Catecholamine innervation of the basal forebrain. II. Amygdala, suprarhinal cortex and entorhinal cortex

The catecholamine (CA) innervation of the posterior basal forebrain, the amygdala, suprarhinal cortex and entorhinal cortex, was studied in the rat using biochemical assay and fluorescence histochemistry. The assay studies demonstrate a moderate norepinephrine (NE) content in the amygdala and entorhinal cortex with a lower value for the suprarhinal cortex. Following destruction of the locus coeruleus, the decrease in NE content of these basal forebrain structures indicates that their principal NE innervation is from locus coeruleus. An additional small NE input arises from the medullary NE neuron groups. Ablation of dopamine (DA) cell groups (substantia nigra-ventral tegmental area, SN-VTA) indicates that the DA input to the amygdala arises from the lateral VTA and medial half of the SN. Fluorescence histochemical studies using the glyoxylic acid-Vibratome technique demonstrate the presence of four distinct types of CA neuron terminal plexus in the posterior basal forebrain. These include two different DA fiber types arising in SN-VTA, small NE fibers with small varicosities arising in locus coeruleus and NE fibers with larger varicosities arising in other brainstem NE cell groups. The large NE fibers appear to enter the amygdala via the ansa peduncularis-ventral amygdaloid bundle to innervate the central and basolateral nucleus and the anterior amygdaloid area. The locus coeruleus NE fibers appear to enter the posterior basal forebrain via both the stria terminalis and ansa peduncularis-ventral amygdaloid bundle system to form a moderately dense innervation of the central and basolateral nuclei of the amygdala and a less dense innervation of the other areas. The DA neuron axons are concentrated in the central and basal nuclei and intercalated cell groups. Other areas receive a more diffuse DA input, with the exception of the moderately dense innervation of the suprarhinal cortex and DA "islands" in the ventral-anterrior entorhinal cortex, The DA input to the posterior basal forebrain is complex and heterogeneous and the axonal morphology differs greatly among the terminal fields within the amygdala and adjacent cortical areas.     

Origin and organization of brainstem catecholamine innervation in the rat

The catecholamine (CA) innervation of the rat brainstem was studied by biochemical analysis of discrete nuclei or areas and by glyoxylic acid-formaldehyde freeze dry fluorescence histochemistry. CA assays demonstrate that the highest norepinephrine (NE) content in brainstem is present in the trigeminal motor nucleus, nucleus tractus solitarius, dorsal motor nucleus of the vagus and nucleus raphe dorsalis. Bilateral locus coeruleus (LC) lesions do not significantly alter NE content in these nuclei but do decrease NE content in the superior and inferior colliculi, medial geniculate body, interpeduncular nucleus, pontine nuclei and the main sensory trigeminal nucleus (60-75%). Dopamine (DA) and epinephrine (E) are found in significant concentration in only a few of the nuclei examined. Fluorescence histochemical analysis indicates that two groups of NE axons innervate rat brainstem. LC neuron axons with a distinctive morphology principally innervate sensory and association nuclei of the brainstem. These disappear completely after bilateral LC lesions. The second group of axons originates from lateral and dorsal tegmental NE cell groups. Primary motor and visceral nuclei are densely innervated by fine and thick axons from these groups. Lesions of LC do not alter the NE innervation in any of the nuclei which contain axons of the second group. These results indicate that the brainstem NE innervation is divided into two major systems. The locus coeruleus complex innervates mainly primary sensory and association nuclei whereas the lateral tegmental NE neurons innervate primary motor and visceral nuclei. Although some overlap is present, the LC and lateral tegmental NE systems predominantly innervate separate and functionally distinct areas of the brainstem. DA and E neurons provide a very minor component of the brainstem CA innervation.     

Ascending projections of the locus coeruleus in the rat. II. Autoradiographic study.

