Fluctuations in relative levels of choline acetyltransferase mRNA in different regions of the rat basal forebrain across the estrous cycle: effects of estrogen and progesterone

Quantitative in situ hybridization techniques were used to compare relative cellular levels of choline acetyltransferase (ChAT) mRNA in different regions of the female rat basal forebrain at different stages of the estrous cycle and at different time points after the administration of physiological levels of estrogen and progesterone. Significant fluctuations in relative levels of ChAT mRNA were detected during the course of the estrous cycle. In the medial septum (MS) and striatum, the highest levels of ChAT mRNA were detected on diestrus 1. Fluctuations in the nucleus basalis magnocellularis (NBM) were highly variable, with the highest levels detected on diestrus 2. In ovariectomized animals, significant increases in ChAT mRNA were detected in the MS, NBM, and striatum within 1-3 d after a single administration of estradiol. In addition, the effects of estradiol on ChAT mRNA expression in the NBM and striatum were significantly enhanced by the subsequent administration of progesterone. The magnitude and timing of the effects of steroid replacement were consistent with the magnitude and time course of the fluctuations detected during the course of the estrous cycle. These data demonstrate that estrogen and progesterone can increase basal forebrain levels of ChAT mRNA significantly in specific regions of the rat basal forebrain, that the magnitude and time course of the effects vary between different subpopulations of cholinergic neurons, and that the effects are associated with changes in the functioning of specific basal forebrain cholinergic neurons across the estrous cycle.     

Projections of GABAergic and cholinergic basal forebrain and GABAergic preoptic-anterior hypothalamic neurons to the posterior lateral hypothalamus of the rat

Within the basal forebrain, gamma-aminobutyric acid (GABA)-synthesizing neurons are codistributed with acetylcholine-synthesizing neurons (Gritti et al. [1993] J. Comp. Neurol. 329:438-457), which constitute one of the major forebrain sources of subcortical afferents to the cerebral cortex. In the present study, descending projections of the GABAergic and cholinergic neurons were investigated to the lateral posterior hypothalamus (LHp) through which the medial forebrain bundle passes and where another major forebrain source of subcortical afferents is situated. Retrograde transport of cholera toxin b subunit (CT) from the LHp was combined with immunohistochemical staining for glutamic acid decarboxylase (GAD) and choline acetyl transferase (ChAT) using a sequential peroxidase-antiperoxidase (PAP) technique. A relatively large number of GAD+ neurons (estimated at approximately 6,200), which represented > 15% of the total population of GAD+ cells in the basal forebrain (estimated at approximately 39,000), were retrogradely labeled from the LHp. These cells were distributed through the basal forebrain cell groups, where ChAT+ cells are also located, including the medial septum and diagonal band nuclei, the magnocellular preoptic nucleus, and the substantia innominata, with few cells in the globus pallidus. In these same nuclei, a small number of ChAT+ cells were retrogradely labeled (estimated at approximately 800), which represented only a small percentage (< 5%) of the ChAT+ cell population in the basal forebrain (estimated at approximately 18,000). Both the GAD+ and ChAT+ LHp-projecting neurons represented a small subset of their respective populations in the basal forebrain, distinct from the magnocellular, presumed cortically projecting, basal neurons. In addition to the GAD+ cells in the basal forebrain, GAD+ cells in the adjacent preoptic and anterior hypothalamic regions were also retrogradely labeled in significant numbers (estimated at approximately 5,500) and proportion (> 20%) of the total population (estimated at approximately 30,000) from the LHp. The retrogradely labeled GAD+ neurons were distributed in continuity with those in the basal forebrain through the lateral preoptic area, medial preoptic area, bed nucleus of the stria terminals, and anterior and dorsal hypothalamic areas. Of the large number of cells that project to the LHp in the basal forebrain and preoptic-anterior hypothalamic regions (estimated at approximately 66,000), the GAD+ neurons represented a significant proportion (> 15%) and the ChAT+ neurons a very small proportion (approximately 2%). The relative magnitude of the GABAergic projection suggests that it may represent an important inhibitory influence of the descending efferent output from the basal forebrain and preoptic-anterior hypothalamic regions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Heterogeneity and selectivity of the degeneration of cholinergic neurons in the basal forebrain of patients with Alzheimer's disease

