Similar memory impairments found in medial septal-vertical diagonal band of Broca and nucleus basalis lesioned rats: are memory defects induced by nucleus basalis lesions related to the degree of non-specific subcortical cell loss?

Variations of Brain Functional Connectivity in Alcohol-Preferring and Non-Preferring Rats with Consecutive Alcohol Training or Acute Alcohol Administration

Alcohol addiction is regarded as a series of dynamic changes to neural circuitries. A comparison of the global network during different stages of alcohol addiction could provide an efficient way to understand the neurobiological basis of addiction. Two animal models (P-rats screened from an alcohol preference family, and NP-rats screened from an alcohol non-preference family) were trained for alcohol preference with a two-bottle free choice method for 4 weeks. To examine the changes in the neural response to alcohol during the development of alcohol preference and acute stimulation, different trials were studied with resting-state fMRI methods during different periods of alcohol preference. The correlation coefficients of 28 regions in the whole brain were calculated, and the results were compared for alcohol preference related to the genetic background/training association. The variety of coherence patterns was highly related to the state and development of alcohol preference. We observed significant special brain connectivity changes during alcohol preference in P-rats. The comparison between the P- and NP-rats highlighted the role of genetic background in alcohol preference. The results of this study support the alterations of the neural network connection during the formation of alcohol preference and confirm that alcohol preference is highly related to the genetic background. This study could provide an effective approach for understanding the neurobiological basis of alcohol addiction.

Age-associated decline in septum neuronal activation during spatial learning in homing pigeons (Columba livia)

The relationship between hippocampal aging and spatial-cognitive decline in birds has recently been investigated. However, like its mammalian counterpart, the avian hippocampus does not work in isolation and its relationship to the septum is of particular interest. The current study aimed to investigate the effects of age on septum (medial and lateral) and associated nucleus of the diagonal band (NDB) neuronal activation (as indicated by c-Fos expression) during learning of a spatial, delayed non-match-to-sample task conducted in a modified radial arm maze. The results indicated significantly reduced septum, but not NDB, activation during spatial learning in older pigeons. We also preliminarily investigated the effect of age on the number of cholinergic septum and NDB neurons (as indicated by expression of choline acetyltransferase; ChAT). Although underpowered to reveal a statistical effect, the data suggest that older pigeons have substantially fewer ChAT-expressing cells in the septum compared to younger pigeons. The data support the hypothesis that reduced activation of the septum contributes to the age-related, spatial cognitive impairment in pigeons.

Measurement of orexin (hypocretin) and substance P effects on constitutively active inward rectifier K(+) channels in brain neurons

Electrophysiological experiments in our laboratory have led to the discovery that the cholinergic neurons in the nucleus basalis in the rat forebrain possess constitutively active inward rectifier K(+) channels. Unlike cloned inward rectifier K(+) channels, these constitutively active inward rectifier K(+) channels were found to have unique properties, and thus were named "KirNB" (inward rectifier K(+) channels in the nucleus basalis). We found that slow excitatory transmitters, such as orexin (hypocretin) and substance P, suppress the KirNB channel, resulting in neuronal excitation. Furthermore, it was discovered that suppression of KirNB channels by these transmitters is through protein kinase C (PKC). This chapter describes detailed electrophysiological techniques for investigating the effects of orexin and substance P on constitutively active KirNB channels. For this purpose, we also present a method for culturing nucleus basalis cholinergic neurons in which KirNB channels exist. Then, we describe the procedures through which PKC has been determined to mediate inhibition of KirNB channels by orexin and substance P. There are probably many other transmitters which may produce effects on KirNB channels. This chapter will enable researchers to investigate the effects of such transmitters on KirNB channels and their roles in neuronal functions.

Effects of Yukmijihwang-tang derivatives (YMJd) on ibotenic acid-induced amnesia in the rat

The present study investigates the effects of Yukmijihwang-tang Derivatives (YMJd) on learning and memory through the Morris water maze task and the central cholinergic system of rats with excitotoxic medial septum (MS) lesion. In the water maze test, the animals were trained to find a platform in a fixed position for 6 d and then received a 60-s probe trial in which the platform was removed from the pool on the 7th day. Ibotenic lesion of the MS showed the impaired performance in the Morris water maze test and severe cell losses in the MS, as indicated by decreased choline acetyltransferase-immunoreactivity in the medial septum. Daily administrations of YMJd (100 mg/kg, i.p.) for 21 consecutive days produced significant reversals of ibotenic acid-induced deficit in learning and memory. These treatments also reduced the loss of choline acetyltransferase (ChAT) immunoreactivity in the MS induced by ibotenic acid. These results suggest that impairments of spatial learning and memory might be attributable to the degeneration of septohippocampal cholinergic (SHC) neurons and that YMJd treatment ameliorated learning and memory deficits partly due through neuroprotective effects on the central acetylcholine system. Our studies suggest that YMJd might be useful in the treatment of Alzheimer's disease.

Behavioral deficits and recovery following transient focal cerebral ischemia in rats: glutamatergic and GABAergic receptor densities

The neurobiologic mechanisms underlying the recovery process following stroke are poorly understood. The present study investigated glutamatergic and gamma-amino butyric acid (GABA)-ergic receptor densities following experimental stroke in rats exposed to different environmental housing or pharmacologic interventions. About 2 days after transient (120 min) middle cerebral artery (MCA) occlusion, the rats were singly housed in standard cages or were moved to an enriched environment and treated for 10 days with either 0.9% NaCl or with the alpha(2)-adrenoceptor antagonist, atipamezole (1.0 mg/kg, s.c.). The limb-placing, foot-slip, and water-maze tests were used to assess behavioral deficits and recovery following ischemia. The rats were decapitated on day 25 after the operation and their brains were processed for [3H]MK-801, [3H]D,L,-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), [3H]kainate, and [3H]muscimol autoradiography. Receptor binding site densities were different between sham-operated rats and ischemic rats only in the lesion core and lateral ventroposterior thalamic nucleus. Ischemic rats housed in an enriched environment and treated with atipamezole had better performance in the limb-placing test. The deficit in the water-maze test was most pronounced in ischemic rats housed in standard cages. There were a number of correlations between the behavioral data and receptor binding densities in ischemic rats. For example, recovery in the limb-placing test correlated with [3H]AMPA receptor binding sites in the contralateral frontal cortex (r=0.616, P<0.05), hindlimb cortex (r=0.649, P<0.05), and parietal cortex (r=0.674, P<0.05) in ischemic rats housed in an enriched environment. There were similar correlations between limb-placing recovery and [3H]kainate binding sites in the contralateral cortices in ischemic rats housed in standard cages. In addition, there were particularly strong clustered correlations between swimming speed in the water-maze test and [3H]AMPA receptor binding sites in the hippocampal subregions in the ischemic rats housed in an enriched environment. The present results suggest that transient focal cerebral ischemia does not induce significant long-term changes in glutamatergic and GABAergic receptors in areas remote from the infarct area. The correlational data, however, suggest an important role for the contralateral cortex in the behavioral outcome and maintenance of the recovered state of ischemic rats, depending on housing conditions. In addition, attenuation of spatial learning deficits observed in ischemic rats housed in an enriched environment might be due to an increase in the swimming speed through hippocampal AMPA receptor-mediated mechanisms.