The ascending projections of the locus coeruleus were studied using an autoradiographic method. The major projection of locus coeruleus neurons ascends in a dorsal pathway traversing the midbrain tegmentum in a position ventrolateral to the periaqueductal gray. At the caudal diencephalon the locus coeruleus axons descend to enter the medial forebrain bundle at a caudal tuberal hypothalamic level. They are jointed in the medial forebrain bundle by a much smaller locus coeruleus projection which takes a ventral course through the midbrain tegmentum and enters the medial forebrain bundle via the mammillary peduncle and ventral tegmental area. Terminal projections are evident in the midbrain to the periaqueductal gray, tegmentum and raphe nuclei. There are widespread projections to the dorsal thalamus. The heaviest of these are to the intralaminar nuclei, the anteroventral and anteromedial nuclei, the dorsal lateral geniculate and the paraventricular nucleus. In the hypothalamus the largest projections are to the lateral hypothalamic area, periventricular nucleus, supraoptic nucleus and paraventricular nucleus. As the locus coeruleus projection ascends in the medial forebrain bundle, fibers leave it to traverse the lateral hypothalamus and zona incerta and enter the internal capsule, the ventral amygdaloid bundle and ansa peduncularis. These appear to terminate in the amygdaloid complex and, via the external capsule, in the lateral and dorsal neocortex. At the level of the septum 4 projections are evident. One group of fibers enters the stria medullaris to terminate in the paraventricular nucleus and habenular nuclei. A second group joins the stria terminalis to terminate in the anygdaloid complex. The third group turns into the diagonal band and medial septum; some fibers terminate in the septal nuclei and others continue into the fornix to termimate in hippocampus. A large component continues around the corpus callosum into the cingulum to terminate in the cingulate and adjacent neocortex, the subiculum and hippocampus. The remaining fibers continue rostrally in the medial forebrain bundle to terminate in olfactory forebrain and frontal neocortex. Commissural projections arise at 4 locations. The first decussation occurs in the dorsal tegmentum just below the central gray rostral to the locus coeruleus. The crossing fibers enter the contralateral dorsal bundle. A second group of fibers leaves the ipsilateral dorsal pathway, crosses in the posterior commissure and enters the contralateral dorsal pathway at the level. The third commissural projection arises more rostrally and crosses in the dorsal supraoptic commissure to enter the contralateral medial forebrain bundle. The fourth commissural projection is through the anterior commissure. The termination of the contralateral projection appears similar to that of the ipsilateral projection.     

Biochemical mapping of noradrenergic nerves arising from the rat locus coeruleus

Norepinephrine (NE) concentration was measured in discrete brain regions of the rat following unilateral electrolytic lesions of the locus coeruleus, to determine the distribution of its noradrenergic neurons. Discrete brain nuclei and subdivisions were dissected from frozen sections, and norepinephrine was measured by a sensitive radio-isotopic assay.A significant reduction by 29–63% of control values in norepinephrine content was observed ipsilateral to the lesion in the following areas: all portions of the cerebral cortex examined (entorhinal, hippocampal, cingulate, parietal, and occipital areas), anterior half of the cerebellar cortex, hypothalamic periventricular and paraventricular nuclei, anterior ventral thalamic nucleus, ventral thalamic nucleus, and habenula. It appears that these regions receive unilateral innervation by axons from the locus coeruleus. In 3 regions (the medial geniculate body, inferior colliculus, and posterior half of the cerebellum), NE was reduced bilaterally in a pattern suggesting bilateral innervation from the locus coeruleus. Since no reduction in NE concentration occurred in the medial preoptic nucleus, nucleus interstitialis stria terminalis (ventralis), dorsomedial hypothalamic nucleus, or medial forebrain bundle, axons from noradrenergic neurons in the locus coeruleus do not appear to innervate these regions.The biochemical mapping of noradrenergic nerves from the locus coeruleus is discussed in relation to distribution studies based on the histofluorescence method.     