Cholinergic neurons were studied by immunohistochemistry, with an antiserum against choline acetyltransferase (ChAT), in the basal forebrain (Ch1 to Ch4) of four patients with Alzheimer's disease (AD) and four control subjects. ChAT-positive cell bodies were mapped and counted in Ch1 (medial septal nucleus), Ch2 (vertical nucleus of the diagonal band), Ch3 (horizontal nucleus of the diagonal band) and Ch4 (nucleus basalis of Meynert). Compared to controls, the number of cholinergic neurons in AD patients was reduced by 50% on average. The interindividual variations in cholinergic cell loss were high, neuronal loss ranging from moderate (27%) to severe (63%). Despite the small number of brains studied, a significant correlation was found between the cholinergic cell loss and the degree of intellectual impairment. To determine the selectivity of cholinergic neuronal loss in the basal forebrain of AD patients, NPY-immunoreactive neurons were also investigated. The number of NPY-positive cell bodies was the same in controls and AD patients. The results (1) confirm cholinergic neuron degeneration in the basal forebrain in AD and the relative sparing of these neurons in some patients, (2) indicate that degeneration of cholinergic neurons in the basal forebrain contributes to intellectual decline, and (3) show that, in AD, such cholinergic cell loss is selective, since NPY-positive neurons are preserved in the basal forebrain.     

Few cholinergic neurons in the rat basal forebrain coexpress galanin messenger RNA

The concept that galanin (GAL) is cosecreted with acetylcholine (ACh) into the ventral hippocampus is a major component of the current model delineating GAL regulation of the cholinergic memory pathways in the rat. Although GAL-immunoreactivity coexists in 50-70% of cholinergic neurons in the basal forebrain (BF) of colchicine-treated rats, the actual coexistence of these neurotransmitters in the basal state may be lower, because colchicine treatment was recently shown to both induce GAL gene expression and inhibit choline acetyltransferase (ChAT) gene expression in this brain region. We have used single and double in situ hybridization histochemistry to examine the distribution and coexistence of GAL and ChAT mRNAs in the BF of male and female rats. Compared with other forebrain regions, few GAL mRNA-expressing neurons are present within the cholinergic fields of the BF. The greatest number of GAL mRNA-expressing cells in this region are located within the nucleus of the horizontal limb of the diagonal band; but, even in this region, they represent only a small percentage (<20%) of ChAT mRNA-expressing cells. Our results indicate that few cholinergic neurons in the rat BF coexpress GAL mRNA and suggest that, in the basal state, GAL is not widely cosecreted with ACh into hippocampal memory centers.     

Evolution of time coding systems

The neurotrophin receptor p75 is a low-affinity receptor that binds neurotrophins. To investigate the role of p75 in the survival and function of central neurons, p75 null-mutant and wild type litter mate mice were tested on behavioral tasks. Null mutants showed significant performance deficits on water maze, inhibitory avoidance, motor activity, and habituation tasks that may be attributed to cognitive dysfunction or may represent a global sensorimotor impairment. The p75 null-mutant and wild type litter mate mice were assessed for central cholinergic deficit by using quantitative stereology to estimate the total neuronal number in basal forebrain and striatum and for subpopulations expressing the high-affinity tyrosine receptor kinase A (trkA) neurotrophin receptor and choline acetyltransferase (ChAT). In the adult brain, cholinergic neurons of the basal forebrain receive target-derived trophic support, whereas cholinergic striatal neurons do not. Adult p75 null-mutant mice had significant reduction of basal forebrain volume by 25% and had a corresponding significant loss of 37% of total basal forebrain neurons. The basal forebrain population of ChAT-positive neurons in p75-deficient mice declined significantly by 27%, whereas the trkA-positive population did not change significantly. There was no significant change in striatal volume or in striatal neuronal number either in total or by cholinergic subpopulation. These results demonstrate vulnerability to the lack of p75 in adult central neurons that are neurotrophin dependent. In addition, the loss of noncholinergic central neurons in mice lacking p75 suggests a role for p75 in cell survival by an as yet undetermined mechanism. Possible direct and indirect effects of p75 loss on neuronal survival are discussed.     

