5-HT2A receptors stimulate ACTH, corticosterone, oxytocin, renin, and prolactin release and activate hypothalamic CRF and oxytocin-expressing cells.

The 5-HT(2A/2C) agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) stimulates hypothalamic neurons to increase the secretion of several hormones. This study addressed two questions: 1) are the neuroendocrine effects of DOI mediated via activation of 5-HT(2A) receptors; and 2) which neurons are activated by 5-HT(2A) receptors. The 5-HT(2A) antagonist (+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol (MDL 100,907; 0.001, 0.01, or 0.1 mg/kg, s.c.) was administered before rats were challenged with DOI (2.5 mg/kg, i.p.). MDL 100,907 produced a dose-dependent inhibition (ED(50) congruent with 0.001 mg/kg) of the effect of DOI on plasma levels of ACTH, corticosterone, oxytocin, prolactin, and renin without altering basal hormone levels. Complete blockade of the effect of DOI was achieved for all hormones at MDL 100,907 doses of 0.01-0.1 mg/kg. In a parallel experiment, DOI was injected 2 hr before killing to determine its effects on the expression of Fos, the product of the immediate early gene c-fos. DOI induced an increase in Fos immunoreactivity in corticotropin-releasing factor (CRF) and in oxytocin-expressing neurons but not in vasopressin-containing neurons in the hypothalamic paraventricular nucleus or CRF cells in the amygdala. Pretreatment with MDL 100,907 (0.1 mg/kg, s.c.) blocked the DOI-induced increase in Fos expression in all regions including the hypothalamus, amygdala (central and corticomedial), bed nucleus of the stria terminalis, and prefrontal cortical regions. The combined neuroanatomical and pharmacological observations suggest that the neuroendocrine responses to DOI are mediated by activation of neurons in the hypothalamic paraventricular nucleus and associated circuitry. Furthermore, selective activation of 5-HT(2A) receptors mediates the hormonal and Fos-inducing effects of DOI.

Functional and anatomical relationships among the amygdala, basal forebrain, ventral striatum, and cortex. An integrative discussion.

Two recent papers have questioned the concept of the amygdala as a functional and anatomically separate entity. Swanson and Petrovich go so far as to state that "the amygdala is neither a structural nor a functional unit." This novel concept is derived from the fact that the amygdala is a structure whose anatomical connections and neurochemical features are more strongly interrelated to adjacent parts of the temporal lobe and basal forebrain than to unique characteristics of its own. This is an emerging hypothetical concept of the "amygdala" that seems to repeat itself in many parts of this volume and merits further examination in the future. The basal forebrain and cortical circuitry described here seem to be critical for a set of behaviors/processes that could be collectively described as cognitive-emotive. For example, this would include arousal, attention, sensory processing, reinforcement, and finally associative learning, decision making, and memory. Collectively this circuitry influences the emotional, motivational, and cognitive state of an organism. More and more studies are demonstrating that small and localized manipulations of the brain can result in equally subtle and specific deficits that are associated with definable parts of the anatomical circuitry, neurotransmitters, and receptors of basal forebrain structures. These studies have been guided and influenced by the refined neuroanatomical and neurochemical investigations of Lennart Heimer and his colleagues. Interpretations of these studies are beginning to uncover distinct deficits that suggest explanations and potential treatments for many psychiatric and pathological degenerative disorders.

D-Fenfluramine induces serotonin-mediated Fos expression in corticotropin-releasing factor and oxytocin neurons of the hypothalamus, and serotonin-independent Fos expression in enkephalin and neurotensin neurons of the amygdala.

