Embryonic substantia nigra grafts in the mesencephalon send neurites to the host striatum in non-human primate after overexpression of GDNF

In spite of partial success in treating Parkinson's disease by using ectopically placed grafts of dopamine-producing cells, restoration of the original neuroanatomical circuits, if possible, might work better. Previous evidence of normal anatomic projections from ventral mesencephalic (VM) grafts placed in the substantia nigra (SN) has been limited to neonatal rodents and double grafting or bridging procedures. This study attempted to determine whether injection of a potent growth-promoting factor, glial cell line-derived neurotrophic factor (GDNF), into the target regions or placement of fetal striatal co-grafts in the nigrostriatal pathway might elicit neuritic outgrowth to the caudate nucleus. Four adult St. Kitts green monkeys received embryonic VM grafts into the rostral mesencephalon near the host SN, and injections of adeno-associated virus 2 (AAV2)/GDNF or equine infectious anemia virus (EIAV)/GDNF into the caudate. Three adult monkeys were co-grafted with fetal VM tissue near the SN and fetal striatal grafts (STR) 2.5 mm rostral in the nigrostriatal pathway. Before sacrifice, the striatal target regions were injected with the retrograde tracer Fluoro-Gold (FG). FG label was found in tyrosine hydroxylase-labeled neurons in VM grafts in the SN of only those monkeys that received AAV2/GDNF vector injections into the ipsilateral striatum. All monkeys showed FG labeling in the host SN when FG labeling was injected on the same side. These data show that grafted dopaminergic neurons can extend neurites to a distant target releasing an elevated concentration of GDNF, and suggest that grafted neurons can be placed into appropriate loci for potential tract reconstruction.

Androgen modulation of hippocampal synaptic plasticity

This review briefly summarizes recent developments in our understanding of the role of androgens in maintaining normal hippocampal structure. Studies in rats and vervet monkeys have demonstrated that removal of the testes reduces the density of synaptic contacts on dendritic spines of cornu ammonis 1 (CA1) pyramidal neurons. This effect is rapidly reversed by treatment with either testosterone or the non-aromatizable androgen dihydrotestosterone, suggesting that maintenance of normal synaptic density is androgen-dependent, via a mechanism that does not require intermediate estrogen biosynthesis. Similar effects of these androgens are observed in ovariectomized female rats, except that in the female the actions of testosterone include a substantial contribution from estrogen formation. The ability to stimulate hippocampal spine synapse density is not directly related to systemic androgenic potency: thus, weak androgens such as dehydroepiandrosterone exert effects that are comparable to those of dihydrotestosterone; while partial agonist responses are observed after injection of the synthetic antiandrogen, flutamide. These data provide a morphological counterpart to observations that androgens enhance cognitive function and mood state, suggesting that these effects may result at least in part from hippocampal neurotrophic responses. The unusual specificity of these responses raises the possibility that effects of androgens on the brain may be mediated via different mechanisms than the masculinizing actions of these steroids in non-neural androgen target organs.

Synaptic remodeling induced by gonadal hormones: neuronal plasticity as a mediator of neuroendocrine and behavioral responses to steroids

During recent decades, it has become a generally accepted view that structural neuroplasticity is remarkably involved in the functional adaptation of the CNS. Thus, cellular morphology in the brain is in continuous transition throughout the life span, as a response to environmental stimuli. The effects of the environment on neuroplasticity are mediated by, to some extent, the changing levels of circulating gonadal steroid hormones. Today, it is clear that the function of gonadal steroids in the brain extends beyond simply regulating reproductive and/or neuroendocrine events. In addition, or even more importantly, gonadal steroids participate in the shaping of the developing brain, while their actions during adult life are implicated in higher brain functions such as cognition, mood and memory. A large body of evidence indicates that gonadal steroid-induced functional changes are accompanied by alterations in neuron and synapse numbers, as well as in dendritic and synaptic morphology. These structural modifications are believed to serve as a morphological basis for changes in behavior and cellular activity. Due to their growing functional and clinical significance, the specificity, timeframe, as well as the molecular and cellular mechanisms of hormone-induced neuroplasticity have become the focus of many studies. In this review, we briefly summarize current knowledge and the most significant recent discoveries from our laboratories on estrogen- and dehydroepiandrosterone-induced synaptic remodeling in the hypothalamus and hippocampus, two important brain areas heavily involved in autonomic and cognitive operations, respectively.

Effects of testosterone on hippocampal CA1 spine synaptic density in the male rat are inhibited by fimbria/fornix transection

This study investigated the contribution of sub-cortical afferent input to the effects of testosterone (T) on spine synapse density in the CA1 subfield of the hippocampus, in adult male rats. Gonadectomized (GDX) male rats exhibited a considerably lower density of spine synapses in the CA1 region than control, intact males. The effects of GDX were reversed by treatment with testosterone propionate (TP; 500 microg/day, for 2 days). Transection of the fimbria/fornix (FF) had no significant effect on the synaptic density in non-GDX males. However, FF transection partially inhibited the responses to TP in GDX animals. These data suggest that the effects of T on spine synapse density in the CA1 region of the male rat hippocampus are partially, but not completely, dependent on afferent sub-cortical input.

Gonadal hormones act extrinsic to the hippocampus to influence the density of hippocampal astroglial processes

The important effects of estrogen on the morphology of hippocampal neurons are well established. The mechanisms leading to such changes, nevertheless, have proved confusingly complex, since interactions between glia and neurons, as well as neuronal influences from other brain fields, are involved. This study addresses the possibility that estrogen-sensitive projections from the medial septum/diagonal band of Broca induce astroglial reactions. Estrogen- and cholesterol-filled (controls) cannulae were implanted into the medial septum/diagonal band of Broca of adult ovariectomized rats. Comparative semiquantitative immunohistochemical analysis on the density of the glial fibrillary acidic protein-containing processes and cells were performed on hippocampal slices of locally estrogen-treated and control animals. Rats that received estrogen-filled cannulae showed a lower density of glial processes in the hippocampal CA1 and CA3 subfields than animals of the control group. These effects could not be observed in the dentate gyrus. Cell counts revealed no significant difference in the number of glial fibrillary acidic protein-positive cells in any of the examined areas. Two major conclusions can be drawn from these results. First, the data show that estrogen, in fact, has an indirect influence on hippocampal cells through septo-hippocampal projections. Furthermore, estradiol can have an indirect negative effect on hippocampal astrocytes, causing a reduction in the density of their processes.

Hormonal regulation of hippocampal spine synapse density involves subcortical mediation

It is well established that estrogen has positive effects on the density of pyramidal cell spines in the hippocampal CA1 subfield. This study explored whether afferent connections of the hippocampus that come from estrogen-sensitive subcortical structures, including the septal complex, median raphe and supramammillary area, play a role in this estrogen-induced hippocampal synaptic plasticity. These particular subcortical structures have major influences on hippocampal activity, including theta rhythm and long-term potentiation. The latter also promotes the formation of new synapses. All of the rats were ovariectomized; the fimbria/fornix, which contains the majority of subcortical efferents to the hippocampus, was transected unilaterally in each, and half of the animals received estrogen replacement. Using unbiased electron microscopic stereological methods, the CA1 pyramidal cell spine synapse density was calculated. In the estrogen-treated rats, contralateral to the fimbria/fornix transection, the spine density of CA1 pyramidal cells increased dramatically, compared to the spine density values of both the ipsilateral and contralateral hippocampi of non-estrogen-treated animals and to that of the ipsilateral hippocampus of the estrogen replaced rats. These observations indicate that fimbria/fornix transection itself does not considerably influence CA1 area pyramidal cell spine density and, most importantly, that the estrogenic effect on hippocampal morphology, in addition to directly affecting the hippocampus, involves subcortical mediation.

Supramammillary area mediates subcortical estrogenic action on hippocampal synaptic plasticity

It is well established that systemically administered estrogen to ovariectomized rats positively affects the density of pyramidal cell spines in the hippocampal CA1 subfield and intact subcortical connections of the hippocampus are essential in this hormonal action. This study explored whether local estrogen administration into the supramammillary area influences the density of CA1 pyramidal cell spine synapses in ovariectomized rats. The first group of experiments using a combination of retrograde tracer technique and immunostaining for estrogen receptor-alpha demonstrated that a large population of supramammillary area estrogen receptor-alpha-containing neurons projects to the hippocampus. Animals belonging to the second experimental group were ovariectomized and received cannulae filled with 0.4% 17 beta-estradiol placed unilaterally into the supramammillary area. Control animals received a cholesterol-containing cannula into the supramammillary area or an estrogen-filled cannula implanted into the head of the caudate nucleus. One week later, rats were killed and CA1 pyramidal cell spine synapse density was determined using electron microscopic unbiased stereological procedures. Animals that received an estrogen-filled cannula into the supramammillary area exhibited a significantly higher (37%) density of CA1 pyramidal cell spine synapses than both other control groups. These observations indicate that the supramammillary area is involved in mediating synaptoplastic, estrogenic effects to the hippocampus.

