Protein SP40,40-like Immunoreactivity in the Rat Brain: Progressive Increase With Age

The pattern of distribution of SP40,40-like immunoreactive structures has been studied in the rat brain using a well-characterized polyclonal antibody raised against the SP40,40 protein. Protein SP40,40 is the human counterpart of the rat sulphated glycoprotein 2, whose mRNA shows widespread expression in the developing and mature brain. In young adult rats few immunoreactive structures were observed. Some immunoreactive neurons were found in the cingulate cortex, the arcuate and perifornical hypothalamic nuclei, as well as glial labelling in the hypothalamus. A striking increase in the number of immunoreactive cells was observed as a function of age. In 20 - 22-month-old rats, numerous immunoreactive cells were observed in the cingulate cortex, several thalamic and hypothalamic nuclei, the red nucleus, olivary nuclei, superior colliculus, and many cranial nerve nuclei. Whereas the immunoreactivity was restricted to a diffuse labelling of the cell bodies and processes in young rats, other forms of labelling were observed in aged rats: punctate cytoplasmic labelling and intensely stained granules with no visible cell membrane. A further increase in the density of the immunoreactive material was observed in 30 - 31-month-old rats. Double labelling experiments demonstrated that the SP40,40 immunoreactivity was almost exclusively located in neurons and not in glial cells (with the exception noted above). The distribution of SP40,40 immunoreactivity in aged rats did not coincide with the distribution of the microtubule-associated tau protein, OX42 or lipofuscin.

Loss of Calbindin-28K Immunoreactivity in Hippocampal Slices from Aged Rats: a Role for Calcium?

Calbindin-28K (CaBP) is a calcium-binding protein widely distributed in the brain. This protein appears to be involved in the sequestration and the translocation of intracellular free calcium. In this study, we have examined the distribution pattern of the structures immunoreactive for CaBP in the hippocampal formation from slices of young (4 months) and aged (24 - 27 months) rats previously submitted to electrophysiological measurements. We demonstrated a marked loss in the number of pyramidal cells immunoreactive for CaBP in aged rats as compared to young rats. A consistent decrease in the staining intensity was also revealed by optical density measurements. Some experiments have suggested that calcium homeostasis is modified in hippocampal neurons of aged rats. The loss of CaBP-like immunoreactivity (CaBP-LI) labelling could result from an increase in intracellular calcium concentrations. To support this hypothesis, we showed that in young rats (i) the CaBP-LI was enhanced in pyramidal neurons when the slice was preincubated in a calcium-free medium, and (ii) CaBP-LI was strongly decreased when the slice was preincubated in a high-calcium medium (5 mM) and when the entry of calcium into the cell was increased by a short application of an excitatory amino acid in the medium. Our results suggest that the loss of CaBP-LI in the hippocampus of aged rats could be due to an increase in intracellular calcium concentration. Preliminary observations of hippocampal slices at different times after induction of long-term potentiation (LTP) failed to show significant changes in CaBP immunoreactivity, suggesting that this calcium-binding protein is not directly involved in LTP processes.

Brain-derived neurotrophic factor increases Ca2+/calmodulin-dependent protein kinase 2 activity in hippocampus

Here we show that brain-derived neurotrophic factor (BDNF) stimulates both the phosphorylation of the Ca2+/calmodulin-dependent protein kinase 2 (CaMK2) and its kinase activity in rat hippocampal slices. In addition, we find that: (i) the time course of BDNF action is not accompanied by a change in the spectrum of either alpha- and beta-subunits of CaMK2 detected by immunoblotting; (ii) both treatment of solubilized CaMK2 with alkaline phosphatase and treatment of immunoprecipitated CaMK2 with protein phosphatase 1 reverse phosphorylation and activation of the kinase; (iii) phospholipase C inhibitor D609 and intracellular Ca2+ chelation by 1,2-bis-(o-aminophenoxy)ethane-N,N,N",N',-tetracetic acid tetra(acetoxymethyl)ester or 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate but not omission of Ca2+ or Ca2+ chelation by EGTA, abolish the stimulatory effect of BDNF on phosphorylation and activation of CaMK2. These results strongly suggest that the conversion of CaMK2 into its active, autophosphorylated form, but not its concentration, is increased by BDNF via stimulation of phospholipase C and subsequent intracellular Ca2+ mobilization.

NMDA receptor activation in the aged rat: electrophysiological investigations in the CA1 area of the hippocampal slice ex vivo

The effects of aging on activation of N-methyl-D-aspartate (NMDA) receptors were studied in the CA1 field of hippocampal slices from young (2-4 months old) and aged (25-32 months old) Sprague-Dawley rats with the use of ex vivo extra- and intracellular electrophysiological recording techniques. No significant age-related changes of the unitary NMDA-receptor mediated excitatory postsynaptic potentials (EPSPs), recorded from the pyramidal cells after stimulation of the stratum radiatum in a magnesium-free medium and isolated in the presence of the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, were found. Simultaneously, the magnitude of synaptic plasticity which involved NMDA receptor activation was not altered. No significant age-related modifications in the mechanisms controlling glutamate release and of postsynaptic NMDA receptor responsiveness were revealed. Considering the 30-40% decrease in NMDA binding sites in the aged hippocampus, our results suggest the occurrence of compensatory mechanisms which are discussed.

Potentiation of glutamatergic EPSPs in rat CA1 hippocampal neurons after selective cholinergic denervation by 192 IgG-saporin

A complete and selective destruction of the basal forebrain cholinergic neurons projecting to the cerebral cortex and the hippocampus was induced in the rat by the toxin 192 IgG-saporin. Using electrophysiologic techniques, we have investigated the consequences of this cholinergic denervation on inhibitory and excitatory synaptic responses of CA1 pyramidal cells in rat hippocampal slices ex vivo. Histochemical experiments were performed in slices from control and 192 IgG-saporin-treated rats to check the efficacy of the intracerebroventricular injection of the immunotoxin. Stimulation of stratum radiatum elicits a glutamatergic excitatory postsynaptic potentials followed by a biphasic GABAergic inhibitory postsynaptic potential (IPSP). No significant change in IPSP was observed in 192 IgG-saporin-treated rats. By contrast, the N-methyl-D-aspartate (NMDA) and to a lesser extent the non-NMDA components of the glutamatergic response were potentiated in these animals. The possible pre- and postsynaptic mechanisms of this potentiation were discussed.

Synaptic functions in the aged rat hippocampus: a target for corticosteroids?

The role of corticosteroids in brain aging remains a controversial issue. Conceivably, if corticosteroids levels are increased in the aged brain, neuronal function might be altered. For instance, GABA-mediated synaptic events, spike accommodation and afterhyperpolarizing potentials (AHPs) might be modified. Our electrophysiological results show that the most consistent alterations observed in the aged rat hippocampus concern cholinergic receptors, glutamatergic NMDA receptors and GABAB receptors mediated synaptic potentials. In contrast no consistent alterations were observed in afterhyperpolarizing potentials, calcium spikes, or GABAA mediated synaptic events. Therefore our electrophysiological results are difficult to reconcile with a 'glucocorticoid cascade hypothesis,' involving an elevated level of corticosterone in the aged rat.

