Remote lateralized changes in cortical [3H]spiperone binding following focal frontal cortex lesions in the rat

The serotonin transporter and 5HT2A receptor in rat brain after localized lesions

OBJECTIVES

Post-stroke depression and depression after traumatic brain lesion are most often seen when the lesion includes frontal areas. The development of depression may include the serotonergic system because selective serotonin reuptake inhibitors (SSRIs) can be used to treat the depression. The purpose of the present study was to examine whether serotonin transporter density or 5HT2A serotonin receptor density is changed in specific brain areas following anterior or posterior lesions in the two hemispheres.

METHODS

Localized heat-induced brain lesions were induced in rats, and the densities of the serotonin transporter and 5HT2A receptor were measured by quantitative autoradiography in eight and 15 different brain areas, respectively.

RESULTS

A decrease in serotonin transporter density was detected in some frontal rat brain areas, and an increase in serotonin transporter density was detected in the right median raphe nucleus. No change was detected for 5HT2A receptor density.

5-Hydroxytryptamine2A (5-HT2A) receptor regulation in rat prefrontal cortex: interaction of a phenethylamine hallucinogen and the metabotropic glutamate2/3 receptor agonist LY354740

5-Hydroxytryptamine2A (5-HT2A) receptor regulation is atypical compared to most other monoaminergic receptors in that chronic administration of both antagonists and agonists results in down-regulation of cortical 5-HT2A receptor number and the functional in vitro and in vivo effects. We have recently found that midline thalamic lesions, which appeared to block glutamate release induced by activation of 5-HT2A receptors, also increased 5-HT2A receptor binding in layers I and Va of the medial prefrontal cortex (mPFC). These layers contain the highest density of both 5-HT2A receptors and thalamocortical terminals from the midline and intralaminar thalamic nuclei. These findings suggest the hypothesis that excitatory amino acid release plays a role in regulation of postsynaptic 5-HT2A receptors, and that down-regulation of 5-HT2A receptors by 5-HT2A agonists may not be attributed only to simple occupancy of the receptor by direct agonists. Therefore, we examined the effect of a single 30 min pretreatment with the metabotropic glutamate2/3 (mGlu2/3) receptor agonist (1S,2S,5R,6S)-2-aminobicyclo[3.1.0] hexane-2,6-dicarboxylate monohydrate (LY354740; 10 mg/kg, i.p.) on the second of three consecutive days of 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) treatment (1.25 mg/kg, i.p.). The subchronic DOI administration significantly decreased binding of [125I]DOI to 5-HT2A receptors in layers I and Va of the mPFC by approximately 25%. In contrast, a single dose of LY354740 on Day 2 of this regimen completely blocked the DOI-induced down-regulation. Thus, a presumed hypoglutamatergic state secondary to thalamic lesions and increased glutamate release induced by a subchronic regimen of a 5-HT2A agonist (and hallucinogenic drug) differentially regulate prefrontal cortical 5-HT2A receptor binding.

Effects of serotonin transporter promoter polymorphisms on serotonin function

The serotonin transporter promoter polymorphism (5-HTTLPR) has been associated with vulnerability to stress-induced depressive symptoms and with the speed and rate of response to antidepressant treatment. The goal of the present study was to evaluate the association between the 5-HTTLPR and the functional response of the serotonin system as measured by the neuroendocrine and cerebral metabolic response to intravenous administration of the selective serotonin reuptake inhibitor citalopram in normal control subjects. Genotyping was performed for 5-HTTLPR insertion/deletion polymorphism long (l) and short (s) variant alleles. The ll genotype was compared with the combined sl+ss and with the ss genotype alone. Citalopram plasma concentrations did not differ significantly between groups. The s allele was associated with a less of an increase in prolactin and cortisol than the ll genotype. The s allele was associated with greater decreases in left frontal, precentral and middle temporal gyri compared to the ll genotype. The ll genotype was associated with greater decreases in right frontal, insula and superior temporal gyrus compared to the ss genotype. These findings suggest that 5-HTTLPR is associated with an altered functional response of the serotonin system, which may represent a neurobiologic substrate for the differential response to antidepressant treatment in late life and the emergence of neuropsychiatric symptoms in neurodegenerative disorders.

Speech rate as a sticky switch: a multiple lesion case analysis of mutism and hyperlalia

Though it has long been known on the basis of clinical associations and serendipitous observation that speech rate is related to mood and psychomotor baseline, it is less known that speech rate is also related to libido and to immune function. We make the case for a bipolar phenomenon of "psychic tonus," encompassing all these dimensions. The elated, agitated, libidinal, immunofacilitated, and talkative pole is an "approach" disposition primarily activated by the normal left hemisphere-especially, though not exclusively, its frontal lobe. The dejected, lethargic, delibidinized, immunosuppressed, and mute pole is an "avoidance" disposition primarily activated by the normal right hemisphere-especially, though not exclusively, its frontal lobe. In support of this proposed model, we present new evidence, via meta-analysis of previously published single lesion case reports, of a highly significant association between right hemisphere lesions and non-aphasic hyperlalia, and between left hemisphere lesions and non-aphasic mutism.

