Neuronal-vascular relationships in the raphe nuclei, locus coeruleus, and substantia nigra in primates

Priorities for research on neuromodulatory subcortical systems in Alzheimer's disease: Position paper from the NSS PIA of ISTAART

The neuromodulatory subcortical system (NSS) nuclei are critical hubs for survival, hedonic tone, and homeostasis. Tau-associated NSS degeneration occurs early in Alzheimer's disease (AD) pathogenesis, long before the emergence of pathognomonic memory dysfunction and cortical lesions. Accumulating evidence supports the role of NSS dysfunction and degeneration in the behavioral and neuropsychiatric manifestations featured early in AD. Experimental studies even suggest that AD-associated NSS degeneration drives brain neuroinflammatory status and contributes to disease progression, including the exacerbation of cortical lesions. Given the important pathophysiologic and etiologic roles that involve the NSS in early AD stages, there is an urgent need to expand our understanding of the mechanisms underlying NSS vulnerability and more precisely detail the clinical progression of NSS changes in AD. Here, the NSS Professional Interest Area of the International Society to Advance Alzheimer's Research and Treatment highlights knowledge gaps about NSS within AD and provides recommendations for priorities specific to clinical research, biomarker development, modeling, and intervention. HIGHLIGHTS: Neuromodulatory nuclei degenerate in early Alzheimer's disease pathological stages. Alzheimer's pathophysiology is exacerbated by neuromodulatory nuclei degeneration. Neuromodulatory nuclei degeneration drives neuropsychiatric symptoms in dementia. Biomarkers of neuromodulatory integrity would be value-creating for dementia care. Neuromodulatory nuclei present strategic prospects for disease-modifying therapies.

Processing of fMRI-related anxiety and bi-directional information flow between prefrontal cortex and brain stem

Brain-heart synchronization is fundamental for emotional-well-being and brain-heart desynchronization is characteristic for anxiety disorders including specific phobias. Recording BOLD signals with functional magnetic resonance imaging (fMRI) is an important noninvasive diagnostic tool; however, 1-2% of fMRI examinations have to be aborted due to claustrophobia. In the present study, we investigated the information flow between regions of interest (ROI's) in the cortex and brain stem by using a frequency band close to 0.1 Hz. Causal coupling between signals important in brain-heart interaction (cardiac intervals, respiration, and BOLD signals) was studied by means of Directed Transfer Function based on the Granger causality principle. Compared were initial resting states with elevated anxiety and final resting states with low or no anxiety in a group of fMRI-naïve young subjects. During initial high anxiety the results showed an increased information flow from the middle frontal gyrus (MFG) to the pre-central gyrus (PCG) and to the brainstem. There also was an increased flow from the brainstem to the PCG. While the top-down flow during increased anxiety was predominant, the weaker ascending flow from brainstem structures may characterize a rhythmic pacemaker-like activity that (at least in part) drives respiration. We assume that these changes in information flow reflect successful anxiety processing.

Central chemoreceptors: locations and functions

Central chemoreception traditionally refers to a change in ventilation attributable to changes in CO2/H(+) detected within the brain. Interest in central chemoreception has grown substantially since the previous Handbook of Physiology published in 1986. Initially, central chemoreception was localized to areas on the ventral medullary surface, a hypothesis complemented by the recent identification of neurons with specific phenotypes near one of these areas as putative chemoreceptor cells. However, there is substantial evidence that many sites participate in central chemoreception some located at a distance from the ventral medulla. Functionally, central chemoreception, via the sensing of brain interstitial fluid H(+), serves to detect and integrate information on (i) alveolar ventilation (arterial PCO2), (ii) brain blood flow and metabolism, and (iii) acid-base balance, and, in response, can affect breathing, airway resistance, blood pressure (sympathetic tone), and arousal. In addition, central chemoreception provides a tonic "drive" (source of excitation) at the normal, baseline PCO2 level that maintains a degree of functional connectivity among brainstem respiratory neurons necessary to produce eupneic breathing. Central chemoreception responds to small variations in PCO2 to regulate normal gas exchange and to large changes in PCO2 to minimize acid-base changes. Central chemoreceptor sites vary in function with sex and with development. From an evolutionary perspective, central chemoreception grew out of the demands posed by air versus water breathing, homeothermy, sleep, optimization of the work of breathing with the "ideal" arterial PCO2, and the maintenance of the appropriate pH at 37°C for optimal protein structure and function.

Central chemoreceptors: locations and functions

Central chemoreception traditionally refers to a change in ventilation attributable to changes in CO2/H(+) detected within the brain. Interest in central chemoreception has grown substantially since the previous Handbook of Physiology published in 1986. Initially, central chemoreception was localized to areas on the ventral medullary surface, a hypothesis complemented by the recent identification of neurons with specific phenotypes near one of these areas as putative chemoreceptor cells. However, there is substantial evidence that many sites participate in central chemoreception some located at a distance from the ventral medulla. Functionally, central chemoreception, via the sensing of brain interstitial fluid H(+), serves to detect and integrate information on (i) alveolar ventilation (arterial PCO2), (ii) brain blood flow and metabolism, and (iii) acid-base balance, and, in response, can affect breathing, airway resistance, blood pressure (sympathetic tone), and arousal. In addition, central chemoreception provides a tonic "drive" (source of excitation) at the normal, baseline PCO2 level that maintains a degree of functional connectivity among brainstem respiratory neurons necessary to produce eupneic breathing. Central chemoreception responds to small variations in PCO2 to regulate normal gas exchange and to large changes in PCO2 to minimize acid-base changes. Central chemoreceptor sites vary in function with sex and with development. From an evolutionary perspective, central chemoreception grew out of the demands posed by air versus water breathing, homeothermy, sleep, optimization of the work of breathing with the "ideal" arterial PCO2, and the maintenance of the appropriate pH at 37°C for optimal protein structure and function.