The neurotransmitters expressed by neurons activated by D-fenfluramine (5 mg/kg, i.p.) were identified in the hypothalamus, amygdala and bed nucleus of the stria terminalis. Induction of Fos immunoreactivity following D-fenfluramine injection was used as an index of neuronal activation. To test whether D-fenfluramine activated neurons by releasing serotonin from the serotonergic nerve terminals, rats were pretreated with fluoxetine (10 mg/kg, i.p.), a serotonin reuptake inhibitor that prevents the release of serotonin stimulated by D-fenfluramine, 12 h before D-fenfluramine injection. The approximate percentages of peptidergic neurons that contained Fos immunoreactivity after D-fenfluramine administration were 94% of corticotropin-releasing factor and 22% of oxytocin cells in the paraventricular nucleus of the hypothalamus, 6% of oxytocin cells in the supraoptic nucleus of the hypothalamus, 36% of enkephalin and 15% of neurotensin cells in the central amygdaloid nucleus, and 19% of enkephalin and 9% of neurotensin cells in the bed nucleus of the stria terminalis. Fluoxetine pretreatment blocked Fos expression in corticotropin-releasing factor- and oxytocin-expressing cells in the hypothalamus, but not in enkephalin-and neurotensin-expressing cells located in the bed nucleus of the stria terminalis and central amygdaloid nucleus. D-Fenfluramine did not induce Fos immunoreactivity in vasopressin-, thyrotropin-releasing hormone-, somatostatin- and tyrosine hydroxylase-containing cells in the hypothalamus, and corticotropin-releasing factor-expressing cells in the central amygdaloid nucleus and bed nucleus of the stria terminalis. These results show that D-fenfluramine stimulates corticotropin-releasing factor- and oxytocin-expressing cells in the hypothalamus via serotonin release. The enkephalin- and neurotensin-expressing cells in the amygdala are activated by D-fenfluramine via non-serotonergic mechanisms. Induction of Fos expression by D-fenfluramine in restricted populations of cells suggests a selective activation of neuronal circuitry that is likely to be involved in the appetite suppressant effects of D-fenfluramine.

Monoamine- and histamine-synthesizing enzymes and neurotransmitters within neurons of adult human cardiac ganglia.

BACKGROUND: Cardiac ganglia were originally thought to contain only cholinergic neurons relaying parasympathetic information from preganglionic brain stem neurons to the heart. Accumulating evidence, however, suggests that cardiac ganglia contain a heterogeneous population of neurons that synthesize or respond to several different neurotransmitters and neuropeptides. Reports regarding monoamine and histamine synthesis and neurotransmission within cardiac ganglia, however, present conflicting information or are limited in number. Furthermore, very few studies have examined the neurochemistry of adult human cardiac ganglia. The purpose of this study was, therefore, to determine whether monoamine- and histamine-synthesizing enzymes and neurotransmitters exist within neurons of adult human cardiac ganglia. METHODS AND RESULTS: Human heart tissue containing cardiac ganglia was obtained during autopsies of patients without cardiovascular pathology. Avidin-biotin complex immunohistochemistry was used to demonstrate tyrosine hydroxylase, L-dopa decarboxylase, dopamine beta-hydroxylase, phenylethanolamine-N-methyltransferase, tryptophan hydroxylase, and histidine decarboxylase immunoreactivity within neurons of cardiac ganglia. Dopamine, norepinephrine, serotonin, and histamine immunoreactivity was also found in ganglionic neurons. Omission or preadsorption of primary antibodies from the antisera and subsequent incubation with cardiac ganglia abolished specific staining in all cases examined. CONCLUSIONS: Our results suggest that neurons within cardiac ganglia contain enzymes involved in the synthesis of monoamines and histamine and that they contain dopamine, norepinephrine, serotonin, and histamine immunoreactivity. Our findings suggest a putative role for monoamine and histamine neurotransmission within adult human cardiac ganglia. Additional, functional evidence will be necessary to evaluate what the physiological role of monoamines and histamine may be in neural control of the adult human heart.

The angiotensinogen gene is expressed in both astrocytes and neurons in murine central nervous system.

Two transgenic mouse models were used to examine the cellular localization of angiotensinogen (AGT) in the brain. The first model was previously described in detail and consists of a human AGT genomic transgene containing all exons and introns of the gene and 1. 2 kb of the 5' flanking DNA. The second model contains a fusion between 1.2 kb of HAGT 5' flanking DNA and the beta-gal reporter gene which exhibits a similar pattern of tissue-specific expression to the HAGT transgene. Expression of both transgenes qualitatively mirrors the expression of endogenous AGT. Double staining of transgenic mouse brain sections with X-gal and GFAP revealed that a majority of beta-gal activity was localized to astrocytes in almost all brain areas. However, both beta-gal activity as identified by X-gal, and HAGT mRNA as detected by in situ hybridization, were also found in neurons in restricted areas of the brain, including the mesencephalic trigeminal nucleus (meV), subfornical organ (SFO) and the external lateral parabrachial nucleus (elPB). The expression of these transgenes provides the first convincing evidence for AGT gene expression in neurons in the brain. We further report by angiotensin II (Ang-II) immunostaining in rat brains after selective lesioning, that Ang-II is likely involved in a neuronal pathway from the PB to the amygdala (Ce). Finally, we performed double-labeling, first by retrograde labeling of HRP injected into the Ce, and then by X-gal on PB neurons in beta-gal transgenic mice, and identified doubly labeled neurons. Based on these results, we propose that AGT is generated in neurons in the elPB, transported to the Ce and converted into Ang-II locally to exert is biological functions.