An HRP study of the afferent connections to rat lateral hypothalamic region

Afferent connections to the lateral hypothalamic region in the rat were studied using horseradish peroxidase (HRP). HRP was injected iontophoretically by a parapharyngeal approach. After HRP injections into the lateral hypothalamic area, labeled cells were found mainly in the medial prefrontal and infralimbic cortices, lateral and dorsal septal nuclei, nucleus accumbens, bed nucleus of the stria terminalis, medial and lateral amygdaloid nuclei, lateral habenular nucleus, peripeduncular nucleus, ventral tegmental area, mesencephalic and pontine central gray, ventral nucleus of the lateral lemniscus, lateral parabrachial area, raphe nuclei and the nucleus locus coeruleus. Labeled cells following HRP injections into the lateral preoptic area were found mainly in the lateral and dorsal septal nuclei, nucleus accumbens, diagonal band, ventral part of the globus pallidus, bed nucleus of the stria terminalis, central amygdaloid nucleus, mesencephalic and pontine central gray, dorsal raphe nucleus, parabrachial area and the nucleus locus coeruleus. The intrahypothalamic connections were also discussed.     

Serotonergic innervation of the forebrain in the North American opossum

The forebrain distribution of axons showing serotonin-like immunoreactivity was studied in the North American opossum. Serotonergic innervation of the hypothalamus was extensive, particularly within the ventromedial nucleus, the periventricular nucleus and the rostral supraoptic nucleus. Serotonergic axons were also present within the fields of Forel and zona incerta, but they tended to avoid parts of the subthalamic nucleus. In the thalamus serotonergic innervation was dense within the midline nuclei (e.g. the central, intermediate dorsal and rhomboid nuclei) and the ventral lateral geniculate nucleus, but relatively sparse in some of the nuclei more readily associated with specific functions (e.g. the ventrobasal nucleus). Serotonergic axons innervate most areas of the rostral and dorsal forebrain. Areas containing the heaviest innervation included the interstitial nucleus of the stria terminalis and the lateral septal nucleus. Serotonergic innervation of the neocortex varied markedly from region to region and within different layers of the same regions. The retrograde transport of True Blue combined with immunofluorescence for localization of serotonin revealed that serotonergic axons within the forebrain arise mainly within the dorsal raphe and superior central nuclei, but that some originate within the midbrain and pontine reticular formation and the locus coeruleus, pars alpha. Neurons of the raphe magnus and obscurus also innervate the forebrain, but few of them are serotonergic. The use of horseradish peroxidase as a retrograde marker provided evidence that raphe projections to the forebrain are topographically organized. Our results suggest that serotonergic projections to the forebrain, like those to the spinal cord, are connectionally heterogeneous.     

Monoamine innervation of the forebrain: Collateralization

The forebrain is characterized by a dense, localized dopamine (DA) innervation pattern, a diffuse, widespread norepinephrine (NE) innervation pattern, and a serotonin (5-HT) innervation intermediate between the DA and NE patterns. These innervation patterns have implied that basic differences exist in the way DA, NE and 5-HT axons collateralize to different brain structures; that is, DA axons are thought to be poorly collateralized and NE and 5-HT axons are presumed to be more highly collateralized. In the present study, we used injections of retrograde labeling fluorescent dyes into various forebrain regions in order to determine axonal branching patterns from nuclei that contain DA, NE and 5-HT neurons, namely the substantia nigra-ventral tegmental area (SN-VTA), locus coeruleus (LC) and raphe nuclei (DR-MR). The results suggest that at least two subpopulations of neurons can be defined in each monoamine nucleus with respect to the way their axons collateralize. Each area contains a centrally located nuclear area with highly collateralized neurons, and more peripherally situated areas with less highly collateralized neurons. Thus, previous suppositions of the branching of monoamine axons must be revised to account for the existence of cells exhibiting totally different collateralization patterns within each monoamine nucleus.     