Protein kinase C isotypes theta, delta and eta in human lymphocytes: differential responses to signalling through the T-cell receptor and phorbol esters

CD-1 mice received daily subcutaneous injections of either cocaine (20 mg/kg or 40 mg/kg) or saline solution (0.9% NaCl) from postnatal days 2 to 15. Pups were tested on days 16-17 for learning and 24-h retention of a passive avoidance task, where entering a dark compartment was punished with a mild foot shock. Locomotor activity and general behaviour in an open field arena were assessed on day 21, following administration of either the muscarinic blocker scopolamine (0.8 mg/kg) or saline solution. In addition, immunostaining for the enzyme choline acetyltransferase (ChAT) was measured in different basal forebrain areas (medial septum, striatum, and nucleus basalis) on day 30. Cocaine treatment failed to affect either learning or retention capabilities. Nonetheless, neophobic behaviour during the learning session was enhanced in control nonpunished mice exposed to the 20-mg/kg dose. In the open field test, although baseline activity levels were unaffected by cocaine exposure, the 40-mg/kg cocaine-treated pups showed decreased sensitivity to the hyperkinetic effects of scopolamine. ChAT immunocytochemistry revealed a significant reduction of the number of ChAT-immunopositive neurons in the nucleus basalis but not in the other cholinergic basal forebrain regions.     

Selective immunotoxic lesions of basal forebrain cholinergic cells: Effects on learning and memory in rats.

Male Long-Evans rats were given injections of either 192 IgG-saporin, an apparently selective toxin for basal forebrain cholinergic neurons (LES), or vehicle (CON) into either the medial septum and vertical limb of the diagonal band (MS/VDB) or bilaterally into the nucleus basalis magnocellularis and substantia innominata (nBM/SI). Place discrimination in the Morris water maze assessed spatial learning, and a trial-unique matching-to-place task in the water maze assessed memory for place information over varying delays. MS/VDB-LES and nBM/SI-LES rats were not impaired relative to CON rats in acquisition of the place discrimination, but were mildly impaired relative to CON rats in performance of the memory task even at the shortest delay, suggesting a nonmnemonic deficit. These results contrast with effects of less selective lesions, which have been taken to support a role for basal forebrain cholinergic neurons in learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

17 beta-estradiol attenuates fimbrial lesion-induced decline of ChAT-immunoreactive neurons in the rat medial septum

We investigated the neuroprotective effects of 17 beta-estradiol (E2) on medial septal cholinergic neurons following partial unilateral lesion of the fimbriafornix. Adult female rats were ovariectomized (OVX) and, 5 days later, treated with a single intravenous (iv) injection of an estradiol (E2)-chemical delivery system (E2-CDS) or its vehicle hydroxypropyl-beta-cyclodextrin (HPCD). All rats were subjected to partial unilateral electrolytic fimbrial lesion the following day. At 20 days postlesion, brain slices from treated animals were assessed for choline acetyltransferase (ChAT) by immunohistochemistry. Animals treated with HPCD or E2-CDS showed a 44 or 4% decrease, respectively, in ChAT-positive neurons on the lesioned side compared to the nonlesioned side of the medial septum. In a second study using the same lesioning procedure, adult OVX rats received either a subcutaneous E2 pellet implant (n = 6), or, 5 days postovariectomy, a single iv injection of E2-CDS (n = 8) or HPCD (n = 6). Animals treated with HPCD showed a 55% decrease in ChAT-positive neurons on the lesioned side compared to the nonlesioned side of the medial septum. By contrast, rats treated with E2-CDS or E2 pellet had a 14 or 13% decrease, respectively, in ChAT-positive neurons. Interestingly, E2 treatment substantially decreased ChAT-positive neurons on the nonlesioned side of the medial septum in comparison to control animals. The present study suggests that cholinergic neurons in the medial septum are protected from lesion-induced degeneration by treatments which increase brain E2 levels. Thus, E2 may play a neuroprotective role in the basal forebrain cholinergic system.     