Cholinergic receptor blockade in prefrontal cortex and lesions of the nucleus basalis: implications for allocentric and egocentric spatial memory in rats

In this study we have examined the involvement of the prefrontal cortex (PFC) along with the Nucleus basalis magnocellularis (NBM) in two types of spatial navigation tasks. We evaluated the effects of excitotoxic (ibotenate-induced) lesions of the NBM in an allocentric and an egocentric task in the Morris water maze, using sham operations for a comparison. In both cases we also assessed the effects of local cholinergic receptor blockade in the PFC by infusing the muscarinic receptor antagonist scopolamine (4 or 20 microg). Anatomically, the results obtained showed that this lesion produced a profound loss of acetylcholinesterase (AChE) positive cells in the NBM, and a loss of AChE positive fibres in most of the neocortex, but hardly in the medial PFC. Behaviourally, such lesions led to a severe impairment in the allocentric task. Intraprefrontal infusions of scopolamine led to a short-lasting impairment in task performance when the high dose was used. In the second experiment, using the same surgical manipulations, we examined the performance in the egocentric task. Like in the allocentric task animals with NBM lesions were also impaired, but with continued training they acquired a level of performance similar to the sham-operated ones. This time, infusions of scopolamine in the medial PFC led to a severe disruption of performance in both groups of animals. We conclude that acetylcholine in the medial PFC is important for egocentric but not allocentric spatial memory, whereas the NBM is involved in the learning of both tasks, be it to a different degree.

An alpha(2)-adrenergic antagonist, atipamezole, facilitates behavioral recovery after focal cerebral ischemia in rats

Previous studies suggest that enhanced noradrenergic neurotransmission promotes functional recovery following cerebral lesions. The present study investigated whether systemic administration of an alpha(2)-adrenergic antagonist, atipamezole, facilitates recovery following transient focal cerebral ischemia in rats. The effect of atipamezole therapy on recovery from ischemia was compared with the effect of enriched-environment housing in rats. Ischemia was induced by occlusion of the right middle cerebral artery (MCA) for 120 min using the intraluminal filament model. Daily atipamezole treatment (1 mg/kg, subcutaneously) was started on day 2 after ischemia induction and drug administration stopped after 10 days. Another group of rats was housed in an enriched environment from day 2 following ischemia induction until the end of the experiment. Several different behavioral tests were used to measure functional recovery during the 26 days following the induction of focal cerebral ischemia. There was improved performance in the limb-placing test from the beginning of atipamezole treatment to day 8, and in wheel-running in the foot-slip test on days 2 and 4. Enriched-environment housing facilitated recovery in the foot-slip test in a later phase of the test period (days 8 to 10). Discovery of a hidden platform in a water-maze task was also facilitated in rats housed in the enriched environment, but this was probably due to the increased swimming speed of these rats. The present data suggest that the alpha(2)-adrenergic antagonist, atipamezole, facilitates sensorimotor recovery after focal ischemia, but has no effect on subsequent water-maze tests assessing spatial learning and memory, when assessed 11 days after the cessation of drug administration.

Selegiline combined with enriched-environment housing attenuates spatial learning deficits following focal cerebral ischemia in rats

Selegiline (l-deprenyl) is an irreversible monoamine oxidase B (MAO-B) inhibitor that is suggested to have neuroprotective and neuronal rescuing properties. The present study investigated whether systemic administration of selegiline facilitates behavioral recovery after transient focal cerebral ischemia in rats using a combination of different behavioral tests (limb placing, foot slip, water maze, and Montoya's staircase test) to measure the outcome of recovery. Selegiline (0.5 mg/kg, SC) or 0.9% NaCl was administered once a day, beginning on the second day after induction of ischemia and continuing for 30 days. Selegiline administration combined with enriched-environment housing attenuated ischemia-induced spatial learning deficits in a water-maze task and enhanced performance of both the contralateral affected and ipsilateral nonaffected forelimbs in a staircase test. Selegiline administration alone was not beneficial in any of the tests. Subsequent histologic examination revealed that the infarct volumes were not different between the experimental ischemic groups. Thus, these results suggest that selegiline combined with enriched-environment housing reduces behavioral and cognitive deficits without affecting infarct size.

Behavioral effects of the alpha(2)-adrenoceptor antagonist, atipamezole, after focal cerebral ischemia in rats

The present study characterized the behavioral effects of the selective alpha(2)-adrenoceptor antagonist, atipamezole, in a rat model of focal cerebral ischemia. Atipamezole (1 mg/kg, s.c.) or desipramine (5 mg/kg, i.p.), a noradrenaline reuptake blocker, was administered either as a single injection 2 days after ischemia induction or for 10 days thereafter (subacute administration). A subacute atipamezole treatment given 30 min before behavioral assessment improved performance in the limb-placing test (days 5, 7, 9, and 11) and in the foot-slip test (days 3 and 7), but not in the beam-walking test. There was no difference between experimental groups in behavioral performance following a single administration of atipamezole or following single or subacute administration of desipramine. The drug treatments did not attenuate the impairment of spatial cognitive performance of ischemic rats in the Morris water-maze test. These results suggest that repeated use-dependent release of noradrenaline by atipamezole facilitates the sensorimotor recovery following focal cerebral ischemia in rats.

Serotonin and acetylcholine release response in the rat hippocampus during a spatial memory task

By using in vivo microdialysis we monitored the extracellular levels of acetylcholine and serotonin in the hippocampus of rats performing a spatial memory task. After rats were trained for 10 consecutive days to master a food-reinforced radial-arm maze task, they were implanted with a microdialysis probe in the dorsal hippocampus. On day 12, rats were tested in the maze and acetylcholine and serotonin outputs were monitored before the test, during the waiting phase and while performing the trials. In trained, food-rewarded rats, hippocampal acetylcholine levels increased during the waiting period (181 +/- 90 of baseline) and further increased during the radial-maze performance to 236 +/- 13% of baseline values, while serotonin levels did not change during the waiting period but increased to 142 +/- 3% during the maze performance. To discriminate whether the increase of acetylcholine and serotonin levels during the testing was associated with memory performance or with food consumption, we monitored hippocampal acetylcholine and serotonin release in rats that were trained, but not food rewarded, or in rats that were not trained, but rewarded only on the test day. In the trained, non-rewarded group, acetylcholine release increased during the waiting phase to 168 +/- 6%, but did not increase further during the task performance. In contrast, no change in serotonin release was observed in this group in any phase of the test. In rats which were not trained, but food rewarded, acetylcholine increased only during the maze period (150 +/- 5%). Serotonin increased gradually and become significant at the end of the trials. (130 +/- 3%). While both neurotransmitters could be implicated in feeding behaviour, only activation of cholinergic neurotransmission appears to be associated with memory function. Our results support the following hypotheses: (i) hippocampal acetylcholine could be involved in attentional and cognitive functions underlying motivational processes; (ii) serotonin could be implicated in non-cognitive processes (i.e. in the control of motor and feeding behaviour). Since serotonin and acetylcholine neurotransmission is simultaneously activated during the spatial memory task, this suggests that these neurotransmitter systems regulate behavioural and cognitive functions.

Studies on the influence of enriched-environment housing combined with systemic administration of an alpha2-adrenergic antagonist on spatial learning and hyperactivity after global ischemia in rats

BACKGROUND AND PURPOSE

The purpose of this study was to determine whether an enriched housing environment and/or systemic administration of the alpha2-adrenergic receptor antagonist atipamezole facilitate the rate of spatial learning after global ischemia in rats.

METHODS

Carotid arteries were closed for 20 minutes after permanent cauterization of vertebral arteries on the previous day. Enriched-environment housing and drug/saline treatment were begun 3 days after ischemia. For rehabilitation, housing in an enriched environment was combined with exploration in a labyrinth. Behavioral tests (the open-arena test and water-maze learning set task) were performed after 1-week periods of drug/saline treatment three times. In addition, the open-arena test was performed to evaluate the baseline level of animals 2 days after the induction of ischemia and at the end of the experiment, when the water-maze task was assessed in another room.