The 5-HT1A and 5-HT2A/2C receptor antagonists WAY-100635 and ritanserin do not attenuate D-fenfluramine-induced fos expression in the brain.

D-Fenfluramine is a serotonin (5-hydroxytryptamine, 5-HT) releaser and reuptake inhibitor. It is used to study the neurochemical control of feeding and has been used to treat obesity. It has also been employed as a pharmacological tool to study changes in serotonergic function in psychiatric patients. Brain sites activated by D-fenfluramine via the release of 5-HT have been mapped via the expression of the immediate early gene c-fos. Studies in our laboratory have indicated that D-fenfluramine induces Fos in the hypothalamus and cortex through 5-HT release. The present study investigated whether 5-HT released by D-fenfluramine induces Fos expression in the brain by activating 5-HT1A or 5-HT2A/2C receptors. Rats were pretreated either with WAY-100635, a 5-HT1A antagonist, or ritanserin, a 5-HT2A/2C antagonist, prior to d-fenfluramine injection. Blockade of either 5-HT1A or 5-HT2A/2C receptors was not sufficient to suppress the Fos response to D-fenfluramine in any region of the brain examined, including the cingulate cortex, frontal cortex, caudate-putamen, paraventricular nucleus of the hypothalamus, amygdala, and brainstem. These results indicate that Fos response elicited by D-fenfluramine may be mediated by other receptors, in addition to the 5-HT1A or 5-HT2A/2C receptors.

p-Chlorophenylalanine and fluoxetine inhibit D-fenfluramine-induced Fos expression in the paraventricular nucleus, cingulate cortex and frontal cortex but not in other forebrain and brainstem regions.

D-Fenfluramine, a putative serotonin releaser and reuptake inhibitor, is commonly prescribed for the treatment of obesity. Brain sites activated by D-fenfluramine have been mapped via the expression of the immediate early gene Fos. However, it is not clear that serotonin release in the brain mediates the effects of D-fenfluramine on Fos expression. The present study determined whether D-fenfluramine induces the expression of Fos in the brain through the release of serotonin. Rats were pretreated either with the serotonin depleting drug p-chlorophenylalanine (PCPA) or with the serotonin reuptake inhibitor fluoxetine. Both drugs inhibited D-fenfluramine-induced Fos expression in the cingulate cortex, frontal cortex, and the parvocellular subdivision of the paraventricular nucleus of the hypothalamus. Neither drug reduced D-fenfluramine-induced Fos responses in several other brain areas, including the caudate-putamen, amygdala, and brainstem regions such as the lateral parabrachial nucleus and nucleus of the solitary tract. These results indicate regional specificity of mechanisms mediating D-fenfluramine-induced Fos expression. It is likely that D-fenfluramine-induced Fos expression at various sites in the brain is mediated via a combination of serotonin release and other, as yet unidentified, neurotransmitters.

The amygdala: corticotropin-releasing factor, steroids, and stress.

The possible function of corticotropin-releasing factor (CRF), adrenal steroids, and gonadal steroids in amygdala-mediated responses to anxiogenic or stressful stimuli is reviewed. The amygdala is part of an endogenous CRF circuitry within the brain that mediates neuroendocrine, autonomic, and behavioral changes in response to stress. The amygdala contains CRF-expressing neurons that communicate with widespread regions of the neural axis. High densities of CRF, CRF-binding protein, and CRF receptors are located in the amygdala. Direct injections of CRF into the amygdala produce anxiety-like behaviors. Release of endogenous CRF can be measured in the amygdala during stress. Potent anxiolytic actions are observed when CRF receptor antagonists are administered into the amygdala. CRF-containing neurons of the amygdala can be directly modulated by alterations in circulating glucocorticoids through glucocorticoid receptors, which are expressed in amygdaloid CRF-containing neurons. Gonadal steroid hormone receptors are found in the amygdala. They are not located in CRF immunoreactive neurons, but they are located adjacent to CRF-expressing neurons and in amygdaloid neurons that are likely to participate in central autonomic and neuroendocrine circuitry. Differences are noted between the steroid influences in the amygdala of male and female animals. Also, evidence is reviewed suggesting a modulatory role in the amygdala for gonadal and adrenal steroids in behavioral, autonomic, and neuroendocrine responses to anxiogenic stimuli.

