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Biomedical subjects

M D Underwood

Publications and source records attributed to M D Underwood.

At least 19 recordsLinked to original sources
PubMed2001

Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims.

Suicide and depression are associated with reduced serotonergic neurotransmission. In suicides, there is a reduction in serotonin transporter (SERT) sites and an increase in postsynaptic 5-HT(1A) receptors in localized regions of the prefrontal cortex. In depression, there is a diffuse decrease in SERT binding throughout the dorsoventral extent of the prefrontal cortex. Serotonergic innervation of the prefrontal cortex arises predominantly from neurons in the brainstem dorsal raphe nucleus (DRN). We, therefore, examined postmortem SERT binding and mRNA expression, as well as 5-HT(1A) autoreceptor binding in the DRN of 10 matched pairs of controls and depressed suicide victims. The concentration of SERT sites, SERT mRNA, and 5-HT(1A) binding was not different between controls and suicides (p >.05). In the DRN of suicides, the volume of tissue defined by 5-HT(1A) binding was 40% smaller than controls. An index of the total number of 5-HT(1A) receptors (receptor binding x volume of receptor distribution) was 43.3% lower in the DRN of suicides, compared with controls. The suicide group had 54% fewer DRN neurons expressing SERT mRNA compared with controls. In the serotonin neurons that expressed the SERT gene, expression per neuron was greater in suicides. Less total 5-HT(1A) and SERT binding is consistent with results of in vivo studies in depression. Less feedback inhibition of serotonin DRN firing via 5-HT(1A) autoreceptors and enhancement of serotonin action due to less uptake of serotonin, is consistent with compensatory changes in response to hypofunction in depressed suicides.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2000

In vitro autoradiography of serotonin 5-HT(2A/2C) receptor-activated G protein: guanosine-5'-(gamma-[(35)S]thio)triphosphate binding in rat brain.

Agonist activation of G protein-coupled receptors induces an increase in the binding of guanosine 5'-(gamma-[(35)S]thio)triphosphate ([(35)S]GTPgammaS); this increase in binding has been used as a tool to investigate receptor interaction with the heterotrimer guanine nucleotide-binding regulatory protein (G protein). The present study uses agonist-stimulated [(35)S]GTPgammaS binding to characterize serotonin 5-HT(2A/2C) receptors in rat brain membrane fractions and demonstrate the anatomical localization of the receptors by in vitro autoradiography on slide-mounted sections. The stimulatory effect of the agonist [1-(2,5-dimethoxy-4-iodophenyl)]-2 aminopropane (DOI) is compared to that of serotonin (5-HT). Autoradiography revealed a similar localization of DOI- and 5-HT-stimulated binding of [(35)S]GTPgammaS in distinct areas of prefrontal and parietal cortex, consistent with previously reported 5-HT(2A) receptor distribution. Specific binding was demonstrated in the frontal and parietal cortex, medial prefrontal, and cingular and orbital-insular areas as well as in the hippocampal formation, septal areas, the nucleus accumbens, and the choroid plexus. MDL 100105, a specific 5-HT(2A) antagonist, and ketanserin, an antagonist of 5-HT(2A/2C) receptors, blocked DOI stimulation in all labeled areas, whereas 5-HT stimulation was only partially blocked (70-80%). A small but significant inhibition was observed with the specific antagonist of 5-HT(2C/2B), SB 206553. This autoradiographic technique provides a useful tool for measuring in situ changes in specific receptor-Gq protein coupling in anatomically discrete brain regions, under physiological and pathological conditions.

Amphetamines↗
PubMed2000

Mixed models and multiple comparisons in analysis of human neurochemical maps.

Examination of brain regional neurochemistry in disease states reveals differences among brain regions. Knowing where alterations in brain function are located is crucial to understanding the disease effect. The anatomical distribution of neurotransmitter receptors is now often studied using quantitative autoradiography, but the large number of brain regions involved raises serious problems for statistical analysis of such data. Due to the dependence among the subjects in case control designs, statistical analysis based on a 'mixed model' is useful. Such an analysis is illustrated using a small autoradiographic data set. The Bonferroni method, the method of Holm, and two 'False Discovery Rate'-controlling methods for adjusting P-values for multiple comparisons are compared.