Estrogen is essential for maintaining nigrostriatal dopamine neurons in primates: implications for Parkinson's disease and memory

There are sexual differences in several parameters of the nigrostriatal dopamine neurons, as well as in the progression of diseases associated with this system, e.g., Parkinson's disease and dementia. These differences, as well as direct experimental data in rodents, suggest that gonadal hormones play a role in modulating this system. To determine whether circulating estrogen might have long-term effects by altering the number of dopamine neurons, the density of dopamine neurons was calculated in the compact zone of the substantia nigra of male and intact female short- (10 d) and longer-term (30 d) ovariectomized and short- and longer-term ovariectomized but estrogen-replaced nonhuman primates (African green monkeys). Furthermore, the number of tyrosine hydroxylase-expressing neurons, the total number of all types of neurons, and the volume of the compact zone of the substantia nigra were calculated in 30 d ovariectomized and in 30 d ovariectomized and estrogen-replaced monkeys. Unbiased stereological analyses demonstrated that a 30 d estrogen deprivation results in an apparently permanent loss of >30% of the total number of substantia nigra dopamine cells. Furthermore, the density calculations showed that brief estrogen replacement restores the density of tyrosine hydroxylase-immunoreactive cells after a 10 d, but not after a 30 d, ovariectomy. Moreover, the density of dopamine cells is higher in females than in males. These observations show the essential role of estrogen in maintaining the integrity of the nigral dopamine system, suggest a new treatment strategy for patients with Parkinson's disease and with certain forms of memory-impairing disorders, and provide another rationale for estrogen replacement therapy for postmenopausal women.

Muscarinic tone sustains impulse flow in the septohippocampal GABA but not cholinergic pathway: implications for learning and memory

Systemic infusions of the muscarinic cholinergic receptor antagonists atropine and scopolamine (atr/scop) produce an amnesic syndrome in humans, subhuman primates, and rodents. In humans, this syndrome may resemble early symptoms of Alzheimer's disease. Behavioral studies in rats have demonstrated that the medial septum/diagonal band of Broca (MSDB), which sends cholinergic and GABAergic projections to the hippocampus, is a critical locus in mediating the amnesic effects of atr/scop. The amnesic effects of atr/scop in the MSDB have been presumed but not proven to be caused by a decrease in hippocampal acetylcholine (ACh) release after blockade of a muscarinic tone in the MSDB. Using electrophysiological recordings and fluorescent-labeling techniques to identify living septohippocampal neurons in rat brain slices, we now report that, contrary to current belief, a blockade of the muscarinic tone in the MSDB does not decrease impulse flow in the septohippocampal cholinergic pathway; instead, it decreases impulse flow in the septohippocampal GABAergic pathway via M(3) muscarinic receptors. We also report that the muscarinic tone in the MSDB is maintained by ACh that is released locally, presumably via axon collaterals of septohippocampal cholinergic neurons. As such, cognitive deficits that occur in various neurodegenerative disorders that are associated with a loss or atrophy of septohippocampal cholinergic neurons cannot be attributed solely to a decrease in hippocampal acetylcholine release. An additional, possibly more important mechanism may be the concomitant decrease in septohippocampal GABA release and a subsequent disruption in disinhibitory mechanisms in the hippocampus. Restoration of impulse flow in the septohippocampal GABA pathway, possibly via M(3) receptor agonists, may, therefore, be critical for successful treatment of cognitive deficits associated with neurodegenerative disorders such as Alzheimer's and Parkinson's disease.

The transentorhinal cortex of the African green monkey: a combined light- and electron-microscopic study of calcium-binding protein containing neurons

The transentorhinal cortex (TEC) is a primate-specific transition zone between the entorhinal allocortex and the temporal isocortex. Neurons in the lamina pre-alpha of TEC are known to be the first to develop intraneuronal changes in the course of Alzheimer's disease. In order to shed light on this important feature, we studied as yet unknown morphological and neurochemical characteristics of the TEC of the African green monkey (Cercopithecus aethiops sabaeus). Using light- and electron-microscopic immunocytochemistry, the distribution and morphology of neurons containing calcium-binding proteins were described and compared with those in the adjacent cortices. Light-microscopic analysis revealed that parvalbumin-containing neurons were distributed in all cortical layers. Calbindin-containing cells were fewer but also present in each layer. Calretinin-containing neurons were largely confined to the upper layers of the TEC. All three types of neuron showed pyramidal-like, multipolar and bipolar shapes; their dendrites were smooth or beaded. Ultrastructural studies revealed immunopositive somata with infolded nuclei and large amounts of cytoplasm. The somata were only sparsely innervated by symmetric synapses. Immunopositive dendrites were almost exclusively covered with immunonegative axon terminals establishing symmetric and asymmetric synapses. Immunopositive terminals established symmetric contacts with immunonegative dendrites and somata. Only occasionally, could synaptic contacts between immunopositive pre- and postsynaptic structures be observed. The comparison of neurons in the TEC and adjacent cortices revealed no striking differences. In summary, the morphological and neurochemical characteristics of TEC neurons as analyzed in our study do not provide an explanation for the early onset of neurodegenerative changes in the TEC.

The supramammillo-hippocampal and supramammillo-septal glutamatergic/aspartatergic projections in the rat: a combined [3H]D-aspartate autoradiographic and immunohistochemical study

It is well established that the supramammillary nucleus plays a critical role in hippocampal theta rhythm generation/regulation by its direct and indirect (via the septal complex) connections to the hippocampus. Previous morphological and electrophysiological studies indicate that both the supramammillo-hippocampal and supramammillo-septal efferents contain excitatory transmitter. To test the validity of this assumption, transmitter specific retrograde tracer experiments were performed. [3H]D-aspartate was injected into different locations of the hippocampus (granular and supragranular layers of the dentate gyrus and CA2 and CA3a areas of the Ammon's horn) and septal complex (medial septum and the area between the medial and lateral septum) that are known targets of the supramammillary projection. Consecutive vibratome sections prepared from the entire length of the posterior hypothalamus, including the supramammillary area, were immunostained for calretinin, tyrosine hydroxylase, or calbindin, and further processed for autoradiography. Radiolabeled, radiolabeled plus calretinin-containing, and calretinin-immunoreactive neurons were plotted at six different oro-caudal levels of the supramammillary area. The results demonstrated that following both hippocampal and septal injection of the tracer, the majority of the retrogradely radiolabeled (glutamatergic/aspartatergic) cells are immunoreactive for calretinin. However, non-radiolabeled calretinin-containing neurons and radiolabeled calretinin-immunonegative cells were also seen, albeit at a much lower density. These observations clearly indicate the presence of glutamatergic/aspartatergic projections to both the hippocampus and septal complex. It may be assumed that this transmitter could play a role in hippocampal theta rhythm generation/regulation.

AMPA receptors colocalize with neuropeptide-Y- and galanin-containing, but not with dopamine, neurons of the female rat arcuate nucleus: a semiquantitative immunohistochemical colocalization study

It is well established that excitatory amino acid (EAA) neurotransmission is an essential component in the regulation of the gonadotropin-releasing hormone (GnRH) delivery system. However, the morphological interconnection of these systems is not fully understood. The objective of the present study was to determine whether or not alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors--as indicators of aspartate/glutamatergic innervation--are present in the major neuronal populations, such as the neuropeptide-Y-(NPY), galanin- (GAL) and tyrosine-hydroxylase- (TH) containing neurons of the arcuate nucleus (AN) of the female rat. Colocalization experiments using the "mirror" technique demonstrated that: (1) AN neurons containing GluR1 are also immunoreactive (IR) for GluR2/3; (2) 38.32% of AMPA-IR cells contain NPY and 31.72% of AMPA-containing neurons are also IR for GAL; in turn, 79.41% of NPY- and 56.19% of GAL-containing neurons are IR for AMPA receptors; none of the neurons are IR for both AMPA receptors and TH. These data suggest that an excitatory aspartate/glutamatergic input is implicated in the regulation of the examined neuropeptide-containing AN neurons but not in that of TH-IR cells of the same area.

Cholinergic excitation of septohippocampal GABA but not cholinergic neurons: implications for learning and memory

The medial septum/diagonal band (MSDB), which gives rise to the septohippocampal pathway, is a critical locus for the mnemonic effects of muscarinic drugs. Infusion of muscarinic cholinergic agonists into the MSDB enhance learning and memory processes both in young and aged rats and produce a continuous theta rhythm in the hippocampus. Intraseptal muscarinic agonists also alleviate the amnesic syndrome produced by systemic administration of muscarinic receptor antagonists. It has been presumed, but not proven, that the cellular mechanisms underlying the effects of muscarinic agonists in the MSDB involve an excitation of septohippocampal cholinergic neurons and a subsequent increase in acetylcholine (ACh) release in the hippocampus. Using a novel fluorescent labeling technique to selectively visualize live septohippocampal cholinergic neurons in rat brain slices, we have found that muscarinic agonists do not excite septohippocampal cholinergic neurons, instead they inhibit a subpopulation of cholinergic neurons. In contrast, unlabeled neurons, confirmed to be noncholinergic, septohippocampal GABA-type neurons using retrograde marking and double-labeling techniques, are profoundly excited by muscarine. Thus, the cognition-enhancing effects of muscarinic drugs in the MSDB cannot be attributed to an increase in hippocampal ACh release. Instead, disinhibitory mechanisms, caused by increased impulse flow in the septohippocampal GABAergic pathway, may underlie the cognition-enhancing effects of muscarinic agonists.