Dissociation of metabolic and neurovascular responses to levodopa in the treatment of Parkinson's disease

We compared the metabolic and neurovascular effects of levodopa (LD) therapy for Parkinson's disease (PD). Eleven PD patients were scanned with both [15O]-H2O and [18F]-fluorodeoxyglucose positron emission tomography in the unmedicated state and during intravenous LD infusion. Images were used to quantify LD-mediated changes in the expression of motor- and cognition-related PD covariance patterns in scans of cerebral blood flow (CBF) and cerebral metabolic rate for glucose (CMR). These changes in network activity were compared with those occurring during subthalamic nucleus (STN) deep brain stimulation (DBS), and those observed in a test-retest PD control group. Separate voxel-based searches were conducted to identify individual regions with dissociated treatment-mediated changes in local cerebral blood flow and metabolism. We found a significant dissociation between CBF and CMR in the modulation of the PD motor-related network by LD treatment (p < 0.001). This dissociation was characterized by reductions in network activity in the CMR scans (p < 0.003) occurring concurrently with increases in the CBF scans (p < 0.01). Flow-metabolism dissociation was also evident at the regional level, with LD-mediated reductions in CMR and increases in CBF in the putamen/globus pallidus, dorsal midbrain/pons, STN, and ventral thalamus. CBF responses to LD in the putamen and pons were relatively greater in patients exhibiting drug-induced dyskinesia. In contrast, flow-metabolism dissociation was not present in the STN DBS treatment group or in the PD control group. These findings suggest that flow-metabolism dissociation is a distinctive feature of LD treatment. This phenomenon may be especially pronounced in patients with LD-induced dyskinesia.

Persistent cerebrovascular effects of MDMA and acute responses to the drug

Acutely, 3,4,-methylenedioxymethamphetamine (MDMA) induces cerebrovascular dysfunction [Quate et al., (2004)Psychopharmacol., 173, 287-295]. In the longer term the same single dose results in depletion of 5-hydroxytrptamine (5-HT) nerve terminals. In this study we examined the cerebrovascular consequences of this persistent neurodegeneration, and the acute effects of subsequent MDMA exposure, upon the relationship that normally exists between local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCMRglu). Dark agouti (DA) rats were pre-treated with 15 mg/kg i.p. MDMA or saline. Three weeks later, rats from each pre-treatment group were treated with an acute dose of MDMA (15 mg/kg i.p.) or saline. Quantitative autoradiographic imaging was used to measure LCBF or LCMRglu with [(14)C]-iodoantipyrine and [(14)C]-2-deoxyglucose, respectively. Serotonergic terminal depletion was assessed using radioligand binding with [(3)H]-paroxetine and immunohistochemistry. Three weeks after MDMA pre-treatment there were significant reductions in densities of 5-HT transporter (SERT)-positive fibres (-46%) and [(3)H]-paroxetine binding (-47%). In animals pre-treated with MDMA there were widespread significant decreases in LCMRglu, but no change in LCBF indicating a persistent loss of cerebrovascular constrictor tone. In both pre-treatment groups, acute MDMA produced significant increases in LCMRglu, while LCBF was significantly decreased. In 50% of MDMA-pre-treated rats, random areas of focal hyperaemia indicated a loss of autoregulatory capacity in response to MDMA-induced hypertension. These results suggest that cerebrovascular regulatory dysfunction resulting from acute exposure to MDMA is not diminished by previous exposure, despite a significant depletion in 5-HT terminals. However, there may be a sub-population, or individual circumstances, in which this dysfunction develops into a condition that might predispose to stroke.

Changes in vascularization in substantia nigra pars compacta of monkeys rendered parkinsonian

The degeneration of nigral dopaminergic neurons in Parkinson's disease is believed to be associated with a glial reaction and inflammatory changes. In turn, local factors may induce changes in vascularization and contribute to neuronal vulnerability. Among these factors, Vascular Endothelial Growth Factor (VEGF) is released in adults under pathological conditions and is thought to induce angiogenesis. In order to determine whether changes in brain vasculature are observed in the affected brain regions in parkinsonism, we quantitatively analysed the VEGF-expressing cells and blood vessels in the substantia nigra of monkeys rendered parkinsonian by MPTP injection and compared the results with those obtained in control monkeys. Using stereological methods, we observed an increase in the number of VEGF-expressing neurons and an increase of the number of blood vessels and their volume occupying the substantia nigra pars compacta of monkeys rendered parkinsonian by chronic MPTP intoxication. These changes in vascularization may therefore modify the neuronal availability of blood nutrients, blood cells or toxic substances and neuronal susceptibility to parkinsonism.

Chemosensitive serotonergic neurons are closely associated with large medullary arteries

We have previously shown that serotonergic neurons of the medulla are strongly stimulated by an increase in CO(2), suggesting that they are central respiratory chemoreceptors. Here we used confocal imaging and electron microscopy to show that neurons immunoreactive for tryptophan hydroxylase (TpOH) are tightly apposed to large arteries in the rat medulla. We used patch-clamp recordings from brain slices to confirm that neurons with this anatomical specialization are chemosensitive. Serotonergic neurons are ideally situated for sensing arterial blood CO(2), and may help maintain pH homeostasis via wide-ranging effects on brain function. The results reported here support a recent proposal that sudden infant death syndrome (SIDS) results from a developmental abnormality of medullary serotonergic neurons.

