Behavioral correlates of cerebrospinal fluid amino acid and biogenic amine neurotransmitter alterations in dementia.

BACKGROUND: Behavioral and psychological signs and symptoms of dementia (BPSD) are a heterogeneous group of behavioral and psychiatric disturbances occurring in dementia patients of any etiology. Research suggests that altered activities of dopaminergic, serotonergic, (nor)adrenergic, as well as amino acid neurotransmitter systems play a role in the etiopathogenesis of BPSD. In this study we attempted to identify cerebrospinal fluid (CSF) neurochemical correlates of BPSD to provide further insight into its underlying neurochemical pathophysiological mechanisms. METHODS: Patients with probable Alzheimer's disease (AD; n = 202), probable AD with cerebrovascular disease (n = 37), probable frontotemporal dementia (FTD; n = 32), and probable dementia with Lewy bodies (DLB; n = 26) underwent behavioral assessment and lumbar puncture. CSF levels of six amino acids and several biogenic amines and metabolites were analyzed using ultraperformance liquid chromatography with fluorescence detection and reversed-phase high-performance liquid chromatography with fluorescence detection. RESULTS: In the AD patients, CSF homovanillic acid/5-hydroxyindoleacetic acid (HVA/5HIAA) ratios correlated positively with anxieties/phobias, whereas CSF levels of taurine correlated negatively with depression and behavioral disturbances in general. In FTD patients, CSF levels of glutamate correlated negatively with verbally agitated behavior. In DLB patients, CSF levels of HVA correlated negatively with hallucinations. CONCLUSIONS: Several neurotransmitter systems can be linked to one specific behavioral syndrome depending on the dementia subtype. In addition to biogenic amines and metabolites, amino acids seem to play a major role in the neurochemical etiology of BPSD as well.

Determination of amino acids associated with cerebral ischaemia in rat brain microdialysates using narrowbore liquid chromatography and fluorescence detection.

Microdialysis coupled to liquid chromatography (LC) has proven to be a valuable in vivo sampling technique for studying neurotransmitter changes in normal and ischaemic brain. However, few analytical methods have described the simultaneous determination of amino acids, relevant in stroke research, together with the nitric-oxide-related compound citrulline. Therefore, we developed a gradient LC method for the quantitative simultaneous determination of aspartate, glutamate, serine, glutamine, arginine, taurine, alanine and citrulline in dialysates of rat brain using narrowbore LC with o-phthalaldehyde-2-mercaptoethanol pre-column derivatisation and fluorescence detection. The proposed method is a thoroughly validated, fully automated and robust LC method for the determination of amino acids in a wide concentration range. The method was applied for the determination of amino acids and the citrulline/arginine ratio in the Et-1 model for focal cerebral ischaemia.

Effects of phosphodiesterase 10 inhibition on striatal cyclic AMP and peripheral physiology in rats.

Phosphodiesterases (PDEs) form a family of enzymes involved in the hydrolysis of cyclic adenosine and guanosine monophosphate (cAMP and cGMP). PDE10A is a member of this family that is almost exclusively expressed in the striatum. Increasing cAMP/cGMP levels via inhibition of PDE10A is under consideration as a novel therapeutic avenue in the discovery of antipsychotics. Papaverine has been used as a pharmacological tool to establish the possible clinical use of PDE10A inhibitors as antipsychotics. Papaverine is known to increase cAMP levels in striatum and to decrease blood pressure, body temperature and locomotor activity after systemic administration. In this study, the effects of papaverine are compared to those of a more specific PDE10A inhibitor MP10. Papaverine raised striatal cAMP levels with hypothermia, hypoactivity and decreased cardiovascular responses. The more selective MP10 had significantly less effects on body temperature and cardiovascular functions, but reduced locomotor activity to a similar extend as papaverine.

Selective D1 agonism but not D2 antagonism is reflected in cAMP and cGMP levels in rat CSF.