GABAergic and cholinergic basal forebrain and preoptic-anterior hypothalamic projections to the mediodorsal nucleus of the thalamus in the cat

The present study examined projections of GABAergic and cholinergic neurons from the basal forebrain and preoptic-anterior hypothalamus to the "intermediate" part of the mediodorsal nucleus of the thalamus. Retrograde transport from this region of the mediodorsal nucleus was investigated using horseradish peroxidase-conjugated wheatgerm agglutinin in combination with peroxidase-antiperoxidase immunohistochemical staining for glutamic acid decarboxylase and choline acetyltransferase. A relatively large number of retrogradely-labelled glutamic acid decarboxylase-positive neurons are located in the basal forebrain, amounting to more than 7% of the total population of glutamic acid decarboxylase-positive cells in this region. Moreover, retrogradely-labelled choline acetyltransferase-positive cells are interspersed among glutamic acid decarboxylase-positive neurons, accounting for about 6% of the total choline acetyltransferase-positive cell population in the basal forebrain. The glutamic acid decarboxylase-positive and choline acetyltransferase-positive retrogradely-labelled neurons are distributed throughout several regions of the basal forebrain, including the medial septum, the diagonal band of Broca, the magnocellular preoptic nucleus, the substantia innominata pars anterior, the substantia innominata pars posterior, and the globus pallidus where only a few retrogradely-labelled neurons were seen. The choline acetyltransferase-positive mediodorsal-projecting neurons are morphologically different from the choline acetyltransferase-positive neurons in the basal forebrain, suggesting that those projecting to the mediodorsal nucleus are a small proportion of the cholinergic neuronal population in the basal forebrain. In the preoptic-anterior hypothalamus, many retrogradely-labelled glutamic acid decarboxylase-positive cells were found, amounting to more than 7% of the total population of glutamic acid decarboxylase-positive cells in this region. These retrogradely-labelled glutamic acid decarboxylase-positive neurons are distributed throughout the preoptic-anterior hypothalamus in a continuous line with those in the basal forebrain, including the lateral preoptic area, the medial preoptic area, the bed nucleus of the stria terminalis, and the anterior and dorsal hypothalamic areas. The highest percentage of mediodorsal-projecting GABAergic neurons is in the anterior lateral hypothalamus where more than 25% of the total population of glutamic acid decarboxylase-positive cells project to the mediodorsal nucleus of the thalamus. Overall, of the large population of retrogradely-labelled neurons in the basal forebrain and preoptic-anterior hypothalamus, a significant proportion are glutamic acid decarboxylase-positive neurons (> 60% in the basal forebrain and > 30% in the preoptic-anterior hypothalamus), while the choline acetyltransferase-positive neurons amount to a smaller percentage of the neurons projecting to the mediodorsal nucleus (< 13% in the basal forebrain and < 2% in the preoptic-anterior hypothalamus). These results provide anatomical evidence of direct GABAergic projections from the basal forebrain and preoptic-anterior hypothalamic regions to the "intermediate" part of the mediodorsal nucleus in the cat. This GABAergic projection field could be the direct pathway by which the basal forebrain directly modulates thalamic excitability and may also be involved in mechanisms modulating electroencephalographic synchronization and sleep through the "intermediate" mediodorsal nucleus.     

Tyrosine kinase A, galanin and nitric oxide synthase within basal forebrain neurons in the rat

