Gregory A. Ordway

Alterations in the N-methyl-D-aspartate (NMDA) receptor complex in the frontal cortex of suicide victims

Chronic antidepressant treatment results in adaptation of the NMDA receptor complex in the rodent cortex. This adaptation consists of a reduction in the potency of glycine to displace [3H]5,7-dichlorokynurenic acid from strychnine-insensitive glycine receptors and a reduction in high affinity, glycine-displaceable [3H]CGP-39653 binding to glutamate receptors. We hypothesized that dysfunction of NMDA receptors might occur in frontal cortices from human suicide victims. We now report that the proportion of high affinity, glycine displaceable [3H]CGP-39653 binding to glutamate receptors is reduced from 45 +/- 5% in controls to 27 +/- 6% in age- and post-mortem interval-matched suicide victims. In contrast, neither the potency nor the maximum efficacy of glycine to inhibit [3H]CGP-39653 binding is altered in the frontal cortex of suicide victims compared to controls. Moreover, neither the potency of glycine to inhibit [3H]5,7-dichlorokynurenic acid binding to the strychnine-insensitive glycine receptor nor the specific binding of [3H]5,7-dichlorokynurenic acid binding differed in suicide victims compared to controls. Likewise, neither basal nor glycine- or glutamate enhanced non-equilibrium binding of [3H]dizocilpine was altered in the frontal cortex of suicide victims compared to controls. These data represent the first demonstration supporting the hypothesis that glutamatergic dysfunction is involved in psychopathology underlying suicide and, potentially in human major depression.

Dopaminergic abnormalities in amygdaloid nuclei in major depression: A postmortem study

BACKGROUND A deficiency of mesolimbic dopamine (DA) is a leading candidate for the etiology of certain symptoms of depression (e.g., anhedonia and loss of motivation). Here we show amounts of dopaminergic proteins in the amygdala, a key brain structure involved in the integration of emotions and stress, in subjects with major depression and in psychiatrically normal control subjects. METHODS The specific binding of [(125)I]RTI 55 to the DA transporter, [(3)H]SCH 23390 to the D1 receptor and [(125)I]epidepride to D2/D3 receptors were measured in the right amygdaloid complex in postmortem brains from 11 subjects with major depression and 11 matched control subjects. RESULTS The binding of [(125)I]RTI 55 to DA transporter was significantly lower in the basal and central amygdaloid nuclei, whereas the binding of [(125)I]epidepride to D2/D3 receptors was significantly higher in the basal, central, and lateral amygdaloid nuclei in major depression compared with control subjects. No difference in the binding of [(3)H]SCH 23390 to D1 receptors was observed. CONCLUSIONS Given that DA depletion in rats can induce a reduction in the DA transporter and an upregulation of D2/D3 receptors, our data are consistent with the hypothesis that major depression is associated with a deficiency of mesolimbic DA.

Elevated tyrosine hydroxylase in the locus coeruleus of suicide victims

Abstract: The amounts of tyrosine hydroxylase protein in locus coeruleus from nine pairs of antidepressant‐free suicide victims and age‐matched, sudden‐death control cases were determined by quantitative blot immunolabeling of cryostat‐cut sections from the caudal portion of the nucleus. In each of the nine age‐matched pairs, the concentration of tyrosine hydroxylase was greater in the sample from the suicide victim, with values ranging from 108 to 172% of the matched control value (\‐x = 136%). By contrast, there were no differences in the concentrations of neuron‐specific enolase protein in the same set of samples. Similarly, the number of neuromelanin‐containing cells, counted in sections of locus coeruleus adjacent to those taken for blot immunolabeling analyses, did not differ between the two groups. These data indicate that locus coeruleus neurons from suicide victims contain higher than normal concentrations of tyrosine hydroxylase, thus raising the possibility that the expression of tyrosine hydroxylase in locus coeruleus may be relevant in the pathophysiology of suicide.