Opioids suppress IPSCs in neurons of the rat medial septum/diagonal band of Broca: involvement of mu-opioid receptors and septohippocampal GABAergic neurons

The medial septum/diagonal band region (MSDB), which provides a major cholinergic and GABAergic input to the hippocampus, expresses a high density of opioid receptors. Behaviorally, intraseptal injections of opioids produce deficits in spatial memory, however, little is known about the electrophysiological effects of opioids on MSDB neurons. Therefore, we investigated the electrophysiological effects of opioids on neurons of the MSDB using rat brain slices. In voltage-clamp recordings with patch electrodes, bath-applied met-enkephalin, a nonselective opioid receptor agonist, decreased the number of tetrodotoxin and bicuculline-sensitive inhibitory synaptic currents in cholinergic- and GABA-type MSDB neurons. A similar effect occurred in brain slices containing only the MSDB, suggesting that opioids decrease GABA release primarily by inhibiting spontaneously firing GABAergic neurons located within the MSDB. Accordingly, in extracellular recordings, opioid-sensitive, spontaneously firing neurons could be found within the MSDB. Additionally, in intracellular recordings a subpopulation of GABA-type neurons were directly inhibited by opioids. All effects of met-enkephalin were mimicked by a mu receptor agonist, but not by delta or kappa agonists. In antidromic activation studies, mu-opioids inhibited a subpopulation of septohippocampal neurons with high conduction velocity fibers, suggestive of thickly myelinated GABAergic fibers. Consistent with the electrophysiological findings, in double-immunolabeling studies, 20% of parvalbumin-containing septohippocampal GABA neurons colocalized the mu receptor, which at the ultrastructural level, was found to be associated with the neuronal cell membrane. Thus, opioids, via mu receptors, inhibit a subpopulation of MSDB GABAergic neurons that not only make local connections with both cholinergic and noncholinergic-type MSDB neurons, but also project to the hippocampus.

Estrogen receptor-alpha in the raphe serotonergic and supramammillary area calretinin-containing neurons of the female rat

It is well established that estrogen affects hippocampal long-term potentiation and hippocampus-related memory processes. Furthermore, theta rhythm, in conjunction with long-term potentiation, influences memory and is regulated by subcortical structures, including the median raphe and supramammillary area. To test the validity of the hypothesis that the effects of estrogen on the hippocampus are mediated, at least partly, via these subcortical structures, it must first be determined whether the neurons of the median raphe and supramammillary area contain estrogen receptors. Light and electron microscopic double immunostaining for estrogen receptor-alpha plus serotonin and estrogen receptor-alpha plus calretinin on vibratome sections of the median raphe and supramammillary area, respectively, demonstrated that large populations of the median raphe serotonin and supramammillary area calretinin neurons exhibit estrogen receptor-immunoreactive nuclei. These observations indicate that circulating gonadal hormones can affect hippocampal electric activity indirectly, via those subcortical structures that are involved in theta rhythm regulation.

Median raphe serotonergic innervation of medial septum/diagonal band of broca (MSDB) parvalbumin-containing neurons: possible involvement of the MSDB in the desynchronization of the hippocampal EEG

Activation of median raphe serotonergic neurons results in the desynchronization of hippocampal electroencephalographic (EEG) activity. This could be a direct effect, because serotonin (5-HT) fibers terminate on a specific population of hippocampal interneurons. On the other hand, it could be an indirect action through the medial septum/diagonal band of Broca (MSDB) pacemaker cells, because, in addition to previously described inhibitory effects, excitatory actions of 5-HT have been demonstrated on MSDB gamma-aminobutyric acid (GABA)-containing neurons through 5-HT2A receptors. Electron microscopic double immunostaining for Phaseolus vulgaris-leucoagglutinin (PHA-L) injected into the median raphe (MR) and parvalbumin, choline acetyltransferase, or calretinin as well as double immunostaining for 5-HT and parvalbumin, and colocalization for parvalbumin and 5-HT2A receptors were done in rats. The results demonstrated that: 1) MR axons form perisomatic and peridendritic baskets and asymmetric synaptic contacts on MSDB parvalbumin neurons; 2) these fibers do not terminate on septal cholinergic and calretinin neurons; 3) 5-HT fibers form synapses identical to those formed by PHA-L-immunolabeled axons with parvalbumin neurons; and 4) MSDB parvalbumin cells contain 5-HT2A receptors. These observations indicate that 5-HT has a dual action on the activity of hippocampal principal cells: 1) an inhibition of the input sector by activation of hippocampal GABA neurons that terminate exclusively on apical dendrites of pyramidal cells, and 2) a disinhibition of the output sector of principal neurons. MSDB parvalbumin-containing GABAergic neurons specifically innervate hippocampal basket and chandelier cells. Thus, 5-HT-elicited activation of MSDB GABAergic neurons will result in a powerful inhibition of these GABA neurons.

Inflammatory responses and their impact on beta-galactosidase transgene expression following adenovirus vector delivery to the primate caudate nucleus

An E1, E3 deleted adenovirus vector, serotype 5, carrying the marker gene LacZ was bilaterally microinfused into the caudate nuclei of 10 St Kitts green monkeys. The location and number of cells expressing transgene and host immunologic response were evaluated at 1 week (n = 2) and 1 month (n = 8) following vector infusion. A large number of cells expressed beta-galactosidase in some monkeys, exceeding 600000 in one monkey, but no expression was seen in three of 10. All monkeys had positive adenoviral antibody titers before vector infusion, indicating the possibility of previous exposure to some adenovirus, but only one showed a significant increase in titer afterwards. Inflammatory cell markers revealed an inverse correlation between transgene expression and the extent of inflammatory response. Dexamethasone administered immediately before and for 8 days following vector delivery, however, had no effect on transgene expression. The demonstration of significant inflammatory responses in the brain of some individual primates, including demyelination, indicates the need for new generations of adenovirus vectors, or the successful suppression of inflammatory responses, before this vector is suitable for non-cytotoxic clinical applications in the CNS.

The entorhino-septo-supramammillary nucleus connection in the rat: morphological basis of a feedback mechanism regulating hippocampal theta rhythm

Recent electrophysiological observations suggest that, in addition to the medial septal area pacemaker system, several alternative or additional mechanisms are involved in the generation/regulation of hippocampal theta activity. Discharging neurons phase-locked to hippocampal theta waves have been observed in the dorsal raphe, nucleus reticularis pontis oralis and especially in the supramammillary region of rats. Since these areas are reciprocally interconnected with the hippocampal formation, including the entorhinal cortex, it would aid our understanding of limbic function to elucidate the location and neurochemical content of the entorhino-septal and septo-supramammillary projection neurons, as well as that of their postsynaptic targets. Light and electron microscopic immunostaining for calretinin, in combination with antero- and retrograde tracer techniques, postembedding immunostaining for GABA and the transmitter specific [3H]D-aspartate retrograde radiolabeling, as well as a co-localization experiment for calretinin and glutamate decarboxylase in rat supramammillary and septal neurons, demonstrated that: (i) a large population of entorhinal cells that forms asymmetric synaptic contacts on calretinin-containing neurons located at the border between the medial and lateral septal areas contains calretinin and are aspartate/glutamatergic; (ii) the overwhelming majority of calretinin-immunoreactive cells located at the border between the lateral and medial septal area are GABAergic; (iii) these neurons can be retrogradely labeled from the supramammillary area; (iv) anterogradely labeled axons originating in the border between the medial and lateral septum are GABAergic and (v) terminate on supramammillary area non-GABAergic, calretinin-containing neurons, which are known to project to the septal complex and hippocampus. These observations indicate that a large population of cells participating in the hippocampal feedback regulation of theta regulation/generation contain the same calcium-binding protein. Furthermore, entorhinal excitatory transmitter-containing neurons can depress the activity of supramammillary theta generating/regulating cells via septal inhibitory neurons.

Adenovirus-mediated transgene expression in nonhuman primate brain

Transgene expression in the brain of St. Kitts green monkey, Cercopithecus aethiops sabeus, was studied following injection of a serotype 5 adenoviral vector deleted in E1 and E3. The vector harbored the transgene for Escherichia coli beta-galactosidase (beta-Gal) with the simian virus 40 (SV40) nuclear localization signal under control of the Rous sarcoma viral (RSV) long terminal repeat. Several titers ranging from 5 x 10(7) to 2 x 10(9) plaque-forming units (PFU) in volumes ranging from 5 to 250 microl were injected into the caudate nuclei of 18 monkeys. Monkeys were treated with dexamethasone for 9 days, beginning the day prior to surgery, and were sacrificed at 1 week or at 1, 2, or 3 months. At 1 week, beta-Gal was expressed in thousands of cells, including both neurons and astrocytes. In addition, some dopaminergic neurons in the substantia nigra expressed transgene, suggesting retrograde transport of the vector. At 1 month 162,000+/-68,000 (SEM) or 65,000+/-29,000 beta-Gal-expressing cells persisted in striatum injected with 6 x 10(8) PFU in 30 microl or 5 x 10(7) PFU in 5 microl, respectively. Transgene expression was also observed in one of two monkeys sacrificed at 2 months and in a single monkey sacrificed at 3 months. No transgene expression was observed at 1 month in striatum injected with a higher titer (2 x 10(9) PFU in 100 microl) or more dilute vector (5 x 10(7) PFU in 30 microl). Staining for the major histocompatibility complex II (MHC II) subtype DR showed intense staining in sites injected with a higher vector titer, in which no transgene persisted at 1 month, whereas low to moderate staining was present in sites with high transgene expression. These observations suggest that there is an optimal range of vector titers for obtaining persistent transgene expression from E1E3-deleted adenovirus in primate brain, above which host responses limit transgene stability.

