Olof Zachrisson

Peptide hormone exendin-4 stimulates subventricular zone neurogenesis in the adult rodent brain and induces recovery in an animal model of parkinson's disease

We investigated the effects of exendin‐4 on neural stem/progenitor cells in the subventricular zone of the adult rodent brain and its functional effects in an animal model of Parkinsons disease. Our results showed expression of GLP‐1 receptor mRNA or protein in the subventricular zone and cultured neural stem/progenitor cells isolated from this region. In vitro, exendin‐4 increased the number of neural stem/progenitor cells, and the number of cells expressing the neuronal markers microtubule‐associated protein 2, β‐III‐tubulin, and neuron‐specific enolase. When exendin‐4 was given intraperitoneally to naïve rodents together with bromodeoxyuridine, a marker for DNA synthesis, both the number of bromodeoxyuridine‐positive cells and the number of neuronal precursor cells expressing doublecortin were increased. Exendin‐4 was tested in the 6‐hydroxydopamine model of Parkinsons disease to investigate its possible functional effects in an animal model with neuronal loss. After unilateral lesion and a 5‐week stabilization period, the rats were treated for 3 weeks with exendin‐4. We found a reduction of amphetamine‐induced rotations in animals receiving exendin‐4 that persisted for several weeks after drug administration had been terminated. Histological analysis showed that exendin‐4 significantly increased the number of both tyrosine hydroxylase‐ and vesicular monoamine transporter 2‐positive neurons in the substantia nigra. In conclusion, our results show that exendin‐4 is able to promote adult neurogenesis in vitro and in vivo, normalize dopamine imbalance, and increase the number of cells positive for markers of dopaminergic neurons in the substantia nigra in a model of Parkinsons disease.

The glucagon-like peptide 1 receptor agonist exendin-4 improves reference memory performance and decreases immobility in the forced swim test.

We have earlier shown that the glucagon-like peptide 1 receptor agonist exendin-4 stimulates neurogenesis in the subventricular zone and excerts anti-parkinsonian behavior. The aim of this study was to assess the effects of exendin-4 treatment on hippocampus-associated cognitive and mood-related behavior in adult rodents. To investigate potential effects of exendin-4 on hippocampal function, radial maze and forced swim test were employed. The time necessary to solve a radial maze task and the duration of immobility in the forced swim test were significantly reduced compared to respective vehicle groups if the animals had received exendin-4 during 1-2weeks before testing. In contrast to the positive control imipramine, single administration of exendin-4 1h before the challenge in the forced swim test had no effect. Immunohistochemical analysis showed that the incorporation of bromodeoxyuridine, a marker for DNA synthesis, as well as doublecortin expression was increased in the hippocampal dentate gyrus following chronic treatment with exendin-4 compared to vehicle-treated controls. The neurogenic effect of exendin-4 on hippocampus was confirmed by quantitative PCR showing an upregulation of mRNA expression for Ki-67, doublecortin and Mash-1. Since exendin-4 significantly improves hippocampus-associated behavior in adult rodents, it may be a candidate for alleviation of mood and cognitive disorders.

PACAP promotes neural stem cell proliferation in adult mouse brain

In recent years, it has become evident that neural stem cells in the adult mammalian brain continuously generate new neurons, mainly in the hippocampus and olfactory bulb. Although different growth factors have been shown to stimulate neurogenesis in the adult brain, very little is known about the role of neuropeptides in this process. Pituitary adenylate cyclase‐activating polypeptide (PACAP) is a neuropeptide with pleiotropic effects acting through three receptors to which it has high affinity, namely, PACAP receptor 1 (PAC1), vasoactive intestinal peptide (VIP) receptor 1, and VIP receptor 2. We show that PAC1 is expressed in the neurogenic regions of the adult mouse brain, namely the ventricular zone of the lateral ventricle and the hippocampal dentate gyrus. Cultured neural stem cells isolated from the lateral ventricle wall of adult mice express PAC1 and proliferate in vitro in response to two PAC1 agonists, PACAP and Maxadilan, but not VIP at physiologic concentrations, indicating PAC1 as a mediator of neural stem cell proliferation. Pharmacologic and biochemical characterization of PACAP‐induced neural stem cell proliferation revealed the protein kinase C pathway as the principal signaling pathway, whereas addition of epidermal growth factor synergistically enhanced the proliferating effect of PACAP. Further in vitro characterization of the effect of PACAP on neural stem cells showed PACAP capable of stimulating ex novo in vitro formation of multipotent neurospheres with the capacity to generate both neuronal and glial cells. Finally, intracerebroventricular infusion of PACAP increases cell proliferation in the ventricular zone of the lateral ventricle and the dentate gyrus of the hippocampus. We conclude that PACAP, through PAC1, is a potent mediator of adult neural stem cell proliferation.