Autoradiography↗
PubMed2000

The human nucleus of the solitary tract: visceral pathways revealed with an "in vitro" postmortem tracing method.

Visceral relay neurons in the nucleus of the solitary tract (NTS) regulate behavior and autonomic reflex functions. NTS projections have been extensively characterized in animal studies but not in humans. For the first time, NTS fiber trajectories in the human medulla oblongata were revealed with an "in vitro" postmortem tracing method. Local intramedullary pathways were labeled by direct pressure injections of free horseradish peroxidase centered on the medial subnucleus at a level adjacent to true obex. Labeled elements were resolved by peroxidase histochemistry as a dark brown intracellular reaction product. A prominent transtegmental system of axons emerged from the NTS injection sites and entered the intermediate reticular zone, a region corresponding to an autonomic reflex center in other mammals. A medial system of axons arched across the dorsomedial reticular formation toward the dorsal medullary raphe and projected ventrally toward the nucleus gigantocellularis. A small lateral fiber trajectory coursed towards the dorsomedial zone of spinal trigeminal nucleus caudalis. Presumptive terminals appeared as dustings of fine punctate processes within the NTS, dorsomotor nucleus and reticular formation. NTS projections in humans resemble those identified in other mammals including primates. Axonal tracing studies predict that visceral impulses in humans may transmit over evolutionarily conserved pathways involved in autonomic feedback control and stress adaptation.

Adult↗
PubMed2000

A serotonin transporter gene promoter polymorphism (5-HTTLPR) and prefrontal cortical binding in major depression and suicide.

BACKGROUND: Major depression and suicide are associated with fewer serotonin transporter (5-HTT) sites. The 5'-flanking promoter region of the 5-HTT gene has a biallelic insertion/deletion (5-HTTLPR). We assayed prefrontal cortical (PFC) 5-HTT binding in major depression and suicide and examine the relationship to the 5-HTTLPR allele. METHODS: Postmortem brain samples from 220 individuals were genotyped for the 5-HTTLPR polymorphism. Binding of 5-HTT was assayed by quantitative autoradiography in the PFC of a subset of subjects (n = 159). Clinical information, including DSM-III-R Axis I diagnoses, was obtained by psychological autopsy and medical chart review. RESULTS: Binding to 5-HTT was lower in the ventral PFC of suicides compared with nonsuicides and was lower throughout the PFC of subjects with a history of major depression. The 5-HTTLPR genotype was associated with major depression but not with suicide or 5-HTT binding. CONCLUSIONS: A diffuse reduction of 5-HTT binding in the PFC of individuals with major depression may reflect a widespread impairment of serotonergic function consistent with the range of psychopathologic features in major depression. The localized reduction in 5-HTT binding in the ventral PFC of suicides may reflect reduced serotonin input to that brain region, underlying the predisposition to act on suicidal thoughts. The 5-HTTLPR genotype was not related to the level of 5-HTT binding and does not explain why 5-HTT binding is lower in major depression or suicide. Arch Gen Psychiatry. 2000;57:729-738

Adult↗
PubMed1999

Morphometry of the dorsal raphe nucleus serotonergic neurons in suicide victims.

