Dimitrinka Y. Atanasova

Agomelatine protects against neuronal damage without preventing epileptogenesis in the kainate model of temporal lobe epilepsy

Recent studies about the novel antidepressant agomelatine, which is a mixed MT1 and MT2 melatonin receptor agonist and 5HT2C serotonin receptor antagonist possessing an anticonvulsant and neuroprotective action, suggest that it may have potential to contribute against epileptogenesis and epilepsy-induced memory impairment. In order to ascertain whether protection of some brain structures could suppress epileptogenesis, in the present study, we evaluated the effect of chronic post-status treatment with agomelatine on epileptogenesis, behavioral and neuronal damage induced by kainate acid (KA) status epilepticus (SE). Agomelatine/vehicle treatment (40mg/kg, i.p.) started one hour after SE and continued up to 10weeks in Wistar rats. Latency for onset of spontaneous motor seizures (SMS) and their frequency was detected by a 24-h video-recording. Locomotor activity, anxiety and hippocampus-dependent spatial memory in open field (OF), elevated plus maze (EPM), light-dark test (LDT) and radial arm maze (RAM) test, respectively, were evaluated during the last two weeks after SE. Agomelatine significantly decreased the latency for onset of SMS and increased the seizure frequency during the 2nd and the 3rd week of treatment. The MT1 and MT2 receptor agonist and serotonin 5HT2C receptor antagonist exacerbated the KA-induced hyperlocomotion and impulsive behavior and it was unable to prevent spatial memory impairment of epileptic rats. However, agomelatine induced a neuroprotection in the dorsal hippocampus, specifically in the CA1, septal CA2 and partially in the CA3c region, the hilus of the dentate gyrus, piriform cortex and septo-temporal and temporal basolateral amygdala. Our findings suggest that the beneficial impact against SE-induced neuronal loss exerted by agomelatine is not crucial for the suppression of epileptogenesis and its deleterious consequences in KA model of temporal lobe epilepsy.

Expression of neurotrophic factors and their receptors in the carotid body of spontaneously hypertensive rats

The carotid body (CB) is a small neural crest-derived structure that senses oxygen levels in blood and monitors ventilation. The spontaneously hypertensive rat (SHR) is considered a good experimental model for primary hypertension and is extensively used to study cardiovascular diseases. The hypertensive CB shows structural plasticity and could enlarge without vasodilation. Our immunohistochemical studies revealed the presence of nuclear Ki-67 protein in the sustentacular cells, nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 and their corresponding receptors p75(NTR), TrkA, TrkB and TrC in the majority of glomus cells and also in a subset of sustentacular cells. In addition, virtually all glomus cells expressed glial cell line-derived neurotrophic factor and its specific receptor GFRα1. The present study demonstrates that in glomus cells of hypertensive animals there is enhanced expression of components of the neurotrophin signaling system compared to normotensive rats. Our results suggest that the elevated production of neurotrophic factors in SHRs could explain CB and sympathetic hyperactivity leading to hypertension.

Histochemical demonstration of tripeptidyl aminopeptidase I in the rat carotid body.

Tripeptidyl aminopeptidase I (TPP I) is a lysosomal exopeptidase that is widely distributed throughout the central nervous system (CNS) and internal organs in many mammalian species. The enzyme is involved in the breakdown of collagen and different peptides. The carotid body (CB) is the main peripheral arterial chemoreceptor playing an important role in the control of breathing and the autonomic control of cardiovascular function. In response to hypoxia its neuron-like glomus cells release a variety of peptide transmitters that trigger an action potential through the afferent fibers, thus conveying the chemosensory information to the CNS. In the present study we investigated the histochemical localization of TPP I in the CB of rats. Enzyme histochemistry showed high activity of TPP I in CB glomeruli. In particular, the glomus cells contained many TPP I-positive granules, while the glial-like sustentacular cells displayed a slightly fainter reaction. The interglomerular connective tissue was also weakly stained. The results show that both the parenchymal cells of the rat CB express, albeit with different intensity, TPP I. Taken together with our previous enzyme histochemical investigations on the rat CB, it seems likely that the glomus cells possess enzymatic equipment necessary for the neuropeptide intracellular and collagen extracellular initial degradation. These findings also suggest that TPP I is involved in the general turnover of chemotransmitters between glomus cells and sensory nerve endings which emphasizes its importance for chemoreception under hypoxic conditions.