Serotonin modulation of cerebral glucose metabolism measured with positron emission tomography (PET) in human subjects

To develop a method to measure the dynamic response of the serotonin system in vivo, the effects of intravenously administered citalopram (the most selective of the serotonin reuptake inhibitors) on cerebral glucose metabolism were evaluated. Cerebral glucose metabolism was measured with positron emission tomography (PET) in 14 normal subjects scanned after administration of saline placebo and citalopram administered on 2 separate days. Citalopram administration resulted in a decrease in metabolism in the right anterior cingulate gyrus (BA 24/32), right superior (BA 9) and right middle frontal gyrus (BA 6), right parietal cortex (precuneus), right superior occipital gyrus, left thalamus, and right cerebellum. Increased metabolism was observed in the left superior temporal gyrus and left occipital cortex. Alterations in metabolism by acute citalopram administration involved the heteromodal association cortices that also show metabolic alterations in patients with geriatric depression and overlap with the regions affected by antidepressant treatment. Future studies will evaluate how the acute metabolic response to citalopram relates to the metabolic response after chronic treatment in patients with geriatric depression.

Pathophysiology of secondary depressions in the elderly

Although the pathophysiology of depression is not fully understood in either primary depression (i.e., no known neuropathology related to depression) or secondary depression (i.e., neuropathologic disorder that leads to depression), a number of studies have begun to identify aspects of the pathophysiology of both primary and secondary depression. This article reviews the findings of studies examining the pathophysiology of depression following stroke, Parkinson's disease, or Huntington's disease and compares them to findings in primary depression. Studies examining glucose metabolic rates or blood flow changes in regional brain areas found that stroke, Parkinson's disease, and Huntington's disease, as well as primary depression, were all associated with decreased activity or brain lesions in the orbital frontal cortex and basal ganglia. There were also abnormalities noted in the basal temporal lobes, cingulate cortex, and thalamus in some but not all disorders. Studies in stroke have also noted depletions of serotonin receptors in left temporal cortex associated with depression. These findings are consistent with the hypothesis that the pathophysiology of secondary and primary depression involves the dysfunction of one or more of the cortical-basal ganglia-thalamic neuronal loops. This dysfunction may be mediated by decreased serotonin release. These studies may ultimately lead to more focused and specific treatments.

A neuroendocrine study of serotonin function in depressed stroke patients compared to non depressed stroke patients and healthy controls

OBJECTIVES

We employed a neuroendocrine challenge paradigm to study serotonergic abnormalities associated with poststroke depression.

METHOD

Twelve depressed stroke patients (major depression N= 5, minor depression N = 7), 8 nondepressed stroke patients and 12 healthy volunteers completed a single-blind, placebo-controlled, challenge tests. Baseline cortisol (CORT) and prolactin (PRL) values, and these hormonal responses to 30 mg of oral d-FEN and placebo over a 4 hour period were measured in the three groups.

RESULTS

There were intergroup differences for baseline adjusted PRL responses (change scores from baseline) to d-FEN (group effect F = 4.38, df = 2,29, p = 0.02) while these responses to placebo were comparable between groups (group effect F = 1.82, df = 2,29, p = 0.18). Peak PRL responses (post d-FEN maximal PRL change from baseline scores) in depressed stroke patients were significantly greater than in nondepressed patients (p = 0.005) but comparable to healthy normals (p = 0.47). However, these responses between major and minor depression were not significant (p = 0.34). There was a trend suggesting a negative correlation between peak PRL response and severity of depression (p = 0.056). Depressed patients were younger than the controls (p = 0.054). Also, the depressed group was more functionally impaired (p = 0.04) and more likely to have right-sided lesions (p = 0.009) compared with the nondepressed group. Differences in baseline adjusted PRL changes between depressed and nondepressed groups became non significant when the influence of laterality of lesions was covaried, whereas covariation of functional scores and age did not alter the significance. CORT responses did not show intergroup differences.

LIMITATIONS

The study group was small and was heterogenous in lesion characteristics, time since stroke and type of depression. A fixed-order design was used in the challenge test paradigm.

CONCLUSIONS

When laterality of stroke lesion was taken into account, depressed and nondepressed stroke patients did not differ in PRL responses to d-FEN.

Dorsal lesions of the prefrontal cortex: effects on alcohol consumption and subcortical monoaminergic systems

Male Wistar rats were subjected to either bilateral aspiration lesions of the dorsal regions of the prefrontal cortex (PFC) or sham lesions and placed on a 6-week, modified sucrose-fading procedure. At the time of sacrifice, the size of the lesion, both in anterior-posterior and medial-lateral dimensions, was measured. Following sacrifice, levels of dopamine (DA), serotonin (5-HT), norepinephrine (NE), and their metabolites were measured in the midbrain (raphe) and nucleus accumbens (NA). Lesioned animals had reductions in 5-HT in the NA, and DA and NE in the raphe. The lesioned group drank more of a solution of 5% alcohol than controls early in the sucrose fading, and less during the later stages. In the lesioned group, the size of the left- and right-hemisphere lesions predicted 5-HIAA levels in the NA, and 5-HT and 5-HIAA levels in the raphe. A laterality effect was noted, such that the size of left-hemisphere lesions were positively associated with raphe 5-HT and 5-HIAA levels, and negatively associated with 5-HT levels in the NA, while right-hemisphere lesions showed the opposite relationships. In addition, the width of the left-hemisphere lesion predicted some measures of alcohol intake. These results suggest that, in the rat, the dorsal PFC is involved in the regulation of monoamines in subcortical regions known to be important in the regulation of reinforced behaviors, and that this regulation differs between hemispheres and shows a laterality effect. In addition, the dorsal PFC appears to have a subtle involvement in the regulation of alcohol intake.