Acidosis-Stimulated Neurons of the Medullary Raphe Are Serotonergic

Neurons of the medullary raphe project widely to respiratory and autonomic nuclei and contain co-localized serotonin, thyrotropin-releasing hormone (TRH), and substance P, three neurotransmitters known to stimulate ventilation. Some medullary raphe neurons are highly sensitive to pH and CO2 and have been proposed to be central chemoreceptors. Here it was determined whether these chemosensitive neurons are serotonergic. Cells were microdissected from the rat medullary raphe and maintained in primary cell culture for 13–70 days. Immunoreactivity for serotonin, substance P, and TRH was present in these cultures. All acidosis-stimulated neurons ( n = 22) were immunoreactive for tryptophan hydroxylase (TpOH-IR), the rate-limiting enzyme for serotonin biosynthesis, whereas all acidosis-inhibited neurons ( n= 16) were TpOH-immunonegative. The majority of TpOH-IR medullary raphe neurons (73%) were stimulated by acidosis. The electrophysiological properties of TpOH-IR neurons in culture were similar to those previously reported for serotonergic neurons in vivo and in brain slices. These properties included wide action potentials (4.55 ± 0.5 ms) with a low variability of the interspike interval, a postspike afterhyperpolarization (AHP) that reversed 25 mV more positive than the Nernst potential for K+, prominent A current, spike frequency adaptation and a prolonged AHP after a depolarizing pulse. Thus the intrinsic cellular properties of serotonergic neurons were preserved in cell culture, indicating that the results obtained using this in vitro approach are relevant to serotonergic neurons in vivo. These results demonstrate that acidosis-stimulated neurons of the medullary raphe contain serotonin. We propose that serotonergic neurons initiate a homeostatic response to changes in blood CO2 that includes increased ventilation and modulation of autonomic function.

Cerebral vessels in ageing and Alzheimer's disease

The integrity of the cerebral vasculature is crucial to the maintenance of cognitive functions during ageing. Prevailing evidence suggests that cerebrovascular functions decline during normal ageing, with pronounced effects in Alzheimer's disease (AD). The causes of these changes largely remain unknown. While previous studies recorded ageing-related impairments, such as atherosclerosis and loss of innervation in basal surface arteries of the brain, it only recently has been realized that a number of subtle alterations in both the intracranial resistance vessels and the smaller capillaries is apparent in both ageing animals and humans. The dominant changes include alterations in composition of connective tissues and smooth muscle of large vessel walls, thickening of the vascular basement membrane, thinning of the endothelium in some species, loss of endothelial mitochondria and increased pericytes. Some of these attributes appear more affected in AD. Other abnormalities entail profound irregularities in the course of microvessels, unexplained inclusions in the basement membrane and changes in unique proteins and membrane lipids associated with the blood-brain barrier. Brain imaging and permeability studies show no clear functional evidence to support the structural and biochemical anomalies, but it is plausible that focal and transient breach of the blood-brain barrier in ageing, and more notably in AD, occurs. Thus, circumscribed neuronal populations in certain brain regions could become vulnerable. Furthermore, the characteristic deposition of amyloid in vessels in AD may exacerbate the decline in vascular function and promote chronic hypoperfusion. Although not explicit from current studies, it is likely that the brain vasculature is continually modified by growth and repair mechanisms in attempts to maintain perfusion during ageing and disease.

Cerebrovascular and metabolic uncoupling in the caudate-putamen following unilateral lesion of the mesencephalic dopaminergic neurons in the rat

Changes in local cerebral blood flow (lCBF) and local cerebral glucose utilization (lCGU) were assessed in dopaminergic primary target areas in the rat 6 weeks after unilateral lesion of dopaminergic neurons within the substantia nigra pars compacta (SNc) and adjacent ventrotegmental area (VTA) using 6-hydroxydopamine (6-OHDA). lCBF and lCGU were determined using the autoradiographic [14C]iodoantipyrine and [14C]2-deoxyglucose method. Dopaminergic deafferentation provoked a marked unilateral lCBF decrease in the dorso-lateral portion of the rostral caudate-putamen. The decrease in lCBF was not associated with significant changes in glucose metabolism. Thus, lesions of dopaminergic afferents to the caudate-putamen appear to provoke a sustained decrease in basal blood flow with unchanged local metabolic activity.

Acute cocaine alters cerebrovascular autoregulation in the rat neocortex

Although cocaine abuse has been associated with an increased incidence of cerebrovascular accident, the underlying mechanisms are unknown. In this study we have investigated the effects of cocaine upon the autoregulation of local cortical blood flow (lCBF) during hypertension. Hypertension was induced in conscious rats by intravenous infusion of angiotensin-II (5 micrograms/ml; 0.5-2.5 ml/h), and animals were subsequently injected IV with either cocaine-HCl (5 mg/kg) or saline, prior to the measurement of lCBF of glucose utilization (lCGU) using [14C]-iodoantipyrine or [14C]-2-deoxyglucose quantitative autoradiography, respectively. Hypertension alone (< 155 mmHg) did not significantly alter lCBF in any cortical areas examined. However, at higher mean arterial blood pressure (MABP), lCBF increased focally (+265%) in parietal cortex. Cocaine did not alter lCBF in normotensive animals, but with increasing levels of hypertension (MABP > 145 mmHg), all cocaine-treated rats showed focal increases (200-400%) in lCBF in parietal cortex. Glucose use remained relatively unaffected in all treatment groups. This hyperaemia in cocaine-treated rats at MABP below the normal upper limit of autoregulation may provide a mechanism to explain haemorrhagic stroke in cocaine abusers.