Cyclic adenosine 3'5'-monophosphate (cAMP) and cyclic guanosine 3'5'-monophosphate (cGMP) serve as second messengers in several cellular pathways within the central nervous system. In various neurological and psychiatric disorders with known deficits in neurotransmission function, CSF levels of cAMP and/or cGMP in patients were studied. Very little information is currently available on cAMP and cGMP levels in CSF of animals. Moreover, this is the first study on the effects of pharmacological treatment on cAMP and cGMP levels in rat CSF. Effect of systemic treatment with a D1 receptor agonist SKF82958 and a D2 receptor antagonist haloperidol on cAMP and cGMP levels, as well as baseline cAMP and cGMP levels in CSF of rats was determined. A significantly increased cAMP and cGMP level in cisternal CSF of rats systemically treated with the D1 receptor agonist SKF82958 was observed, while when treated with the D2 antagonist haloperidol, no effect on cAMP and only a slight decrease of cGMP was observed after treatment with the highest dose. Determining cAMP and/or cGMP in CSF of experimental animals can serve as a useful tool to study neural processes affected by disease and treatment.

Excitatory amino acids and monoaminergic neurotransmitters in cerebrospinal fluid of acute ischemic stroke patients.

BACKGROUND AND PURPOSE: Improved insight in the role of neurotransmitters in acute cerebral ischemic injury may be fundamental for the successful development of novel therapeutic approaches. We investigated excitatory amino acids and monoaminergic neurotransmitters in cerebrospinal fluid (CSF) of acute ischemic stroke patients and their relation to stroke characteristics. METHODS: CSF concentrations of glutamate, aspartate, glutamine, glycine, proline, taurine, norepinephrine, 5-hydroxyindoleacetic acid, homovanillic acid and 3,4-dihydroxyphenylacetic acid were assessed in 89 stroke patients at admission (median 6.3h after stroke onset) and in 31 controls. We evaluated the relation between CSF concentrations and (a) stroke severity (NIHSS score at admission, lesion volume), (b) stroke evolution in the subacute phase, (c) long-term stroke outcome, (d) lesion location, and (e) stroke etiology. RESULTS: Neurotransmitter systems display relevant interrelations, however, no significant associations between neurotransmitter concentrations in CSF and stroke characteristics were found, with the exception of higher 5-hydroxyindoleacetic acid levels in CSF of patients with progressing stroke and poor long-term outcome. CONCLUSIONS: The study results question the added value of neurotransmitter assessment in CSF for research on ischemic cerebral injury.

Post-ischaemic mild hypothermia inhibits apoptosis in the penumbral region by reducing neuronal nitric oxide synthase activity and thereby preventing endothelin-1-induced hydroxyl radical formation.

Previously, we showed that treatment with resuscitative, post-ischaemic mild hypothermia (34 degrees C for 2 h) reduced apoptosis in the penumbra (cortex), but not in the core (striatum) of an endothelin-1 (Et-1)-induced focal cerebral infarct in the anaesthetized rat. Therefore, the purpose of this study was to investigate by which pathways resuscitative mild hypothermia exerts its neuroprotective effect in this model. The amino acids glutamate, serine, glutamine, alanine, taurine, arginine and the NO-related compound citrulline were sampled from the striatum and cortex of the ischaemic hemisphere using in vivo microdialysis. The in vivo salicylate trapping method was applied for monitoring hydroxyl radical formation via 2,3 dihydroxybenzoic acid (2,3 DHBA) detection. Caspase-3, neuronal nitric oxide synthase (nNOS) immunoreactivity and the volume of ischaemic damage were determined 24 h after the insult. In both the striatum and the cortex, Et-1-induced increases in glutamate, taurine and alanine were refractory to mild hypothermia. However, mild hypothermia significantly attenuated the ischaemia-induced 2,3 DHBA levels and the nNOS immunoreactivity in the cortex, but not in the striatum. These observations were associated with a decreased caspase-3 immunoreactivity. These results suggest that mild hypothermia exerts its neuroprotective effect in the penumbra partially by reducing nNOS activity and thereby preventing oxidative stress. Furthermore, we confirm our previous findings that the neuroprotective effect of resuscitative hypothermia is not mediated by changes in ischaemia-induced amino acid release as they could not be associated with the ischaemia-induced damage in the Et-1 rat model.

Neuroprotective effect of N-acetyl-aspartyl-glutamate in combination with mild hypothermia in the endothelin-1 rat model of focal cerebral ischaemia.