Limbic effects of repeated electroconvulsive stimulation on neuropeptide Y and somatostatin mRNA expression in the rat brain.

The aim of this study was to determine the effect of repeated electroconvulsive stimulation (ECS) on the expression of neuropeptide Y (NPY) and somatostatin (SS) mRNA in the rat brain. For that purpose, quantitative in situ hybridization histochemistry and RNA blot analysis were used. In the hippocampal formation the prevalence of NPY mRNA positive neurons increased in the hilus of the dentate gyrus and the CA3 while a decrease was seen in layers II-III of the entorhinal cortex. In contrast, SS mRNA was increased in the granule cells of the dentate gyrus and in most neurons of the outer parts of the layer III in the entorhinal cortex with cell bodies of perforant pathway projections to the hippocampal CA1 region. Both NPY and SS mRNA expressing neurons were increased in numerical density in the prefrontal cortex with similar amounts of mRNA in individual NPY positive neurons after the stimulations while SS mRNA levels decreased in hybridization positive neurons. In the striatum the only observed significant effect was an increased prevalence of NPY mRNA positive neurons in the caudal nucleus accumbens. Our results provide an outline of a complex functional anatomy of ECS in the rat brain. This type of investigations contributes to map the neuronal systems involved in the action of ECT used in the treatment of affective and schizophrenic disorders.

Region-specific effects of chronic lithium administration on neuropeptide Y and somatostatin mRNA expression in the rat brain

The aim of this study was to examine the effects of 4-week lithium (Li+) food supplementation on neuropeptide mRNA expression in the rat brain. In situ hybridisation was used to determine the effects on the expression of neuropeptide Y (NPY) and somatostatin (SS) mRNA. Increases in NPY mRNA levels were seen in the hippocampus, layers II-III of the entorhinal cortex, nucleus accumbens shell and in the medial caudate-putamen. Increases in SS mRNA expression were seen in the layers IV-VI of the entorhinal cortex and in the lateral caudate putamen. Thus, Li+ appears to affect discrete populations of NPY and SS mRNA expressing neurons, with possible relevance to beneficial effects of Li+ in affective disorders.

A tachykinin NK1 receptor antagonist, CP-122,721-1, attenuates kainic acid-induced seizure activity

Substance P (SP) can play an important role in neuronal survival. To analyze the role of SP in excitotoxicity, kainic acid (KA) was administered to rats and in situ hybridization was used to analyze the levels of the SP encoding preprotachykinin-A (PPT-A) mRNA in striatal and hippocampal subregions 1, 4, and 24 h and 7 days after KA. In striatum and piriform cortex, PPT-A mRNA peaked 4 h after KA while in hippocampus, levels peaked after 24 h. KA caused seizures and neuronal toxicity as indicated by a reduction of the number of neurons in the hippocampal CA1 subregion after 7 days. KA was later administered alone or following pretreatment with the tachykinin NK1 receptor antagonist CP-122,721-1 (0.3 mg/kg). The pretreatment decreased seizure activity and a negative correlation was found between seizure activity and survival of CA1 neurons. Conclusively, treatment with CP-122,721-1 has a seizure inhibiting property and may possibly counteract KA-induced nerve cell death in CA1.

Safety and tolerability of intracerebroventricular PDGF-BB in Parkinson's disease patients.

BACKGROUND. Recombinant human PDGF-BB (rhPDGF-BB) reduces Parkinsonian symptoms and increases dopamine transporter (DAT) binding in several animal models of Parkinsons disease (PD). Effects of rhPDGF-BB are the result of proliferation of ventricular wall progenitor cells and reversed by blocking mitosis. Based on these restorative effects, we assessed the safety and tolerability of intracerebroventricular (i.c.v.) rhPDGF-BB administration in individuals with PD. METHODS. We conducted a double-blind, randomized, placebo-controlled phase I/IIa study at two clinical centers in Sweden. Twelve patients with moderate PD received rhPDGF-BB via an implanted drug infusion pump and an investigational i.c.v. catheter. Patients were assigned to a dose cohort (0.2, 1.5, or 5 μg rhPDGF-BB per day) and then randomized to active treatment or placebo (3:1) for a 12-day treatment period. The primary objective was to assess safety and tolerability of i.c.v.-delivered rhPDGF-BB. Secondary outcome assessments included several clinical rating scales and changes in DAT binding. The follow-up period was 85 days. RESULTS. All patients completed the study. There were no unresolved adverse events. Serious adverse events occurred in three patients; however, these were unrelated to rhPDGF-BB administration. Secondary outcome parameters did not show dose-dependent changes in clinical rating scales, but there was a positive effect on DAT binding in the right putamen. CONCLUSION. At all doses tested, i.c.v. administration of rhPDGF-BB was well tolerated. Results support further clinical development of rhPDGF-BB for patients with PD. TRIAL REGISTRATION. Clinical Trials.gov NCT00866502. FUNDING. Newron Sweden AB (former NeuroNova AB) and Swedish Governmental Agency for Innovation Systems (VINNOVA).