Entorhinal cortical innervation of parvalbumin-containing neurons (Basket and Chandelier cells) in the rat Ammon's horn

Physiological data suggest that in the CA1-CA3 hippocampal areas of rats, entorhinal cortical efferents directly influence the activity of interneurons, in addition to pyramidal cells. To verify this hypothesis, the following experiments were performed: 1) light microscopic double-immunostaining for parvalbumin and the anterograde tracer Phaseolus vulgaris-leucoagglutinin injected into the entorhinal cortex; 2) light and electron microscopic analysis of cleaved spectrin-immunostained (i.e., degenerating axons and boutons) hippocampal sections following entorhinal cortex lesion; and 3) an electron microscopic study of parvalbumin-immunostained hippocampal sections after entorhinal cortex lesion. The results demonstrate that in the stratum lacunosum-moleculare of the CA1 and CA3 regions, entorhinal cortical axons form asymmetric synaptic contacts on parvalbumin-containing dendritic shafts. In the stratum lacunosum-moleculare, parvalbumin-immunoreactive dendrites represent processes of GABAergic, inhibitory basket and chandelier cells; these interneurons innervate the perisomatic area and axon initial segments of pyramidal cells, respectively. A feed-forward activation of these neurons by the entorhinal input may explain the strong, short-latency inhibition of pyramidal cells.

A novel method for concurrent visualization of immunostain under light and electron microscopy in pancreatic islets

We developed a simple method employing the use of flat-embedding techniques on thick frozen sections which allows correlation of light and electron microscopic immunohistochemistry. This method has been particularly useful in visualization of pancreas sections, an adaptation especially important because this tissue is not amenable to conventional vibratome sectioning. In this study we demonstrate the use of this technique to examine the same tissue section at the light and the electron microscopic level while maintaining morphology.

Efferent synaptic connections of dopaminergic neurons grafted into the caudate nucleus of experimentally induced parkinsonian monkeys are different from those of control animals

This study investigated the question of whether grafted dopamine cells in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys form synapses and, if they do, whether their postsynaptic targets were the same as those in control monkeys or in previous studies in rats. Electron-microscopic single immunostaining was performed for tyrosine hydroxylase on vibratome sections prepared from the head of the caudate nucleus of controls and MPTP-treated African green monkeys (Cercopithecus aethiops sabaeus) that received a graft. Furthermore, correlated light- and electron-microscopic double immunostaining was carried out for tyrosine hydroxylase and calbindin in the same brain area of MPTP-treated plus grafted animals. In control monkeys, the majority (97%) of dopamine boutons terminate on spines that were also synaptic targets of immunonegative boutons forming asymmetric synaptic contacts: synaptic triads. In MPTP-treated, grafted animals, the majority of transplanted dopamine cells terminate on dendritic shafts (67%) and somata (32%), and only a few (1.33%) form axospine synapses. The results of the double immunostaining experiments indicated that these newly formed axosomatic and axodendritic synapses are associated with calbindin-immunoreactive, medium-sized, spiny striatonigral projection neurons. These observations indicate that: (1) dopamine from transplanted embryonic tissue acts via synaptic contacts on host neurons; (2) the primary synaptic targets of transplanted dopamine cells are not spines but dendrites and somata of host neurons; (3) these target neurons are the same as in control animals; and (4) comparing these observations with results of control and grafted rats, there are major species differences between rats and monkeys in the dopamine innervation of both control and transplanted animals.

Dual (excitatory and inhibitory) calretinin innervation of AMPA receptor-containing neurons in the rat lateral septum

A recent study demonstrated both an extrinsic and an intrinsic calretinin (CR) innervation of the rat septal complex and that a population of the extrinsic calretinin fibers is aspartate/glutamate-containing. The aim of this study was to determine which types (GluR1, GluR2/3, or both) of AMPA receptor-containing lateral septal area neurons are innervated by extrinsic and intrinsic CR neurons and whether the intrinsic CR cells are GABAergic. Light- and electron-microscopic single immunostaining for CR, GluR1, and GluR2/3, as well as light- and electron-microscopic-double immunostaining experiments for CR plus GluR1 and CR plus GluR2/3 were performed in the lateral septal area. Furthermore, the "mirror" colocalization technique was employed on consecutive vibratome sections of the septal complex to investigate whether the intrinsic septal CR neurons are GABAergic. The results are summarized as follows: (1) both GluR1- and GluR2/3-immunoreactive neurons are innervated by CR-containing fibers; (2) the majority of these synapses, observed mainly on the soma and, to a lesser extent, on proximal dendrites of AMPA receptor-containing neurons, represent asymmetric synaptic membrane specializations; (3) a minority of CR-containing axon terminals associated with both GluR1- and GluR2/3-immunoreactive neurons form symmetric contacts, predominantly on their soma; and (4) 93% of the lateral septal area CR cells are GABAergic. These observations indicate that both GluR1- and GluR2/3-containing lateral septal area neurons receive a dual intrinsic and extrinsic CR innervation. The former (intrinsic) CR boutons are GABAergic, while the latter form asymmetric synaptic contacts, are excitatory, and probably originate in the supramammillary area, since previous work has demonstrated that a population of supramammillo-septal fibers contain aspartate and/or glutamate.

Substance P innervation of the rat hippocampal formation

Light and electron microscopic substance P (SP) immunostaining was performed on hippocampal sections of colchicine-pretreated, control, untreated fimbria-fornix-transected (5 days), as well as perforant path-stimulated Sprague-Dawley rats fixed in 5% acrolein. Numerous SP-immunoreactive neurons could be observed in the stratum oriens of the Ammon's horn and subiculum, fewer were seen in the dentate hilar area and stratum radiatum of CA2 and CA3, and even fewer were seen at the border between the CA1 strata radiatum and the lacunosum moleculare of CA1 subfield. A higher dose of colchicine resulted in SP immunoreactivity in a large population of granule cells and mossy axon terminals. The entire CA2 region, the stratum oriens of CA1, CA3, and the subiculum were densely innervated by SP-containing axon terminals. A homogeneous SP innervation was found in the stratum radiatum of CA1. Only a few SP fibers were seen adjacent to the granule cell layer. Symmetric axosomatic contacts were seen between SP-containing boutons and somata in the stratum oriens of the Ammon's horn. However, throughout the hippocampal formation, the majority of SP-containing axons formed axodendritic symmetric synapses. A dense population of SP-immunoreactive boutons that formed axodendritic asymmetric synapses was observed in the strata oriens and radiatum of the CA3a and CA2 regions, and a few were found in the supragranular and subgranular layers of the dentate gyrus. Fimbria-fornix transection resulted in a marked loss of SP fibers in the strata oriens, pyramidale, and radiatum of the CA3a and CA2 subfields. In perforant pathway-stimulated animals, a population of granule cells and a large number of mossy axon terminals were immunoreactive for SP. These observations suggest two sources of SP innervation to the hippocampal formation: one arising from intrinsic sources (interneurons and granule cells) and one arising from extrinsic sources, most likely the supramammillary region.

Dual role of substance P/GABA axons in cortical neurotransmission: synaptic triads on pyramidal cell spines and basket-like innervation of layer II-III calbindin interneurons in primate prefrontal cortex

In spite of accumulating evidence on the potent neuromodulatory, neuroprotective, trophic and memory-enhancing effects of the neuropeptide substance P (SP) in the cerebral cortex, the excitatory or inhibitory nature of the cortical SP innervation remains unclear and the postsynaptic targets of SP fibers are not defined. To obtain further insight into these issues, we have examined SP-containing axons and their postsynaptic targets in the prefrontal cortex of adult monkeys with single- and double label immunocytochemistry combined with light and correlated electron microscopy. SP fibers in the primate prefrontal cortex, unlike those in the rat cortex, preferentially innervate cortical layers I, II and upper layer III. Our results demonstrate for the first time that all SP-immunoreactive boutons in all cortical layers contain GABA. Of the entire sample of SP boutons, 53% synapse on dendritic shafts, 39% on dendritic spines and 8% on cell bodies. Another new finding is that synapse-forming SP boutons, in addition to their known innervation of pyramidal cells, form pericellular baskets around interneurons in layers II and upper III, a subpopulation of which contains calbindin D28k. Finally, the study also revealed that SP boutons frequently participate in 'synaptic triads' with spines which receive another (asymmetric, putatively excitatory amino acid-utilizing) synapse. Our findings indicate that SP/GABA axons in the primate prefrontal cortex modulate excitatory amino acid-mediated neurotransmission and control feed-forward disinhibitory GABAergic circuits in supragranular cortical layers.