RESULTS

Rats housed in an enriched environment after ischemia showed better acquisition of the water-maze learning set task after 1 week of housing. The influence of atipamezole treatment on this parameter did not reach statistical significance. In the open-arena test, ischemic animals were slightly hyperactive; however, this symptom was eliminated by housing in an enriched environment.

CONCLUSIONS

The present data suggest that housing in an enriched environment facilitates the rate of spatial learning in rats with global ischemia. Rehabilitation also alleviated the hyperactivity observed in ischemic animals.

Effect of active fragments of arginine-vasopressin on the disturbance of spatial cognition in rats

The effect of arginine8-vasopressin (AVP1-9) and its metabolite C-terminal fragments on the scopolamine-induced disruption of spatial cognition were investigated using an 8-arm radial maze task in rats. AVP1-9 (10 micrograms/kg s.c.) markedly improved the disruption of spatial cognition by treatment with scopolamine (0.5 mg/kg i.p.), and 60% of the rats recovered to a normal level. The main metabolite of AVP1-9, AVP4-9 (0.5 and 1 ng/kg s.c.) also significantly improved the scopolamine-induced deficit of spatial memory. The activity of AVP4-9 was determined to be about 10000 fold greater than that of AVP1-9. An intracerebroventricular (i.c.v.) injection of 10 fg of AVP5-8, however, showed a lower activity. Both AVP6-8 and AVP5-7, which are both metabolites of AVP5-8, demonstrated no activity. The scopolamine-induced disruption of spatial memory was found to improve after a microinjection of AVP4-9 (1 fg) into the ventral hippocampus (VH) region, but not into the dorsal hippocampus (DH). In an in vivo microdialysis study, the scopolamine-induced acetylcholine (ACh) release from the VH was slightly potentiated by treatment with AVP4-9 (10 fg i.c.v.). In addition, an AVP4-9 analogue, No. 302, which is a synthetic hexapeptide and has a longer half-life, also demonstrated a markedly improved effect, which had a 10-fold higher activity than that with AVP4-9. AVP4-9 is the most potent activity of all the endogenous metabolites of the AVP1-9 and the new synthetic AVP4-9 analogue, No. 302 (obtained from Nippon Chemiphar Co.), substituting Ser for Cys-Cys in hexapeptide, has higher activity than that of AVP4-9. These results indicated [Ser6] hexapeptide has an important role in behavioral activity. Based on these results, it is possible that AVP1-9 and its metabolite AVP4-9 could, thus, be useful in treating cholinergic dysfunction diseases, such as Alzheimer's disease. Hexapeptide may play an important role in improving the spatial memory by promoting the release of ACh in the VH region.

Central cholinergic systems and cognition

The organization and possible functions of basal forebrain and pontine cholinergic systems are reviewed. Whereas the basal forebrain cholinergic neuronal projections likely subserve a common electrophysiological function, e.g. to boost signal-to-noise ratios in cortical target areas, this function has different effects on psychological processes dependent upon the neural network operations within these various cortical domains. Evidence is presented that (a) the nucleus basalis-neocortical cholinergic system contributes greatly to visual attentional function, but not to mnemonic processes per se; (b) the septohippocampal projection is involved in the modulation of short-term spatial (working) memory processes, perhaps by prolonging the neural representation of external stimuli within the hippocampus; and (c) the diagonal band-cingulate cortex cholinergic projection impacts on the ability to utilize response rules through conditional discrimination. We also suggest that nucleus basalis-amygdala cholinergic projections have a role in the retention of affective conditioning while brainstem cholinergic projections to the thalamus and midbrain dopamine neurons affect basic arousal processes (e.g. sleep-wake cycle) and behavioral activation, respectively. The possibilities and limitations of therapeutic interventions with procholinergic drugs in patients with Alzheimer's disease and other neurodegenerative disorders in which basal forebrain cholinergic neurons degenerate are also discussed.

Effects of intraseptal injection of 192-IgG-saporin in mature and aged Long-Evans rats

In this study, the effects intraseptal injections of the selective cholinergic immunotoxin, 192-IgG-saporin, were investigated in mature (6-month-old) and aged (24-26-month-old) male Long-Evans rats. Ten days following intraseptal injection of either 192-IgG-saporin or saline, testing began in a battery of behavioral tests modulated by the septohippocampal system including two versions of the Morris water maze (i.e. submerged platform task, and 2-platform spatial discrimination), inhibitory avoidance, and pre-pulse inhibition of acoustic startle. In both mature and aged rats, intraseptal injection of 192-IgG-saporin selectively reduced ChAT activity in the hippocampus and posterior cingulate cortex, without affecting ChAT activity of amygdala or parietal cortex. In general, in all of the behavioral tests analyzed, intraseptal 192-IgG-saporin treatment had no effect in mature animals. Age-related deficits were observed in the spatial memory tasks, however this impairment was largely a function of the poor performance of aged rats treated with the toxin. In addition, an increase in the response to an acoustic startle was found in aged rats treated with 192-IgG-saporin. Thus, although intraseptal injection of 192-IgG-saporin produced similar reductions of ChAT activity, performance of mature and aged rats in tasks believed to be modulated by the septohippocampal pathway tended to be differentially affected in mature and aged rats.

Tiagabine prevents seizures, neuronal damage and memory impairment in experimental status epilepticus

A novel antiepileptic drug, tiagabine ((R)-N-[4,4-di-(3-methylthien-2-yl) but-3-enyl] nipecotic acid hydrochloride), was studied in rats in order to determine its efficacy in preventing seizures, seizure-induced neuronal damage and impairment of spatial memory in the perforant pathway stimulation model of status epilepticus. In pilot experiments, administration of tiagabine (50, 100 or 200 mg/kg/day) with subcutaneously implanted Alzet osmotic pumps led to a dose-dependent increase in tiagabine concentrations in the serum and brain. Two days of tiagabine treatment at a dose range of 50-200 mg/kg/day did not change the levels of gamma-aminobutyric acid (GABA), glutamate or aspartate in cisternal cerebrospinal fluid (CSF) compared to the controls. In the pentylenetetrazol test, the maximal anticonvulsive effect of tiagabine administered via osmotic pumps was achieved already with a dose of 50 mg/kg/day. In the perforant pathway model of status epilepticus, subchronic treatment with tiagabine (Alzet pumps, 50 mg/kg/day) completely prevented the appearance of generalized clonic seizures during stimulation (P < 0.001). In the same rats, tiagabine treatment reduced the loss of pyramidal cells in the CA3c and CA1 fields of the hippocampus (P < 0.05) but not the loss of somatostatin immunoreactive neurons in the hilus. Two weeks after perforant pathway stimulation, the tiagabine-treated rats performed better in the Morris water-maze test than the vehicle-treated rats did (P < 0.001). Our results show that tiagabine treatment reduces the severity of seizures in the perforant pathway stimulation model of status epilepticus. Possibly associated with the reduction in seizure number and severity, tiagabine treatment also reduced seizure-induced damage to pyramidal cells in the hippocampus as well as the impairment of the spatial memory associated with hippocampal damage.