A species-specific population of tyrosine hydroxylase-immunoreactive neurons in the medial amygdaloid nucleus of the Syrian hamster

The medial amygdaloid nucleus (Me) is part of a neural pathway that regulates sexual behavior in the male Syrian hamster. To characterize the neurochemical content of neurons in this nucleus, brains from colchicine-treated adult male and female hamsters were immunocytochemically labeled using antibodies that recognize the catecholamine-synthesizing enzymes, tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT), as well as dopamine. A large population of TH-immunoreactive (TH-IR) neurons was observed throughout Me of male and female hamsters, primarily concentrated in the midrostral and caudal portions of the nucleus. The somata were generally small to medium in size and bipolar. Brains from animals that did not receive colchicine contained a limited number of TH-IR neurons in Me as reported previously. The DBH and PNMT antisera did not label any cells in Me of colchicine-treated animals, and the dopamine antiserum labeled neurons in the same location as the caudal group of TH-IR cells. Therefore, these caudal TH-IR neurons are interpreted to be dopaminergic. The rostral group of TH-IR neurons, on the other hand, may be producing only the immediate precursor of dopamine, L-3,4-dihydroxyphenylalanine (L-DOPA). The TH-synthesizing neurons in Me of the Syrian hamster appear to be a species-specific group of cells located outside of the previously described catecholaminergic cell groups.

Dopaminergic receptors linked to adenylate cyclase in human cerebromicrovascular endothelium

Cultured endothelium derived from three fractions of human cerebral microvessels was used to characterize dopamine (DA) receptors linked to adenylate cyclase activity. DA or D1 agonist, (+/-)-SKF-82958 hydrobromide, stimulated endothelial cyclic AMP formation in a dose-dependent manner. The selective D1 antagonist, (+/-)SCH-23390, inhibited in a dose-dependent manner the production of cyclic AMP induced by DA. The affinity for the D1 receptor appeared to be greater in endothelium derived from large and small microvessels than from capillaries. Cholera toxin ADP-ribosylation of Gs proteins abolished the DA stimulatory effect on endothelial adenylate cyclase, whereas pertussis toxin ADP-ribosylation enhanced the DA-inducible formation, indicating the presence of both D1 and D2 receptors. Agonists of alpha 1-adrenergic receptors (phenylephrine, 6-fluoronorepinephrine) or serotonin (5-HT), which stimulated the production of cyclic AMP, had no additive effect on DA-stimulated cyclic AMP formation. Incubation of these agents with DA produced the same or lower levels of cyclic AMP as compared to that formed by DA alone. The effect of alpha 1-adrenergic agonists or 5-HT on DA production of cyclic AMP was partially prevented by the D2 antagonist, S(-)-sulpiride, or ketanserin (5-HT2 greater than alpha 1 greater than H1 antagonists), respectively. These findings represent the first demonstration of D1- (stimulatory) and D2- (inhibitory) receptors linked to adenylate cyclase in microvascular endothelium derived from human brain. The data also indicate that dopaminergic receptors can interact with either alpha 1-adrenergic or or 5-HT receptors in endothelium on the adenylate cyclase level.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of age on blood vessels and neurovascular appositions in the CA1 region of the rat hippocampus

Rats aged 3, 9, 24 and 30 months were used in this study. Increased basal lamina thickening in capillaries, muscular large vessels and nonmuscular large vessels was shown with advancing age. There is also an age-related increase in the area of mitochondria in smooth muscle cells. These ultrastructural changes may underlie observed age-related functional changes in the vasculature. They may be a compensatory response of the vessel wall cells to a declining capacity to handle the continual and varying shear stress exerted by the blood. Ultrastructural differences between capillaries and the two types of large vessels are reported and discussed in terms of their functional significance. It was noted that there are more dendrites adjacent to capillaries than to large vessels, however, this was unaffected by increasing age. Since advancing age did not alter the number of neuronal processes adjacent to vessels, age-related compromises in vessel function may not be subjected to neuronal regulation.

The therapeutic potential for tryptophan and melatonin: possible roles in depression, sleep, Alzheimer's disease and abnormal aging

Evidence suggests that stress and/or a dietary lack of tryptophan may make deficiencies of serotonin and melatonin common. In addition, older animals and human beings have a reduced ability to synthesize melatonin. Disorders of melatonin levels and rhythms are suggested to be a cause of affective disease, abnormal sleep, Alzheimer's disease, and some age related disorders. If these ideas prove to be true, then preventive measures are possible.

Fluorescence histochemical techniques for catecholamines as tools in neurobiology

Formaldehyde-induced and glyoxylic-acid-induced fluorescence histochemistry permits the tissue localization of catecholamines in the central nervous system (CNS) and peripheral nervous system (PNS), and in culture. Counterstains such as ethidium bromide provide excellent background identification of specific innervated regions in both the CNS and the periphery. Use of fluorescence histochemistry with immunocytochemistry can elucidate catecholamine-peptide relationships. Gelatin-ink perfusion used with fluorescence histochemistry permits the investigation of neuro-vascular relationships and documentation of vascular and parenchymal compartmentation of innervation. Combined use of fluorescence histochemistry and retrograde tracing methods demonstrates the specific cellular sources of innervation of target regions. Micropunch neurochemical analysis provides quantitative data for correlation with fluorescence histochemistry within a target region of innervation, and microspectrofluorometric analysis provides a semi-quantitative evaluation of the amount of fluorophore within a target region or within specific subcellular compartments such as the cell body or terminals.