Distinct substance P- and calretinin-containing projections from the supramammillary area to the hippocampus in rats; a species difference between rats and monkeys

Our recent studies showed the co-existence of substance P and calretinin in the supramammillo-hippocampal pathway of monkeys, as well as species differences in the synaptic targets of extrinsic substance P fibers in the hippocampi of monkeys and rats. Experiments used: (1) single and multiple stereotaxic injection of wheat germ agglutinin-conjugated HRP into the hippocampus and immunostaining for substance P in the supramammillary area; (2) colocalization of substance P and calretinin in supramammillary area cells; and (3) colocalization of these two neurochemicals in retrogradely labeled supramammillary projective cells of both male and female rats. These demonstrated: (a) many calretinin- and fewer substance P-immunoreactive neurons retrogradely labeled in the ipsilateral supramammillary area; (b) approximately 74% of all substance P cells contain calretinin and 9% of the calretinin neurons co-contain substance P; and, most importantly (c) none of the retrogradely labeled supramammillary cells colocalize calretinin and substance P. These results indicate the presence of two distinct supramammillo-hippocampal projections in the rat, one that contains substance P and the other calretinin. The latter innervates the same areas as those in the monkey, and the former terminates only in the CA2 hippocampal subfield.

Heterogeneity in the neuropeptide Y-containing neurons of the rat arcuate nucleus: GABAergic and non-GABAergic subpopulations

Neuropeptide Y, produced in the arcuate nucleus of the hypothalamus, plays a key role in the central regulation of anterior pituitary and appetitive functions. The pleiotropic nature of neuropeptide Y in these mechanisms indicates the existence of heterogeneity in the hypothalamic neuronal population producing neuropeptide Y. In this study, we report the coexistence of neuropeptide Y and the amino acid transmitter, gamma-aminobutyric acid (GABA), in neuronal perikarya of the arcuate nucleus. Fluorescent double immunolabeling for neuropeptide Y and glutamic acid decarboxylase was carried out on vibratome sections collected through the hypothalamic arcuate nuclei of animals that were pretreated with colchicine. It was found that about one third of the neuropeptide Y-producing arcuate nucleus perikarya co-expressed glutamic acid decarboxylase. This population of neuropeptide Y-containing GABAergic neurons were distributed longitudinally within the arcuate nucleus located predominantly in its dorsomedial aspects. These results show that there are at least two distinct populations of neuropeptide Y-producing neurons in the arcuate nucleus: a subset of neuropeptide Y and GABA-co-producing neurons located in the dorsomedial arcuate nucleus and a subset of non-GABAergic neuropeptide Y cells located in the ventral arcuate nucleus. This heterogeneity in the neuropeptide Y-producing perikarya of the hypothalamus may help explain adverse neuroendocrine and behavioral effects of arcuate nucleus neuropeptide Y.

Neurochemical characterization of AMPA receptor-containing neurons in the mediolateral septal area of the rat

The lateral septum receives a massive innervation by excitatory amino acid-containing limbic cortical and hypothalamic afferents, and previous studies have described a wide distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-containing neurons in this area. The aim of this study was to determine whether different subtypes of AMPA receptors are expressed in the same neurons. Furthermore, considering the fact that a population of lateral septal cells, the "somatospiny neurons," are GABAergic calbindin-containing cells, the coexistence of each subtype of AMPA receptor with calbindin was also investigated. Colocalization experiments were performed on adjacent vibratome sections of the lateral septal area for GluR1 and GluR2/3 AMPA-receptor subunits, GluR1 and calbindin, GluR2/3 and calbindin, as well as GluR1 plus calbindin and GluR2/3 plus calbindin, using the "mirror" colocalization technique. The results are summarized as follows: (1) GluR1 is present in the soma and most intensively expressed in dendrites and somatic and dendritic spines; while GluR2/3 is associated with the soma and proximal dendrites of the neurons. (2) Forty-one percent of the AMPA receptor-containing neurons cocontain GluR1 and GluR2/3. (3) Thirty-eight percent of GluR1- and 28% of GluR2/3-labeled cells express calbindin. (4) Sixty-two percent of the calbindin-immunoreactive neurons contain GluR1 and 51% of them express GluR2/3. (5) Half of the neurons expressing both GluR1 and GluR2/3 also contain calbindin. (6) The distribution of GluR1 plus GluR2/3-containing, GluR1 plus calbindin-containing, and GluR2/3 plus calbindin-containing neurons in the lateral septum are homogeneous. This study indicates the existence of multiple populations of AMPA receptor- and calbindin-containing neurons in the lateral septal area.

Hypothalamo-septal enkephalinergic fibers terminate on AMPA receptor-containing neurons in the rat lateral septal area

A large number of septal neurons express alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA)-type excitatory glutamate receptors. It has been demonstrated that in the mediolateral part of the rat lateral septum, calbindin-containing neurons are heavily innervated by hypothalamic, enkephalinergic fibers forming exclusively asymmetric synaptic contacts. This connection was suggested to be excitatory. In order to further elucidate this hypothesis, the aim of the present study was to determine whether these enkephalinoceptive neurons express GluR1 and GluR2/3 AMPA receptor subunits. Correlated light and electron microscopic analysis, using single immunostaining for GluR1 and GluR2/3, and double immunostaining for Leu-enkephalin and GluR1 or GluR2/3, was performed on vibratome sections of the rat lateral septal area. The studies revealed that while GluR1 is mainly associated with dendritic and somatic spines, GluR2/3 is mostly present in the perisomatic area. Leu-enkephalin boutons establish asymmetric synaptic contacts at the level of the soma and initial dendrites of both of these cells. A semiquantitative analysis showed that these enkephalin-targeted cells represent 50% of the total number of both GluR1 and GluR2/3-containing lateral septal neurons. These results suggest that: (1) AMPA receptor-expressing neurons appear to be the exclusive recipient of hypothalamic Leu-enkephalin boutons; (2) these enkephalinoceptive neurons contain both GluR1 and GluR2/3 AMPA receptor subunits; however, (3) only the GluR2/3 subtype, located in the perisomatic area, may be associated with Leu-enkephalin-containing inputs.

Parvalbumin-containing cells of the angular portion of the vertical limb terminate on calbindin-immunoreactive neurons located at the border between the lateral and medial septum of the rat

In the septal complex, both parvalbumin and calbindin neurons cocontain GABA. In the same area, a large number of GABA-GABA synaptic connections can be observed. In order to further characterize their neurochemical nature, as well as the extrinsic and/or intrinsic origin of these GABA terminals, the following experiments were performed: (1) correlated light- and electron-microscopic double immunostaining for calbindin and parvalbumin on septal sections of control rats: (2) light microscopic parvalbumin immunostaining of septal sections after surgical isolation (5 days) of the septum from its telencephalic or (3) hypothalamic afferents; and (4) parvalbumin immunostaining of sections prepared from the entire brain 2 days following horseradish peroxidase injection into the border between the lateral and medial septum. The results demonstrated that: (1) in a well-circumscribed, vertically longitudinal area located between the lateral and medial septum, 0.1-0.6 mm anterior to the bregma, a group of calbindin-containing, nonsomatospiny neurons are surrounded by parvalbumin-immunoreactive baskets; (2) these basket-forming axon terminals establish symmetric synaptic contacts with their targets; and (3) their cells of origin are not in the medial septum, but in the angular portion of the vertical limb. These observations indicate that a portion of the septal complex GABA-GABA synaptic connections represent functional interaction between two different types of GABAergic neurons. The presynaptic GABAergic neurons contain parvalbumin, and the postsynaptic GABAergic cells are immunoreactive for calbindin. Furthermore, a population of the medial septum/diagonal band parvalbumin neurons project only to the hippocampus, while others, which may also send axons to the hippocampus, terminate on lateral septum calbindin cells as well.

A population of supramammillary area calretinin neurons terminating on medial septal area cholinergic and lateral septal area calbindin-containing cells are aspartate/glutamatergic

The excitatory amino acid, aspartate/glutamate content of septal complex calretinin (CR)-, choline acetyltransferase plus substance P-, and Leu-enkephalin (Leu-enk)-containing extrinsic afferents was examined. Experiments were carried out using the transmitter-specific [3H]-D-aspartate retrograde tracer technique in combination with immunostaining for CR, choline acetyltransferase, and Leu-enk. The extrinsic and intrinsic CR innervation of the same brain areas were elucidated on control rats and on animals in which the septum was surgically separated from its ventral afferents. Correlated light and electron microscopic double-immunostaining experiments were used to determine the synaptic connections between CR axon terminals and lateral septal area calbindin (CB)- and medial septal area choline acetyltransferase-immunoreactive neurons. Furthermore, to determine the synaptic power of supramammilloseptal aspartate/glutamatergic neurons on the septal complex, semiquantitative analyses were performed in the supramammillary area on retrogradely (1) [3H]-D-aspartate-radiolabeled and (2) HRP-labeled material. The results demonstrated that a population of the extrinsic CR axons originating in the supramammillary area are aspartate/glutamatergic. These fibers forming asymmetric synaptic contacts terminate on both CB and cholinergic neurons. Intraseptal CR neurons, which establish symmetric synapses, innervate only lateral septal area neurons, including the CB-containing cells. These observations, together with other published data, raise the possibility of a hippocampus-lateral septal (GABAergic CB-containing neurons)-supramammillary area (aspartate/glutamatergic cells)-medial septal (cholinergic neurons)-hippocampus signal loop, which might be involved in the generation and regulation of hippocampal theta rhythm activity.