Previously we showed that treatment with mild hypothermia (34 degrees C for 2 h) after a focal cerebral infarct was neuroprotective by reducing apoptosis in the penumbra (cortex), but not in the core (striatum) of the infarct. In this study we examined whether administration of N-acetyl-aspartyl-glutamate (NAAG) in combination with mild hypothermia could improve striatal neuroprotection in the endothelin-1 rat model. NAAG (10 mg/kg i.p.) was injected under normothermic (37 degrees C) or mild hypothermic conditions, either 40 min before or 20 min after the insult. NAAG reduced caspase 3 immunoreactivity in the striatum, irrespective of the time of administration and brain temperature. This neuroprotective effect could be explained, at least partially, by decreased nitric oxide synthase activity in the striatum and was blocked by the group II metabotropic glutamate receptor antagonist, LY341495. Hypothermia applied together with NAAG reduced both cortical and striatal caspase 3 immunoreactivity, as well as the overall ischaemic damage in these areas. However, no pronounced improvement was seen in total damaged brain volume. Extracellular glutamate levels did not correlate with the observed protection, whatever treatment protocol was applied. We conclude that treatment with NAAG causes the same degree of neuroprotection as treatment with hypothermia. Combination of the two treatments, although reducing apoptosis, does not considerably improve ischaemic damage.

Effect of resuscitative mild hypothermia on glutamate and dopamine release, apoptosis and ischaemic brain damage in the endothelin-1 rat model for focal cerebral ischaemia.

The relationship between glutamate and dopamine release, apoptosis and ischaemic damage was studied following induction of transient focal cerebral ischaemia under normothermic (37 degrees C) and postischaemic (resuscitative) mild hypothermic (34 degrees C for 2 h) conditions in sevoflurane anaesthetized male Wistar rats. Focal ischaemia was induced by infusing endothelin-1 adjacent to the middle cerebral artery. In vivo microdialysis was used to sample glutamate and dopamine from striatum and parietal cortex of the ipsilateral hemisphere. The volume of ischaemic damage and the degree of apoptosis were determined 24 h after the insult. In both striatum and cortex of the normothermic group an initial increase in extracellular glutamate and dopamine levels following endothelin-1 infusion was observed. Striatal glutamate levels remained enhanced (250% of baseline) throughout the experiment, while the other neurotransmitter levels returned to baseline values. Hypothermia significantly attenuated the endothelin-1 induced glutamate release in the striatum. It also reduced apoptosis and infarct volume in the cortex. These results indicate that: (i) postischaemic mild hypothermia exerts its neuroprotective effect by inhibiting apoptosis in the ischaemic penumbral region; and (ii) this effect is not associated with an attenuation of glutamate or dopamine release in the cortex.

In vivo characterization of somatodendritic dopamine release in the substantia nigra of 6-hydroxydopamine-lesioned rats.

We investigated the effect of an injection of 6-hydroxydopamine (6-OHDA) into the rat medial forebrain bundle (MFB) on the degeneration and the function of the dopaminergic cell bodies in the substantia nigra (SN) 3 and 5 weeks after lesioning. After injection of 6-OHDA into the MFB a complete loss of dopamine content was apparent in the striatum 3 weeks after lesioning. In the SN the amount of tyrosine hydroxylase-immunoreactive dopamine cells decreased gradually, with a near-complete lesion (> 90%) obtained only after 5 weeks, indicating that neurodegeneration of the nigral cells was still ongoing when total dopamine denervation of the striatum had already been achieved. Baseline dialysate and extracellular dopamine levels in the SN, as determined by in vivo microdialysis, were not altered by the lesion. A combination of compensatory changes of the remaining neurones and dopamine originating from the ventral tegmental area may maintain extracellular dopamine at near-normal levels. In both intact and lesioned rats, the somatodendritic release was about 60% tetrodotoxin (TTX) dependent. Possibly two pools contribute to the basal dopamine levels in the SN: a fast sodium channel-dependent portion and a TTX-insensitive one originating from diffusion of dopamine. Amphetamine-evoked dopamine release and release after injection of the selective dopamine reuptake blocker GBR 12909 were attenuated after a near-complete denervation of the SN (5 weeks after lesioning). So, despite a 90% dopamine cell loss in the SN 5 weeks after an MFB lesion, extracellular dopamine levels in the SN are kept at near-normal levels. However, the response to a pharmacological challenge is severely disrupted.