Origin, course and termination of the mesohabenular dopamine pathway in the rat

This study describes the organization of the mesohabenular dopamine (DA) system in the rat as revealed by fluorescence histochemistry in combination with lesions, DA uptake experiments and injections of a retrograde tracer. The DA axons were found to be aggregated in a dense terminal field located in the caudal two thirds of the medial part of the lateral habenular nucleus. Microknife lesions of the stria medullaris left this DA innervation unaffected while cuts through the fasciculus retroflexus resulted in the virtual disappearance of the DA innervation. Injections of the fluorescent retrograde tracer True Blue (TB) into the lateral habenula produced labeling of both DA and non-DA-containing cells in the ventral mesencephalon, mainly in the interfascicular nucleus ipsilateral to the injection. This study thus documents the existence of a mesohabenular DA pathway whose cell bodies are located in the ventral mesencephalon and whose axons ascend with the fasciculus retroflexus to terminate in the caudomedial part of the lateral habenular nucleus. This information, taken together with insights gained from other studies, suggests a role for the mesohabenular DA system in modulating telencephalic feedback onto the mesencephalic DA-neurons and also in regulating the output from the dorsal raphe nucleus.     

Cholinergic and catecholaminergic afferents to the olfactory bulb in the hamster: a neuroanatomical, biochemical, and histochemical investigation

A series of neuroanatomical, biochemical, and histochemical studies have been conducted to determine the sources of cholinergic afferents to the main olfactory bulb (MOB) in the hamster. Following horseradish peroxidase (HRP) injections that are restricted to the MOB, retrograde neuronal labeling is observed bilaterally in the anterior olfactory nucleus, locus coeruleus, and raphe nuclei, and ipsilaterally in the ventral hippocampal rudiment, dorsal peduncular cortex, piriform cortex, nucleus of the lateral olfactory tract, anterior pole of the medial septal area and vertical limb of the diagonal band, nucleus of the horizontal limb of the diagonal band (HDB), and hypothalamus. Spread of HRP into the accessory olfactory bulb results in additional neuronal labeling ipsilaterally in the bed nucleus of the accessory olfactory tract, medial amygdaloid nucleus, and bed nucleus of the stria terminalis, and bilaterally in the posteromedial cortical amygdaloid nucleus. Retrograde tracing studies also have been conducted in cases with lesions in the basal forebrain or hypothalamus to assess the extent to which such lesions interrupt fibers of passage from other sources of centrifugal afferents, and the effects of such lesions on choline acetyltransferase (CAT) activity and catecholamine content in the MOB and on acetylcholinesterase (AChE) activity in the forebrain have been evaluated. Lesions in the basal forebrain reduce or eliminate CAT and AChE activity in the MOB in direct relationship to the extent of damage to the HDB. Norepinephrine (NE) content in the MOB also is reduced by basal forebrain lesions, but in relationship to damage of the medial forebrain bundle (MFB). The hypothalamic lesions have no effect on AChE activity in the forebrain or on CAT activity in the MOB, but they eliminate retrograde labeling in the locus coeruleus and raphe nuclei and reduce the NE content of the MOB to undetectable levels. The dopamine content of the MOB is not reduced by any of the lesions. Anterograde tracing studies have been conducted to compare the rostral projection patterns of the HDB with the distribution of AChE activity. Most of the rostrally directed axons travel in association with the MFB. A small component of axons travels in association with the lateral olfactory tract. Within the MOB, the axons terminate predominantly in the glomerular layer and in the vicinity of the internal plexiform layer. The projection and termination patterns of the HDB correspond well with the distribution of AChE activity. These various results indicate that the HDB is the major source of cholinergic afferents to the MOB.     

Catecholaminergic innervation of the septal area in man: immunocytochemical study using TH and DBH antibodies