Morphological and pharmacological evidence for neuropeptide Y-galanin interaction in the rat hypothalamus

Galanin (GAL) and neuropeptide Y (NPY) have been shown to play important roles in the regulation of pituitary hormone secretion, as well as ingestive and sexual behaviors, by acting within the hypothalamus. While the mechanism of action of these regulatory peptides is under intensive investigation, less attention has been paid to the possible interaction between them in influencing these central regulatory processes. Because NPY and GAL augment pituitary gonadotropin release, the present study was undertaken to evaluate the nature of morphological and functional relationships between these excitatory hypothalamic peptidergic systems. Double immunolabeling for NPY and GAL was carried out on vibratome sections taken from the hypothalamus of colchicine-pretreated female rats. Avidinbiotin peroxidase technique and a dark blue diaminobenzidine reaction was used to visualize NPY profiles, while the GAL neurons were labeled with a light brown diaminobenzidine reaction using either the avidin-biotin peroxidase or the peroxidase antiperoxidase technique. Light microscopic examination of the immunostained material showed that in the arcuate nucleus, paraventricular nucleus, supraoptic nucleus, anterior hypothalamus, and medial preoptic area, an abundant network of NPY-immunoreactive axons surrounded GAL-immunostained cells. Numerous dark blue NPY-containing putative boutons were observed in close proximity to GAL-immunolabeled cell bodies and dendrites. Correlated light and electron microscopic examination revealed that most of the immunoreactive NPY axon terminals established synaptic connections with GAL-expressing cells. Synaptic connections were most frequently found in the medial preoptic area and in the magnocellular region of the paraventricular nucleus and arcuate nucleus. Fewer connections were observed in the supraoptic nucleus. These morphological observations demonstrate the existence of a strong NPY input to hypothalamic GAL neurons, thereby suggesting a modulatory role for NPY in monitoring GAL release. To evaluate the functional relevance of this anatomical relationship, the effects of intraventricular injection of a GAL receptor antagonist, galantide, were examined on NPY-induced LH release in ovarian steroid-primed ovariectomized rats. As expected, intraventricular injection of NPY readily stimulated LH release. Although, while on its own, galantide was ineffective in altering basal LH release, it markedly attenuated the NPY-induced LH response, thereby suggesting that GAL released in response to NPY administration may, in part, mediate the excitatory effects of NPY. These experimental results, taken together with the morphological observations, document the involvement of an NPY --> GAL signaling modality in the release of gonadotropins and, likewise, raise the possibility of a similar signaling process in the release of other pituitary hormones and elicitation of behavioral effects attributed to NPY and GAL.

Distribution of substance P-immunoreactive neurons and fibers in the monkey hippocampal formation

Substance P containing neurons was visualized by immunocytochemistry in the monkey hippocampus, subicular complex, and entorhinal cortex. Immunoreactive neurons were found solely in the hilar region of the dentate gyrus, and in strata oriens and pyramidale of Ammon's horn. In the subicular complex, immunoreactive neurons were located in those layers which were close to the alveus, whereas in the entorhinal cortex most of the substance P-positive neurons appeared in the second and third layers above the lamina dissecans. The majority of substance P-containing neurons were large multipolar cells, but small bipolar and multipolar cells also occurred in Ammon's horn, subiculum and entorhinal cortex. Dendrites of immunoreactive cells were smooth and displayed a few small, faintly stained spines which were hard to identify in the light microscopic preparations, but were visible with electron microscopy. Substance P-positive dendrites were exclusively found in the hilar region and never observed in the upper two-thirds of the molecular layer of the dentate gyrus. Moreover, immunoreactive dendrites rarely penetrated the stratum lacunosum-moleculare of Ammon's horn. In the electron microscopic preparations, somal and dendritic features of substance P-positive neurons were similar to those observed for GABAergic local circuit neurons. Axons of the substance P-immunoreactive local circuit neurons were thin and richly arborized in the upper two-thirds of the molecular layer of the dentate gyrus, in the stratum lacunosum-moleculare of Ammon's horn as well as in the subpial layers of the subicular complex and entorhinal cortex. Their terminals formed exclusively symmetric synapses with dendrites and spines. However, substance P-immunoreactive boutons were not found to make symmetric, axosomatic synapses on the granule cells of the dentate gyrus and very few were present on the pyramidal neurons of Ammon's horn, subicular complex, and entorhinal cortex. Hippocampal neurons, which were immunoreactive for substance P, also contained the neuropeptide somatostatin. However, not all of the somatostatin-containing neurons were substance P-immunoreactive. Thus, substance P-positive neurons are a subpopulation of somatostatin immunoreactive, GABAergic neurons. In conclusion, substance P-immunoreactive neurons are ideally suited for feed-back dendritic inhibition which may control the effectiveness of the main excitatory cortical input to the granule cells of the dentate gyrus and pyramidal neurons of the Ammon's horn.

Potential neuronal mechanisms of estrogen actions in synaptogenesis and synaptic plasticity

1. Studies conducted on the rat arcuate nucleus, an area involved in the development and control of LH and FSH secretion, have shown the existence of hormonally regulated developmental sex differences in synaptic patterns and estrogen-induced synaptic plasticity during adult life. Several questions raised by these findings are examined in this review: 2. The mechanisms of estrogen-regulated developmental synaptogenesis. These include the role of glycocalyx glycoproteins in neuronal membranes, neural cell adhesion molecules, and insulin-like growth factor I. 3. The relationship among circulating estrogen, gonadotropin levels, and hypothalamic synaptic plasticity. Recent evidence for the role of GABAergic and dopaminergic synaptic inputs and POMC projections from the arcuate nucleus to the GnRH cells is discussed. 4. The synaptologic basis of age-related failure of positive feedback. The role of the cumulative effect of repeated preovulatory synaptic retraction and reapplication cycles on sensescent constant estrus is analyzed.

AMPA receptors in the rat and primate hippocampus: a possible absence of GluR2/3 subunits in most interneurons

Amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors are assembled from the four subunits GluR1, 2, 3, 4 (or GluRA, B, C, D). AMPA channels that do not contain the GluR2 subunit are permeable to calcium. Recent studies indicate that excitotoxic as well as epileptic and ischemic cell damage may be mediated not only by N-methyl-Daspartate receptors, but also by AMPA receptors. The majority of interneurons in the hippocampus are resistant, but subsets of interneurons are consistently damaged in different disease states. Single immunolabeling using antibodies against AMPA receptor subunits, together with double immunolabeling for calcium-binding proteins (parvalbumin, calbindin and calretinin) and the neuropeptide somatostatin, were performed to study GluR1-4 immunoreactivity in interneuronal populations and principal cells. The ultrastructure of GluR1-4 labeled neurons was also examined using electron microscopy. With the exception of calbindin-positive interneurons, GluR2/3 was absent from hippocampal interneurons in both rat and monkey. In the rat, interneurons were more strongly immunoreactive against GluR1 than principal cells. In the monkey, immunoreactivity for GluR4 in interneurons was stronger than for GluR1. All GluR subunits were confined to spines, dendritic membrane and cytoplasm surrounding the nucleus but absent from axons and presynaptic terminals. Our findings suggest that hippocampal principal cells and interneurons express different complements of AMPA receptor subunits. Furthermore, the absence of GluR2 and/or GluR3 in both vulnerable and resistant interneurons subtypes indicates that knowledge of receptor subunit composition is not sufficient to predict neuronal vulnerability.

Aromatase immunoreactivity in axon terminals of the vertebrate brain. An immunocytochemical study on quail, rat, monkey and human tissues

Intraneuronal production of estradiol from testosterone has been shown to play a pivotal role in gender-specific brain development of most vertebrates, and to participate in numerous functions of the adult central nervous system. Previous biochemical and morphological approaches demonstrated that estrogen synthetase (aromatase) is present in specific limbic and hypothalamic structures. On the other hand, less attention has been paid to revealing its subcellular distribution. The possibility of aromatase presence in axonal processes has been indicated by recent biochemical and morphological observations suggesting new insights for the role of aromatase in neural functions. The objective of the present study was to provide morphological evidence for the subcellular location of aromatase in neurons of different vertebrate species including Japanese quail, rat, monkey, and human. Immunocytochemistry using a purified polyclonal antiserum against human placental aromatase localized immunoreactivity to hypothalamic and limbic cell groups in all of these species. Light and electron microscopic examination of vibratome sections revealed the presence of aromatase immunoreactivity throughout the neuronal perikarya, including dendrites and axonal processes. In each species there were numerous boutons which contained labeled small clear synaptic vesicles. Many of these axon terminals formed synapses with immuno-negative and immuno-positive dendrites and perikarya. This study furnishes the first immunolocalization of aromatase in the brains of two primate species, humans and monkeys. The provision of further evidence for estrogen synthesis in axons and axon terminals may help resolve apparent differences between the measurement of aromatase activity and the lack of aromatase-immunopositive cell bodies in previous studies. The present findings may be coupled with recent evidence regarding the molecular biology and the diversity of functional properties of P450 aromatase to indicate previously unexpected effects of brain aromatase at the synaptic level.