Effects of dopamine on pial arteriolar diameter and CSF prostanoid levels in piglets

We examined effects of topically applied dopamine on pial arteriolar diameter and CSF prostanoid levels in newborn pigs. Vascular responses were determined using the closed cranial window technique and intravital microscopy, and prostanoids were determined by radioimmunoassay. Topical application of dopamine did not change arteriolar diameter at 10(-7)-10(-5) M, but constricted arterioles at 10(-4) (16%) and 10(-3) M (30%). Intravenous administration of indomethacin (5 mg/kg) did not alter this constriction. In addition, CSF prostanoid levels did not increase in response to application of dopamine except for a modest increase of prostaglandin E2 at 10(-3) M. We conclude that dopamine is a constrictor at high doses of piglet pial arterioles and that this response is not modified by endogenous prostanoids.

Effects of physiological manipulations on locus coeruleus neuronal activity in freely moving cats. III. Glucoregulatory challenge

Insulin-induced hypoglycemia and the subsequent administration of glucose were examined for their effects on single unit activity of locus coeruleus noradrenergic (LC-NE) neurons in unanesthetized, unrestrained cats. LC-NE neuronal activity showed an inverse relationship to blood glucose levels. The activity of most cells increased during sustained hypoglycemia, and then decreased following glucose administration. Some neurons were unaffected by hypoglycemia, but were inhibited following glucose. The activation of LC-NE neurons in response to insulin administration generally paralleled the increase in plasma epinephrine, although the adrenal response was more sensitive. These data, together with those reported in the preceding papers, suggest the following general conclusions: (1) physiological stimuli can influence the activity of LC-NE neurons in unanesthetized subjects (although they do so less strongly than environmental stimuli); (2) these effects of physiological stimuli upon LC-NE neurons can be exerted independent of changes in behavioral state; (3) LC-NE neurons do not appear to play a specific role in the regulation of any of the systems examined, but may instead play a more global role in the response to physiological challenges in general; (4) LC-NE neurons are generally co-activated with both the neural and hormonal components of the sympatho-adrenal system, although sympathetic activation can occur in the absence of increased LC-NE activity. A previously hypothesized role for LC-NE neurons in facilitating the behavioral response to environmental stressors may thus be extended to include the response to physiological challenges, and perhaps facilitation of the physiological as well as the behavioral components of the stress response.

Cholecystokinin facilitates ejaculation in male rats: blockade with proglumide and apomorphine

Systemic administration of the active, sulfated form of cholecystokinin-octapeptide (CCK-8S), at a dose known to inhibit dopamine (DA) release, significantly reduced the latency to ejaculate and number of intromissions preceding ejaculation in sexually active male rats. This effect was identical to that reported for low doses of the DA receptor agonist apomorphine, which bind preferentially to presynaptic DA autoreceptors. The facilitatory effect of CCK-8S on ejaculation was blocked by the putative CCK receptor antagonist proglumide and by a presynaptic dose of apomorphine. Blockade of the effect of CCK-8S with a presynaptic dose of apomorphine is consistent with CCK induction of depolarization block in DA neurons. These data suggest that CCK-8S and apomorphine may reduce the ejaculation threshold in sexually active male rats by inhibition of DA release via two different mechanisms of action.

Ventral tegmental (A10) system: neurobiology. 1. Anatomy and connectivity

The VTA contains the A10 group of DA containing neurons. These neurons have been grouped into nuclei to be found on the floor of the midbrain tegmentum--Npn, Nif, Npbp and Nln rostralis and caudalis. The VTA is traversed by many blood vessels and nerve fibers. Close to its poorly defined borders are found DA (A8, A9, A11) and 5-HT containing neurons (B8). Efferent projections of the VTA can be divided into 5 subsystems. The mesorhombencephalic projects to other monoaminergic nuclei, the cerebellum and a fine projection descends to other tegmental nuclei as far as the inferior olive. Fibers to the spinal cord have not been demonstrated. The mesodiencephalic path projects to several thalamic and hypothalamic nuclei and possibly the median eminence. Functionally important examples are the anterior hypothalamic-preoptic area, N. medialis dorsalis and reuniens thalami. These two subsystems are largely non-dopaminergic. A minor mesostriatal projection is overshadowed by the large mesolimbic projection to the accumbens, tuberculum olfactorium, septum lateralis and n. interstitialis stria terminalis. There are also mesolimbic connections with several amygdaloid nuclei (especially centralis and basolateralis), the olfactory nuclei and entorhinal cortex. A minor projection to the hippocampus has been detected. The mesocortical pathway projects to sensory (e.g. visual), motor, limbic (e.g. retrosplenial) and polysensory association cortices (e.g. prefrontal). Prefrontal, orbitofrontal (insular) and cingulate cortices receive the most marked innervation from the VTA. A more widespread presence of DA in other cortices of rodents becomes progressively more evident in carnivores and primates. Most but not all projections are unilateral. Some neurons project to more than one area in mesodiencephalic, limbic and cortical systems. The majority of these fibers ascend in the MFB. Most areas receiving a projection from the VTA (DA or non-DA) project back to the VTA. The septohippocampal complex in particular and the limbic system in general provide quantitatively much less feedback than other areas. The role of the VTA as a mediator of dialogue with the frontostriatal and limbic/extrapyramidal system is discussed under the theme of circuit systems. The large convergence of afferents to certain VTA projection areas (prefrontal, entorhinal cortices, lateral septum, central amygdala, habenula and accumbens) is discussed under the theme of convergence systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Neonatal 6-hydroxydopamine lesion of spinal noradrenergic terminals: nociception, clonidine analgesia and spinal alpha two adrenoceptors