The catecholaminergic innervation of the human septal area and closely related structures has been visualized by using tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) as immunocytochemical markers. TH-like immunoreactivity with no corresponding DBH labelling was considered to be indicative of dopaminergic fibers. Catecholaminergic innervation offered the following similarities to that of rodents: moderate innervation in the medial septal division, with predominant DBH immunolabelling; dense dopaminergic innervation in the lateral septal nuclei, organized in a laminar pattern; presence of dopaminergic pericellular arrangements in the dorsal septum and bed n. of the stria terminalis; clustering of dopaminergic terminals in n. accumbens associated with a medioventral zone of DBH-like immunoreactive fibers; close overlap between dopaminergic fields and acetylcholinesterase-reactive zones in both the lateral septum and the n. of the stria terminalis. Differences with the catecholaminergic septal innervation of rodents consisted of general caudal extension of the dopaminergic fields, possibly accounted for by the vertical stretching and caudal displacement of the septal nuclei in man; complementary lateromedial topography of dopaminergic and DBH-immunoreactive inputs in the n. of the stria terminalis as opposed to their dorsoventral organization in rodents; presence of TH-immunolabelled cell group in the anterior olfactory nucleus and parolfactory cortex, which seems specific for primates. Precise topographical mapping of the catecholaminergic structures in this central region of the limbic forebrain seems to be a prerequisite for accurate tissue sampling in the biochemical investigations of pathological cases and should help in the interpretation of aminergic dysfunction in a variety of human diseases.     

Effects of estrogen and progesterone on plasma gonadotropins and on catecholamine levels and turnover in discrete brain regions of ovariectomized rats.

Estradiol benzoate (EB) was administered, either alone or followed 48 h later by progesterone to ovariectomized rats. Plasma gonadotropins (FSH and LH) and steady state levels of norepinephrine (NE) and dopamine (DA) in 17 individual brain nuclei were assayed. In addition, catecholamines were measured after administration of the synthesis inhibitor alpha-methyltyrosine (alpha-MT) in order to assess hormonal influences on turnover. Treatment with EB, which lowered plasma FSH and LH, reduced the depletion of NE produced by alpha-MT in the lateral septum, interstitial nucleus of the stria terminalis, and central gray catecholamine area, and reduced the depletion of DA in the nucleus of the tractus diagonalis. EB enhanced NE depletion in the periventricular and anterior hypothalamic nuclei, and raised steady state levels of NE in the medial amygdaloid nucleus. These effects were reversed by subsequent treatment with progesterone, which stimulated FSH and LH release. EB plus progesterone enhanced the alpha-MT-induced depletion of NE over that observed with EB alone in the arcuate nucleus, and similarly enhanced DA depletion in the interstitial nucleus of the stria terminalis. EB plus progesterone prevented the depletion of NE by alpha-MT in the paraventricular and ventromedial nuclei, and also lowered resting NE levels in the paraventricular nucleus. The results suggest that catecholamine neurons in several discrete brain regions participate in the stimulatory and inhibitory feedback effects of ovarian hormones on gonadotropin secretion, and perhaps also on the hormonal induction of sexual receptivity.     

The efferent connections of the ventromedial nucleus of the hypothalamus of the rat.

The efferent connections of the ventromedial nucleus of the hypothalamus (VMH) of the rat have been examined using the autoradiographic method. Following injections of small amounts (0.4-2.0 muCi) of tritium labeled amino acids, fibers from the VMH can be traced forward through the periventricular region, the medial hypothalamus and the medial forebrain bundle to the preoptic and thalamic periventricular nuclei, to the medial and lateral preoptic areas, to the bed nucleus of the stria terminalis and to the ventral part of the lateral septum. Some labeled axons continue through the bed nucleus of the stria terminalis into the stria itself, and hence to the amygdala, where they join other fibers which follow a ventral amygdalopetal route from the lateral hypothalamic area and ventral supraoptic commissure. These fibers terminate in the dorsal part of the medial amygdaloid nucleus and in the capsule of the central nucleus. A lesser number of rostrally directed fibers from the VMH crosses the midline in the ventral supraoptic commissure and contributes a sparse projection to the contralateral amygdala. Descending fibers from the VMH take three routes: (i) through the medial hypothalamus and medial forebrain bundle; (ii) through the periventricular region; and (iii) bilaterally through the ventral supraoptic commissure. These three pathways are interconnected by labeled fibers so that it is not possible to precisely identify their respective terminations. However, the periventricular fibers seem to project primarily to the posterior hypothalamic area and central gray, as far caudally as the anterior pole of the locus coeruleus, while the medial hypothalamic and medial forebrain bundle fibers apparently terminate mainly in the capsule of the mammillary complex, in the supramammillary nucleus and in the ventral tegmental area. The ventral supraoptic commissure fibers leave the hypothalamus closely applied to the medial edges of the two optic tracts. After giving off their contributions to the amygdala, they continue caudally until they cross the dorsal edge of the cerebral peduncle to enter the zona incerta. Some fibers probably terminate here, but others continue caudally to end in the dentral tegmental fields, and particularly in the peripeduncular nucleus. Within the hypothalamus, the VMH appears to project extensively to the surrounding nuclei. However, we have not been able to find evidence for a projection from the VMH to the median eminence. Isotope injections which differentially label the dorsomedial or the ventrolateral parts of the VMH have shown that most of the long connections (to the septum, amygdala, central tegmental fields and locus coeruleus) originate in the ventrolateral VMH, and there is also some evidence for a topographic organization within the projections of this subdivision of the nucleus.     