GABAergic neurons in the rat dentate gyrus are innervated by subcortical calretinin-containing afferents

Fibers of supramammillary origin establish putatively excitatory asymmetric synaptic connections with dentate granule cells. The present study was designed to determine whether hippocampal gamma-aminobutyric acid (GABA)-ergic nonprincipal cells are also targets of these calretinin (CR)-containing subcortical afferents. Light and electron microscopic double immunostaining for CR and parvalbumin (PA) or calbindin (CB) were performed in the rat dentate gyrus ipsilateral and contralateral to a unilateral fimbria-fornix transection. GABA-postembedding immunostaining was performed on ultrathin sections of this double-labeled material. Contralateral to the transection, CR-immunoreactive fibers formed multiple large boutons in the inner molecular layer. These fibers also impinged on PA-containing basket cells located adjacent to the granular layer and on CB-immunoreactive hilar neurons. Ipsilateral to the transection, CR-containing fibers in the inner molecular layer and boutons impinging on PA-containing or CB-immunoreactive neurons were absent. Parent cell bodies of extrinsic CR-containing afferents were traced using wheat germ agglutinin-conjugated horseradish peroxidase. Additional CR immunostaining of the subcortical region unveiled retrogradely labeled neurons that were also immunostained for CR only in the supramammillary area and the nucleus reuniens. The latter projection, however, terminates in CA1 and not in the dentate gyrus. Subcortical afferents impinging on dentate nonprincipal cells formed exclusively asymmetric synapses. Postembedding immunostaining demonstrated that CB-containing cells contain GABA, whereas CR-positive axon terminals forming asymmetric synapses are devoid of this labeling. These data indicate that dentate inhibitory neurons receive a putative excitatory input originating from the supramammillary nucleus. Thus, the supramamillo-hippocampal pathway may exert a powerful feed-forward inhibitory control of the signal flow in the rat dentate gyrus.

Extrinsic and intrinsic substance P innervation of the rat lateral septal area calbindin cells

The electrophysiological observations that substance P administration to the lateral septal area elicits both excitatory and inhibitory responses, together with earlier reports on the multiple sources of substance P innervation of the septum, implies that these axons with distinct origins have different functions. This prompted us to examine the origin and neurochemical character of substance P afferents to the lateral septal area. Chronic surgical isolation of the septum from its ventral afferents and retrograde tracer experiments using wheat germ agglutinin-conjugated horseradish peroxidase, both followed by an immunostaining for substance P, were employed to elucidate the origin of these axon terminals. In order to assess the possible co-existence of substance P with other neurotransmitter substances in the parent cells of the septopetal projections, co-localization studies for substance P and choline acetyltransferase, as well as substance P and GABA, were performed. The comparative distribution of substance P fibers and septal calbindin-containing neurons was also investigated using correlated light and electron microscopic double immunostaining. The results are summarized as follows: (i) the substance P innervation of the lateral septal area derives from several hypothalamic nuclei (including the lateral and lateroanterior hypothalamic area, tuber cinereum and ventromedial hypothalamic nucleus) and tegmental nuclei (the majority of fibers from the laterodorsal and a few from the pedunculopontine tegmental nucleus), as well as intrinsic septal cells; (ii) the septopetal substance P fibers of tegmental origin are cholinergic; intraseptal substance P neurons located in the dorsolateral part of the lateral septum also contain GABA, while substance P neurons seen on the border between the medial and lateral septal area and septopetal hypothalamic substance P cells do not contain GABA or acetylcholine; (iii) substance P fibers from pericellular baskets around calbindin-containing lateral septal neurons with a high degree of selectivity; (iv) approximately 90% of the entire calbindin cell population are postsynaptic targets of substance P axons; (v) their terminals contact the soma and the dendrites of these cells, among them the somatospiny neurons; and (vi) the extrinsic substance P boutons establish asymmetric, while the intrinsic substance P axon terminals form symmetric membrane specializations. Because neurons in the lateral septal area receive hippocampal input and project massively to hypothalamic areas, the different types of substance P input on these neurons can modify the information flow arriving from the hippocampus to diencephalic brain structures at the level of the lateral septal area.

Psychiatric status after human fetal mesencephalic tissue transplantation in Parkinson's disease

This report describes the prospective and systematic psychiatric assessment of nine patients who received transplantation of human fetal mesencephalic tissue into the caudate nucleus for treatment of Parkinson's disease. Unlike adrenal medullary transplantation, which often causes psychosis or delirium, this procedure appeared to have few perioperative sequelae. On longer-term follow-up, there was some statistical evidence of deterioration in psychiatric status, as manifested primarily in depressive and nonspecific emotional and behavioral symptoms. This group effect was partly attributable to the occurrence of discrete episodes of illness (major depression and panic disorder with agoraphobia) in some patients, but it was unclear whether such episodes occurred more often than would ordinarily be expected in Parkinson's disease. Differences in the neurobiological effects of fetal mesencephalic and adrenal medullary grafts may account for differences in the psychiatric sequelae of patients receiving these procedures.

Hypothalamic Leu-enkephalin-immunoreactive fibers terminate on calbindin-containing somatospiny cells in the lateral septal area of the rat

Correlated light and electron microscopic double-immunostaining experiments for Leu-enkephalin and calbindin were employed to determine the postsynaptic targets in the septal complex of Leu-enkephalin fibers. Chronic surgical isolation of the septal complex from its hypothalamic afferents and retrograde tracer studies using wheat germ agglutinin-conjugated horseradish peroxidase, both followed by an immunostaining for Leu-enkephalin, were performed to elucidate the location of the origin of these axon terminals. Furthermore, a colocalization study for glutamic acid decarboxylase and Leu-enkephalin was carried out on hypothalamic sections to determine their possible coexistence in cells projecting to the lateral septum. These studies revealed that 1) Leu-enkephalin-immunoreactive axons form pericellular baskets around a population of lateral septal area neurons; 2) they establish exclusively asymmetric synaptic contacts on their soma and initial dendritic segments; 3) 10% of the lateral septal area calbindin-containing cells, which are all of the gamma-aminobutyric acid (GABA)-ergic somatospiny type, are innervated by Leu-enkephalin-immunoreactive baskets; 4) only 40% of the Leu-enkephalin target neurons are calbindin immunopositive; 5) the septopetal Leu-enkephalin fibers derive from neurons located in the ipsilateral perifornical area and anterior hypothalamus; and 6) none of their cells of origin cocontains the inhibitory transmitter GABA. These observations indicate that hypothalamic Leu-enkephalin-containing neurons are non-GABAergic excitatory cells. Hence, they can effectively stimulate a population of lateral septal area neurons, including the somatospiny cells, which are all GABAergic. Therefore, after stimulatory Leu-enkephalin action, these neurons can inhibit their postsynaptic targets, including other projective lateral septal neurons.

Morphological evidence for a galanin-opiate interaction in the rat mediobasal hypothalamus

It is well established that hypothalamic galanin- and beta-endorphin-containing circuits play important roles in the neuroendocrine regulation of pituitary hormone secretion and sexual behaviors, as well as in feeding. Recent experimental evidence suggests that an opiate-galanin interaction may be involved in these neuroendocrine responses. In particular, galanin and beta-endorphin have been shown to stimulate prolactin release from the pituitary, and concurrently, evoke feeding in the rat. The present study was designed to elucidate the morphological component underlying these responses in the hypothalamus. Sections of the mediobasal hypothalamus of colchicine-pretreated female rats were double immunostained for galanin and beta-endorphin. A dark blue nickel ammonium sulfate-intensified diaminobenzidine reaction was used to visualize galanin profiles, while beta-endorphin neurons were labeled with a light brown diaminobenzidine reaction. Light microscopy revealed putative connections between galanin boutons and beta-endorphin cells. Electron microscopic examination showed that galanin boutons form axo-somatic and axo-dendritic synaptic connections with beta-endorphin neurons. The vast majority (89.6%) of the beta-endorphin-immunoreactive neurons were found to be contacted by galanin-immunopositive fibers in the hypothalamus. To determine the origin of the galanin fibers innervating this region, the arcuate nuclei of additional rats were isolated unilaterally using a Halász-knife. After a ten day survival period, immunostaining was carried out for galanin. The relative surface occupied by galanin immunoreactive profiles on the ipsi- and contralateral sides were compared using an image analyzer. This analysis revealed that deafferentation of the arcuate nucleus did not decrease the density of galanin immunoreactive profiles on the isolated side of the arcuate nucleus compared to the control side, thus, indicating that the galanin boutons contacting beta-endorphin cells are most probably of local origin. These studies support the proposal that galanin-evoked prolactin secretion and feeding behavior may, in part, be mediated by enhanced beta-endorphin release and raises the possibility that a hypothalamic galanin-beta-endorphin axis may operate in the control of other pituitary hormones.