BACKGROUND: The serotonin deficiency hypothesis of suicide has been important heuristically. Few studies have directly examined the brainstem dorsal raphe nucleus (DRN) serotonin neurons. We determined the number and morphometry of DRN serotonergic neurons in suicide victims (n = 7) compared to controls (n = 6). METHODS: Brainstems were collected at autopsy, fixed and cryoprotected. Tissue was sectioned, stained for Nissl and processed with an antiserum that cross-reacts with tryptophan hydroxylase. All DRN neurons were identified, counted and analyzed every 1000 microns. Neuron morphometry was characterized by soma area (micron 2), sphericity, perimeter, length and density (neurons per mm3). RESULTS: Neuron number and density was higher in suicide victims (1,780 +/- 127 neurons/mm3) than controls (1,349 +/- 68). The DRN volume did not differ between groups (66 +/- 9 mm3 for controls vs. 67 +/- 5 mm3 for suicides). Mean neuronal area and sphericity did not differ between suicides and controls. The total number and the density of DRN neurons did not correlate with age. CONCLUSIONS: The finding of an increased number of neurons indicates that impaired serotonergic transmission found in association with serious suicide attempts is not due to fewer neurons.

Adolescent↗
PubMed1999

Dorsal raphe nucleus serotonergic neurons innervate the rostral ventrolateral medulla in rat.

Stimulation of the dorsal raphe nucleus (DRN) alters arterial pressure, heart rate and cerebral blood flow, yet projections from the DRN to medullary autonomic nuclei have not been described. We examined whether serotonergic (5-HT) projections from the DRN terminate in the rostral ventrolateral medulla (RVL) and if so, whether the projection mediates cardiovascular responses to DRN stimulation. Studies were performed in adult male Sprague-Dawley rats. Horseradish peroxidase or choleratoxin B was injected unilaterally or bilaterally into the RVL. Levels of 5-HT, its precursors L-tryptophan and 5-hydroxytryptophan and the metabolite 5-hydroxyindole acetic acid were measured in the ventral medulla by HPLC three weeks following placement of electrolytic lesions in DRN. Serotonin transporter (3H-cyanoimipramine binding) was quantified by autoradiography in DRN-lesioned animals. Horseradish peroxidase or choleratoxin B injections into the medulla at the level of the RVL resulted in retrogradely labeled neurons bilaterally, with ipsilateral predominance, in the DRN. Labeled cells were preponderant in rostral ventrolateral portions of the DRN, but were also observed in the dorsal, lateral and interfascicular DRN subnuclei; fewer neurons were observed in caudal portions of the DRN. Three weeks following placement of electrolytic lesions in the DRN, the concentrations of 5-HT and 5-hydroxyindole acetic acid, but not L-tryptophan or 5-hydroxytryptophan, were reduced in the medulla by 45 and 48%, respectively, compared to sham-operated or unoperated controls. DRN lesions reduced binding to the 5-HT transporter in the RVL by approximately 30% compared to unlesioned controls. Unilateral lesions of the RVL reduced the evoked blood pressure response by 53+/-15%; bilateral RVL lesions reduced the response by 86+/-9%. The increase in cortical blood flow elicited by DRN stimulation was unchanged after unilateral or bilateral RVL lesions. These studies demonstrate that there is a descending serotonergic projection from the DRN to the RVL. This projection may mediate autonomic changes elicited by DRN stimulation.

Animals↗
PubMed1999

Corticotropic-releasing hormone and serotonin interact in the human brainstem: behavioral implications.

The objective of this human post mortem study was to determine whether neurons which synthesize corticotropic-releasing hormone and serotonin form circuits implicated in the pathophysiology of major depression and suicide. For the first time, a sensitive, dual immunocytochemical procedure was used to identify circuits formed by corticotropic-releasing hormone-synthesizing and serotonergic cell groups. Corticotropic-releasing hormone-immunoreactive varicose fibers and puncta with morphological characteristics of terminals were labeled in the midline raphe, periventricular gray and pontine parabrachial complex, on single-labeled tissues processed immunocytochemically with a rabbit antibody to rat/human corticotropic-releasing hormone. Presumptive synaptic interactions with monoaminergic neurons were demonstrated with dual labeling techniques. Corticotropic-releasing hormone-immunoreactive terminals apposed neuronal somata and primary dendrites of serotonergic neurons in the pontine raphe. Serotonergic neurons were immunolabeled with a mouse antibody to phenylalanine hydroxylase, an enzyme with substantial sequence homology to tryptophan hydroxylase. Interactions in the lateral parabrachial nucleus were suggested by precise overlap of corticotropic-releasing hormone and serotonergic terminal fields. Corticotropic-releasing hormone projections were confirmed to noradrenergic neurons containing neuromelanin in the locus ceruleus. Maps of corticotropic-releasing hormone fiber trajectories suggest that these pathways may derive from the forebrain and, locally, from the human homologue of Barrington's nucleus--a neurochemically specialized division of the laterodorsal tegmental complex. Chemosensory functions were predicted by novel evidence for corticotropic-releasing hormone- and monoaminergic neurovascular and subependymal fiber plexuses. In conclusion, corticotropic-releasing hormone may influence the activity of two major monoaminergic cell systems implicated in the stress-diathesis model of mental illness, through neural and humoral mechanisms.