Castration attenuates prolactin response but potentiates ACTH response to conditioned stress in the rat.

The purpose of this study was to examine the effect of circulating androgens on neuroendocrine, autonomic, and behavioral responses to stress. The effects of conditioned stress were studied in male Sprague-Dawley rats that were intact, gonadectomized, or gonadectomized and treated with dihydrotestosterone (DHT). Intact animals received sham surgeries. Animals were stressed 3 wk after surgery. The adrenocorticotropic hormone (ACTH) response to conditioned stress was significantly potentiated (P < 0.01) in gonadectomized males compared with sham-operated and gonadectomized DHT-treated animals. In stressed rats, plasma corticosterone levels were significantly higher (P < 0.05) in gonadectomized animals compared with DHT-treated castrates. The prolactin response to stress was decreased (P < 0.01) in gonadectomized males compared with sham-operated and gonadectomized DHT-treated rats. The stress-induced increases in plasma renin activity and concentration were not altered in gonadectomized or in gonadectomized DHT-treated animals. Nonstressed DHT-treated castrates exhibited more "fearlike" behavior compared with nonstressed sham-operated and gonadectomized animals. However, conditioned stress produced the same behavioral effects in all treatment groups. The results demonstrate that the ACTH/corticosterone, prolactin, and behavioral responses to a psychological stressor are differentially regulated by circulating androgens.

Catecholamine and NPY efferents from the ventrolateral medulla to the amygdala in the rat.

Anatomical tracing studies have demonstrated an efferent pathway to central nucleus of the amygdala (CeA) from the ventrolateral medulla. The combined retrograde tracing/immunohistochemical method was used to test for the presence of catecholamines and neuropeptide Y (NPY) in ventrolateral medulla neurons that innervate the CeA. Numerous retrogradely labeled neurons were observed in the ventrolateral medulla caudal to the area postrema. Fewer retrogradely labeled neurons were also observed in the rostral ventrolateral medulla. Retrogradely labeled neurons immunoreactive for both tyrosine hydroxylase and NPY were found in the caudal ventrolateral medulla. Double-labeled phenylethanolamine-N-methyltransferase neurons were present at levels rostral to the area postrema. A substantial portion of the ventrolateral medulla projection to the CeA arises from adrenergic cells of the C1 group, because nearly 40% of the retrogradely labeled cells were also immunoreactive for phenylethanolamine-N-methyl-transferase. The high percentage of double-labeled NPY-immunoreactive neurons suggests NPY is colocalized in CeA-projecting catecholamine neurons, indicating that input from the ventrolateral medulla to the CeA primarily arises from C1 adrenergic neurons that also express NPY. This contrasts with previous data suggesting the catecholaminergic projection from the nucleus of the solitary tract to the CeA originates from the A2 noradrenergic cell group. Thus, the input to the CeA from catecholaminegic groups in the caudal medulla is chemically coded in terms of a dorsal noradrenergic and a ventrolateral adrenergic pathway.

Androgen inhibits the increases in hypothalamic corticotropin-releasing hormone (CRH) and CRH-immunoreactivity following gonadectomy.

To characterize the effect of androgens on the hypothalamo-pituitary-adrenal (HPA) axis we examined the regulation of corticotropin-releasing hormone (CRH) following gonadectomy and hormone replacement. Three-month-old male Fischer 344 (F344) rats were gonadectomized (GDX) or sham GDX. Control animals remained intact. Animals were sacrificed 1, 4, 7, 10, or 21 days following surgery. GDX rats had significantly elevated (p < 0.05) levels of hypothalamic CRH 21 days after surgery compared to intact and sham-operated rats. In a second study, 3-month-old male F344 rats were GDX and treated with the non-aromatizable androgen, dihydrotestosterone (DHT), using a Silastic capsule containing crystalline DHT propionate subcutaneously implanted in each animal's back. Control animals were GDX and sham-treated or left intact (INT). Three weeks following gonadectomy, CRH levels in the hypothalamus of GDX rats showed a significant increase (p < 0.05) compared to intact animals. DHT treatment, beginning at the time of gonadectomy prevented this increase. CRH or arginine vasopressin (AVP) immunoreactivity was examined using immunocytochemistry. The number of CRH-immunoreactive (IR) cells in the paraventricular nucleus (PVN) of GDX, DHT-treated animals was significantly decreased (p < 0.05) compared to GDX rats. No differences were seen between treatment groups in CRH-IR cell numbers in the bed nucleus of the stria terminalis or the central amygdaloid nucleus or in AVP-IR cell numbers in the PVN. These data demonstrate that long-term castration increases hypothalamic CRH content and CRH-IR cell numbers in the PVN by removal of an androgen-dependent repression.