Morphological changes in the rat carotid body following acute sodium nitrite treatment

The carotid body (CB) is a small neural crest-derived chemosensory organ that detects the chemical composition of the arterial blood and responds to its changes by regulating breathing. The effects of acute nitrite treatment on the CB morphology in rats were examined by morphometry. We found that 1h after administrating a single dose of sodium nitrite, the CB underwent structural changes characterized by a prominent increase in its size with a marked, several-fold dilation of the blood vessels. The obvious CB enlargement mostly due to apparent vasodilation and glomus cell hypertrophy was at its highest one day later and persisted until the fifth day. 20 days after the treatment, the CB regained its size to the normoxic control state. Morphometric analysis revealed that the CB size increase in treated animals is statistically significant when compared to that of untreated controls. It can be inferred that the nitrite-exposed CB displays remarkable structural plasticity and enlarges its size mostly through vascular expansion.

Expression of nitric oxide-containing structures in the rat carotid body

The carotid body (CB) is a major peripheral arterial chemoreceptor organ that evokes compensatory reflex responses so as to maintain gas homeostasis. It is dually innervated by sensory fibers from petrosal ganglion (PG) neurons, and autonomic fibers from postganglionic sympathetic neurons of the superior cervical ganglion (SCG) and parasympathetic vasomotor fibers of intrinsic ganglion cells in the CB. The presence of nitric oxide (NO), a putative gaseous neurotransmitter substance in a number of neuronal and non-neuronal structures, was examined in the CB, PG and SCG of the rat using nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry, nitric oxide synthase (NOS) immunohistochemistry and retrograde tracing. One week after injecting the retrograde tracer Fast Blue (FB) in the CB, we found that a subset of perikarya in the caudal portions of the PG and SCG were FB-labeled. Histochemistry and immunohistochemistry revealed that the majority of large- and medium-sized PG and SCG cells were NADPH-d positive and displayed a strong NOS immunostaining. We also observed that many varicose nerve fibers penetrating the CB and enveloping the glomus cells and blood vessels were NADPH-d reactive and expressed the constitutive isoforms of NOS, nNOS and eNOS. In addition, some autonomic microganglion cells embedded within, or located at the periphery of the CB, and not glomus or sustentacular cells were nNOS-immunopositive while CB microvasculature expressed eNOS. The present results suggest that NO is a transmitter in the autonomic nerve endings supplying the CB and is involved in efferent chemoreceptor inhibition by a dual mechanism.

Tripeptidyl Peptidase I and Its Role in Neurodegenerative and Tumor Diseases

Tripeptidyl peptidase I (TPPI) is a lysosomal enzyme widely distributed in mammals and humans. Its genetically determined deficiency causes the classical late-infantile form of neuronal ceroid lipofuscinosis, a fatal hereditary neurodegenerative disease associated with severe symptoms and early death, usually in the second decade of life. Many studies also show that TPPI is differentially regulated under various pathological conditions such as malignancy, neurodegeneration, ischemia, and inflammation, pointing at possible enzyme involvement in the pathogeneses of these entities. This chapter focuses on the TPPI participation in neurodegenerative and neoplastic diseases.

Histochemical Demonstration of Tripeptidyl Aminopeptidase I

Enzyme histochemical methods are valuable for the studies on the enzyme involvement in different pathological processes. Here we describe two protocols for chromogenic and fluorogenic histochemical demonstration of tripeptidyl aminopeptidase I (TPPI), a protease that is crucial for neuronal functions. The procedures are based on newly synthesized substrates for TPPI-glycyl-L-prolyl-L-metionyl-5-chloro-1-anthraquinonylhydrazide (GPM-CAH) and glycyl-L-prolyl-L-metionyl-4-hydrazido-N-hexyl-1,8-naphthalimide (GPM-HHNI). Using such protocols, precise enzyme localization can be obtained in tissue sections of mammalian organs.