Agonist Binding to α2‐Adrenoceptors Is Elevated in the Locus Coeruleus from Victims of Suicide

Abstract: The binding of an agonist, p‐[125I]iodoclonidine, and an antagonist, [3H]yohimbine, to α2‐adrenoceptors was measured autoradiographically in the locus coeruleus from 10 pairs of antidepressant‐free victims of suicide and age‐matched controls. Agonist binding to α2‐adrenoceptors was significantly greater in the locus coeruleus from victims of suicide compared with control subjects. In contrast, antagonist binding to α2‐adrenoceptors in the locus coeruleus did not differ significantly between control and suicide subjects. HPLC analysis of norepinephrine in tissue sections of the locus coeruleus did not reveal any differences between control subjects and suicide victims, suggesting that differences in agonist binding are not a result of differences in retention of the endogenous agonist norepinephrine in tissue sections. The increase in agonist binding to α2‐adrenoceptors in the locus coeruleus of victims of suicide links an altered expression of the high‐affinity state of autoinhibitory α2‐adrenoceptors with suicide.

Reduced Neuropeptide Y Concentrations in Suicide Brain

Neuropeptide Y (NPY) was measured in postmortem brain tissue from victims of suicide and from individuals dying a sudden natural or accidental death (controls). Concentrations of NPY‐immunoreactivity were measured by radioimmunoassay in frontal cortex (BA 10), temporal cortex (BA 22), caudate nucleus, and cerebellum. Concentrations of NPY‐immunoreactivity were significantly lower in postmortem frontal cortex (−14%) and caudate nucleus (−27%) from suicide victims compared with age‐matched controls. A subgroup of suicides with evidence of a history of depression revealed more robust reductions in concentrations of NPY‐immunoreactivity in frontal cortex and caudate nucleus, as did four individuals who died from natural causes and also were described as having a possible history of depression. Concentrations of NPY‐immunoreactivity in temporal cortex and cerebellum from victims of suicide or from the subgroup of subjects with a possible history of depression were not significantly different from those of age‐matched controls. We suggest there is a deficit in the brain NPY system leading to region‐specific reductions in peptide concentrations in subjects who have a history of depression.

Elevated levels of tyrosine hydroxylase in the locus coeruleus in major depression

BACKGROUND Levels of tyrosine hydroxylase (TH) are regulated in the noradrenergic locus coeruleus (LC) in response to changes in the activity of LC neurons and in response to changes in brain levels of norepinephrine. To study the potential role of central noradrenergic neurons in the pathobiology of major depression, TH protein was measured in the LC from postmortem brains of 13 subjects with a diagnosis of major depression and 13 age-matched control subjects having no Axis I psychiatric diagnosis. Most of the major depressive subjects died as a result of suicide. METHODS Protein from sections cut through multiple rostro-caudal levels of LC was transferred to Immobilon-P membrane, immunoblotted for TH, and quantified autoradiographically. RESULTS The distribution of TH-immunoreactivity (TH-ir) along the rostro-caudal axis of the LC was uneven and was paralleled by a similar uneven distribution of neuromelanin-containing cells in both major depressive and psychiatrically normal control subjects. Amounts of TH-ir in the rostral, middle and caudal levels of the LC from major depressive subjects were significantly higher than that of matched control subjects. There were no significant differences in the number of noradrenergic cells at any particular level of the LC comparing major depressive subjects to control subjects. CONCLUSIONS Elevated expression of TH in the LC in major depression implies a premortem overactivity of these neurons, or a deficiency of the cognate transmitter, norepinephrine.

Down‐Regulation of Norepinephrine Transporters on PC12 Cells by Transporter Inhibitors

Abstract: To investigate the regulation of norepinephrine transporters (NETs) in vitro, we measured the binding of the NET‐selective ligand [3H]nisoxetine in homogenates of PC12 cells after exposure of intact cells to the NET inhibitor desipramine (DMI). A 3‐day exposure of PC12 cells to DMI robustly reduced the Bmax, but not the KD, of [3H]nisoxetine binding to NETs. Reduction of the binding of [3H]nisoxetine was dependent on both the concentration of DMI and the time of exposure to DMI. Reduction of [3H]nisoxetine binding to NETs produced by a 1‐day exposure to DMI reverted to preexposure levels 48 h after cessation of DMI exposure. Similar down‐regulation of NETs was found when PC12 cells were exposed to another NET‐selective drug, nisoxetine, which is structurally unrelated to DMI. In contrast, exposure of cells to the serotonin transporter‐selective drug citalopram, or the NET substrate norepinephrine, had no effects on the binding of [3H]nisoxetine to NETs. The down‐regulation of NETs was paralleled by a DMI‐induced reduction in the uptake of [3H]norepinephrine in intact PC12 cells. It can be inferred from these data that inhibitors of the NET can down‐regulate NETs directly, and do so in the absence of changes in the synaptic concentration of norepinephrine.

