In both diurnal and nocturnal mammals, the timing of activity is regulated by the central circadian clock of the suprachiasmatic nucleus (SCN). The SCN is synchronized to the external light cycle... Show moreIn both diurnal and nocturnal mammals, the timing of activity is regulated by the central circadian clock of the suprachiasmatic nucleus (SCN). The SCN is synchronized to the external light cycle via the retinohypothalamic tract (RHT). To investigate potential differences in light processing between nocturnal mice and the diurnal rodent Rhabdomys pumilio, we mimicked retinal input by stimulation of the RHT ex vivo. Using Ca2+ imaging, we observed excitations as well as inhibitions of SCN neurons in response to electrical RHT stimulation. In mice, the vast majority of responses were excitatory (85%), whereas in Rhabdomys, the proportion of excitatory and inhibitory responses was similar (51% excitatory, 49% inhibitory). Glutamate blockers AP5 and CNQX blocked the excitatory responses to RHT stimulation but did not abolish the inhibitory responses in mice or Rhabdomys, indicating that the inhibitions were monosynaptically transmitted via the RHT. Simultaneous application of glutamate blockers with the GABA(A) antagonist gabazine blocked all inhibitory responses in mice, but not in Rhabdomys. Collectively, our results indicate that in Rhabdomys, considerably more inhibitory responses to light are present and that these responses are driven directly by the RHT. We propose that this increased proportion of inhibitory input could reflect a difference in the entrainment mechanism employed by diurnal rodents. Show less
The experimental research in this thesis aims to gain more understanding of how the SCN network is organized and what is needed for network changes. More specifically, this work focused on the... Show moreThe experimental research in this thesis aims to gain more understanding of how the SCN network is organized and what is needed for network changes. More specifically, this work focused on the potential role of GABA and the GABAeric E/I balance in SCN network plasticity. Communication and synchronization in the SCN are important for the generation of a strong and coherent output signal. Under certain conditions, like long photoperiod, the phases of the individual SCN cells are more dispersed over the 24 hour cycle as evidenced by measurements of electrical activity and clock gene expression. Aging is also known to affect the network organization of the SCN with deterioration in synchronization among the individual SCN neurons. In this thesis, I present work that contributes to research questions regarding the effect of light exposure and/or aging on several characteristics of SCN network plasticity. Show less
This thesis aimed to explore biochemical processes related to migraine outside (interictal) and during upcoming attacks. Chapter 2 describes the biochemical profiling of plasma samples from... Show moreThis thesis aimed to explore biochemical processes related to migraine outside (interictal) and during upcoming attacks. Chapter 2 describes the biochemical profiling of plasma samples from interictal migraine patients and healthy controls from eight Dutch cohorts with a proton nuclear magnetic resonance based metabolomics platform. In Chapter 3 cerebrospinal fluid (CSF) and plasma samples from interictal migraine with and without aura patients and healthy volunteers, were profiled using an ultra-performance liquid chromatography mass spectrometry (UPLC-MS) platform for amine measurements, as multiple amines have been implicated in migraine pathophysiology. Alcoholic beverages are frequently reported migraine triggers. Chapter 4 assessed the potential of various alcohol beverages as a migraine attack trigger using a questionnaire study in a large cohort of migraine patients. In Chapter 5, the frequently used pharmacological migraine trigger glyceryl trinitrate (GTN) was studied in migraine patients and healthy controls to investigate whether previously reported premonitory symptoms are indeed specific to migraine patients. In Chapter 6 glutamate, glutamine, and GABA were assed in the visual cortex of migraine patients before and over the course of a GTN-provoked attack to detect possible involvement of the glutamatergic system in the onset of attacks using proton magnetic resonance spectroscopy. Show less
Both inhibitory and excitatory GABA transmission exist in the mature suprachiasmatic nucleus (SCN), the master pacemaker of circadian physiology. Whether GABA is inhibitory or excitatory depends on... Show moreBoth inhibitory and excitatory GABA transmission exist in the mature suprachiasmatic nucleus (SCN), the master pacemaker of circadian physiology. Whether GABA is inhibitory or excitatory depends on the intracellular chloride concentration ([Cl-](i)). Here, using the genetically encoded ratiometric probe Cl-Sensor, we investigated [Cl-](i) in AVP and VIP-expressing SCN neurons for several days in culture. The chloride ratio (R-Cl) demonstrated circadian rhythmicity in AVP + neurons and VIP + neurons, but was not detected in GFAP + astrocytes. R-Cl peaked between ZT 7 and ZT 8 in both AVP + and VIP + neurons. R-Cl rhythmicity was not dependent on the activity of several transmembrane chloride carriers, action potential generation, or the L-type voltage-gated calcium channels, but was sensitive to GABA antagonists. We conclude that [Cl-](i) is under circadian regulation in both AVP + and VIP + neurons. Show less