Effects of metrifonate, a cholinesterase inhibitor, on local cerebral glucose utilization in young and aged rats

The effects of the centrally acting anti-cholinesterase metrifonate (MFT) and its metabolite dichlorvos (2,2-dichlorovinyl dimethyl phosphate; DDVP) on local cerebral glucose utilization (LCGU) have been studied in 3- and 27-month-old rats, using the autoradiographic [14C]deoxyglucose technique. In 3-month-old rats, MFT (80 mg/kg i.p.) increased LCGU significantly in 17 of the 54 regions studied, including insular, cingulate, and temporal cortices, ventral hippocampus, thalamus, lateral habenula, substantia nigra, and superior colliculus. In these regions, the average MFT-induced increase in LCGU was 23% above control. The average hemispheric LCGU increased by 10% (p < 0.01). DDVP (5 mg/kg) increased LCGU in 19 regions (average increase 26%). The average hemispheric LCGU increased by 9% (p < 0.01). Regional distributions of MFT- and DDVP-induced increases in LCGU were similar and overlapped the distribution of the acetylcholinesterase activity. In 27-month-old rats, MFT was active in 18 regions (average increase 25%). The whole-brain mean LCGU increased by 10% (p < 0.01). MFT compensated for the age-related hypometabolism in some brain areas including insular, temporal, and retrosplenial cortices, substantia nigra, and superior colliculus. The effects of MFT on LCGU were preserved in old rats, at variance with other anticholinesterases (tacrine, physostigmine). Which are less active in the aged rat brain.

Deficits in memory and hippocampal long-term potentiation in mice with reduced calbindin D28K expression

The influx of calcium into the postsynaptic neuron is likely to be an important event in memory formation. Among the mechanisms that nerve cells may use to alter the time course or size of a spike of intracellular calcium are cytosolic calcium binding or "buffering" proteins. To consider the role in memory formation of one of these proteins, calbindin D28K, which is abundant in many neurons, including the CA1 pyramidal cells of the hippocampus, transgenic mice deficient in calbindin D28K have been created. These mice show selective impairments in spatial learning paradigms and fail to maintain long-term potentiation. These results suggest a role for calbindin D28K protein in temporally extending a neuronal calcium signal, allowing the activation of calcium-dependent intracellular signaling pathways underlying memory function.

[Study methods of drugs in Alzheimer disease]

The availability of new drugs for Alzheimer's disease, with different pharmacological profiles, leads to a redefinition the relevant methodology for developing drugs in this indication, including the inclusion/exclusion criteria, the duration of the studies, and therefore, the relevant guidelines. This was the purpose of the Giens Round-table devoted to the new methodology for drug development in Alzheimer disease.

Synaptic mechanisms and calcium binding proteins in the aged rat brain

Synaptic mechanisms were studied ex vivo in the aged rat hippocampus, using a slice preparation and intracellular electrophysiological recordings of the CA1 pyramidal neurons. A dramatic depression of the slow cholinergic excitatory postsynaptic potential (EPSP) and of the slow, GABAB-mediated inhibitory postsynaptic potential (IPSP) were observed. These age-related changes were consistently found in three different strains of rats. The mechanisms involve 1) changes in the properties of the postsynaptic muscarinic receptors, and possibly in acetylcholine release (for the postsynaptic muscarinic receptors, and possbily in acetylcholine release (for the cholinergic EPSP), and 2) alterations in the presynaptic GABAergic interneurons, as shown by a loss in calbindin immunoreactivity (for the GABAergic IPSP). The immunoreactivity for three calcium binding proteins (calbindin, parvalbumin and calretinin) was studied in the aged rat brain. Immunoreactivity for calbindin was dramatically reduced in the pyramidal neurons of the CA1 field and in a subpopulation of interneurons in the hippocampus. Immunoreactivity for parvalbumin was reduced in the medial septal area, and in the cingulate cortex, whereas no change was observed for calretinin. These age-related alterations could 1) modify the functions of the hippocampal networks, and possibly contribute to the age-related cognitive deficits, and 2) compromise intraneuronal calcium buffering, and thus make neurons more vulnerable to toxic insults.

Persistence of CA1 hippocampal LTP after selective cholinergic denervation

The possible role of endogenous cholinergic innervation in hippocampal plasticity is controversial. We studied the role of acetylcholine (ACh) in short- and long-term potentiation (STP and LTP), using the cholinergic neurotoxin 192 IgG-saporin. It was still possible to induce STP the LTP in the CA1 field following complete and selective cholinergic denervation of the hippocampus. This study therefore demonstrates that integrity of the endogenous cholinergic system is not necessary for the induction or maintenance of LTP in the CA1 field of the hippocampus. The consequences in terms of relationship between hippocampal cholinergic system, LTP and memory are discussed.

Correlations between water maze performance and cortical somatostatin mRNA and high-affinity binding sites during ageing in rats

Somatostatin levels and high-affinity (somatostatin-1) binding sites are decreased in post-mortem cortical samples of Alzheimer's disease patients but the relationships between such modifications and the cognitive deficits remain to be established. We investigated these relationships in the ageing rat. Three age groups (3-4, 14-15 and 26-27 months) were tested in a modified version of the Morris water maze. Somatostatin mRNA levels were quantified by in situ hybridization and somatostatin binding sites by radioautography using the selective agonist octreotide (SMS 201995) as a competing drug to evaluate high-affinity (somatostatin-1) and low-affinity (somatostatin-2) binding sites. The number of somatostatin mRNA-containing cells was not modified with age or memory performance in cortical, hippocampal and hypothalamic regions, but somatostatin mRNA densities were significantly decreased with age and with memory performance in the frontal and parietal cortex. In the frontal cortex somatostatin mRNA densities were already decreased in 14- to 15-month-old rats, whereas the decrease was observed only in 26- to 27-month-old rats in the parietal cortex. A decrease in somatostatin-1 binding was observed with memory performance, independently of age, in the basolateral amygdala only, while somatostatin-2 binding sites were not affected. In the frontal and parietal cortex, a significant correlation occurred between the latency to find the invisible platform in the water maze and somatostatin mRNA (r = -0.54 and 0.59 respectively, P < 0.02). These results indicate that ageing rats with memory impairments display some of the features of the somatostatinergic deficits observed in Alzheimer's disease.