Cholinergic basal forebrain neurons appear to play a key role in cognition and attention. In rat, basal forebrain neurons express multiple proteins including the high-affinity signal transducing tyrosine kinase A receptor for nerve growth factor, the neuropeptide galanin and nitric oxide synthase, a marker for the novel neurotransmitter nitric oxide. The present study was undertaken to define the relationship between neurons expressing each of these markers within the medial septum-vertical limb of the diagonal band, horizontal limb of the diagonal band and nucleus basalis in colchicine pre-treated rats. Tyrosine kinase A-immunopositive neurons were seen throughout all subfields of the basal forebrain. In contrast, nitric oxide synthase- and galanin-immunoreactive neurons were mainly distributed within the septal-diagonal band complex. Co-localization experiments revealed that virtually all nitric oxide synthase-positive neurons (visualized by nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry) also contained tyrosine kinase A, whereas many fewer tyrosine kinase A neurons were nicotinamide adenine dinucleotide phosphate-diaphorase positive within the medial septum-vertical limb of the diagonal band. Within the horizontal limb of the diagonal band, numerous nicotinamide adenine dinucleotide phosphate-diaphorase neurons expressed tyrosine kinase A, whereas only a small number of tyrosine kinase A neurons contained nicotinamide adenine dinucleotide phosphate-diaphorase. Within the nucleus basalis very few neurons were nicotinamide adenine dinucleotide phosphate-diaphorase reactive, and a minor number contained tyrosine kinase A. Additional co-localization experiments revealed minor percentages of neurons containing nicotinamide adenine dinucleotide phosphate-diaphorase and galanin immunoreactivity within the various subfields of the basal forebrain. Within the horizontal limb of the diagonal band minor numbers of nicotinamide adenine dinucleotide phosphate-diaphorase-reactive perikarya displayed galanin. Similarly, only a few galanin-containing neurons expressed nicotinamide adenine dinucleotide phosphate-diaphorase. The existence of tyrosine kinase A, nitric oxide synthase and galanin within select neuronal subgroups of the cholinergic basal forebrain suggests that these perikarya are responsive to a complex set of chemical signals. A greater understanding of the chemical signature of the cholinergic basal forebrain neurons will provide the insight required to develop novel pharmacological approaches aimed at preventing or slowing the degenerative processes that effect these neurons in aging and pathologic disorders.     

A risk-benefit assessment of flumazenil in the management of benzodiazepine overdose

The basal forebrain appears to be important in cognitive function. It has been suggested that this region is composed of several cholinergic cell groups, mainly the medial septum, the diagonal band of Broca, and the nucleus basalis of Meynert. To elucidate the functional differences between these subregions, we have recorded single-unit activity from the periventricular areas involving the medial septum, the diagonal band of Broca (ms/dbB), and the substantia innominata (SI), including the nucleus basalis of Meynert, of an object-discriminating monkey. Of 226 ms/dbB and 439 SI neurons analyzed, 36 (15.9%) and 115 (26.2%), respectively, responded to the sight of some complex object. Thirteen (5.8%) ms/dbB and 80 (18.2%) SI neurons responded to virtually all objects and the ratio of these neurons in the SI was higher than that in the ms/dbB. The other 23 (10.2%) ms/dbB and 35 (8.0%) SI neurons responded preferentially to one or two of three categories (rewarding, aversive, or meaningless) of familiar or to unfamiliar objects, and response selectivity to one category of the ms/dbB neurons (15; 6.6%) was higher than that to the SI neurons (14; 3.2%). The results suggest that the SI, including the nucleus basalis of Meynert, may encode visual information about objects more broadly and participate more fully in visual attention than the ms/dbB region, which may be more closely related to learning.     

Cellular localizations of AMPA glutamate receptors within the basal forebrain magnocellular complex of rat and monkey

The cellular distributions of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors within the rodent and nonhuman primate basal forebrain magnocellular complex (BFMC) were demonstrated immunocytochemically using anti-peptide antibodies that recognize glutamate receptor (GluR) subunit proteins (i.e., GluR1, GluR4, and a conserved region of GluR2, GluR3, and GluR4c). In both species, many large GluR1-positive neuronal perikarya and aspiny dendrites are present within the medial septal nucleus, the nucleus of the diagonal band of Broca, and the nucleus basalis of Meynert. In this population of neurons in rat and monkey, GluR2/3/4c and GluR4 immunoreactivities are less abundant than GluR1 immunoreactivity. In rat, GluR1 does not colocalize with ChAT, but, within many neurons, GluR1 does colocalize with GABA, glutamic acid decarboxylase (GAD), and parvalbumin immunoreactivities. GluR1- and GABA/GAD-positive neurons intermingle extensively with ChAT-positive neurons. In monkey, however, most GluR1-immunoreactive neurons express ChAT and calbindin-D28 immunoreactivities. The results reveal that noncholinergic GABAergic neurons, within the BFMC of rat, express AMPA receptors, whereas cholinergic neurons in the BFMC of monkey express AMPA receptors. Thus, the cellular localizations of the AMPA subtype of GluR are different within the BFMC of rat and monkey, suggesting that excitatory synaptic regulation of distinct subsets of BFMC neurons may differ among species. We conclude that, in the rodent, BFMC GABAergic neurons receive glutamatergic inputs, whereas cholinergic neurons either do not receive glutamatergic synapses or utilize GluR subtypes other than AMPA receptors. In contrast, in primate, basal forebrain cholinergic neurons are innervated directly by glutamatergic afferents and utilize AMPA receptors.     