Neurotensin immunoreactive structures in the human infant striatum, septum, amygdala and cerebral cortex

Neurotensin immunoreactive (NT-IR) neuronal perikarya are present in small numbers in the bed nucleus of the stria terminalis, lateral olfactory stria, substantia innominata, caudate nucleus and putamen of the human infant forebrain. Larger numbers of perikarya are present in the amygdala and related structures. NT-IR axons are present in the medial septal area, bed nucleus of the stria terminalis, caudate nucleus, putamen and amygdala. The cerebral cortex contains a rich network of NT axons with an accentuation in layer II. This network appears to be derived from bundles of axons which traverse the deep white matter from the thalamus.     

Differential visualization of dopamine and norepinephrine uptake sites in rat brain using [3H]mazindol autoradiography

Mazindol is a potent inhibitor of neuronal dopamine (DA) and norepinephrine (NE) uptake. DA and NE uptake sites in rat brain have been differentially visualized using [3H]mazindol autoradiography. At appropriate concentrations, desipramine (DMI) selectively inhibits [3H]mazindol binding to NE uptake sites without significantly affecting binding to DA uptake sites. The localization of DMI-insensitive specific [3H] mazindol binding, reflecting DA uptake sites, is densest in the caudate-putamen, the nucleus accumbens, the olfactory tubercle, the subthalamic nucleus, the ventral tegmental area, the substantia nigra (SN) pars compacta, and the anterior olfactory nuclei. In contrast, the localization of DMI-sensitive specific [3H]mazindol binding, representing NE uptake sites, is densest in the locus coeruleus, the nucleus of the solitary tract, the bed nucleus of the stria terminalis, the paraventricular and periventricular nuclei of the hypothalamus, and the anteroventral thalamus. The distribution of DMI-insensitive specific [3H]mazindol binding closely parallels that of dopaminergic terminal and somatodendritic regions, while the distribution of DMI-sensitive specific [3H]mazindol binding correlates well with the regional localization of noradrenergic terminals and cell bodies. Injection of 6-hydroxydopamine, ibotenic acid, or colchicine into the SN decreases [3H]mazindol binding to DA uptake sites in the ipsilateral caudate-putamen by 85%. In contrast, ibotenic acid lesions of the caudate-putamen do not reduce [3H]mazindol binding to either the ipsilateral or contralateral caudate-putamen. Thus, the DA uptake sites in the caudate-putamen are located on the presynaptic terminals of dopaminergic axons originating from the SN.     

Alterations in Cyclic AMP Concentration and Adenylate Cyclase Activity in Specific Brain Areas of Rats with Inherited Hypothalamic Diabetes Insipidus (Brattleboro Rats)