Newborn rats received intraspinal injections of 6-hydroxydopamine to enduringly deplete spinal norepinephrine (NE). When tested in adulthood for pain sensitivity with a hot water-tail immersion procedure, this neonatal spinal NE lesion lowered tail flick latencies of females but not males. It was postulated that this sexually dimorphic sparing or recovery of function reflected the development of denervation supersensitivity for males but not females. Contrary to expectation from such an hypothesis, females, not males, showed exaggerated sensitivity to the analgesic effects of a test dose of clonidine. Furthermore, neither males nor females showed an increased number of spinal cord binding sites for (3H)para-amino-clonidine [(3H)PAC]. These receptor binding data failed to indicate proliferation of the spinal alpha two adrenoceptor in either sex. That the lesioning of spinal NE terminals did not reduce (3H)PAC binding sites suggests that the spinal alpha two adrenoceptor does not reside exclusively on NE terminals. This is consistent with current conclusions concerning the alpha two adrenoceptor in the cerebral cortex.

Origin and distribution of cerebral vascular innervation from superior cervical, trigeminal and spinal ganglia investigated with retrograde and anterograde WGA-HRP tracing in the rat

Peripheral sources of cerebral vascular innervation have been investigated with retrograde and anterograde neuronal tracing of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) in the rat. For retrograde identification of sources of innervation, WGA-HRP was applied to the exposed basilar artery through a fine slit in the overlying meninges, and sections of brain and peripheral ganglia were reacted with tetramethylbenzidine for detection of the tracer. A high density of tetramethylbenzidine reaction product was observed around the basilar artery and in the surrounding pial tissue, but the application sites were not completely selective since some tracer always had spread into the ventral brain stem. Retrogradely labelled cell bodies were identified in the superior cervical, stellate, first and second spinal, and trigeminal ganglia, i.e. these ganglia may represent origins of basilar artery innervation. In a second series of experiments, microinjections of WGA-HRP were placed into the indicated ganglia to obtain anterograde labelling of nerve fibres on whole-mounts of the cerebral vessels. Injections into trigeminal ganglia labelled nerve fibres on the ipsilateral half of the circle of Willis, as well as the contralateral anterior cerebral artery and the rostral part of the basilar artery. The first and second spinal ganglia projected to the vertebrobasilar arteries, while the ipsilateral part of the internal carotid (outside the circle of Willis) received fibres from the second spinal ganglion. Nerve fibres originating in trigeminal and spinal ganglia were organised in bundles, and between these a sparse plexus of thin single fibres appeared. Injection of WGA-HRP into superior cervical ganglion labelled a plexus of nerve fibres on the ipsilateral circle of Willis and the (rostral) basilar artery. These experiments demonstrated the origin and distribution of sympathetic and sensory innervation to major cerebral arteries in the rat.

Vasomotor responses of cerebral arterioles in situ to putative dopamine receptor agonists

The vasomotor responses of individual cerebral pial arterioles on the convexity of the cerebral cortex to subarachnoid perivascular micro-injections of dopamine and the putative dopamine receptor agonists, apomorphine, SKF 38393 and LY 141865, have been examined in 38 anaesthetized cats. The perivascular microapplication of dopamine (10(-9)-10(-3)M) effected dose-dependent reductions in pial arteriolar calibre, with the maximum reductions in calibre (22 +/- 2% from preinjection levels: mean +/- s.e.) being observed at 10(-3)M. The cerebrovascular constriction produced by dopamine (10(-5)M) could be significantly attenuated by the concomitant perivascular administration of phentolamine (10(-6)M) or methysergide (10(-6)M). The perivascular microapplication of apomorphine (10(-8)-10(-4)M) effected dose-dependent increases in arteriolar calibre, with the maximum increase (31 +/- 6%) being observed with apomorphine (10(-5)M). The perivascular administration of the putative dopamine D1-receptor agonist, SKF 38393 (10(-9)-10(-4)M) increased arteriolar calibre, with the maximum response (24 +/- 3%) being observed with injection of 10(-7)M. The putative dopamine D2-receptor agonist, LY 141865, also increased cerebral arteriolar calibre, but only at high concentrations (maximum calibre increase 25 +/- 6.1 with 10(-4)M). The cerebrovascular dilatations elicited by apomorphine and by SKF 38393 were markedly attenuated by the concomitant perivascular microapplication of the putative dopamine D1-receptor antagonist, SCH 23390 (10(-8)M). The perivascular administration of SCH 23390 (10(-9)-10(-5)M) per se did not alter arteriolar calibre nor the arteriolar dilatation provoked by microinjections of acidic cerebrospinal fluid. These results point to the presence on cat cerebral arterioles of dopamine receptors (probably of D1 subtype) mediating dilation.

Why was the 1918 influenza pandemic so lethal? The possible role of a neurovirulent neuraminidase

Epidemiological, viral, behavioral and neuropathological evidence suggests that some influenza epidemics were neurovirulent. Re-examination of the data from the lethal 1918 pandemic armed with recent observations about the influenza virus implicates a neurovirulent influenza virus in manic-depressive disease, schizophrenia and Parkinson's disease. The neurovirulence seems to have been related to the species of neuraminidase.