Obsessive-compulsive disorder in schizophrenia: epidemiologic and biologic overlap

AF64A (ethylcholine mustard aziridinium ion) was stereotaxically administered bilaterally (1 nmol/side) into rat lateral cerebral ventricles. Choline acetyltransferase (ChAT) activity and ChAT mRNA levels were measured at predetermined time points in the septo-hippocampal pathway and striatum, both well identified as rich in cholinergic neurons. AF64A caused a rapid but transient increase in ChAT mRNA (167%, P < 0.05) and ChAT activity (164%, P < 0.01) in the septum. By day 7 post treatment, there was a significant decrease in ChAT mRNA (42.5% of control, P < 0.05) in the septum although the ChAT activity still stayed high. This decreased ChAT mRNA level in the septum lasted for at least four weeks, and was paralleled by a long-lasting decrease in ChAT activity in the hippocampus. In the striatum, on the other hand, there were no observed changes in either ChAT activity or ChAT mRNA. These data suggest that the long term effect of AF64A on the septo-hippocampal cholinergic pathway may, at least in part, be due to an action of AF64A on gene expression in the cholinergic neuron. The difference in the response to AF64A between the septo-hippocampal and striatal cholinergic systems might be due to their difference in neuron types.     

Serotonin1A receptors are expressed by a subpopulation of cholinergic neurons in the rat medial septum and diagonal band of Broca--a double immunocytochemical study

The possible colocalization of 5-hydroxytryptamine1A receptors and choline acetyltransferase in the same neurons of the medial septum and diagonal band of Broca was investigated using double immunocytochemical techniques, either on the same section or on adjacent thin sections of the rat brain. The presence of both antigens in the same neurons was demonstrated at the light and electron microscopic levels. The proportion of cholinergic neurons that express 5-hydroxytryptamine1A receptors was similar in the different parts of the septal complex (around 25%). By contrast, the proportion of 5-hydroxytryptamine1A receptor-positive neurons also exhibiting choline acetyltransferase immunoreactivity was much higher (40-44%) in the dorsal and ventral groups of cholinergic cells, than in the intermediate group (18%). In line with the topographical distribution of cholinergic projections, this result points out the potential involvement of 5-hydroxytryptamine1A receptors in the control of the septohippocampal cholinergic projection by serotonin. This connection might be relevant to learning and memory, and in the appearance of age-dependent or neurodegenerative cognitive deficits, which have been shown to involve alterations in both the serotoninergic and the cholinergic systems.     

Technical note: a blind test of mandibular ramus flexure as a morphologic indicator of sexual dimorphism in the human skeleton

Following axotomy most medial septal neurons in the adult rat brain have dramatically reduced numbers of choline acetyltransferase (ChAT) positive neurons. Since leukemia inhibitory factor (LIF) promotes cholinergic expression in several neuronal populations, the aim of this study was to determine if LIF would continue to support cholinergic expression in axotomized medial septal neurons. Mini-osmotic pumps were used to infuse saline or LIF into the lateral cerebral ventricle. Counts of ChAT and low-affinity nerve growth factor (p75NGFR) immunostained neurons indicated that LIF-treated animals retained ChAT expression in > 90% of axotomized neurons whereas in saline-infused animals this was < 30%. Also, LIF was equally effective in maintaining p75NGFR expression levels in axotomized medial septal neurons.     

Kidney cografts enhance fiber outgrowth from ventral mesencephalic grafts to the 6-OHDA-lesioned striatum, and improve behavioral recovery