Elevated agonist binding to α2-adrenoceptors in the locus coeruleus in major depression

BACKGROUND Recent postmortem studies demonstrate disrupted neurochemistry of the noradrenergic locus coeruleus (LC) in major depression (MD). Increased levels of tyrosine hydroxylase and decreased levels of norepinephrine transporter implicate a norepinephrine deficiency in the LC in MD. Here we describe a study of alpha2-adrenoceptors in the LC and raphe nuclei of subjects with MD compared with psychiatrically normal control subjects. METHODS The specific binding of p-[125I]iodoclonidine to alpha2-adrenoceptors was measured at multiple levels along the rostrocaudal extent of the LC in postmortem tissue from 14 control and 14 MD subjects. In addition, p-[125I]iodoclonidine binding was measured in the dorsal and median raphe nuclei in the same tissue sections. RESULTS The specific binding of p-[125I]iodoclonidine to alpha2-adrenoceptors was significantly elevated throughout the LC from MD compared with matched control subjects. No significant differences were observed in p-[125I]iodoclonidine binding to alpha2-adrenoceptors in the raphe nuclei comparing MD and control subjects. CONCLUSIONS Given that alpha2-adrenoceptors are upregulated in laboratory animals by treatment with drugs that deplete norepinephrine, our findings implicate a premortem deficiency of brain norepinephrine in the region of the locus coeruleus in subjects with MD.

Down-regulation of the human norepinephrine transporter in intact 293-hNET cells exposed to desipramine

Abstract: The effects of continuous exposure of cultured cells expressing the human norepinephrine transporter (hNET) to the hNET inhibitor desipramine on hNET expression and function were studied. Exposure of HEK‐293 cells transfected stably with the hNET cDNA (293‐hNET cells) to desipramine for 3 days reduced the specific binding of [3H]nisoxetine in membrane homogenates in a concentration‐dependent manner. The magnitude of the reductions in [3H]nisoxetine binding to hNET was dependent on the length of time of the exposure to desipramine, reaching 77% after a 21‐day exposure. The reduction of [3H]nisoxetine binding returned to control levels within 72 h after a 3‐day exposure to desipramine. Reductions in [3H]nisoxetine binding to hNET were accompanied by time‐dependent and exposure concentration‐dependent reductions in hNET protein levels as determined by western blotting. Similar to binding, hNET protein levels returned to control levels 72 h after cessation of desipramine exposure. Northern blotting indicated that exposure of 293‐hNET cells to desipramine did not significantly alter hNET mRNA levels. Uptake of [3H]norepinephrine by 293‐hNET cells was markedly reduced after a 3‐day exposure to desipramine. However, desipramine exposure had no effect on uptake of [3H]glutamate or [3H]‐alanine. The present findings imply that down‐regulation of the hNET in 293‐hNET cells induced by desipramine results from a selective reduction in hNET protein levels, presumably a consequence of either a reduction in the translation of hNET mRNA or from an enhanced degradation of hNET protein.

Brain Noradrenergic Receptors in Major Depression and Schizophrenia

The binding of [125I]p-iodoclonidine to alpha-2, and/or [125I]iodopindolol to beta-1 and beta-2 adrenoceptors was measured in right prefrontal cortex (Brodmanns area 10) and right hippocampus from subjects with DSM-III-R diagnoses of major depression (n = 15) or schizophrenia (n = 8) as well as from control subjects (n = 20). No significant differences between study groups were observed in binding to alpha-2 adrenoceptors in any of the six layers of prefrontal cortex or in any of the hippocampal fields. Likewise, there were no significant differences in beta-1 or beta-2 adrenoceptor binding in any of the hippocampal fields between control and major depressive subjects. In contrast, binding to beta-1 adrenoceptors, but not beta-2 adrenoceptors, was significantly lower (−13 to −27%) in most hippocampal fields of schizophrenic subjects as compared to control subjects or to major depressives. Alterations in beta-1 adrenoceptor binding in the hippocampus of schizophrenics provide further evidence for a role of central noradrenergic neurons in the neurochemical pathology of schizophrenia.