Failure of carbamazepine to prevent behavioural and histopathological sequels of experimentally induced status epilepticus

Sustained electrical stimulation of the perforant pathway was used to induce long-lasting hippocampal seizures in conscious rats. One hour prior to stimulation, rats were given i.p. injections of either saline or a commonly used antiepileptic drug, carbamazepine (5H-dibenz[b, f]azepine-5-carboxamide; CBZ; 20 mg/kg). When tested 2 weeks later in a water maze, both the saline- and the carbamazepine-pretreated rats showed similarly a severe impairment in spatial learning compared to non-stimulated controls. Histological evaluation revealed that the pyramidal cell damage was (P < 0.05) milder in the carbamazepine-pretreated group in the CA1, but not the CA3c subfield. However, the number of somatostatin-immunoreactive neurons in both stimulated groups was reduced equally. Thus, at the dose of 20 mg/kg, which is a usual anticonvulsive dose in humans, carbamazepine seems to offer only partial protection against pyramidal cell damage, but no protection against the hilar somatostatin-immunoreactive neuron loss or the spatial learning deficit after perforant pathway stimulation in rats. The result clearly differs from that obtained either with a GABA (gamma-aminobutyric acid)-enhancing drug and a novel antiepileptic, vigabatrin (4-amino-hex-5-enoic acid) or with a competitive NMDA (N-methyl-D-aspartate) receptor antagonist, CGP 39551 (DL-[E]-2-amino-4-methyl-5-phosphono-3-pentenoic acid carboxyethylester) in the same test situation.

Combined treatment with a 5HT1A receptor agonist and a muscarinic acetylcholine receptor antagonist disrupts water maze navigation behavior

The present study was designed to investigate the effects of combined treatment with a serotonin (5-HT)1A receptor agonist, 8-hydroxy-2-(dipropylamino)-tetralin (8-OH-DPAT), and a muscarinic acetylcholine receptor antagonist, scopolamine, on water maze (WM) navigation. Treatment with either 8-OH-DPAT or scopolamine before daily behavioral training disrupted spatial navigation at medium doses and cue navigation at high doses. Pretraining treatment with a combination of subthreshold doses of 8-OH-DPAT and scopolamine impaired WM spatial and cue navigation, but did not impair the WM performance if the drugs were injected post-training. In trained rats, combined injections of subthreshold doses of 8-OH-DPAT and scopolamine given pretraining did not impair the rats' ability to find the platform in a familiar or in a novel position. The combination of 8-OH-DPAT and scopolamine also disrupted WM navigation in rats with central 5-HT depletion. A combination of a peripheral muscarinic acetylcholine receptor antagonist and 8-OH-DPAT had no effect on WM navigation. These data suggest that combined treatment with drugs blocking muscarinic acetylcholine receptors and activating 5-HT1A receptors greatly impairs WM learning/performance, but does not impair spatial memory per se.

Effects of scopolamine infusions into the anterior and posterior cingulate on passive avoidance and water maze navigation

We examined the role of anterior and posterior cingulate cortical muscarinic receptors in water maze spatial learning and passive avoidance. Pretraining and posttraining trial scopolamine (a mixed a muscarinic acetylcholine antagonist) infusions into the anterior cingulate cortex dose dependently (3 no effect; 10 and 30 micrograms impaired) impaired passive avoidance performance. Pretesting infusion into the anterior cingulate had no effect on passive avoidance. Scopolamine infusion into the anterior cingulate did not impair spatial navigation. On the contrary, scopolamine (3 micrograms no effect, 10 and 30 micrograms impaired) infusions into the posterior cingulate before daily training trials impaired water maze navigation to a hidden platform, but did not affect navigation to a visible escape platform or passive avoidance. Posttraining and pretesting infusion into the posterior cingulate did not impair WM spatial navigation. The present results indicate that muscarinic acetylcholine receptor antagonist may modulate passive avoidance performance via cholinergic receptors located in anterior cingulate cortex and the ability to develop a spatial navigation strategy via muscarinic receptors located in posterior cingulate.

Calcium deposit formation and glial reaction in rat brain after ibotenic acid-induced basal forebrain lesion

The mechanisms underlying amino acid neurotoxicity may involve a rise in the intracellular concentration of calcium. Some neurons appear to die as a consequence of increased intracellular calcium levels induced by excitatory amino acids. One month after injection of ibotenic acid in the rat basal forebrain, the induced formation of calcium deposits and concomitant glial reaction were studied. Alizarine Red-positive calcium deposits were observed after ibotenic acid injection in the ventral part of the globus pallidus, but not in the medial septum. These deposits were present in the globus pallidus, ventral pallidum, substantia innominata, zona incerta, lateral hypothalamic area, entopeduncular nucleus, medial amygdaloid nucleus and several thalamic nuclei. Three types of round shaped deposit were identified morphologically. Differential astroglial and microglial reactions, studied autoradiographically with the monoamine oxidase-B marker [3H]Ro19-6327 and the peripheral benzodiazepine receptor marker [3H]Ro5-4864 respectively, were observed after both lesions. Our data suggest that excitotoxic lesions in the globus pallidus and medial septum lead with time to different neurodegenerative consequences and glial reactions. This differential sensitivity is discussed on the basis of the presence of different glutamate receptor subtypes and calcium-binding proteins.

Effects of tetrahydroaminoacridine and nicotine in nucleus basalis and serotonin-lesioned rats

The present study was designed to investigate the hypothesis that concurrent degeneration of serotonin and acetylcholine cells may decrease the therapeutic effects of cholinergic drugs on cognitive functioning in Alzheimer dementia. Therefore, we compared the effects of pretraining injections of a cholinesterase inhibitor, tetrahydroaminoacridine (1, 3 and 5 mg/kg i.p.), and nicotine (0.03, 0.1 and 0.3 mg/kg i.p.) on spatial navigation (water maze) and passive avoidance in nucleus basalis- and nucleus basalis+p-chlorophenylalanine-lesioned rats. Nicotine (0.1 and 0.3 mg/kg) promoted passive avoidance performance of nucleus basalis-lesioned rats, but nicotine did not improve performance of combined-lesioned rats. Tetrahydroaminoacridine (3 mg/kg) facilitated passive avoidance performance of nucleus basalis- and combined-lesioned rats. However, tetrahydroaminoacridine-treated nucleus basalis+p-chlorophenylalanine-lesioned rats were not performing better than vehicle-treated nucleus basalis-lesioned rats. Spatial navigation of nucleus basalis and nucleus basalis+p-chlorophenylalanine-lesioned rats was slightly impaired during the first training day and tetrahydroaminoacridine 3 mg/kg restored the performance of combined-lesioned rats. Combined-lesioned rats performed as well as the controls during the other training days. The present results suggest that, in Alzheimer's disease, combined degeneration of nucleus basalis cholinergic and brainstem serotonergic cells decreases the therapeutic effect of nicotine, but not that of tetrahydroaminoacridine.

Ageing: the cholinergic hypothesis of cognitive decline

The concept that memory loss in ageing might be attributable to deficiencies in cholinergic function was first proposed two decades ago. This proposal gained additional definition when pathology was found in the basal forebrain cholinergic system of patients with Alzheimer's disease, and substantial deterioration of these neurons was detected in several animal models of ageing. A recently developed method for selectively removing basal forebrain cholinergic neurons using an immunotoxin provides a powerful tool for examining the function of the basal forebrain cholinergic system. This review will address new information that has come from this approach, with an emphasis on understanding the contribution of basal forebrain cholinergic neurons to age-related cognitive impairment.