Behavior↗
PubMed1999

The neurobiology of suicide risk: a review for the clinician.

Suicidal behavior has neurobiological determinants independent of the psychiatric illnesses with which it is associated. We have found that some patients with major depression are vulnerable to acting on suicidal impulses. This vulnerability results from the interaction between triggers or precipitants and the threshold for suicidal behavior. An important factor in setting an individual's threshold for acting on suicidal impulses is brain serotonergic function. Serotonin function has been shown to be lower in suicide attempters by studies measuring serotonin metabolites in cerebrospinal fluid and studies of prolactin response to fenfluramine. Postmortem studies of suicide victims also reveal decreased serotonin activity in the ventrolateral prefrontal cortex. New neuroimaging paradigms, such as positron emission tomography (PET), offer an opportunity to visualize serotonin function in vivo in a more direct way than has previously been available. This technology may provide the possibility of timely therapeutic intervention in patients at high risk for suicide.

Acting Out↗
PubMed1997

Postmortem findings in suicide victims. Implications for in vivo imaging studies.

Alterations in serotonergic and noradrenergic receptor binding in membrane homogenates from the brain of suicide victims suggest a biological substrate for the vulnerability to commit suicide. We and others have employed high-resolution quantitative autoradiography of full coronal sections of the prefrontal cortex to map the locus of maximal change in receptor binding. We found alterations in binding to the serotonin transporter, the 5-HT1A, and the 5-HT2A receptors primarily in the ventral and ventrolateral prefrontal cortex of suicide victims. Importantly, these changes are often modest in magnitude and anatomically restricted to one or two Brodmann areas. Furthermore, we have found that care in case selection is essential, because sex, age, drugs, and comorbid diagnoses contribute to receptor binding. The implications for in vivo imaging are considerable, directing the focus of such studies toward the ventrolateral prefrontal cortex. However, because ligands are limited, as is the resolution of current methods, including PET, automated analyses that produce statistical images, rather than manual selection of individual slices, will likely lack the ability to detect the discrete receptor changes found postmortem. Alternatively, the advantages of examining large numbers of subjects, imaging the entire brain, obtaining detailed clinical information in the living patient, and magnifying the changes with neuropharmacological challenges present a promising outlook for making major advances into the identification of brain abnormalities associated with suicide risk.

Brain↗
PubMed1997

Biologic alterations in the brainstem of suicides.

This article reviews the data supporting the notion that there are alterations in serotonin and norepinephrine in the ventral prefrontal cortex and brainstem of suicide victims. Normal amounts of serotonin are found in terminal fields such as the dorsolateral prefrontal cortex, but serotonin responses are defective at least in the hypothalamus. Suicide victims appear to have fewer noradrenergic LC neurons, containing more of the tyrosine hydroxylase enzyme needed for transmitter synthesis. A failure of behavior restraint mechanisms involving the prefrontal cortex as a consequence of alterations in brainstem monoaminergic nuclei may result in a predisposition to suicidal behavior.

Brain Stem↗
PubMed1996

Fewer pigmented locus coeruleus neurons in suicide victims: preliminary results.