The concentration of cyclic AMP (cAMP) and the activity of sodium-fluoride-stimulated adenylate cyclase was measured in 29 microdissected brain areas of homozygous Brattleboro rats and their Long-Evans control rats. In ten of the investigated brain areas a decreased cAMP level was measured in Brattleboro rats. It was particularly decreased in the supraoptic nucleus, cingulate and parietal cortex, hippocampus, habenula and organum vasculosum laminae terminalis. Significantly lower cAMP levels were also found in the periventricular nucleus, bed nucleus of the stria terminalis, area postrema and locus coeruleus. An increased cAMP concentration was detected only in the subcommissural organ of Brattleboro rats. In most brain areas, where cAMP was decreased, sodium fluoride-stimulated adenylate cyclase activity was significantly increased (supraoptic nucleus, parietal cortex, periventricular nucleus, bed nucleus of the stria terminalis, locus coeruleus) or unchanged (hippocampus, habenula, organum vasculosum laminae terminalis). The coincidence of alterations in cAMP concentration and adenylate cyclase activity in brain areas of Brattleboro rats with relatively dense vasopressinergic innervation and/or vasopressin receptor population in control rats, suggests an influence of brain vasopressin on the cAMP-adenylate cyclase second messenger system.     

Synapse formation after injury in the adult rat brain: Failure of fimbrial axons to reinnervate the bed nucleus of the stria terminalis

Selectivity in the reinnervation of denervated postsynaptic sites in the adult rat septal nuclei has been studied by both light and electron microscopic degeneration techniques after lesions of the fimbria and stria terminalis. In the mid-rostrocaudal septum the ventral border of the lateral septal nucleus is coextensive with the dorsal border of the strial bed nucleus. In the normal rat, fimbrial axons establish synapses throughout the lateral septal nucleus of the same side, and also in the dorsal part of the lateral septal nucleus on the opposite side. The stria terminalis establishes synapses in the ipsilateral but not in the contralateral bed nucleus at this level.Both the fimbria and the stria terminalis were completely severed on the left side, and after adequate survival for the removal of all degeneration, the distribution of the remaining fimbria was plotted. Interesting changes were found on the side contralateral to the second lesion, where the fimbria both increases the number of its synaptic terminals within its proper contralateral territory (the dorsal part of the lateral septal nucleus) and also extends its distribution into the ventral part of the lateral septal nucleus — the territory normally reserved for the ipsilateral fimbria. Although completely surrounding the strial bed nucleus, fimbrial axons fail to invade the bed nucleus, and fimbrial terminals are no obvious structural barriers between the neuropil postsynaptic sites. Since there are no obvious structural barriers between the neuropil of the lateral septal nucleus and that of the strial bed nucleus it is suggested that this failure is most likely to be due either to some biochemical incompatibility between fimbrial axons and strial postsynaptic sites, or to the fact that the fimbrial axons are denied access because some other (unidentified) axonal system forms new presynaptic terminals which effectively pre-empt the sites in the strial bed nucleus.     

Catecholamine innervation of the basal forebrain. III. Olfactory bulb, anterior olfactory nuclei, olfactory tubercle and piriform cortex.

The catecholamine innervation of the olfactory bulb, anterior olfactory nuclei, olfactory tubercle and piriform cortex was studied in the rat using biochemical analysis and fluorescence histochemistry. Biochemical studies demonstrate a moderate norepinephrine (NE) content in all olfactory structures, a high dopamine (DA) content in the olfactory tubercle and a low DA content in the olfactory bulb, anterior olfactory nucleus and piriform cortex. Following locus coeruleus lesions NE content decreases 71% in the olfactory bulb, 82% in the anterior olfactory nucleus, 62% in olfactory tubercle and 77% in piriform cortex...     

Immunocytochemical localization of dopamine-β-hydroxylase in rat locus coeruleus and hypothalamus

Dopamine-beta-hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, has been localized in light and electron microscopic preparations of rat brain by an immunocytochemical method using a peroxidase--anti-peroxidase Fab complex. In light microscopic preparations, DBH-specific reaction product was observed in somata and proximal processes of neurons in the locus coeruleus and subcoeruleus as well as within distal axons of the principal adrenergic fiber system. DBH-specific reaction product was also observed within small (1--2 micrometer), punctate structures in the interstitial nucleus of the stria terminalis and the para- and periventricular nuclei of the hypothalamus. Electron microscopic results demonstrated on association of DBH-specific reaction product with the Golgi apparatus of neuronal somata in the locus coeruleus and subcoeruleus. DBH-positive reaction product was also seen in association with small (35-55 nm) agranular synaptic vesicles and large (80--100 nm), probable granular vesicles within axonal varicosities and terminals in the interstitial nucleus of the stria terminalis. Occasionally, DBH-containing axonal varicosities and terminals were observed to form synapse-like junctions with dendritic profiles, but most of the observed DBH-positive axonal structures did not establish identifiable synaptic relationships.     