Direct intracerebral nerve growth factor gene transfer using a recombinant adenovirus: effect on basal forebrain cholinergic neurons during aging

Gene therapy in the nervous system offers an attractive strategy for the administration of therapeutic factors in a potentially region-specific, sustained, and well-tolerated manner. We tested the trophic effect of a recombinant adenovirus encoding nerve growth factor (AdNGF) in vivo on basal forebrain cholinergic neurons of aged rats, a neuronal population affected during normal and pathological aging. Three weeks after unilateral injection of the recombinant adenovirus into the nucleus basalis magnocellularis, a significant increase in the somal areas of cholinergic neurons ipsilateral to the injection was observed. No increase was detected in animals receiving a recombinant adenovirus carrying the Escherichia coli Lac Z reporter gene. Injected animals did not lose weight, an adverse effect usually described after intracerebroventricular infusion of NGF, and no tissue loss or massive local inflammatory response was observed around injection sites. Thus, a single intracerebral injection of AdNGF produces trophic effects similar to those resulting from chronic intracerebroventricular high levels of NGF. These findings indicate that recombinant adenoviruses encoding growth factors are potentially powerful tools for improving neuronal deficits associated with degenerative processes.

Calretinin-containing pathways in the rat forebrain

The anatomy of pathways containing the calcium binding protein calretinin was investigated in the forebrain of the rat, using a combination of immunohistochemical and retrograde tract tracing techniques. Numerous well identified pathways do contain calretinin, whereas others do not. Pathways arising from the substantia nigra/ventral tegmental area, the dorsal raphe, the lateral mammillary nucleus, the supramammillary nucleus, the triangular septal and septo-fimbrial nuclei, several thalamic nuclei, the parabrachial nucleus, the peripeduncular nucleus, the medial amygdala contain at least some calretinin. The proportion of projection neurons containing calretinin ranged from 2% (dorsal raphe to caudate) to about 75% (triangular septal nucleus to habenula, medial amygdala to the ventromedial hypothalamus). More than 50% of the nigro-striatal neurons contain calretinin immunoreactivity. In contrast, other pathways do not contain any calretinin immunoreactivity (for instance the pathways arising from cerebral cortex, locus coeruleus, cholinergic forebrain nuclei), although calretinin may be present in local neurons in these structures. The present study demonstrates that calretinin is not associated specifically with projection neurons or local neurons, identified transmitter systems or functionally related pathways in the forebrain of the rat.

Metabolic response to tacrine (THA) and physostigmine in the aged rat brain

The effects of the centrally acting anti-cholinesterases tacrine (tetrahydroaminoacridine, THA) and physostigmine (PHY), on local cerebral glucose utilization (LCGU) have been studied in 27-month-old rats, using the autoradiographic [14C]deoxyglucose technique. THA (10 mg/kg i.p.) increased LCGU significantly in 13 of the 54 regions studied (24%) including insular, parietal, temporal, and retrosplenial cortices, septohippocampal system, thalamus, lateral habenula, and superior colliculus. In these regions, the average THA-induced increase in LCGU was 24% above control. The whole brain mean LCGU was not significantly increased. PHY (0.5 mg/kg) increased LCGU in 18% of the regions (average elevation, 23%). The whole brain mean LCGU increased by 7% (p < 0.05). The regional distributions of THA- and PHY-induced increases in LCGU were extremely similar and overlapped the distribution of the M2 muscarinic receptors and that of acetylcholinesterase activity, suggesting that the major effects of THA and PHY on LCGU result from their anticholinesterase action. As compared to those of 3-month-old rats, both the number of regions affected and the amplitude of the metabolic activation were significantly less in aged rats. However, the drugs were still active in old rats and compensated for the age-related hypometabolism in some brain areas.

Decreased monosynaptic GABAB-mediated inhibitory postsynaptic potentials in hippocampal CA1 pyramidal cells in the aged rat: pharmacological characterization and possible mechanisms

1. gamma-Aminobutyric acid (GABA)-mediated inhibitory postsynaptic potentials (IPSPs) were compared in young and aged rats in CA1 area of the rat hippocampus, with the use of the in vitro intracellular recording technique. D-2-Amino-5-phosphonovaleric acid (APV) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were used to suppress synaptic potentials mediated by the excitatory amino acids. 2. Under these conditions, stimulation of the stratum radiatum elicited a monosynaptic fast GABAA (fIPSP) and a slow GABAB (sIPSP)-mediated IPSP. The fIPSP and the sIPSP were further isolated in the presence of the GABAB antagonist CGP 35348 or the GABAA antagonists bicuculline or picrotoxin. No age-related changes were observed in the amplitude and the duration of the fIPSP. In contrast, the amplitude (but not the duration) of the sIPSP was significantly reduced in the aged rat. 3. The postsynaptic hyperpolarization and increase in membrane conductance induced in pyramidal cells by bath application of the GABAB agonist baclofen were comparable in both groups of animals, indicating that the postsynaptic GABAB receptors are not altered in the aged rats. 4. Paired-pulse depression of IPSPs was used in young and aged rats to study possible alterations in GABA release or in presynaptic GABAB receptors that control GABA release. When fIPSPs were isolated by bath application of tetrahydro-9-aminoacridine (THA), no significant difference in the magnitude of the paired-pulse depression was observed between young and aged rats. A similar result was found with the paired-pulse depression of isolated sIPSPs in the presence of bicuculline or picrotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in parvalbumin- and GABA-immunoreactive cells in the rat septum

The calcium binding protein parvalbumin is present in GABAergic neurons of the medial septum-diagonal band of Broca (MS-DBB) region that project to the hippocampal formation. We examined the distribution pattern, the number, and the morphological features of the parvalbumin-containing cells (parv+) in the MS-DBB region of 2- to 3-, 8- to 9-, 15- to 16-, and 26- to 27-month-old Sprague-Dawley rats. A significant reduction in the number of parv+ cells was observed as a function of age. The mean somal area of the parv+ cells was significantly reduced in the 26- to 27-month-old rats. A significant reduction in the number of parv+ cells was also observed in the 26- to 27-month-old rats in the cingulate cortex, but not in the striatum or the hippocampal formation. No significant age-related changes were observed in the number of the GABA-immunoreactive cells in the MS-DBB region nor in the cingulate cortex. In conclusion, there is an age-related decrease in the number of parv+ cells, with no change in the number of GABA-immunoreactive cells in the MS-DBB region of the rat. Because GABA and parvalbumin are colocalized in the MS-DBB neurons, the results suggest that the level of parvalbumin is decreased, but that the cells are not lost.

Loss of calbindin-immunoreactivity in CA1 hippocampal stratum radiatum and stratum lacunosum-moleculare interneurons in the aged rat

Alterations in hippocampal circuitry may underly age-related learning and memory impairment. We showed in a previous study that the GABAB-mediated slow inhibitory postsynaptic potential (IPSP) induced in CA1 pyramidal neurons by electrical stimulation of stratum radiatum, is depressed in the hippocampus of the aged rat. This could be due to alterations in GABAergic interneuron functions. We report in this study that the number of hippocampal calbindin-immunoreactive (CaBP-IR) GABAergic interneurons is decreased in the aged rat. The mean number of CaBP-IR interneurons per slice decreases by 50% in the aged rat. The most severe loss was observed in the stratum radiatum of CA1 (78%), with a less consistent loss of immunoreactivity in CA3 (35%). In contrast, the mean number of interneurons containing parvalbumin (PV), was not significantly decreased in the aged rat. Our results show a loss of CaBP immunoreactivity in a population of GABAergic interneurons, which might be related to an altered function of these interneurons and consequently of GABAergic synaptic transmission in the aged rat. In contrast, PV immunoreactivity in interneurons located close to the pyramidal layer does not decrease in the hippocampus of the aged rat.