The effects of NMDA receptor antagonists at anticonvulsive doses on the performance of rats in the water maze task

In the present study we investigated the effects of two competitive NMDA receptor antagonists, CGP 37849 (DL-(E)-2-amino-4-methyl-phosphono-3-pentonoic acid) and CGP 39551 (carboxyethyl ester of CGP 37849) as well as MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenz(a,d)cycloheptene-5,10-imine hydrogen maleate), a non-competitive antagonist, administered systemically before training, on the acquisition of a water maze task used to assess spatial learning and memory in rats. The competitive NMDA receptor antagonists dose dependently impaired water maze acquisition (increased escape distance), but did not significantly affect swimming speed in rats. MK-801 induced clear behavioral effects and impaired the acquisition of the water maze task. However, as training advanced drug-treated rats did show a decrease in distance swam per trial before encountering the platform in the water pool. This suggests that drug treatments did not abolish learning. When the anticonvulsive properties of the drugs were determined, MK-801 did not show any protection in the maximal electroshock (MES) test at doses already impairing the acquisition of the water maze task while the two competitive NMDA receptor antagonists protected the rats against seizures at doses not impairing acquisition. This result suggests a wider therapeutic range for CGP 39551 and especially for CGP 37849 than for MK-801 in the treatment of epilepsy.

Serotonin depletion decreases the therapeutic effect of nicotine, but not THA in medial septal-lesioned rats

The present study compares the effects of systemic pretraining trial injections of a cholinesterase inhibitor, tetrahydroaminoacridine (THA, 1, 3 and 5 mg/kg, i.p.) and nicotine (0.03, 0.1 and 0.3 mg/kg, i.p.) on spatial navigation water maze (WM) and passive avoidance (step-through PA) performance in medial septal (MS)--or MS+p-chlorophenylalanine (PCPA, a serotonin synthesis inhibitor)-lesioned rats. MS-lesion impaired WM and PA acquisition, and serotonin depletion significantly aggravated PA failure of MS-lesioned rats. THA (3 mg/kg) and nicotine (0.1 and 0.3 mg/kg) promoted PA and WM navigation of MS-lesioned rats. THA at a dose of 3 mg/kg improved performance of MS+PCPA-lesioned rats in WM and PA tests, but nicotine did not promote test performance of combined-lesioned rats. This result demonstrates that serotoninergic pathology may decrease the therapeutic effect of nicotine.

5-HT1A and muscarinic acetylcholine receptors jointly regulate passive avoidance behavior

The present study was designed to investigate the effects of combined stimulation of 5-HT1A or 5-HT2 receptors and blockade of muscarinic acetylcholine receptors on passive avoidance behavior. Administration of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), a 5-HT2 receptor agonist, impaired passive avoidance acquisition (pre-training injections) and consolidation (post-training injections) performance. Ketanserin, a 5-HT2 receptor antagonist, blocked the performance-impairing effect of DOI on passive avoidance consolidation. Interestingly, 5-HT receptor agonists may affect passive avoidance consolidation only during the immediate post-training period, as passive avoidance testing performance was not modulated by 8-OH-DPAT or DOI injected 30 min after the training trial. Furthermore, passive avoidance retention (pre-testing injections) performance was impaired only by the highest dose of 8-OH-DPAT, and DOI had no effect on passive avoidance retention. Next, the effects of combined 5-HT and acetylcholine receptor manipulations on passive avoidance behavior were studied. The effects on passive avoidance behavior of a combination of subthreshold doses of scopolamine, a muscarinic acetylcholine receptor antagonist, and 8-OH-DPAT were compared to those of a single high dose of scopolamine. A combination of small doses of scopolamine and 8-OH-DPAT impaired acquisition and consolidation of passive avoidance performance, but a single high dose of scopolamine impaired only acquisition performance. The small dose of 8-OH-DPAT also aggravated medial septal lesion-induced passive avoidance acquisition and consolidation failure. The combination of small doses of scopolamine and DOI had no effect on passive avoidance behavior. Peripherally acting scopolamine methylbromide alone or in combination with 8-OH-DPAT had no effect on passive avoidance performance. Motor activity in a swimming pool was altered by single and combined drug treatments; high doses of 8-OH-DPAT and scopolamine, and the combination of small doses of 8-OH-DPAT + scopolamine increased speed of swimming. Medial septum-lesioning also increased speed of swimming but the speed was not increased further by 8-OH-DPAT. The present data suggest that behavioral defect caused by hypostimulation of muscarinic acetylcholine receptors is aggravated by concurrent 5-HT1A receptor stimulation.

Neurochemical, histopathological and mnemonic effects of combined lesions of the medial septal and serotonin afferents to the hippocampus

Male Long-Evans rats received micro-injections of either N-methyl-D-aspartate (NMDA) in the medial septum/vertical diagonal band (MS/DB), 5,7-dihyroxytryptamine (5,7-DHT) in the fimbria/fornix and cingulate bundle or combined NMDA/5,7-DHT micro-injections. NMDA administration caused considerable damage to the MS and enlarged the lateral ventricles. It reduced the activity of choline acetyltransferase as well as the intensity of acetylcholinesterase staining in the hippocampus. 5,7-DHT selectively reduced the concentration of hippocampal serotonin. The rats were assessed for spatial memory in the Morris water maze and the radial arm maze (reference and working memory version). The 5,7-DHT-induced lesion of hippocampal serotonin had no effect by itself on either task. However, it augmented the reference memory impairment caused by the NMDA-induced lesion and delayed the recovery from NMDA-induced impairment of working memory on the radial maze. Combined damage of hippocampal cholinergic and serotonergic afferents did not severely affect spatial memory.

Differential behavioral effects of supracallosal and infracallosal lesions of the septohippocampal pathways: no ameliorative effects of oxotremorine or pilocarpine on radial-maze performance

We examined the effects in young adult female Long-Evans rats of single or combined lesions of the infracallosal and supracallosal septohippocampal pathways on a battery of behavioral tasks over two postoperative periods (14-65 and 75-150 days, respectively). During the first period, rats with lesions of the infracallosal pathways, whether given alone or in combination with lesions of the supracallosal pathways, were more active in the open field and in their home cage, and showed increased reactivity to novel extracage stimuli. Behavioral results during the second postoperative period were similar to those of the first except that rats with lesions of the infracallosal pathways (either alone or in combination with lesions of the supracallosal pathways) were no longer hyperactive in their home cage and rats with the infracallosal lesion alone were no longer hyperactive in the open field. We also observed in rats with lesions of the infracallosal pathways impaired performance in the radial-arm maze task, whether conducted under an uninterrupted protocol (first and second postoperative periods) or with a 1-min intratrial interruption (second postoperative period). Thus, behavioral deficits were observed only in rats with a lesion to the infracallosal component of the septohippocampal pathways, the behavior of rats with the combined lesions being similar to that of rats with single lesions of the infracallosal pathways in most measures. The behavior of rats with lesions of the supracallosal pathways did not differ from that of sham-operated controls in any measure at either postoperative period. Acute, systemic injections of oxotremorine (0.03 or 0.1 mg/kg, ip) or pilocarpine (0.32 or 1.0 mg/kg, ip), two muscarinic agonists, did not affect radial-arm maze performance under either the uninterrupted or interrupted protocol. The use of nonspecific muscarinic agonists does not appear to be sufficient to enhance radial-arm maze performance in rats with infracallosal septohippocampal lesions which, in contrast to supracallosal lesions, were shown to induce a deficit in this task.