Distribution of dopamine β-hydroxylase-like immunoreactive fibers within the shell subregion of the nucleus accumbens

The nucleus accumbens (Acb) can be divided into distinct subfields, delineated on the basis of histochemical markers as well as by afferent and efferent projection patterns. The shell subregion has reciprocal relationships with a variety of limbic areas and brainstem autonomic structures, and has been suggested to participate in motivation-related processes, including reward, stress, and arousal. The locus coeruleus (LC)-noradrenergic system has similarly been implicated in the modulation of behavioral state and stress-related processes, and previous studies have demonstrated reciprocal projections between the locus coeruleus and Acb shell. To better understand the anatomical substrate through which LC could influence activity within Acb shell, immunohistochemical methods were used to visualize the extent and the distribution of noradrenergic axons within this structure. Coronal sections of rat brain were processed to visualize immunoreactivity for the norepinephrine synthetic enzyme dopamine β-hydroxylase (DBH), a specific marker for noradrenergic processes. In some cases, alternate sections were processed for immunohistochemical localization of substance P, in order to delineate core, shell, and pallidal compartments. Moderate-to-dense DBH-like immunoreactivity (DBHir) was found in approximately the caudal half of the shell subregion, particularly in caudalmost (septal pole) and ventral zones. The innervation of the septal pole was contiguous with a dense innervation of the bed nucleus of the stria terminalis. Few immunoreactive fibers were observed in the caudate-putamen, Acb core, or rostral Acb shell. Many DBHir fibers within the shell region were highly arborized with numerous varicosities, features indicative of terminal fields. These observations suggest noradrenergic systems might modulate certain processes associated with stress, behavioral state, or reinforcement via actions within the Acb shell. Synapse 27:230–241, 1997. © 1997 Wiley-Liss, Inc.     

Neuropeptide Y localization in the rat amygdaloid complex

Neuropeptide Y (NPY)-, avian pancreatic polypeptide (APP)-, and molluscan cardioexcitatory peptide (FMRF)-like immunoreactivity in the amygdaloid complex of the rat was investigated immunohistochemically. The distribution of each of these peptides within the amygdala is identical and cross-blocking studies indicate that all three antisera recognize the NPY antigen. Morphologically distinct populations of NPY immunoreactive neurons are differentially distributed in the medial amygdaloid nucleus and at the base of the stria terminalis. Dense plexuses of immunoreactive axons are present in the medial third of the central nucleus and in the dorsal half of the medial nucleus, with light to moderate fiber plexuses present in the lateral and basolateral nuclei and scattered axons present throughout the remainder of the amygdala. The distribution and appearance of NPY immunoreactive plexuses in the amygdala is similar to that described previously for noradrenergic axons arising from brainstem cell groups (Fallon, Koziell, and Moore: J. Comp. Neurol. 180:509-532, '78). However, injections of the noradrenergic neurotoxin 6-hydroxydopamine into the amygdala result in a complete loss of dopamine-beta-hydroxylase (DBH) immunoreactivity in the amygdala and surrounding cortex but leave much of the NPY immunoreactive plexus intact. Similarly, lesions of the locus coeruleus deplete DBH immunoreactivity, leaving NPY-like immunoreactivity in the amygdala unaffected. These results indicate that much of the NPY immunoreactive plexus observed in the amygdala does not arise from brainstem sources in which NPY and noradrenaline are colocalized. Lesions of the stria terminalis or medial nucleus have no observable effect on the density or distribution of NPY immunoreactive terminal fields in the basal forebrain and hypothalamus, suggesting that immunoreactive neurons in the amygdaloid complex do not contribute significantly to this innervation.