Recent studies have demonstrated the presence of many different neurotrophic factors in the developing and adult kidney. Due to its production of this mixture of neurotrophic factors, we wanted to investigate whether fetal kidney tissue could be beneficial for neuritic fiber growth and/or cell survival in intracranial transplants of fetal ventral mesencephalic tissue (VM). A retrograde lesion of nigral dopaminergic neurons was performed in adult Fischer 344 male rats by injecting 6-hydroxydopamine into the medial forebrain. The animals were monitored for spontaneous locomotor activity in addition to apomorphine-induced rotations once a week. Four weeks following the lesion, animals were anesthetized and embryonic day 14 VM tissue from rat fetuses was implanted stereotaxically into the dorsal striatum. One group of animals received a cograft of kidney tissue from the same embryos in the same needle track. The animals were then monitored behaviorally for an additional 4 months. There was a significant improvement in both spontaneous locomotor activity (distance traveled) and apomorphine-induced rotations with both single VM grafts and VM-kidney cografts, with the VM-kidney double grafts enhancing the motor behaviors to a significantly greater degree. Tyrosine hydroxylase (TH) immunohistochemistry and image analysis revealed a significantly denser innervation of the host striatum from the VM-kidney cografts than from the single VM grafts. TH-positive neurons were also significantly larger in the cografts compared to the single VM grafts. In addition to the dense TH-immunoreactive innervation, the kidney portion of cografts contained a rich cholinergic innervation, as evidenced from antibodies against choline acetyltransferase (ChAT). The striatal cholinergic cell bodies surrounding the VM-kidney cografts were enlarged and had a slightly higher staining density for ChAT. Taken together, these data support the hypothesis that neurotrophic factors secreted from fetal kidney grafts stimulated both TH-positive neurons in the VM cografts and cholinergic neurons in the host striatum. Thus, these factors may be combined for treatment of degenerative diseases involving both dopaminergic and cholinergic neurons.     

Evidence for normal aging of the septo-hippocampal cholinergic system in apoE (-/-) mice but impaired clearance of axonal degeneration products following injury

The association of the epsilon4 allele of apoE with increased risk for Alzheimer's disease (AD) and with poor clinical outcome after certain acute brain injuries has sparked interest in the neurobiology of apoE. ApoE (-/-) mice provide a tool to investigate the role of apoE in the nervous system in vivo. Since integrity of the basal forebrain cholinergic system is severely compromised in AD, with severity of dysfunction correlating with apoE4 gene dosage, the present study tested the hypothesis that apoE is required to maintain the normal integrity of basal forebrain cholinergic neurons (BFCNs). Histological and biochemical analyses of the septo-hippocampal cholinergic system were performed in apoE (-/-) mice during aging and following injury. Using unbiased quantitative methods, there was little or no evidence for defects in the septo-hippocampal cholinergic system, as assessed by p75(NTR)-immunoreactive neuron number and size in the medial septum, cholinergic fiber density in the hippocampus, and choline acetyltransferase activity in the hippocampus, cortex, and striatum in aged apoE (-/-) mice (up to 24 months of age) as compared to age-matched wild-type mice of the same strain. In addition, cholinergic neuronal survival and size following fimbria-fornix transection in apoE (-/-) mice did not differ from controls. However, following entorhinal cortex lesion, there was persistence of degeneration products in the deafferented hippocampus in apoE (-/-) mice. These data suggest that although apoE is not required for the maintenance of BFCNs in vivo, it may play a role in the clearance of cholesterol-laden neurodegeneration products following brain injury.     

NGF mRNA is expressed by GABAergic but not cholinergic neurons in rat basal forebrain

Nerve growth factor (NGF) supports the survival and biosynthetic activities of basal forebrain cholinergic neurons and is expressed by neurons within lateral aspects of this system including the horizontal limb of the diagonal bands and magnocellular preoptic areas. In the present study, colormetric and isotopic in situ hybridization techniques were combined to identify the neurotransmitter phenotype of the NGF-producing cells in these two areas. Adult rat forebrain tissue was processed for the colocalization of mRNA for NGF with mRNA for either choline acetyltransferase, a cholinergic cell marker, or glutamic acid decarboxylase, a GABAergic cell marker. In both regions, many neurons were single-labeled for choline acetyltransferase mRNA, but cells containing both choline acetyltransferase and NGF mRNA were not detected. In these fields, virtually all NGF mRNA-positive neurons contained glutamic acid decarboxylase mRNA. The double-labeled cells comprised a subpopulation of GABAergic neurons; numerous cells labeled with glutamic acid decarboxylase cRNA alone were codistributed with the double-labeled neurons. These data demonstrate that in basal forebrain GABAergic neurons are the principal source of locally produced NGF.