Localization of androgen receptor within peptidergic neurons of the rat forebrain.

This study tested for the presence of androgen receptor-immunoreactivity in somatostatin, galanin, vasopressin, corticotropin-releasing hormone, and oxytocin neurons in the rat forebrain. The brains of adult male Sprague-Dawley rats were fixed with 4% paraformaldehyde. Androgen receptor was visualized in coronal sections using nickel intensification of diaminobenzidine, and the neuropeptides were identified using a brown diaminobenzidine reaction product. Androgen receptor was localized to the nuclei of neurons in the septum, amygdala, cortex, hippocampus, and hypothalamus. The majority of somatostatin-containing neurons in the periventricular hypothalamic nucleus also contained androgen receptor. Androgen receptor was also found within galanin-expressing cells in the bed nucleus of the stria terminalis and in the amygdala. Androgen receptor was not observed in corticotropin-releasing hormone, vasopressin, or oxytocin neurons in all areas examined. The data suggest that androgens may be capable of directly regulating somatostatin-expressing neurons of the periventricular nucleus of the hypothalamus and galanin-containing neurons of the bed nucleus of the stria terminalis and amygdala.

Corticotropin releasing factor neurons are innervated by calcitonin gene-related peptide terminals in the rat central amygdaloid nucleus.

The central nucleus of the rat amygdala (CeA) contains many corticotropin releasing factor (CRF) immunoreactive neurons. Previous studies have demonstrated that these CRF neurons project to brain stem regions responsible for modulation of autonomic outflow. Calcitonin gene-related peptide (CGRP) terminals overlap the distribution of CRF cell bodies in the CeA. These CGRP terminals mainly originate from cell bodies that are located in the pontine parabrachial nucleus. The present study examined the possibility that CRF cell bodies are innervated by CGRP terminals. The results suggest that over 35% of the CRF neurons in the CeA are contacted by CGRP terminals as judged by the indiscernible distances between the terminals and cell bodies and or dendrites. In addition, a dual-labeled electron microscopic technique demonstrates that CGRP terminals form synaptic contacts with CRF cell bodies and dendrites. This suggests that CGRP neurons in the parabrachial nucleus can modulate the activity of CRF amygdaloid brain stem efferents. Previous studies have shown that CRF, when administered into the central nervous system, produces increases in heart rate, blood pressure, and plasma catecholamines. CGRP administration into the amygdala has been shown to have a similar effect on the autonomic nervous system. It is, therefore, possible that CGRP could exert these effects via an amygdaloid CRF pathway.

Amygdaloid CRF pathways. Role in autonomic, neuroendocrine, and behavioral responses to stress.

The results of numerous studies have provided compelling evidence that CRF plays an important function in the amygdala. Stimulation of the amygdala produces physiological changes similar those observed after central injections of CRF. Central injections of CRF activate neurons in the amygdala as measured by increases in c-fos protein expression. Destruction of cells or injections of CRF antagonist in the amygdala can attenuate some of the central effects of CRF. The amygdala is the origin of major CRF-containing pathways in the brain. Amygdaloid CRF neurons project to widespread regions of the basal forebrain and brain stem. These amygdaloid pathways mainly arise from the central amygdaloid nucleus where there are a large number of CRF immunoreactive neuronal perikarya. Glucocorticoid and CRF-binding protein are located in cells of the central amygdaloid nucleus. CRF neurons in the central nucleus send their axons to the bed nucleus of the stria terminalis, lateral hypothalamus, midbrain central gray, raphe nuclei, parabrachial region, and the nucleus of the solitary tract. Tract tracing studies have suggested that amygdaloid CRF neurons also innervate CRF neurons in some of these regions and, furthermore, that CRF neurons in some of these areas project back to the CRF neurons in the amygdala. Thus, the amygdala is part of a network of brain nuclei interconnected by CRF pathways. In addition, amygdaloid CRF neurons may project directly to dopaminergic, noradrenergic, and serotonergic neurons, which have widespread projections throughout the neuroaxis.(ABSTRACT TRUNCATED AT 250 WORDS)

Ibotenic acid lesions in the bed nucleus of the stria terminalis attenuate conditioned stress-induced increases in prolactin, ACTH and corticosterone.