Cholinergic synaptic circuitry in the macaque prefrontal cortex

Surprisingly little is known about the synaptic architecture of the cholinergic innervation in the primate cerebral cortex in spite of its acknowledged relevance to cognitive processing and Alzheimer's disease. To address this knowledge gap, we examined serially sectioned cholinergic axons in supra- and infragranular layers of the macaque prefrontal cortex by using an antibody against the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT). The tissue bound antibody was visualized with both immunoperoxidase and silver-enhanced diaminobenzidine sulfide (SEDS) techniques. Both methods revealed that cholinergic axons make synapses in all cortical layers and that these synapses are exclusively symmetric. Cholinergic axons formed synapses primarily on dendritic shafts (70.5%), dendritic spines (25%), and, to a lesser extent, cell bodies (4.5%). Both pyramidal neurons and cells exhibiting the morphological features of GABAergic cells were targets of the cholinergic innervation. Some spiny dendritic shafts received multiple, closely spaced synapses, suggesting that a subset of pyramidal neurons may be subject to a particularly strong cholinergic influence. Analysis of synaptic incidence of cholinergic profiles in the supragranular layers of the prefrontal cortex by the SEDS technique revealed that definitive synaptic junctions were formed by 44% of the cholinergic boutons. An unexpected finding was that cholinergic boutons were frequently apposed to spines and small dendrites without making any visible synaptic specializations. These same spines and dendrites often received asymmetric synapses, presumably of thalamocortical or corticocortical origin. Present ultrastructural findings suggest that acetylcholine may have a dual modulatory effect in the neocortex: one through classical synaptic junctions on dendritic shafts and spines, and the other through nonsynaptic appositions in close vicinity to asymmetric synapses. Further physiological studies are necessary to test the hypothesis of the nonsynaptic release of acetylcholine in the cortex.

General cognitive ability following unilateral and bilateral fetal ventral mesencephalic tissue transplantation for treatment of Parkinson's disease

OBJECTIVE

To contrast the neuropsychological profiles of Parkinsonian patients, before and after fetal ventral mesencephalic tissue transplantation.

DESIGN

Case series of personally examined patients.

SETTING

Patients were evaluated by neurologists, neurosurgeons, and neuropsychologists as outpatients at a university hospital.

PATIENTS

Fetal mesencephalic tissue was implanted in the right caudate nucleus of three patients and both nuclei of one patient. These patients were evaluated prior to surgery and at 12, 24, and 26 months postoperatively.

RESULTS

Factor analysis of the test battery identified four statistically orthogonal test clusters. No statistically significant changes were identified postoperatively for clusters assessing verbal cognitive ability, nonverbal cognitive ability, and information-processing speed. An improvement of verbal memory cluster index was observed 12 months after surgery, and the improvement reached the level of statistical significance at 24 months after surgery. However, the verbal memory of all patients declined between 24 and 36 months after surgery.

CONCLUSIONS

Fetal tissue transplantation to one or both caudate nuclei did not permanently arrest cognitive dysfunction. Although there is some evidence of improved cognitive ability after transplantation, it is improbable that normal cognitive function can be restored by this procedure because the impairments of cognitive ability associated with Parkinson's disease do not appear to originate solely from dopamine deficiency.

Galanin neurons exhibit estrogen receptor immunoreactivity in the female rat mediobasal hypothalamus

Galanin has been shown to augment the hypothalamic luteinizing hormone releasing hormone and pituitary luteinizing hormone release and to play an important role in the feedback effects of ovarian steroids on pituitary hormone secretion. To further characterize estrogen effects on galanin, we tested for the existence of estrogen receptors in arcuate nucleus galanin-producing cells. Hypothalamic vibratome sections from colchicine-pretreated female rats were double immunolabeled for estrogen receptor and galanin. Neurons which exhibited immunoreactivity for either estrogen receptor or galanin were distributed throughout the hypothalamus; and a population of neurons, located predominantly in the mediobasal hypothalamus, displayed immunoreactivity for both galanin and estrogen receptor. These results raise the possibility that estrogen may act directly on galanin-producing arcuate nucleus neurons to regulate pituitary hormone secretion.

Distribution of estrogen receptor-immunoreactive cells in monkey hypothalamus: relationship to neurones containing luteinizing hormone-releasing hormone and tyrosine hydroxylase

The precise sites and mechanisms by which gonadal steroids influence the activity of neuroendocrine cells controlling pituitary hormone secretion are poorly understood. The present study has determined the distribution of estrogen receptor (ER)-immunoreactive cells in the monkey hypothalamus and examined whether ERs are expressed by luteinising hormone-releasing hormone (LHRH)-and/or dopamine-containing neurones. The distribution of ER-immunoreactive cells was determined in ovariectomised (n = 2) and estrogen plus progesterone-treated (n = 2) cynomolgus macaques and in a single ovariectomised African green monkey. Large numbers of cells immunoreactive for the ER were detected in the preoptic area, bed nucleus of the stria terminalis, periventricular area and ventromedial and arcuate nuclei of all monkeys irrespective of the steroid status. Smaller numbers of ER-immunoreactive cells were found in the paraventricular, but not supraoptic nucleus. Double-labeling experiments in sections from all 5 monkeys revealed that none of the 432 LHRH neurons examined possessed detectable ER immunoreactivity. Neurones stained for tyrosine hydroxylase (TH) were identified in the A11, A12, and A14 cell groups and, although A11 and A12 neurones were intermingled amongst and found adjacent to ER-immunoreactive cells, none of the 1,652 TH-immunoreactive cells examined contained ER immunoreactivity. These results show that ER-immunoreactive cells in the monkey hypothalamus are distributed in a manner similar to that observed in other mammalian species although not all brain regions reported to contain progesterone receptors (PRs) in these species of monkey were found to express ERs. The double-labelling experiments provide further evidence that LHRH neurones do not possess ERs and indicate that, as in other species, estrogen influences on primate LHRH neurones are indirect and/or non-genomic in nature. Unlike the rat and sheep, no evidence was found for ER immunoreactivity in hypothalamic dopaminergic neurones of the monkey. The discrepancy in ER and reported PR receptor localisation within specific hypothalamic nuclei as well as in dopaminergic neurones raises the possibility that not all PR-containing cells may express ERs in the primate hypothalamus.

Naloxone reduces the feeding evoked by intracerebroventricular galanin injection

Central injection of galanin elicits feeding in satiated rats. We recently observed galanin-immunoreactive fibers in synaptic connection with a population of beta-endorphin-immunopositive cell bodies and dendrites in the basal hypothalamus. Because beta-endorphin also stimulates food intake, these morphological findings raised the possibility that stimulation of feeding by galanin may, in part, be mediated by beta-endorphin release. First, we observed that ICV injection of galanin (1.5-6.0 nmol) stimulated feeding in a dose-related fashion. Next, the effect on food intake of the opioid receptor antagonist naloxone (20-200 micrograms, ICV) administered immediately preceding galanin (3 nmol, ICV) was evaluated. Galanin-induced feeding was suppressed by naloxone in a dose-dependent manner with a maximal suppression of 76% at the highest naloxone dose. These findings support the existence of a functional link between galanin and beta-endorphin and are in accord with the view that stimulation of food intake by galanin may, in part, be mediated by increased beta-endorphin release.

Substance P-containing hypothalamic afferents to the monkey hippocampus: an immunocytochemical, tracing, and coexistence study

In order to identify the synaptic connections of substance P-containing afferents within the hypothalamo-hippocampal projection of the monkey, we performed a combined light and electron microscopic, immunocytochemical study, made lesions of the fimbriafornix, and employed retrograde tracing using WGA-HRP. Furthermore, coexistence studies for substance P and GAD were performed to identify the putative transmitters of these hypothalamic projection neurons. A plexus of large substance P-immunoreactive terminals was identified in both the innermost portion of the molecular layer and in CA2. Axon terminals in both plexuses established exclusively asymmetric synapses with spines and dendritic shafts. Substance P-immunoreactive boutons were degenerating 5 days after lesioning, and had disappeared 10 days after ipsilateral fimbria-fornix transection. Thus, these terminals were of extrinsic origin. In contrast, immunoreactive fibers in the outer third of the dentate molecular layer remained unaffected by the lesion. Retrograde tracing combined with immunostaining for substance P revealed the parent cell bodies of the extrinsic substance P-containing afferents in the supramammillary nucleus. Colocalization studies employing a consecutive semi-thin sections technique indicate that these large substance P-containing projection neurons lack GABA as an inhibitory transmitter. These results suggest that hypothalamic afferents of the monkey hippocampus contain substance P. Because these afferents lack GABA as an inhibitory transmitter and establish exclusively asymmetric synapses, this projection may excite hippocampal target neurons.

Sprouting of remaining substance P-immunoreactive fibers in the monkey dentate gyrus following denervation from its substance P-containing hypothalamic afferents

This study analyzed the response of intrinsic substance P-immunoreactive fibers in the monkey dentate gyrus to disruption of the supramammillo-hippocampal projection. This projection normally forms a thin plexus of large, substance P-immunoreactive terminals in the innermost portion of the dentate molecular layer and establishes exclusively asymmetric synapses with dendritic shafts and spines of dentate neurons. Conversely, substance P-containing terminals have never been observed in synaptic contact with granule cell bodies. Ten days after ipsilateral fimbria-fornix transection, the prominent band of large immunostained axons in the inner molecular layer of the ipsilateral fascia dentata disappeared. Four and five weeks following transection, however, some small, substance P-containing terminals were observed in the innermost portion of the dentate molecular layer and the granule cell layer. These terminals established exclusively symmetric synapses with the somata and proximal dendritic shafts of granule cells. These results suggest that, following transection of the hypothalamo-hippocampal fiber tract, presumptive intrinsic substance P-containing axons are capable of sprouting into the granule cell layer and the former termination field of the hypothalamic fibers. The symmetric synapses established with granule cell bodies and their proximal dendrites might indicate a shift from an extrinsic excitation to an intrinsic inhibition of granule cells following disruption of substance P-containing hypothalamic afferents.