Cholinergic denervation of the rat hippocampus by 192-IgG-saporin: electrophysiological evidence

The consequences of intracerebroventricular injection of the toxin 192-IgG-saporin on the electrophysiological properties of CA1 pyramidal cells were investigated using intracellular recordings in the in vitro hippocampal slice preparation. We present the first electrophysiological evidence of a dysfunction of hippocampal cholinergic afferents following injection of 192-IgG-saporin. The synaptic events mediated by acetylcholine were altered in such animals: the slow cholinergic excitatory postsynaptic potentials as well as the cholinergic activation of GABAergic interneurones were dramatically depressed or even absent; the amplitude and duration of the afterhyperpolarization following a burst of spikes were increased, while other neuronal properties were not modified. These specific alterations suggest that the toxin 192-IgG-saporin is a specific tool for the experimental study of cholinergic denervation in the hippocampus.

The age-related increase in galanin binding sites in the rat brain correlates with behavioral impairment

The regional distribution of [125I]galanin specific binding sites was determined in young (three- to four-month-old), 14-15-month-old and aged (26-27-month-old) male Sprague-Dawley rats, previously tested for their performances in the Morris water-maze task, using the radioautographic method on brain sections. A significant increase in specific binding was observed in piriform and entorhinal cortex, ventral subiculum, and dorsal dentate gyrus in the aged rats, whereas no significant changes were observed in dorsal subiculum, amygdala, septal area and various subcortical structures. The area-specific regional increase in specific binding density in aged rats was significantly correlated with the impairment of the behavioral performance in the Morris water-maze task. The change in [125I]galanin specific binding was a result of an increase in the number of galanin binding sites, but not of an increase in affinity.

Alzheimer's disease: a review of recent findings

The recent development of biological research on dementias of the Alzheimer's type has lead to a better understanding of their pathophysiology. We know the nature of the proteins present in senile plaques and in the neurofibrillary degeneration. Pathophysiological hypotheses are more precise, and clearly involve genetic factors. The rapid progress in this field raises the hope that more efficient treatments will appear in the near future.

Age-related increase in galanin-binding sites in the rat brain: correlation with behavioral impairment

The regional distribution of 125I-galanin specific binding sites was determined by radioautography on brain sections in young (3- to 4-month-old) and aged (26- to 27-month-old) male Sprague-Dawley rats, previously tested for their performances in the Morris water maze task. In aged rats, a significant increase in specific binding was observed in piriform, perirhinal and entorhinal cortex, the CA1 field of the ventral hippocampus, ventral subiculum, and dorsal dentate gyrus, whereas no significant change was observed in the ventral dentate gyrus, the dorsal subiculum, the CA3 field of the hippocampus, the amygdala or the septal area. The area-specific regional increase in specific binding density in aged rats was significantly correlated with the impairment of their behavioral performances in the Morris water maze task. The change in 125I-galanin specific binding in the aged rats was a result of an increase in the number of galanin-binding sites, without change in affinity.

Cholinergic and non-cholinergic synaptic mechanisms in the aged rat hippocampus

We compared age-related alterations in the electrophysiological and pharmacological properties of CA1 hippocampal pyramidal neurons in three strains of rats (Sprague-Dawley, Fisher 344 and Wistar) at 3-4 and 25-32 months of age, using the in vitro slice preparation. The most consistent age-related alterations were: a decrease in membrane excitability, a decrease in the amplitude and duration of inhibitory postsynaptic potentials and a decreased sensitivity to the effect of the cholinergic agonist carbachol. In contrast, no consistent alterations in calcium-dependent events were observed in these strains of rats. The age-related changes in the duration of the after-hyperpolarization (AHP) were different (and even opposite) depending on the strain studied. Our results show that age-related changes observed in a given strain are not necessarily present in all strains of the same species.

Tetrahydroaminoacridine and physostigmine increase cerebral glucose utilization in specific cortical and subcortical regions in the rat

The effects of the anticholinesterases tetrahydroaminoacridine (THA) and physostigmine on local cerebral glucose utilization (LCGU) were studied in the conscious rat, using the autoradiographic [14C]deoxyglucose technique. THA (5 mg/kg i.p.) increased LCGU significantly in 8 of the 43 regions studied. A higher dose of THA (10 mg/kg) produced a metabolic activation in 19 of the 43 regions. LCGU increased in cortical areas (including parietal and temporal cortices), the septohippocampal system, the thalamus, the lateral habenula, the basolateral amygdala, the superior colliculus, and the substantia nigra. Scopolamine (4 mg/kg i.p.) reversed the THA-induced LCGU increase. Physostigmine (0.2 and 0.5 mg/kg) increased LCGU in 15 and 22 regions, respectively. The average magnitude of the change induced by 0.5 mg/kg of physostigmine was similar to that observed after THA at 10 mg/kg, but the topography of the effects was somewhat different. Physostigmine increased LCGU in the preoptic magnocellular area, the brainstem, and the cerebellum but not in the parietal cortex. The effects in the septohippocampal system were smaller than those induced by THA. The regional topography of the LCGU increase overlapped the distribution of the M2 muscarinic receptors and that of acetylcholinesterase activity. These data suggest that the major effects of THA and physostigmine on LCGU result from their anticholinesterase action.

Different effects of omega-conotoxin GVIA at excitatory and inhibitory synapses in rat CA1 hippocampal neurons

The nature of the coupling mechanism of presynaptic calcium channels involved in the release of neurotransmitters in the mammalian central nervous system is unknown. Using intracellular recordings from CA1 neurons in the rat hippocampal slice preparation, we show that the N-type calcium channels antagonist omega-conotoxin GVIA (omega-CgTx) blocks partially the excitatory (EPSP) and totally the inhibitory (IPSP) synaptic transmission in CA1 hippocampal pyramidal neurons. In addition, the inhibitory effect of omega-CgTx on IPSPs is strongly depressed by intrahippocampal injection of PTX, while the effect on EPSP is not. The results suggest that the nature or the regulation of calcium channels might be different, depending on the location of these channels on excitatory or inhibitory terminals.