Electron microscopic analysis of the mesencephalic ventromedial tegmentum in the cat

We have studied the normal ultrastructure of the ventral mesencephalic tegmentum (VMT) in the cat, particularly the morphology and distribution of presynaptic terminals and the types of synaptic junctions. The following subnuclei of the region were examined: n. linearis rostralis (LR), n. paranigralis (PN), and n. interfascicularis (IF). The qualitative and quantitative data revealed significant ultrastructural differences between these subnuclei. Each subnucleus had a characteristic dendritic structure. In LR the dendrites were nonspinous and cylindrical and had presynaptic terminals randomly distributed over their surface. In PN we observed varicose dendrites with spines; the presynaptic terminals formed clusters on the narrow segments of the dendrites and around the spines. Dendrodendritic synapses were also observed in this nucleus. In IF, there was an internal division regarding dendritic structure: in the rostral part of the nucleus there were cylindrical dendrites while in the caudal part irregularly shaped dendrites bearing long spines were found. In IF and LR some of the cylindrical dendrites were seen to be in direct contact with the basal lamina of blood vessels. Four types of presynaptic terminals were distinguished by the morphology of their vesicles, and the proportion of each type in the total terminal population was determined. On this basis the compositions of the presynaptic terminal population in the three subnuclei were found to be very similar. Most terminals contained clear, round vesicles (62.6%), or both clear and dense-cored vesicles (35.1%). Few terminals were seen with dense-cored vesicles only (1.4%) or with pleomorphic vesicles (0.9%). The majority of synapses in the VMT were found to have symmetrical densities. LR had twice as many asymmetrical synapses as the other two subnuclei. Eighty percent of the terminals formed synapses with dendrites, although axosomatic and axoaxonic synapses were also seen. The density of the terminals was significantly different for each subnucleus: 191/1,000 micrometers 2 in IF, 120/1,000 micrometers 2 in PN, and 81/1,000 micrometers 2 in LR. These data indicate that while the subnuclei of the VMT receive morphologically similar afferents, each has a unique way of processing the information provided by them, through a different internal circuitry.

Cholecystokinin-octapeptide produces inhibition of lordosis in the female rat

The peripheral administration of 3 micrograms/kg CCK-8 produced inhibition of lordosis behavior in ovariectomized female rats primed with estradiol benzoate (EB) and progesterone (P). In Experiment 2, an interaction between CCK-8 and P was evident, with the inhibitory effects of CCK-8 being observed with P doses of 100 and 150 micrograms, but not 250 micrograms. No interaction between CCK-8 and EB was evident, as CCK-8 had no effect on lordosis behavior induced by chronic administration of EB alone. The ineffectiveness of CCK-8 in animals treated with high doses of P, or EB administered chronically, suggests that CCK-8 does not inhibit lordosis via a toxic or non-specific mechanism.

Influenza and schizophrenia: a possible connection with the substantia nigra

The neurovirulent influenza virus of the 1918 pandemic induced clinical schizophrenia. The biochemistry, the neurovascular anatomy, the afferent connections, and the efferent connections of the substantia nigra suggest that a (Na+K)-ATPase injury could be a cause of some positive schizophrenias. The genetic trait in schizophrenia may be an inheritable susceptibility to an infectious agent.

The circulation and function of cerebrospinal fluid

Corpora amylacea (brain sand) were, hypothetically, considered as precipitates of a substance present in the cerebrospinal fluid (CSF). Melatonin, a non-polar indol, present in CSF could enter fibrous astrocytes and could generate corpora. The site of secretion of the corpora generating substance and the flow of CSF should dictate the distribution pattern of corpora. Neuropeptides present in the fluid were also considered as a possible precipitating agents. The distribution of corpora and the action of intrathecal vincristine suggested that CSF is recirculated through the ventricular system. A complete cycle of ventricular fluid could set the pace of the 100 minute ultradian rhythm found in human beings. Arachnoid granulations were not in an area of high volume of flow of the fluid and probably do not act as a major site of fluid reabsorption.

Neonatal 6-hydroxydopamine prevents adaptation to chemical disruption of the pituitary-adrenal system in the rat

Three days after the subcutaneous implant of a dexamethasone pellet, which depletes both corticosterone and ACTH, normal rats showed impaired acquisition of a two-way avoidance task. Rats who had received systemic 6-hydroxydopamine at birth to lesion the forebrain noradrenergic terminals from the locus coeruleus did not show this impairment. After a single injection of metyrapone, which inhibits corticosterone synthesis and increases ACTH release, both intact and norepinephrine (NE)-depleted rats showed impaired avoidance acquisition. After the seventh injection, however, acquisition in normal rats was no longer impaired by the drug while the NE-depleted rats were still deficient. These results indicate that the simple combination of forebrain NE loss with reduced corticosterone levels does not necessarily retard avoidance acquisition. Rather, they suggest that the NE efferents from the locus coeruleus are essential for the brain's adaptation to at least some behavioral consequences of changes in the circulating level of ACTH.

Immunohistochemical demonstration of serotonin in nerves supplying human cerebral and mesenteric blood-vessels. Some speculations about their involvement in vascular disorders

Serotonin (5-hydroxytryptamine, 5-HT) can produce vasoconstriction or vasodilatation and has been implicated in the pathogenesis of many vascular disorders. Nerves containing 5-HT were demonstrated by immunofluorescence histochemistry in fetal cerebral and mesenteric blood-vessels.

