the generality of the finding of Feigley, et al. [8] that scopolamine increases sensitivity/reactivity to footshock, rats were tested under either scopolamine or saline conditions for sensitivity to footshock in an automated version of the flinch-jump paradigm. There was no significant trend toward increased sensitivity following scopolamine injection at any of the response magnitudes assessed. Since the previous study included an operant response in the measure of sensitivity, it was suggested that apparent effects of scopolamine on reactivity to footshock are dependent on the inclusion of an operant response in the measure of reactivity, and are not due to changes in sensory thresholds.

The role of the septal nuclei in the release of acetyl-choline from the rabbit cerebral cortex and dorsal hippocampus and the effect of atropine

Acetylcholine (ACh) was collected from the alvear surface of the dorsal hippocampus and cerebral cortex in chloralose-urethane anaesthetized or unanaesthetized rabbits. With anaesthesia, the resting release of ACh from the hippocampus was greater than that from the cortex. Wthout anaesthesia, the resting release from both areas was much higher and very similar. The addition of atropine sulphate (1 microgram/ml) to the collecting fluid or the administration of Artane (2 mg/kg i.v.) increased resting ACh release from both the hippocampus and cortex to similar output levels. Atropine also increased ACh release due to stimulation of the medial septum (MS) or mesencephalic reticular formation (MRF). Removal of the septum abolished the effect of atropine on resting ACh release and on release evoked by MRF stimulation from both the hippocampus and cortex. The data indicate that the septum is an essential pathway for cholinergic fibres ascending to the cerebral cortex and hippocampus. They also demonstrate that the septal cholinergic fibres must be intact and active for atropine to increase ACh release from their terminals.

Ontogenetic development of locomotor activity and rate of tyrosine hydroxylation

A combined biochemical and behavioral study was performed postnatally on albino rats. An almost linear increase in total motor activity was observed from 1 to 15 days of age followed by a pronounced decrease in motor activity between days 15 and 18. The in vivo rate of tyrosine hydroxylase activity in whole brain was estimated by means of measuring accumulation of L-3,4-dihydroxyphenylalanine (Dopa) after administration of an inhibitor of aromatic amino acid decarboxylase NSD 1015. Additionally, Dopa accumulation was studied in regional brain areas in 10 and 14-day-old animals. A slight gradual increase in the amount of Dopa accumulation in whole brain was observed from 1 to 10 days of age, followed by a pronounced increase between 10 and 14 days. Regional studies revealed that the increase in Dopa accumulation was primarily located to striatum. The data suggest an involvement of central catecholamine neurons possibly dopaminergic, terminating in striatum. The decrease in motor activity observed after 15 days of age is interpreted as involvement of maturing inhibitory pathways of noncatecholaminergic origin.

High affinity choline uptake: an early index of cholinergic innervation in rat brain

The uptake of [3H]choline was investigated in nuclei-free homogenates or crude synaptosomal fractions (P2) from rat brain under various stages of development. A comparable sensitivity of uptake to treatment by hyposmotic shock suggested the involvement of synaptosomal populations in choline uptake in immature as well as in adult brains. However, significant changes in the "apparent" Km for the high affinity transport system and quantitative differences in the Na ion requirement for maximal uptake at 0.43 muM choline concentration were found during development; facts which suggested a greater contribution of the low affinity system in the more immature brains. Assuming that the uptake with high and low sensitivity to Na+ reduction reflected that via the high and low affinity system reslectively, we have attempted to obtain real Km values for the high affinity system. These Km values changed less than those measured directly, suggesting that the affinity constant for the high affinity system does not change during development. On these assumptions, the developmental changes of cholinergic synaptogenesis were examined in 5 distinct regions of the brain. It was found that the synaptogenesis begins several days earlier than the increase of choline acetyltransferase (ChAc) level in the frontal cortex, the hippocampus, the superior colliculus and the cerebellum. These regions may be included among the terminal-rich regions according to available evidence related to cholinergic systems. On the other hand, synaptogenesis accompanied the concomitant ChAc increase in the striatum, where the cholinergic interneurons are present. It is concluded that the increase of ChAc in the terminal-rich regions is delayed by the axoplasmic flow; therefore, the earlier index of cholinergic synaptogenesis in these regions is the high affinity uptake activity rather than the enzyme activity.

Disinhibitory effects of intrahippocampal of intrahypothalamic injections of anticholinergic compounds in the rat

The effects of intrahippocampal or intrahypothalamic injections of anticholinergic compounds on operant responding were observed in a multiple schedule paradigm consisting of reinforced, punished, and nonreinforced components and on a punished ingestive passive avoidance task. The pattern of results suggests that cholinergic components of the hippocampus and hypothalamus mediate responding suppressed by nonreinforcement but not by punishment. The data are discussed with reference to Carlton's proposed central cholinergic inhibitory mechanisms.