Sustained cortical metabolic responsivity to physostigmine after nucleus basalis magnocellularis ablation in rats

Unilateral nucleus basalis magnocellularis (NBM) ablation, which causes partial cholinergic denervation of the ipsilateral anterior neocortex, results in an acute but transient depression of regional cerebral metabolic rates for glucose (rCMRglc) in deafferented areas; rCMRglc normalizes within 2 weeks. To seek possible compensatory changes in cholinergic mechanisms following NBM ablation that could lead to rapid metabolic normalization, we studied rCMRglc responses to the receptor agonists nicotine and arecoline and the cholinesterase inhibitor physostigmine in rats at 2 weeks after unilateral NBM destruction. Physostigmine increased rCMRglc in 10 of 30 cortical areas contralateral to the NBM lesion. Compared to the unlesioned side, rCMRglc after physostigmine in the lesioned cortex was significantly lower in 2, significantly higher in 1 and not different (P < 0.05) in 27 areas. Neither arecoline nor nicotine treatment produced rCMRglc asymmetry in lesioned rats. These results demonstrate that responsivity to physostigmine is maintained in most regions of the rat neocortex after extrinsic cholinergic denervation by NBM ablation. This adaptive response appears not to result from cholinergic receptor upregulation and may reflect instead reorganization of cholinergic synapses.

Age-related alterations in the properties of hippocampal pyramidal neurons among rat strains

We compared age-related alterations in the electrophysiological and pharmacological properties of CA1 hippocampal pyramidal neurons in three strains of rats (Sprague-Dawley, Fisher 344, and Wistar) at 3-4 and 25-32 months of age, using the in vitro slice preparation. The most consistent age-related alterations in the properties of rat hippocampal neurons were: a decrease in membrane excitability, a decrease in the amplitude and duration of inhibitory postsynaptic potentials and a decreased sensitivity to the effect of the cholinergic agonist carbachol. In contrast, no consistent alterations in calcium-dependent events were observed in these strains of rats. The age-related changes in the duration of the afterhyperpolarizations (AHPs) were different (and even opposite) depending on the strain studied. Our results show that age-related changes observed in a given strain are not necessarily present in all strains of the same species.

Alterations in the properties of hippocampal pyramidal neurons in the aged rat

The electrophysiological and pharmacological properties of CA1 hippocampal pyramidal neurons were studied in slices from young (three to four months) and aged (25-32 months) Sprague-Dawley rats having previously performed two behavioral tasks. About 20% of the aged rats were impaired in either the spontaneous alternation task or the water maze task. Electrophysiological parameters were measured and compared in young and aged animals using intracellular recordings. No age-related differences were observed in membrane potential, input resistance, amplitude of action potentials or amplitude of calcium spikes. The amplitude and duration of individual afterhyperpolarizations following a single spike were unchanged. In contrast, the neuronal excitability was significantly decreased and the spike duration significantly enhanced in aged rats as compared to young rats. The comparison of afterhyperpolarizations (which follow a burst of spikes) between young and aged rats was more complex. An increase in the amplitude and duration of afterhyperpolarizations generally occurred in aged animals. However, this increase was not consistent among animals and was dependent on the holding potential of the neuron and on the number of action potentials used to trigger the afterhyperpolarization. The depolarizing effect of bath-applied carbachol, as well as the associated increase in membrane resistance were reduced in neurons from aged rats. In contrast, the effects of carbachol on the depression of synaptic events and the blockade of the afterhyperpolarizations were similar in young and aged animals. In addition, the amplitude of the slow cholinergic excitatory postsynaptic potential induced by stimulation of cholinergic afferents in the presence of physostigmine was also decreased in aged rats. Excitatory postsynaptic potentials and inhibitory postsynaptic potentials following electrical stimulation of stratum radiatum were compared. The amplitude and duration of excitatory postsynaptic potentials were increased in aged rats. The amplitude and duration of the fast inhibitory postsynaptic potential were not significantly affected in aged animals. In contrast, the duration of the slow inhibitory postsynaptic potential was decreased in aged rats. Since the mean baclofen-induced hyperpolarization was only slightly reduced in aged rats, the most likely explanation is a decrease in the release of GABA rather than an alteration in the postsynaptic response mediated by GABAB receptors. A statistically significant correlation was found between the degree of impairment in the spontaneous alternation task and the amplitude of the carbachol-induced depolarization.

Arousal-dependent properties of medial septal neurons in the unanesthetized rat

We have performed a qualitative and quantitative analysis of the electrophysiological properties of medial septal neurons in the unanesthetized rat. The rat's head was held in a stereotaxic apparatus by a painless head-restrained system that was implanted seven days prior to the recording sessions. Extracellular recordings were made in a mixed population of antidromically identified septohippocampal neurons and unidentified medial septal neurons in different states of arousal and in response to peripheral and reticular stimulations. The spontaneous activity as well as the percentage of rhythmically bursting septal neurons varied significantly according to the state of arousal. Higher values were noted in paradoxical sleep (28 imp/s and 94% of bursting neurons) as compared with wakefulness with hippocampal theta rhythm (17.4 imp/s and 64.2% of bursting neurons) and slow wave sleep (12.3 imp/s and 8% of bursting neurons). The frequency of the bursts was significantly higher during paradoxical sleep. In individual medial septal neurons, arousing stimuli and paradoxical sleep could induce rhythmic bursting activity in previously non-bursting neurons provided that they were fast-firing neurons. No differences were noted in the functional characteristics of neurons in the medial septal nucleus as compared with the diagonal band of Broca. When the unanesthetized rats were compared with a group of urethane-anesthetized rats, the spontaneous activity was higher and more irregular in the absence of anesthesia. The percentage of the bursting neurons was significantly lower in the unanesthetized rats (32.3% vs 43.3%). However, the frequency of the bursts was higher (5.9 +/- 0.1 Hz vs 3.5 +/- 0.1 Hz). Since the patterns of activity of medial septal neurons fluctuate in different physiologically relevant states, previous classifications of these neurons made by ourselves and other authors, in urethane-anesthetized rats, may not be appropriate.

[Physiopathology of dementia of the Alzheimer type: role of the amyloid beta-protein]

Biological research on Alzheimer's disease is expanding quickly, and the mechanisms of the disease are better understood today. Progress has been specially impressive in the knowledge of the brain lesions (senile plaques, neurofibrillary degeneration). It is likely that the beta-amyloid protein, which accumulates in the senile plaques plays a major role in the development of the brain lesions and, subsequently of the clinical symptoms. The metabolism of the precursor of this protein might be abnormal, leading to the beta-amyloid protein deposits. Some discrete genetic abnormalities (such as punctate mutations on the beta amyloid precursor gene) have been described recently in familial cases of the disease. It seems unlikely that such punctate mutations would be responsible for the majority of the cases. Therefore it is possible that Alzheimer's disease has multiple causes, the genetic factors being only one of them.