Studies of the noradrenergic system in suicide victims have found evidence of alterations in cortical beta- and alpha-adrenergic receptor binding. Since these receptor changes may be secondary to altered noradrenergic input, we sought to determine whether the pigmented neurons of the locus coeruleus (LC), which provide the noradrenergic innervation to the cerebral cortex, are altered in suicide victims. We studied 11 controls without known psychiatric or neurologic disorders and six suicide victims. LC neuron number, LC volume, and neuron density were determined by computer-assisted mapping. The suicide group had 23% fewer LC neurons and a 38% lower density of LC neurons than controls. The reduction in neuron number was localized to the rostral two thirds of the LC. Neither the LC length nor the LC volume in suicide victims differed from controls. Altered brain noradrenergic neurotransmission in suicide victims may be due to fewer noradrenergic neurons in the LC. Further studies are needed to determine whether this noradrenergic neuron loss is associated with an underlying major depression or specifically with suicidal behavior.

Adolescent↗
PubMed1996

Differential age-related loss of pigmented locus coeruleus neurons in suicides, alcoholics, and alcoholic suicides.

We previously reported fewer locus coeruleus (LC) neurons in both suicide victims and alcoholics than among a group of nonpsychiatric controls. In the present paper we examine the rate of decline in the number of LC neurons with age, looking for possible differential rates among suicide victims, alcoholics, and controls. We also compare these groups with a group of alcoholics who died by suicide, and consider the effects of sex, race, and postmortem interval. LC neuron counts were obtained from a total of 32 subjects. In all groups, the number of neurons decreased with age, but by roughly age 40 the average LC count among the three suicide and/or alcoholic groups was lower than among controls. The rate of LC neuron loss was greater among suicides than among controls, but the rate of loss among alcoholics who were at least 30 years old was the same as that among the controls. Our group of alcoholic suicides had counts that were statistically indistinguishable from those of suicides. Differences among groups appear to be most pronounced in the middle third of the LC. Further studies are needed to determine the mechanisms of noradrenergic neuron loss and whether it is associated with an underlying major depression in suicide victims, or acquired after a period of excessive alcohol consumption.

Adolescent↗
PubMed1995

Effect of chemical stimulation of the dorsal raphe nucleus on cerebral blood flow in rat.

We have previously shown that electrical stimulation of the dorsal raphe nucleus (DRN) can increase or decrease cerebral blood flow (CBF). We now sought to determine whether the CBF responses are mediated by DRN neurons or fibers of passage. In anesthetized rat, the DRN was stimulated chemically (L-glutamate, kainate) and CBF in parietal cortex was measured by laser-Doppler flowmetry. Microinjection of kainate (5 nmol), but not L-glutamate, into DRN increased CBF (28 +/- 22%; P < 0.05). Decreased CBF to DRN stimulation was not observed. We conclude that stimulation of DRN neurons increases CBF.

Animals↗
PubMed1995

Localized alterations in pre- and postsynaptic serotonin binding sites in the ventrolateral prefrontal cortex of suicide victims.

Altered serotonin indices have been reported in the brain of suicide victims. We sought to localize the changes in presynaptic and postsynaptic serotonin receptors and identify an area of prefrontal cortex that may influence suicide risk. Quantitative autoradiography was performed in coronal sections of prefrontal cortex to determine whether serotonin 5-HT1A receptor (postsynaptic in cortex) and serotonin transporter (presynaptic) binding are different in suicide victims compared to matched controls. 5-HT1A receptor binding was higher in 85 of the 103 sampled areas in the suicide group (n = 18 pairs; P < 0.0001). The increase ranged from 17 to 30%. The increase was more pronounced in the ventrolateral prefrontal cortex. Serotonin transporter binding was found to be lower in the suicide group in all but one of the 43 sampled regions (n = 22 pairs; P < 0.0001). The reduction in binding was most pronounced in the ventrolateral prefrontal cortex, where the difference between suicides and controls ranged between 15 and 27%. Serotonin transporter and 5-HT1A binding were negatively correlated (r = -0.35 to -0.44, P = 0.04 to 0.007) within the same brain areas, suggesting common regulatory factors with opposite effects on binding to the two receptors. We conclude that suicide victims have an abnormality in the serotonin system involving predominantly the ventrolateral prefrontal cortex, and hypothesize that the serotonergic dysfunction in this brain region contributes to the risk for suicidal behavior.