Nucleus locus coeruleus: a morphometric Golgi study in rats of three age groups

Using Rapid Golgi and Nissl techniques, 3 major cell types: fusiform, multipolar and ovoid shaped cells were identified in the nucleus locus coeruleus of male rats. Each cell type was described and quantitated as to age-related changes between 30 and 90 and between 90 and 220 days of age. The orientation and dendritic architecture of each type of cell in the locus coeruleus and relationship of these cells to blood vessels in the locus coeruleus and to surrounding structures is also described. One hundred neurons per age group were measured as to their maximal linear extent and the number of spines on the somal surfaces were counted. Dendritic number, linear extent, diameter and number of spines along a 50 microns segment near the mid-point of dendritic extensions in an equal number of primary and secondary dendrites were quantified for each age group and comparisons of these parameters between each cell group were made. Axons of each cell type were defined as to their origin and general orientation and trajectory. Axon collaterals of multipolar cells were shown to be recurrent in type projecting back onto the dendrites and soma of multipolar cells. One of the most striking findings was that between 30 and 90 days there were significant decreases in spine density on both primary and secondary dendrites in all three cell types in the locus coeruleus. This was followed by significant increases in spine density on both primary and secondary dendrites between 90 and 220 days in each of the 3 cell types. It is of interest that these age-related cell changes in spine density in the nucleus locus coeruleus are exactly out-of-phase with those of the nucleus raphe dorsalis.

Relationship between catecholamine neurons and cerebral blood vessels studied by their simultaneous fluorescent revelation in the rat brainstem

In order to study the relationship between catecholamine neurons and cerebral blood vessels, a technique was developed which permitted the simultaneous visualization of blue-green fluorescent catecholamine neurons and red fluorescent stained blood vessels in the brain of the normal rat. Sympathetic nerve fibers were found on the major arteries and in the pia-arachnoid at the base of the brainstem and also along paramedia and lateral perforating arteries as small as 10-12 microns within the brain. Running within the parenchyma, central catecholamine nerve fibers occasionally approached and intersected smaller blood vessels, either arterioles or venules of 8-12 microns, and infrequently climbed along or encircled these vessels for a limited distance, particularly within the lateral tegmentum. Across the nuclei of the brainstem, no overall contiguity of catecholamine terminals with capillaries was apparent, and no correlation between the density of catecholamine varicosities and that of capillaries existed. Only in regions with a high density of both catecholamine varicosities and capillaries, such as in the principal olivary nucleus, did a significant overlap of the two occur. But in most cases of moderately to densely innervated and vascularized regions, such as the solitary tract nuclei, the greatest concentration of terminals appeared over the parenchyma. Regarding the blood supply to the catecholamine neurons, their perikarya did not receive a particularly dense capillary supply relative to other nuclei. However, a special relationship of catecholamine cells to blood vessels was suggested, particularly in the case of dopamine neurons in the substantia nigra by the close apposition of cellular processes to adjacent small vessels. This morphological study was undertaken to determine whether central catecholamine neurons may significantly innervate cerebral blood vessels and accordingly, may function analogously to the peripheral sympathetic adrenergic neurons in the regulation of the vascular system. Although a limited number of associations between central catecholamine nerve terminals and small blood vessels suggested the possibility of an innervation in a few regions, the lack of an overall correspondence and correlation between the two across brainstem nuclei indicated that the analogy of central catecholamine neurons to the sympathetic nervous system was inappropriate. On the other hand, evidence of contact with vessels by presumed dendrites of the catecholamine neurons suggested a possible vascular sensory function.

The effects of protein deprivation on the nucleus raphe dorsalis: a morphometric Golgi study in rats of three age groups

In a previous study we identified 3 cell types in the nucleus raphe dorsalis (NRD): fusiform, multipolar and ovoid. In the present study, we have investigated the effect of an 8% casein diet on these 3 cell types using quantitative techniques on rapid Golgi-impregnated neurons from rats of 3 different ages: 30, 90 and 220 days. Major and minor axes of the cell body and dendritic diameter were unaffected and primary dendritic linear extent was only slightly affected by the diet. All 3 cell types in control rats showed an increase in synaptic spines on both primary and secondary dendrites between 30 and 90 days followed by a decrease for all 3 of the cell types at 220 days. Protein-deprived rats failed to show these age-related changes. Other parameters of comparison showed clear differences between the 3 cell types. These differences could be readily seen when total synaptic spine input to the primary and secondary dendrites was calculated from the data on dendritic number, linear extent and spine density. When viewed in this way the fusiform and ovoid cells show either little change or a decreased synaptic input at all ages, while the presumed serotonergic multipolar cells showed an increase. This is in agreement with neurochemical studies in these rats showing increased levels of this biogenic amine in protein malnourished rats.

Nucleus raphe dorsalis: a morphometric Golgi study in rats of three age groups

Using Rapid Golgi and Nissl techniques, three major cell types: fusiform, multipolar and ovoid-shaped were identified in the nucleus raphe dorsalis of male rats at 30, 90, and 220 days of age. We have described the orientation and dendritic architecture of raphe cells as to type and the relationships of these cells to blood vessels and surrounding structures. For each cell type, the origin of the axon is characteristic. One hundred neurons per age group were measured at their maximal linear extent and the number of spines on the somal surface was counted. Dendritic number, linear extent, diameter and the number of spines along a 50 micron segment near the mid-point of dendritic length in an equal number of primary and secondary dendrites were quantified in each age group. The most striking age-related changes in the multipolar and ovoid-shaped cells were dendritic number, diameter and spine number as well as the number of perisomatic spines. The fusiform cells showed the least age-related changes. In general, the nucleus raphe dorsalis is organized as a reticular nucleus with neurons having few, straight and poorly ramified dendrites.