Age-related changes in galanin-immunoreactive cells of the rat medial septal area

Age-related changes in the cholinergic cells have been reported in the rat medial septal area. The neuropeptide galanin is colocalized with acetylcholine in the majority of the medial septal neurons. To assess possible age-related changes in the galanin-containing septal cells, we have examined, with immunohistochemical methods, the distribution pattern, density, and morphological features of galanin-containing cells in the rat medial septal nucleus (MS) and the nucleus of the diagonal band of Broca (DBB) in 1, 3-6, 9-12, 16-18, 24-27, and 28-30 month-old rats. A morphometric computerized analysis was also performed. In addition, the intensity of the immunolabelling was measured by densitometry. Galanin-like immunoreactivity (galanin-LI) was present in both the MS and the DBB. Our results clearly indicate a progressive age-related decrease in the number of galanin-positive cells throughout the MS-DBB complex. Our quantitative study revealed a significant loss of galanin-positive cells in the MS-DBB complex of 16-18 (50.4%), 24-27 (52.3%), and 28-30 (52.4%) month-old rats compared to 3-6 month-old animals. A non-significant reduction (28.6%) in galanin-LI cell number was observed in 3-6 month-old rats compared to 1 month-old animals. The morphometric analysis demonstrated a significant reduction (18%) in the surface of galanin-positive cells remaining in the 28-30 month-old group. Furthermore, a significant decrease in the immunolabelling intensity was consistently observed in animals of 16 month-old and older. To determine whether changes in galanin-positive cells were associated with cholinergic changes, the number of cells stained for acetylcholinesterase (AChE) was estimated in 3-6, 9-12, 16-18, and 24-27 month-old rats. There was a 43% decrease in the number of AChE-positive cells and a 71% loss of galanin-positive cells in 24-27 month-old rats compared to 3-6 month-old. The galanin-cell loss in the medial septal area was therefore associated with a parallel, although smaller, cholinergic septal cell loss.

Comparative study of the effects of tianeptine and other antidepressants on the activity of medial septal neurons in rats anesthetized with urethane

Tianeptine is a tricyclic antidepressant which enhances serotonin uptake in certain brain areas. Tianeptine has been reported to improve both working and reference memories in rodents. The effects of tianeptine on the spontaneous activity of medial septal neurons were studied in rats anesthetized with urethane. Systemic administrations (0.2-1 mg/kg i.v.) of tianeptine decreased the spontaneous activity and disorganized or suppressed the rhythmically bursting activity of medial septal neurons, in a dose related manner. Iontophoretic administrations of tianeptine did not modify the spontaneous activity of medial septal neurons. Changes of the bursting activity were inconsistent. However, tianeptine blocked partially or completely the inhibition induced by the serotonin in 68% of the cases. In contrast, other antidepressants (amitriptyline, clomipramine and fluoxetine) potentiated the inhibitory effect of serotonin in 50%-60% of the cases. Our results show that tianeptine, applied by iontophoresis, has an effect on the medial septal neurons which was opposite to that of other antidepressants. On the basis of our findings, it can be tentatively proposed that tianeptine may have a beneficial effect on memory by counteracting the serotonin-induced inhibition of medial septal neurons.

In vivo brain incorporation of [1-14C]arachidonate in awake rats, with or without cholinergic stimulation, following unilateral lesioning of nucleus basalis magnocellularis

Regional brain incorporation of a radiolabeled unsaturated fatty acid, [1-14C]arachidonic acid (14C-AA), was measured in awake rats following unilateral lesioning of the nucleus basalis magnocellularis (NBM). Right-sided lesions were produced in 3-month-old, male rats by stereotaxic injection of 10 micrograms ibotenic acid. Two weeks after lesioning, rats were subjected to one of two protocols: (1) 5 min intravenous infusion of 14C-AA (170 microCi/kg); or (2) i.p. injection of arecoline (5 mg/kg), a cholinergic agonist, followed by 5 min intravenous infusion of 14C-AA. All animals were killed 15 min postinfusion. Brains were frozen and sectioned for quantitative autoradiography or were stained for acetylcholinesterase (AChE). Animals with unilateral NBM lesions displayed reduced AChE staining in prefrontal, frontal and parietal cortices of the lesioned side, but there was no right-left difference in incorporation of 14C-AA without cholinergic stimulation. Arecoline administration increased 14C-AA incorporation into the prefrontal and frontal cortices ipsilateral to the NBM lesion as compared to the contralateral side and the increase was most prominent in deeper cortical layers such as layers IV and V. Right-left differences in incorporation were not apparent in parietal, temporal, or occipital cortices, where reduction of AChE activity was minimal or absent, nor in subcortical structures. The results suggest that the intravenous 14C-AA technique combined with cholinergic stimulation can be used to detect compensatory regulation of phospholipid-coupled signal transduction caused by a deficit in cholinergic input into the cerebral cortex.

Senile dementia of the Alzheimer type: is there a correlation between entorhinal cortex and dentate gyrus lesions?

Senile plaques (SP) are one of the neuropathological hallmarks of senile dementia of the Alzheimer type (SDAT). In 14 patients affected with SDAT (over 74 years of age), thioflavine S, Tau and acetylcholinesterase (AChE) stainings demonstrated an increased density of SP in the outer two thirds of the dentate gyrus molecular layer. However, a wide range of SP density was observed among the cases. The molecular layer of the dentate gyrus is one of the termination site of the perforant pathway that originates in layers II and III of the entorhinal cortex. We have found that the number of AChE-, thioflavine S- and Tau-positive SP that accumulate in the dentate gyrus is positively correlated with the density of thioflavine S-stained neurofibrillary tangles in layers II and III of the entorhinal cortex. In contrast, a similar correlation is not found when using Tau immunolabeling of the entorhinal tangles. These observations show an association between the accumulation of AChE-positive SP in the dentate molecular layer and the lesions of the perforant pathway. Furthermore, they suggest that the density of SP in the dentate gyrus correlates with the late stages of neurofibrillary tangles formation (thioflavine S positive), but not with the early stages (Tau positive).

Iontophoretic study of medial septal neurons in the unanesthetized rat

The effects of the iontophoretic applications of glutamate (Glu), gamma-aminobutyric acid (GABA), acetylcholine (ACh) and carbachol (CARB) were studied on neurons located in the medium septal area (MSA) in the unanesthetized rat. In the absence of anesthesia, functional properties of the MSA neurons were significantly different from those observed in the urethane-anesthetized rat (higher variability of discharge rate, lower percentage of rhythmically bursting neurons). Glu excited 80% and GABA inhibited 96% of the MSA neurons. These percentages were similar to those obtained in the urethane-anesthetized rats. In contrast, the percentage of neurons excited by ACh (28%) or by CARB (27.2%) were significantly lower than in the urethane-anesthetized rat. Our results suggest that urethane might alter cholinergic sensitivity in the MSA and confirm that anesthesia can induce a bias in the iontophoretic study of some brain structures.