Adult↗
PubMed1994

Fewer pigmented neurons in the locus coeruleus of uncomplicated alcoholics.

Altered noradrenergic function is associated with alcoholism. Reduced brain norepinephrine (NE) concentrations and beta-adrenergic receptor supersensitivity following chronic alcohol consumption suggest a reduced level of noradrenergic neurotransmission. To further elucidate the reason for changes in noradrenergic function, we determined the number of melanin-containing noradrenergic neurons in the locus coeruleus (LC) postmortem from 11 controls and 7 alcoholics. Controls did not have a known history of psychiatric or neurologic disorders and were drug-free by toxicological screen. The diagnosis of alcohol-dependence was based on DSM-III-R criteria. Alcoholics differed from controls in having 23% fewer LC neurons (control: 43,472 +/- 1,021; alcoholic: 33,398 +/- 2184; P < 0.0005) and 46% lower density of neurons (control: 1,227 +/- 89 cells per mm3; alcoholic: 663 +/- 94 cells per mm3; P = 0.001). The reduction in neurons was bilateral and throughout the middle third of the LC. The two groups did not differ with respect to LC length (control: 16.1 +/- 0.6 mm; alcoholic 15.3 +/- 0.9 mm; P = 0.47) or total LC volume (control: 37.3 +/- 2.8 mm3; alcoholic: 46.5 +/- 4.2 mm3; P = 0.09). Changes in noradrenergic neurotransmission in alcoholics may be due to fewer noradrenergic neurons in the locus coeruleus and may contribute to memory loss and depression, common consequences of alcoholism.

Adolescent↗
PubMed1994

Lesions of the rostral ventrolateral medulla reduce the cerebrovascular response to hypoxia.

Sympathoexcitatory neurons of the rostral ventrolateral medulla are tonically active and required for maintenance of resting levels of arterial pressure. They are also selectively excited by hypoxia and responsible for the associated sympathoexcitation. Since electrical or chemical stimulation of RVL will increase regional cerebral blood flow (rCBF) independently of changes in regional cerebral glucose utilization (rCGU) we investigated whether the RVL was also required to maintain resting levels of rCBF and also participated in the cerebrovascular vasodilation elicited by hypoxia. Rats were anesthetized (chloralose; 40 mg/kg, s.c.), paralyzed (tubocurarine) and ventilated (100% O2). rCBF was measured in 10 dissected brain regions using [14C]iodoantipyrine; rCGU was measured by 2-deoxy-D-[14C]glucose. In controls (n = 6) rCBF ranged from 56 +/- 5 in corpus callosum to 101 +/- 6 ml/min x 100 g in inferior colliculus. Hypoxic-hypoxia (PaO2 = 36 +/- 1 mmHg, n = 6) increased rCBF in all structures maximally, at 204% of control, in occipital cortex. Hypercapnia (PaCO2 = 63.5 +/- 0.9, n = 5) also increased rCBF (P < 0.01) maximally to 299% of control in superior colliculus. Spinal cord transection with maintenance of arterial pressure did not affect resting rCBF and increased the vasodilation to hypoxia (PaO2 = 39 +/- 1 mmHg, n = 5) from 2- to 3-fold in all structures (P < 0.01). Bilateral lesions within the RVL had no effect on resting rCBF or rCGU. However, they significantly reduced, in all areas by 50-69% (P < 0.01, n = 5), the cerebrovascular dilation elicited by hypoxia but not hypercapnia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