The contribution of the bed nucleus of the stria terminalis (BST) to the expression of stress-induced increases in ACTH/corticosterone, prolactin and renin secretion was assessed. Neurons in the lateral part of the BST were destroyed with bilateral injections of the cell-selective neurotoxin ibotenic acid (1.5 micrograms in 0.1 microliter of solution per side). Two weeks later, the rats were stressed using an immobilization or conditioned stress paradigm. Rats with lesions in the lateral part of the BST showed attenuated ACTH and corticosterone responses to conditioned stress. Bilateral ablation of lateral BST significantly reduced the prolactin secretory response to conditioned stress. The same lesions had no effect upon plasma increases in renin that occur in response to conditioned stress. Also, destruction of neurons in the BST did not affect immobilization-induced increases in ACTH, corticosterone, prolactin or renin. Previous studies have demonstrated that ibotenic acid lesions in the central amygdala reduce corticosterone and renin response to conditioned stress. Thus, both the BST and central amygdala are important for the adrenocortical response to conditioned stress. Neurons in the central nucleus of the amygdala are part of the circuitry that mediates renin responses to conditioned stress. Neurons in the BST are important for the full expression of prolactin responses to conditioned stress. The neuronal circuitry and stressor specificity in the mediation of prolactin, renin and ACTH/corticosterone responses are discussed.

Peptide immunoreactive neurons in the amygdala and the bed nucleus of the stria terminalis project to the midbrain central gray in the rat.

The central nucleus of the amygdala, bed nucleus of the stria terminalis, and central gray are important components of the neural circuitry responsible for autonomic and behavioral responses to threatening or stressful stimuli. Neurons of the amygdala and bed nucleus of the stria terminalis that project to the midbrain central gray were tested for the presence of peptide immunoreactivity. To accomplish this aim, a combined immunohistochemical and retrograde tracing technique was used. Maximal retrograde labeling was observed in the amygdala and bed nucleus of the stria terminalis after injections of retrograde tracer into the caudal ventrolateral midbrain central gray. The majority of the retrogradely labeled neurons in the amygdala were located in the medial central nucleus, although many neurons were also observed in the lateral subdivision of the central nucleus. Most of the retrogradely labeled neurons in the BST were located in the ventral and posterior lateral subdivisions, although cells were also observed in most other subdivisions. Retrogradely labeled neurotensin, corticotropin releasing factor (CRF), and somatostatin neurons were mainly observed in the lateral central nucleus and the dorsal lateral BST. Retrogradely labeled substance P-immunoreactive cells were found in the medial central nucleus and the posterior and ventral lateral BST. Enkephalin-immunoreactive retrogradely labeled cells were not observed in the amygdala or bed nucleus of the stria terminalis. A few cells in the hypothalamus (paraventricular and lateral hypothalamic nuclei) that project to the central gray also contained CRF and neurotensin immunoreactivity. The results suggest the amygdala and the bed nucleus of the stria terminalis are a major forebrain source of CRF, neurotensin, somatostatin, and substance P terminals in the midbrain central gray.

Organization of amygdaloid projections to brainstem dopaminergic, noradrenergic, and adrenergic cell groups in the rat.

The distribution of amygdaloid axons in the various brainstem dopaminergic, noradrenergic, and adrenergic cell groups was examined. This was accomplished by means of the Phaseolus vulgaris leucoagglutinin lectin (PHA-L) anterograde tracing technique combined with glucose-oxidase immunocytochemistry to catecholamine markers (i.e., tyrosine hydroxylase, dopamine beta hydroxylase, and phenylethanolamine N-methyltransferase). Injections of PHA-L in the medial part of the central amygdaloid nucleus resulted in axonal and terminal labeling in most catecholamine cell groups in the brainstem. Amygdaloid terminals appeared to contract catecholaminergic cells in several brainstem regions. The most heavily innervated catecholaminergic cells were the A9 (lateral) and A8 dopaminergic cell groups and the C2/A2 adrenergic/noradrenergic cell groups in the nucleus of the solitary tract. The medial part of the A9 and adjacent A10 dopaminergic cell groups was moderately innervated. A moderate innervation by amygdaloid terminals was observed on rostral locus coeruleus noradrenergic cells (A6 rostral) and adrenergic cells of the rostral ventrolateral medulla (C1). Noradrenergic cells of the A5, main body of the locus coeruleus (A6), A7, and subcoeruleus were sparsely innervated. Amygdaloid axons were not observed on noradrenergic neurons of the A4 cell group, area postrema, and A1 cells of the ventrolateral medulla. The results demonstrate that the amygdala primarily innervates the dopaminergic cells of midbrain (i.e., A8 and lateral A9 cells) and the adrenergic cells (C2) and noradrenergic (A2) cells in the nucleus of the solitary tract. The possible functional significance of amygdaloid innervation of catecholaminergic cells is discussed.