Interaction between 5-HT1A and nicotinic cholinergic receptors in the regulation of water maze navigation behavior

The interaction between serotonin (5-HT)1A and nicotinic cholinergic receptors in the regulation of spatial navigation behavior in the Morris water maze (WM) test was studied. Pretraining intraperitoneal (i.p.) injections of a combination of subthreshold doses of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (a 5-HT1A receptor agonist) at 30 micrograms/kg and mecamylamine (a nicotinic cholinergic receptor antagonist) a 2500 micrograms/kg greatly impaired WM navigation to a hidden platform and slightly, but not statistically significantly, impaired WM navigation to a visible platform. Post-training i.p. injections of this combination had no effect on WM navigation performance. Serotonin depletion induced by p-chlorophenylalanine (PCPA) increased the performance impairing action of pretraining injected combination of 8-OH-DPAT 30 micrograms/kg and mecamylamine 2500 micrograms/kg. In trained rats combined injections of 8-OH-DPAT 30 micrograms/kg and mecamylamine 2500 micrograms/kg given pretraining had no effect on the navigation to a hidden platform located in a familiar or in a novel position. Pretraining trial injected combination of hexamethonium 2000 micrograms/kg (a peripherally acting nicotinic antagonist) and 8-OH-DPAT 30 micrograms/kg had no effect on navigation. These data suggest that a combined treatment with a 5-HT1a receptor agonist and a nicotinic cholinergic receptor antagonist more severely impair non-mnemonic acquisition performance processes than consolidation and retrieval processes.

Preservation of hippocampal NMDA receptors may be crucial for spatial learning after epileptic seizures in rats

Sustained electrical stimulation of the perforant pathway (PP) was used to induce hippocampal seizures in conscious rats. About 4.5 h prior to stimulation, animals were given i.p. injections of either saline or CGP 39551 (10 mg/kg), a competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. When tested 2 weeks later in water maze, the saline pretreated rats showed a severe impairment in spatial learning whereas the animals treated with CGP 39551 had the same escape latencies as the non-stimulated controls. Histological evaluation of cellular degeneration revealed that the number of somatostatin-immunoreactive (SOM-IR) neurons in both stimulated groups was reduced almost equally, but in the CGP 39551 treated animals pyramidal cell damage was partly protected. However, in contrast to the placebo group, NMDA-sensitive [3H]glutamate binding in strata radiatum and oriens of the CA1 area was not significantly reduced in the CGP 39551 group. Thus, the present results suggest that the CGP 39551 treatment was able to protect against the delayed phase of the excitotoxic cell damage, and that the preservation of NMDA receptors partly accounts for the good learning ability of the CGP 39551 pretreated, PP-stimulated rats.

Comparative effects of excitotoxic lesions of the hippocampus and septum/diagonal band on conditional visual discrimination and spatial learning

Several experiments compared the effects of excitotoxic lesions of the septal/vertical limb nuclei of the diagonal band of Broca (VDB) complex with those of the hippocampus (sparing the subiculum) on different forms of visual discrimination learning. The septal/VDB lesions, which produced significant reductions in choline acetyltransferase activity in the hippocampus and the cingulate cortex, impaired acquisition of a conditional visual discrimination in an operant chamber, while the hippocampal lesion had no effect, unless there was a delay interposed between the discriminative stimulus and the response. Neither lesion affected simple visual or spatial discrimination or reversal learning, also carried out in operant chambers, but both significantly impaired the acquisition and retention of a spatial navigation task (Morris water maze), with the septal/VDB lesions again producing greater deficits than the hippocampal lesions. Possible explanations for this surprising result are discussed and it is concluded that; (1) additional cholinergic de-afferentation of the cingulate cortex produced by the septal/VDB lesion is of functional significance; (2) this may lead to deficits in conditional rule learning, which can contribute to spatial navigation performance under certain circumstances; and (3) the contribution of septal-hippocampal cholinergic projections to spatial learning is in need of re-appraisal.

The interaction of L-deprenyl and scopolamine on spatial learning/memory in rats

L-Deprenyl, a specific MAO-B inhibitor, has been reported to improve learning/memory in some cognitive tests in aged rats. The present study investigated whether L-deprenyl could alleviate the spatial learning deficit induced by muscarinic blockade and aging in OFA rats. Scopolamine (0.25 mg/kg) impaired the acquisition of a water maze task in adult rats and increased their swimming speeds. L-Deprenyl (0.25 mg/kg, 14 days) had no effect on water maze performance in saline treated adult rats, but markedly alleviated the learning deficit induced by scopolamine and increased the time and distance of swimming in the training quadrant when the platform was removed (spatial probe trial). L-Deprenyl partly reduced the effect of scopolamine on speed of swimming. Nevertheless, administration of l-deprenyl (0.25 mg/kg, 14 days) had no effect on spatial learning/memory in aged rats. We suggest that the l-deprenyl-scopolamine interaction in the water maze test may be considered as a premise for further investigations of l-deprenyl as cognition enhancer.

Pharmacological consequences of nicotinergic plus serotonergic manipulations

The present study investigates the effects of concurrent manipulations of nicotinic cholinergic receptors (nicotinic cholinergic agonist: nicotine 0.03, 0.1, 0.3 mg/kg, nicotinic cholinergic antagonist: mecamylamine 7.5 mg/kg) and serotonin neurons (p-chlorophenylalanine (PCPA), 400/kg mg on each of 3 days) on spatial navigation (water maze, WM) and passive avoidance (PA) performance. Nicotine did not affect PA performance but at the highest dose slightly impaired WM performance. PCPA did not affect WM navigation or PA performance in saline or nicotine-treated rats. Nicotine restored WM and PA performance defect in mecamylamine pretreated rats. PCPA aggravated the WM defect and decreased the WM performance-improving effect of nicotine in mecamylamine pretreated rats. PCPA did not aggravate the PA performance defect of mecamylamine but completely blocked the PA performance-improving effect of nicotine in mecamylamine pretreated rats. These results suggest that serotonergic and nicotinergic cholinergic systems jointly modulate performance in WM and PA tests.

The behavioral effects of serotonin synthesis inhibition and quisqualic acid induced lesions of the nucleus basalis magnocellularis in rats

1. To investigate the role of the cholinergic and serotonergic systems in the regulation of cognitive functions, the effects of concurrent lesioning of nucleus basalis magnocellularis (NB) with quisqualic acid (quis) and inhibition of brain serotonin synthesis by systemic p-chlorophenylalanine (PCPA) treatment on passive avoidance (PA) retention and water maze (WM) spatial navigation performance were studied in rats. 2. Quis NB lesioning induced a marked reduction (-62%) in frontal cortical choline-acetyltransferase activity, impaired retention of PA, and slightly and transiently impaired acquisition of WM spatial navigation. 3. PCPA (400 mg/kg/day x 3, i.p.) treatment depleted frontal cortical concentrations of both serotonin (82% depletion) and its major metabolite 5-HIAA (90% depletion) and slightly affected the noradrenergic and dopaminergic systems. PCPA treatment alone had no effect on WM or PA behavior, but potentiated the PA retention deficit and slightly aggravated the WM deficit in rats subjected to quis NB lesioning. 4. The present results further support the view that serotonergic and NB neurons interact in the regulation of cognitive functions.

Elevated seizure threshold and impaired spatial learning in transgenic mice with putrescine overproduction in the brain

We have studied the role of putrescine by using transgenic mouse lines overexpressing the human ornithine decarboxylase gene in most of their tissues. The aberrant expression of the transgene is most strikingly manifested in the brain, leading to an increase of up to 20-fold in putrescine content. We report that the transgenic mice with grossly elevated putrescine in all brain regions analysed (cortex, striatum, hippocampus and cerebellum) showed a significantly elevated seizure threshold to chemical and electrical stimuli, and impaired performance in spatial learning and memory tests. The view that putrescine may be primarily responsible for these changes was supported by the fact that the concentrations of the major neurotransmitter amino acids, glutamate and GABA in the brain, were not changed in the transgenic animals, and by the finding that a further increase in brain putrescine, achieved by inhibition of the catabolism of L-ornithine, appeared to provide additional protection against electroshock-induced seizures. These results suggest that the commonly observed increase in ornithine decarboxylase activity and the massive increase in brain putrescine in connection with neuron damage is a neuroprotective measure rather than a cause of the damage.