Effects of calcium channel agonist and antagonists on calcium-dependent events in CA1 hippocampal neurons

The effects of a variety of calcium channel modulators on different calcium-dependent events in CA1 pyramidal hippocampal neurons were analysed using intracellular recordings in an in vitro slice preparation. The following substances were tested: the dihydropyridine calcium agonist BAY K 8644, the dihydropyridine calcium antagonist nimodipine, the phenylalkylamine verapamil and the snail toxin omega-conotoxin GVIA (omega-CgTx). BAY K 8644 increased the repolarization time of the after hyperpolarization (AHP) following a spike burst. This effect was antagonized by nimodipine. BAY K 8644 also prolonged the calcium spike and, in some cases, increased the size of the synaptic events resulting from activation of the Schaffer collateral/commissural system. Nimodipine decreased the size of the AHP in some neurons but had no consistent effect on synaptic events. Verapamil at low concentrations (1-10 microM) had no significant effects on the calcium-dependent events in the hippocampus. Increasing the concentration (up to 100 microM) led to a progressive suppression of the AHP and of the slow inhibitory postsynaptic potential (IPSP), probably via an action on potassium conductances. In addition, the baclofen-induced hyperpolarization was blocked by verapamil. Interestingly, at this higher concentration, verapamil could suppress the AHP without depressing the calcium spike. omega-CgTx selectively blocked the synaptic events (especially the IPSPs) but had no effect on non-synaptic events. This last compound exhibits a high degree of selectivity, acting on N-type calcium channels which are involved in neurotransmitter release. Our results provide evidence that different classes of agents which act on calcium channels can be used to discriminate between different calcium-dependent responses in CA1 hippocampal neurons.

Effect of aging on dopamine metabolism in the rat cerebral cortex: a regional analysis

Age-related changes in the levels of dopamine (DA) and its metabolites were measured in seven cerebral cortical areas and in the striatum of 3, 10 and 27 month-old Sprague-Dawley rats. An age-related increase in DA levels was observed in the somatomotor (SM) cortex. In contrast, a decrease was observed in the temporal (T) cortex. Decreases in homovanillic acid (HVA) levels were observed in prelimbic (PL), pyriform (PY) and T cortex of aged rats, whereas significant increases in the levels of 3-methoxytyramine (3-MT) were observed in PL, prefrontal (PF), cingulate (C) as well as in T cortex. In the striatum, DA and HVA were decreased but the level of 3-MT remained unchanged. Norepinephrine (NE) levels increased in rats from 3 to 27 months in all the cortical areas. The increase in the levels of the DA extraneuronal metabolite, 3-MT, confirms our previous results showing that the release of DA might be increased with age in some cortical areas. The present results show that there is no general age-related decrease in the level of monoamines and of their metabolites in the rat cerebral cortex and that the changes display a complex, area-specific pattern.

[Neuropathologic validation of clinical diagnosis of senile dementia of the Alzheimer type]

The purpose of this work was to establish a neuropathological confirmation of the clinical diagnosis of senile dementia of the Alzheimer type (SDAT) in a group of patients prospectively studied in a geriatric hospital since 1984 (Charles Richet Study). The sample consisted of 45 cases, 35 of which had received a clinical diagnosis of SDAT and 10 others a diagnosis of either vascular or mixed dementia. The mean age at death was 85 +/- 6.9 years (range 64-97). The neuropathological diagnosis was established independently of the clinical findings. Senile lesions typical of SDAT were found in 32/35 cases, giving a 91.4% rate of clinico-pathologic agreement. However, vascular lesions were present in 10 cases (28.5%) and the final pathologic diagnosis was mixed dementia, lowering the score of agreement for SDAT to 63%. Considering that the pathological criteria for the diagnosis of SDAT are not uniform, we independently applied 3 inclusion (senile lesions) and 3 exclusion (vascular lesions) criteria for the diagnosis of SDAT to each of the 45 cases. This permitted a comparison of nine combinations of neuropathological criteria with the clinical diagnosis. The sensitivity values ranged from 37 to 80% and the specificity values ranged from 55 to 100%. The highest agreement rate with the clinical diagnosis was achieved when were associated the criterion which specified that plaques and tangles must be present in the hippocampus regardless of neocortical findings and the criterion which excluded cases with vascular lesions of any site if their volume was 50 ml or more.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of tetrahydro-9-aminoacridine on cortical and hippocampal neurons in the rat: an in vivo and in vitro study

The effects of tetrahydro-9-aminoacridine (THA), an anticholinesterase drug, have been studied in the rat both in vivo (cerebral cortex) and in vitro (CA1 field of the hippocampus) and compared with those of physostigmine. In the cerebral cortex THA potentiated the excitatory effect of acetylcholine in most neurons, including cortical neurons recorded from chronic unanesthetized animals. In vitro, THA (but not physostigmine) had a depolarizing, atropine- and tetrodotoxin-insensitive effect. This effect is associated with an increase in membrane resistance which suggests a direct effect of THA on hippocampal neurons. In addition THA blocked the slow inhibitory postsynaptic potential. At the same concentration THA potentiated the slow cholinergic excitatory postsynaptic potential produced by electrical stimulation of the cholinergic afferents. Its potency was, however, about 10 times lower than that of physostigmine. These results show that THA: (1) is an anticholinesterase much less potent than physostigmine; but (2) has also direct effects on central neurons, not observed with physostigmine and unrelated to its anticholinesterase activity.

Medial septal neurons containing N-acetyl-aspartyl-glutamate-like immunoreactivity project to the hippocampal formation in the rat

We have examined the distribution of N-acetyl-aspartyl-glutamate (NAAG)-like immunoreactive cell bodies in the medial septal nucleus and the nucleus of the diagonal band of Broca of the rat and assessed the involvement of these cells in the septo-hippocampal pathway. A series of experiments was carried out using immunohistochemistry alone or combined with the retrograde transport of a protein-gold complex injected into the dorsal hippocampal formation. A large number of NAAG-positive cells was observed in the medial septum and the diagonal band. Quantitative analysis revealed that 26% of the NAAG-like immunoreactive cells in the medial septum project to the dorsal hippocampal formation. These results demonstrate that the dipeptide NAAG is a major component of the rat septo-hippocampal pathway.

Regional distribution of 3-O-methyl-DOPA in the cortex and subcortical structures in the rat: effect of aging

Dihydroxyphenylalanine (DOPA) and its metabolite 3-O-methyl-DOPA (3-OMDOPA) have been identified as normal constituents in blood, CSF and brain in human and several animal species. In the present study, we report results of 3-OMDOPA measurements in seven cortical areas, hippocampus and striatum of young (3-month-old), middle aged (10-month-old) and aged (27-month-old) rats. 3-OMDOPA was identified in all the areas considered. Regional differences were observed, with the highest levels being found in the hippocampus and the somatomotor and pyriform cortex. A marked increase in the level of 3-OMDOPA was observed in all the cortical areas and in the hippocampus of aged rats. In contrast, this level remained unchanged in the striatum. These modifications were compared to those observed in the levels of dopamine (DA) in the same areas.