Restorative effects of platelet derived growth factor-BB in rodent models of Parkinson's disease.

Parkinsons disease is characterized by motor deficits caused by loss of midbrain dopaminergic neurons. Neurotrophic factors and cell transplantation have partially restored function in models of Parkinsons disease, but have had limited effects in humans. Here we show that intracerebroventricular administration of platelet-derived growth factor-BB can offer an alternative strategy to restore function in Parkinsons disease; In animal models of nigrostriatal injury, a two weeks treatment with platelet-derived growth factor-BB resulted in long-lasting restoration of striatal dopamine transporter binding sites and expression of nigral tyrosine hydroxylase. It also normalized amphetamine-induced rotational behavior in 6-hydroxydopamine lesioned rats. Platelet-derived growth factor-BB promoted proliferation of neural progenitor cells in the subventricular zone. The effects on dopaminergic neurons and functional recovery could be blocked by co-infusion with a proliferation inhibitor, indicating a link between the proliferative and anti-parkinsonian effects. Based on the current data, we consider platelet-derived growth factor-BB a clinical candidate drug for treatment of Parkinsons disease.

Effect of chronic antipsychotic drug treatment on preprosomatostatin and preprotachykinin A mRNA levels in the medial prefrontal cortex, the nucleus accumbens and the caudate putamen of the rat.

In situ hybridization histochemistry was used to study the expression of preprosomatostatin (PPSOM) and preprotachykinin A (PPT-A) mRNA in the medial prefrontal cortex (mPFC), the nucleus accumbens (NAC) and the caudate putamen (CP) of the rat after chronic (21 days) treatment with the classical antipsychotic drug haloperidol (1 mg/kg i.p.), the atypical antipsychotic drugs clozapine (15 mg/kg i.p.) and amperozide (5 mg/kg i.p.), and the selective dopamine (DA)-D2/D3 receptor antagonist raclopride (2 mg/kg i.p.). Whereas amperozide markedly elevated the numerical density of PPSOM mRNA expressing neurons in the mPFC (52%), the other drugs did not significantly affect PPSOM mRNA levels in any of the brain regions studied. Amperozide also altered PPT-A mRNA expression in the mPFC, i.e. a decrease (22%) was found. Of the other drugs tested only haloperidol significantly decreased PPT-A mRNA levels in the NAC shell (14%), in the dorso-lateral CP (19%) and in the medial CP (15%). In view of the differences between amperozide and the other drugs studied, as regards both pre-clinical and clinical characteristics, we suggest that the specific effects of amperozide on PPSOM and PPT-A mRNA in the mPFC may be related to its 5-HT releasing action in the frontal cortex, an effect possibly caused by its alpha2-adrenoceptor blocking activity. This effect, in turn, may be related to an antidepressant-like action that this compound exhibits in animal studies. The decrease in PPT-A mRNA levels seen after the haloperidol treatment is probably due to its potent DA-D2 receptor antagonism and may be related to side-effects, rather than therapeutic effects of this drug.

Neuronal coexistence of trkB and glutamic acid decarboxylase67 mRNAs in rat hippocampus

We have in earlier studies shown that brain derived neurotrophic factor (BDNF) mRNA expression is increased in the hippocampus following stimulation of excitatory cortical afferents and spatial learning. Furthermore, we have observed that excitatory influence in the hippocampus seems to increase in vivo release of gamma-aminobutyric acid (GABA), indicated by microdialysis perfusion of the CA1 region. In this study we have investigated whether the receptor for BDNF, TrkB, may be expressed in GABA containing neurons in the CA1, thereby suggesting a possible role for BDNF in the trophic regulation of these neurons. We provide evidence of a neuronal coexistence of the mRNA encoding TrkB and glutamic acid decarboxylase, the key enzyme in the synthesis of GABA. This finding indicates that TrkB can be synthesized in GABA producing neurons in the hippocampus.