Effects of NBM lesions with two neurotoxins on spatial memory and autoshaping

Four groups of Wistar rats received either vehicle, quisqualate, or one of two different ibotenic acid infusions into the basal forebrain. Following recovery from surgery, all rats were tested in three distinct behavioral paradigms: the Bättig radial arm maze, the Barnes circular platform, and autoshaping in an operant chamber. The results showed that the size and site of the ibotenic acid lesion had a profound effect on acquisition performance in some, but not all, procedures. Performance in the Bättig maze and acquisition of a food-rewarded lever press were in particular disrupted by ibotenic acid lesions. The severity of the reduction in cortical choline acetyltransferase (ChAT) did not correlate with performance in the tests. Quisqualate produced the largest reduction in ChAT levels but had no significant effect on performance in any of the three procedures used. Anatomic analysis revealed severe nonspecific damage to the striatum following ibotenic acid that was more pronounced in the group receiving a highly concentrated solution of ibotenic acid as compared to rats infused with a greater volume but less concentrated solution of the neurotoxin. Striatal damage was much less severe following quisqualic acid infusions. However, both types of neurotoxins produced equivalent nonspecific degeneration of the reticular thalamic nucleus. These data confirm reports that nonspecific damage appears to define the severity of ibotenic acid lesions on subsequent behavioral performance.

Neocortical, hippocampal and septal parvalbumin- and somatostatin-containing neurons in young and aged rats: correlation with passive avoidance and water maze performance

Aged (26-month-old) rats were impaired compared with young (three-month-old) rats in passive avoidance and water maze tasks. In order to study whether changes in inhibitory circuits are involved in these age-related cognitive impairments, the number of two different subpopulations of GABAergic neurons, i.e. somatostatin- and parvalbumin-containing neurons, were counted in the hippocampal formation, septum and neocortex. We found that the number of parvalbumin-containing neurons was decreased in the entorhinal, somatosensory and motor cortex as well as in the medial septum and vertical limb of the diagonal band of Broca, but not in the hippocampus of aged rats. Somatostatin-containing neurons were affected in the somatosensory and motor cortex, and in the dorsolateral septum, but not in the hippocampus or in the entorhinal cortex. The decreased number of parvalbumin-containing neurons in the entorhinal cortex of the aged rats correlated with their performance deficits in passive avoidance and spatial learning. We propose that impaired functioning of the entorhinal cortex parvalbumin-containing inhibitory neurons may, to some extent, be responsible for the learning and memory defects found in aged rats.

The neuropharmacological and neurochemical basis of place learning in the Morris water maze

The Morris water maze (MWM) offers several advantages over other methods of studying the neurochemical basis of learning and memory, particularly with respect to its ability to dissociate deficits in memory formation from deficits in sensory, motor, motivational and retrieval processes. The contributions of nearly all of the major neurotransmitter systems have been investigated and consistent patterns have emerged. Normal function in glutamatergic and cholinergic systems is necessary for spatial learning, as blockade of NMDA receptors and cholinergic hypofunction prevents spatial learning but does not impair recall. Peptides such as adrenal and sex hormones and somatostatin may also be necessary for spatial learning. In contrast, activity in either GABAergic or opioidergic systems impairs spatial learning, though by quite different means. GABAergic activity prevents memory function, whereas opioidergic activity reduces motivation. Normal monoaminergic activity is necessary for normal performance in the MWM, but not for spatial learning per se. However, noradrenergic and serotonergic systems may enhance cholinergic-mediated mnemonic processes. Further research into the relative contributions of different receptor subtypes as well as interactions between neurochemical systems should provide significant advances in our understanding of the neural basis of learning and memory in mammals.

Brain and cerebrospinal fluid cholinesterases in Alzheimer's disease, Parkinson's disease and aging. A critical review of clinical and experimental studies

Acetylcholinesterase (AChE), an enzyme responsible for the break-down of acetylcholine, is found both in cholinergic and non-cholinergic neurons in the central nervous system. In addition to its role in the catabolism of acetylcholine, AChE have other functions in brain, e.g. in the processing of peptides and proteins, and in the modulation of dopaminergic neurons in the brain stem. Several clinical and experimental studies have investigated AChE in brain and cerebrospinal fluid (CSF) in aging and dementia. The results suggest that brain AChE and its molecular forms show interesting changes in dementia and aging. However, CSF-AChE activity is not a very reliable or sensitive marker of the integrity and function of cholinergic neurons in the basal forebrain complex. Additional work is needed to clarify the role of AChE abnormality in the formation of pathology changes in patients with Alzheimer's disease.

Attenuation by the benzodiazepine receptor antagonist, ZK 93 426, of the deficit in spatial navigation induced by nucleus basalis lesions

The effects of the benzodiazepine receptor antagonist, beta-carboline ZK 93,426 treatment were studied both in NB-lesioned (ibotenic acid) and in unoperated Kuo-Wistar rats in a water maze task. The ZK 93,426 administered in the doses of 1 and 5 mg/kg, 30 min prior to the testing in a water maze apparatus, attenuated the NB lesion-induced spatial navigation deficit, although it had no effect on the performance of unoperated rats. The results suggest functional interactions between GABAergic system and ibotenic acid-induced lesion of the basal forebrain in rats.

Effects of combined methysergide and mecamylamine/scopolamine treatment on spatial navigation

In the present study, we investigated the effects of a 5-HT2 receptor antagonist, methysergide (2.5, 7.5 and 20 mg/kg), on spatial learning in saline, mecamylamine (10 mg/kg) and scopolamine (0.8 mg/kg) treated rats. Methysergide had no effect on water-maze (WM) spatial learning in rats subjected to saline or mecamylamine pretreatments. However, scopolamine-induced WM learning deficit was augmented by methysergide at doses of 7.5 and 20 mg/kg. These results further suggest (A) that cholinergic and serotonergic systems may interact in the regulation of spatial learning, and (B) that the cholinergic component of this interaction with serotonin2 receptors is mediated by muscarinic receptors, but not by nicotinic receptors.

Atipamezole, an alpha 2 antagonist, stabilizes age-related high-voltage spindle and passive avoidance defects

The present study investigates the effects of an alpha 2 antagonist, atipamezole (Ati), on the high-voltage spindle (HVS; Ati at 0.1, 1.0, and 3.0 mg/kg) activity, passive avoidance retention (PA; Ati at 3 mg/kg; injected before retention trial), and water maze (WM; Ati at 3 mg/kg; injected after daily training trials) acquisition of young and aged rats. PA retention trial performance defect of aged rats was partially alleviated by Ati at a 3-mg/kg dose. Ati at 3 mg/kg had no effect on the PA performance of young rats. Retention trial performance of nonshocked young or aged rats was not altered by a 3-mg/kg Ati dose. WM acquisition was not affected by posttraining Ati injections. Age-related increase of HVS was stabilized by Ati at 1 or 3 mg/kg. Ati at 1 and 3 mg/kg completely suppressed HVS of young rats. Ati at 0.1 mg/kg had no effect on HVS of young or aged rats. The results suggest that alpha 2-antagonist-administration-induced increase in noradrenergic activity may stabilize age-related HVS activity increase and PA performance defect.