Effects of acetylcholine on single cortical somatosensory neurons in the unanesthetized rat

Experiments have been performed on unanesthetized rats using a chronic restraint system. The animal's head was held in a stereotaxic apparatus by means of two metallic tubes fixed on the skull with dental cement. Electrodes consisted of a recording micropipette (filled with 1 M NaCl and 2% Pontamine Blue) attached to a multibarreled micropipette for iontophoresis. Electrode penetrations were reconstructed on camera lucida drawings of frontal brain sections. The overall percentage of spontaneously active somatosensory neurons was 77% with a mean spontaneous activity of 5.9 impulse/s (n = 405). Yet differences were observed in the proportions of active cells as well as in the mean spontaneous activity between cortical layers (both parameters being significantly higher in layers V and VI). Comparison with results obtained under urethane anesthesia [Dykes R. W. and Lamour Y. (1988) J. Neurophysiol. 60, 703-724] shows that the percentage of the spontaneously active neurons and the mean spontaneous activity were both significantly higher in unanesthetized rats (77 vs 36%; 5.9 vs 2.6 impulse/s). Nevertheless, the laminar distribution of the most active cells was similar under both conditions. In the present study, 52.3% of the neurons (n = 380) were excited by acetylcholine and 46% (n = 198) by carbachol. Significantly larger percentages of neurons excited by acetylcholine were found in layers Vb and VIb. These effects of cholinergic agonists--observed for the first time in unanesthetized rats--differed significantly from those previously obtained under anesthesia (33 and 34% of neurons excited by acetylcholine and carbachol, respectively) [Lamour Y. et al. (1982) Neuroscience 7, 1483-1494].(ABSTRACT TRUNCATED AT 250 WORDS)

Neuronal localization of the nerve growth factor precursor-like immunoreactivity in the rat brain

The distribution of the nerve growth factor precursor(proNGF)-like immunoreactivity was examined in the adult rat brain with affinity-purified antisera directed against synthetic peptides that reproduce sequences of the precursor protein. Immunoreactivity was localized in defined areas of the neocortex, hippocampal formation, thalamus/hypothalamus, striatum, olfactory bulb, pons and spinal cord, which are regions previously reported to contain NGF mRNA. Interestingly, immunoreactivity was also observed in the septum and diagonal band of Broca known to contain very low NGF mRNA levels. Using immunohistochemical methods combined with the retrograde transport of a protein gold complex we demonstrate that proNGF-like immunoreactivity is localized within neuronal cell bodies, in the cortex, hippocampus and septum. These results suggest that the immunological approach may not only identify NGF-synthesizing cells, but also cells which may accumulate proNGF or some cleavage products by an uptake mechanism.

Effects of iontophoretically applied monoamines on somatosensory cortical neurons of unanesthetized rats

The response of somatosensory cortical neurons to iontophoretic applications of monoamines was studied in unanesthetized rats. The animal's head was held in a stereotaxic apparatus by means of a painless head-restraining system implanted 8 days prior to the recording sessions. The electrodes consisted of a recording micropipette attached to a multibarreled iontophoresis micropipette. The electrode penetrations were reconstructed on camera lucida drawings of frontal brain sections. The percentage of cortical neurons responding to application of monoamines were 76% after noradrenaline, 58% after dopamine and 66% after serotonin. The differences observed among percentages of responses seemingly correlate with the relative abundance of terminal axons and receptors for each of the three monoamines in the somatosensory cortex. The vast majority of the responding neurons were inhibited by monoamines and this inhibitory effect was independent of the level of spontaneous activity. The depressant effect of the monoamines on glutamate and acetylcholine-evoked responses supports a modulatory role for these substances. Serotonin was the most potent, followed by noradrenaline and dopamine. The present study shows that when the influence of anesthesia is eliminated, the predominant effect of monoamines on cortical first somatosensory neurons is one of inhibition. These findings contrast with results obtained under some anesthetic conditions, as well as under in vitro conditions.

Omega-conotoxin GVIA blocks synaptic transmission in the CA1 field of the hippocampus

The effects of omega-conotoxin GVIA (omega-CgTx), a peptide isolated from the venom of a marine mollusc, were studied in rat hippocampal neurons. Intracellular recordings from the CA1 area were made for the purpose in in vitro slice preparations. Omega-CgTx (0.1-1 microM) rapidly and irreversibly blocked the EPSP and the IPSPs elicited by electrical stimulation of Schaffer collaterals/commissural fibers. Omega-CgTx also blocked the slow cholinergic EPSP induced by electrical stimulation of cholinergic afferents. The postsynaptic effects of baclofen or carbachol remained unchanged in the presence of omega-CgTx and other postsynaptic calcium-dependent events such as afterhyperpolarization were not affected by omega-CgTx. These results suggest a presynaptic action of omega-CgTx through the blockade of neurotransmitter release. Omega-CgTx might act in the hippocampus by blocking presynaptic N-type voltage-sensitive calcium channels.

Age-related loss of galanin-immunoreactive cells in the rat septal area

We have examined the distribution of galanin-like immunoreactive (LI) cell bodies in the medial septal nucleus (MS) and the nucleus of the diagonal band of Broca (nDBB) of young (3 months) and aged (25-30 months) rats, and assessed their respective contribution to the septohippocampal pathway. Immunohistochemical techniques were used alone or combined with the retrograde transport of a protein-gold complex injected into the dorsal hippocampus. In both groups, galanin-LI cells were observed in the MS and the nDBB. In aged rats, a significant decrease in both the staining intensity and the number of galanin-LI perikarya throughout the MS-nDBB complex was observed. Some immunoreactive cells appeared shrunken. The reduction in cell number ranged from 30 to 85%. There was also a decrease in the proportion of septohippocampal neurons containing galanin in aged rats (13% vs 20% in young animals) which however did not reach statistical significance. These results suggest that galanin-positive cells in the medial septal area undergo alterations with aging in the rat.

Rhythmical bursting activity and GABAergic mechanisms in the medial septum of normal and pertussis toxin-pretreated rats

The possible involvement of GABA in the control of the rhythmical bursting activity (RBA) of septo-hippocampal neurons (SHNs) has been studied in the rat in vivo. The discharge frequency of SHNs was modified by the iontophoretic application of a GABA agonist and antagonist as well as by the application of the GABA uptake blocker, nipecotic acid. The GABAB agonist baclofen inhibited the SHNs' activity, this effect being antagonized by the GABAB antagonist phaclofen. However, these different pharmacological manipulations did not modify the RBA frequency. Pretreatment of the rats with pertussis toxin, a substance which is known to block the events mediated by G-proteins (Gi or Go), decreased the RBA frequency. Neither agonists nor antagonists of GABAA or GABAB types had significant effects on the rhythmical bursting activity of SHNs. The effect of pertussis toxin suggests that other neurotransmitters or intrinsic mechanisms involving a G-protein influence this rhythm.