Amygdaloid lesions: differential effect on conditioned stress and immobilization-induced increases in corticosterone and renin secretion.

The purpose of this study was to examine the contribution of the central nucleus of the amygdala to the expression of stress-induced increase in corticosterone and renin secretion. Neurons in the central amygdaloid nucleus of male rats were destroyed by bilateral injections of ibotenic acid, a neurotoxin that destroys cells but leaves fibers of passage intact. Two weeks later, the rats were subjected to immobilization for 20 min or to a conditioned stress (conditioned emotional response) procedure. Central amygdala lesions inhibited the increases in plasma corticosterone after exposure to both conditioned stress and immobilization. Lesions in the lateral amygdala had no effect on the corticosterone response to either stressor. Lesions in the central amygdala attenuated the renin response to conditioned stress but not to immobilization. In contrast, lateral amygdala lesions potentiated the renin response to immobilization but did not affect the renin response to conditioned stress. The results confirm previous studies that demonstrate the importance of the central amygdaloid nucleus in the expression of corticosterone to immobilization stress. In addition, the results show that neurons within the central amygdaloid nucleus are necessary for the full expression of conditioned stress-induced increase in corticosterone and renin secretion. The results are discussed with respect to the potential pathways that mediate stress-induced increases in corticosterone and renin secretion.

Bombesin immunoreactive neurons in the hypothalamic paraventricular nucleus innervate the dorsal vagal complex in the rat.

Bombesin-like immunoreactivity has been localized within neuronal cell bodies of the hypothalamus and nerve terminals within the dorsal vagal complex. The possibility that the hypothalamus is a source for bombesin-like immunoreactive terminals within the dorsal vagal complex was examined using the combined retrograde tracing and immunohistochemical technique. After injections of retrograde tracer were made into the dorsal vagal complex, cells in the hypothalamus labeled with both retrograde tracer and bombesin immunoreactivity were localized in the parvocellular part of the paraventricular nucleus. In the paraventricular nucleus most of the vagal projecting bombesin immunoreactive neurons were located within the medial parvocellular subdivision. Approximately 30% of the bombesin immunoreactive neurons in this subnucleus projected to the dorsal vagal complex. The results suggest that the paraventricular hypothalamic nucleus is a major source of bombesin terminals within the dorsal vagal complex. This pathway may mediate some of the autonomic nervous system changes that are observed when bombesin is injected within the central nervous system. Additionally, this data adds to a growing amount of evidence supporting the role of bombesin as a peptide neurotransmitter.

Central nervous system site of action of bombesin to elevate plasma concentrations of catecholamines.

To identify the central nervous system site of action of bombesin to elevate plasma concentrations of catecholamines, this peptide has been injected into numerous brain ventricular and parenchymal sites. Low doses of bombesin (1-10 ng) injected into the region of the rostral nucleus tractus solitarius (NTS) elicited an elevation of plasma catecholamines greater than those observed following an injection of bombesin into other brain regions. Bombesin-induced (10 ng) elevation of plasma epinephrine but not norepinephrine was prevented by co-administration of somatostatin-28 (100 ng). Mean arterial pressure (MAP) and heart rate (HR) were measured following injection of bombesin into the NTS. Bombesin injected into the NTS resulted in prolonged decreases in HR without significantly altering MAP. These studies demonstrate that bombesin injected into the dorsal medulla resulted in significant changes of plasma catecholamine levels and HR. Based on these actions of bombesin and the neuroanatomic distribution of bombesin-like peptide, it is suggested that this peptide may play an important role in regulation of sympatho-adrenal and cardiac functions.