The effects of alpha-2 adrenoceptor antagonist, atipamezole, on spatial learning in scopolamine-treated and aged rats

In order to study whether noradrenergic drugs improve age-related cognitive dysfunctions the present experiments investigated whether atipamezole, a selective and specific alpha-2 antagonist, improves spatial learning impairment due to cholinergic blockade (scopolamine 0.8 mg/kg) or aging in rats. Previously, it has been shown that atipamezole dose-dependently (0.03-3.0 mg/kg) increases the turnover of noradrenaline in rat brain. According to the present results, atipamezole (0.1, 0.3, 0.6 mg/kg) did not affect spatial learning/memory when assessed in a free swim trial of the water maze task in control rats. Furthermore, atipamezole (0.1, 0.6 mg/kg) did not improve learning deficit in scopolamine treated young rats. Higher doses (greater than or equal to 1.0 mg/kg) of atipamezole could not be tested, because they induce floating behaviour in rats. In aged rats, which were screened to be impaired in the initial acquisition of the water maze task, 0.3 mg/kg atipamezole impaired further learning of this task. Because previous studies suggest that age-related learning impairment in the water maze may be, at least partly, due to a cholinergic deficit, the present results suggest that atipamezole which increases the release of noradrenaline in brain does not alleviate this learning deficit.

Vitamin D nuclear binding to neurons of the septal, substriatal and amygdaloid area in the Siberian hamster (Phodopus sungorus) brain

Autoradiographic experiments were performed on brains of Siberian hamsters (Phodopus sungorus) injected with tritiated 1,25-dihydroxycholecalciferol. Nuclear labeling was prevented in the presence of excess unlabeled hormone. Strong nuclear concentration of radioactivity was observed in neurons of the nucleus basalis of Meynert, the medial septal nucleus, the nucleus of the diagonal band of Broca and the central amygdaloid group. The latter has been defined as consisting of the central nucleus of the amygdala, its extension into the sublenticular part of the substantia innominata of Reichert, and the lateral division of the bed nucleus of the stria terminalis. All these structures have been reported to be involved in memory and other cognitive processes, and to be affected by age-dependent neurodegenerative disorders such as Alzheimer's disease. Corresponding localization of 1,25-dihydroxycholecalciferol receptor sites in these select basal forebrain nuclei of the Siberian hamster may implicate vitamin D (soltriol), the steroid hormone of sunlight, in memory processing.

Learning deficits after unilateral AF64A lesions in the rat basal forebrain: role of cholinergic and noncholinergic systems

Rats were given unilateral infusions of ethylcholine aziridinium ion (AF64A) into the basal forebrain (BF). BF-lesioned rats had significant acquisition and retention deficits in two different types of learning tasks (water maze and active avoidance). Choline acetyltransferase activity was lower than control in the frontal cortex but not in the hippocampus or striatum. AF64A markedly reduced the levels of norepinephrine, dopamine, and serotonin in all brain regions studied. However, L-glutamic acid decarboxylase activity was not altered by AF64A injection. Cholinergic agents (physostigmine and arecoline) ameliorated the AF64A-induced learning deficits in the water maze task but not in the active avoidance task. Noncholinergic agents (desipramine and L-dopa) ameliorated the AF64A-induced avoidance deficits in the active avoidance task but not in the water maze task. 5-Methoxy-N,N-dimethyltryptamine did not improve either active avoidance or water maze learning. These results suggest that intra-BF injection of AF64A produces extensive brain dysfunction and that different neuronal systems are involved in associative and spatial learning.

Loss of cholinergic neurons in the nucleus basalis induces neocortical electroencephalographic and passive avoidance deficits

The present experiments were designed to examine the hypothesis that the degeneration of cholinergic nucleus basalis is related to the cognitive and neurophysiological deficits found in old age. Aged (26 months) rats were impaired both in the acquisition of spatial (water-maze) task and retention of passive avoidance task. During aging, neocortical electroencephalographic fast activity was decreased and high-voltage spindles increased. Loss of choline acetyltransferase-positive neurons correlated with the high-voltage spindle incidence and passive avoidance retention deficit. Unilateral ibotenate nucleus basalis lesioning decreased choline acetyltransferase activity in the cortex and produced a large nonspecific subcortical cell loss in young rats. Ibotenate-lesioned rats were impaired in spatial learning and passive avoidance retention in young rats. Quisqualic acid produced a greater decrease in cortical choline acetyltransferase activity and smaller nonspecific subcortical cell loss than ibotenate lesioning. Spatial learning was not impaired, but passive avoidance performance was disrupted. Slow waves and high-voltage spindles were increased and beta activity decreased on the side of either quisqualate or ibotenate nucleus basalis lesioning. These results demonstrate that age-related neurophysiological and cognitive deficits result partially from the loss of cholinergic neurons in the nucleus basalis and that quisqualic acid nucleus basalis-lesioning in young rats may be used as a pharmacological model of the age-related cholinergic neuron loss.

Amygdala kindling increased fear-response, but did not impair spatial memory in rats

The behavioral effects of amygdala kindling, a model of experimental epilepsy in rats, are reported. The animals were stimulated twice a day until stage 5 (generalized clonic) seizures were obtained three times. Two weeks later the performance of the amygdala-kindled and sham-operated rats was tested in the open-field test, on the elevated plus maze, elevated bridges, and in the Morris water maze. The results show that amygdala kindling decreased exploratory and other motor activity in the open-field test, had anxiogenic effects on the elevated plus-maze, decreased boldness on the elevated bridges, but had a negligible affect in the spatial memory task. These results suggest that amygdala kindling affects the normal fear reaction of rats, a response that is known to be mediated through the amygdaloid pathways.

Effects of concurrent nicotinic antagonist and PCPA treatments on spatial and passive avoidance learning

The present study investigates the effects of concurrent manipulations of nicotinic cholinergic receptors (mecamylamine 10 mg/kg, i.p.) and serotonin neurons (PCPA, 400 mg on each of 4 days) on spatial navigation (water maze, WM) and passive avoidance (PA) performance. PCPA treatment had no effect on WM navigation or PA performance of intact rats, but greatly aggravated mecamylamine induced performance deficit. Either single or combined treatments with hexamethonium (5.0 mg/kg, s.c.) and PCPA had no effect on WM or PA performance. These findings may suggest that nicotinic cholinergic receptors are also importantly involved in the cholinergic-serotonergic regulation of cognitive functioning.

The effects of dexmedetomidine, an alpha2 agonist, on learning and memory, assessed using passive avoidance and water maze tasks in rats

The effects of dexmedetomidine, a specific and potent alpha 2 agonist, on the performance of rats in passive avoidance and water maze tasks were studied. Pre-training administration of subanaesthetic dose (9.0 micrograms/kg) of dexmedetomidine impaired the retention of the passive avoidance task (assessed 24 hr after training) but it did not affect the training of this task. Smaller doses (0.3, 0.9 and 3.0 micrograms/kg) did not affect the training or retention of this aversively motivated task. On the other hand, pre-training administration of 0.3 and 0.9 microgram/kg dexmedetomidine impaired the acquisition of the water maze task, whereas larger doses (3.0 and 9.0 micrograms/kg) had no significant effect on spatial learning. Pre-training administration of dexmedetomidine (0.3-9.0 micrograms/kg) increased swimming speed in rats. Only a large dose (300 micrograms/kg) of dexmedetomidine, administered immediately after training, impaired the retention of the passive avoidance task and the acquisition of the water maze task. These data agree with previous findings that pharmacological manipulation of the noradrenergic system affects the retention of aversively-motivated (passive avoidance) tasks. The present results suggest that the dose-response curve of dexmedetomidine for impairment of learning/memory differs between the passive avoidance and water maze tasks.