Enhanced activity of the glutamatergic system has been linked to migraine pathophysiology. The present study aimed to assess the involvement of the glutamatergic system in the onset of attacks. We... Show moreEnhanced activity of the glutamatergic system has been linked to migraine pathophysiology. The present study aimed to assess the involvement of the glutamatergic system in the onset of attacks. We provoked attacks by infusion of glyceryl trinitrate (GTN; 0.5 mu g/kg/min over 20 min) in 24 female episodic migraineurs without aura and 13 female age-matched healthy controls. Over the course of a single day participants were scanned three times at fixed time slots (baseline before GTN infusion, 90 min and 270 min after start of GTN infusion). Single volume proton magnetic resonance spectra (H-1-MRS) were acquired at 7 Tesla from a volume of interest (VOI, 2x2x3 cm) in the visual cortex. We assessed the concentrations of glutamate, its major precursor glutamine, and its product gamma-aminobutyric acid (GABA) over the course of a provoked attack. The preictal state was defined as the period after GTN infusion until the migraine-like headache started, independent of possible experienced premonitory symptoms, and the ictal state was defined as the period with provoked migraine-like headache. Data were analyzed using a linear mixed-effect model for repeated measures. Glutamate and glutamine levels did not change from interictal to the preictal and ictal state. GABA levels increased from interictal towards the preictal state for migraine patients compared with healthy controls. We conclude that high resolution 7T MRS is able to show changes in the glutamatergic system towards a triggered migraine attack, by revealing an increased GABA concentration associated with the onset of a migraine attack. Show less
The thesis describes the use of extensive pharmacodynamic effect profiling to characterise the clinical pharmacology of classic and non-classical analgesia. Analgesic drugs that modulate widespread... Show moreThe thesis describes the use of extensive pharmacodynamic effect profiling to characterise the clinical pharmacology of classic and non-classical analgesia. Analgesic drugs that modulate widespread targets in the nervous system can be expected to affect numerous CNS functions, which requires multimodal characterisation of pain processing and neurocognition. This is illustrated on the basis of two case studies of pharmacological agents that target cannabinoid CB1 and GABA-ergic GABAA receptors: two of the most widely distributed systems of receptors and neurotransmitters that are involved in a myriad of physiological functions. The distribution of receptors throughout the central nervous system render an oral formulation of ∆9-THC and a positive allosteric modulator of α2/3/5 subunit-containing GABAA receptors, ideal candidates for extensive neurophysiological and analgesic effect profiling in early phase clinical research. Profiling human pharmacology with a strong focus on pharmacodynamics may help to better understand the therapeutic potential and safety limitations of a compound before selection of doses and patient populations for phase II proof-of-concept studies. Show less
The central circadian pacemaker in mammals, the suprachiasmatic nucleus (SCN), is important for daily as well as seasonal rhythms. The SCN encodes seasonal changes in day length by adjusting phase... Show moreThe central circadian pacemaker in mammals, the suprachiasmatic nucleus (SCN), is important for daily as well as seasonal rhythms. The SCN encodes seasonal changes in day length by adjusting phase distribution among oscillating neurons thereby shaping the output signal used for adaptation of physiology and behavior. It is well-established that brief light exposure at the beginning and end of the day, also referred to as "skeleton" light pulses, are sufficient to evoke the seasonal behavioral phenotype. However, the effect of skeleton light exposure on SCN network reorganization remains unknown. Therefore, we exposed mice to brief morning and evening light pulses that mark the time of dawn and dusk in a short winter- or a long summer day. Single-cell PER2::LUC recordings, electrophysiological recordings of SCN activity, and measurements of GABA response polarity revealed that skeleton light-regimes affected the SCN network to the same degree as full photoperiod. These results indicate the powerful, yet potentially harmful effects of even relatively short light exposures during the evening or night for nocturnal animals. Show less
Without even realizing, human beings perform extraordinary feats on a daily basis. We navigate an increasingly complicated and demanding world by using our sophisticated ability to override... Show moreWithout even realizing, human beings perform extraordinary feats on a daily basis. We navigate an increasingly complicated and demanding world by using our sophisticated ability to override habitual tendencies. Furthermore, we can meticulously plan, carry out and adapt actions in order to achieve goals that we set for ourselves. This capacity for goal-directed behavior—often considered a hallmark of human excellence over other animals—is commonly referred to as ‘cognitive control’ or ‘executive function’. These are rather vague, typically synonymous concepts that serve more as an umbrella term for many different processes rather than referring to a single, unitary function. Decades of neuropsychological research have been devoted to understanding cognitive control and its component processes, the way it is implemented in the brain, and how we can alter—and possibly improve—its efficacy. These issues have driven the work included in this dissertation. In particular, the research presented in this dissertation concerns itself with the overarching questions of how chemical processes in the brain (dopamine, glutamate, and GABA) enable and affect cognitive control, and how we might non-invasively measure and manipulate these biological underpinnings of goal-directed behavior. Show less
Engberink, A.H.O.O.; Meijer, J.H.; Michel, S. 2018
Doublecortin (DCX) and DCX-domain containing Doublecortin-Like Kinase (DCLK) gene splice variants function during embryonic development, where they play a role in microtubule binding. Although a... Show moreDoublecortin (DCX) and DCX-domain containing Doublecortin-Like Kinase (DCLK) gene splice variants function during embryonic development, where they play a role in microtubule binding. Although a role for the DCLK gene during embryogenesis is clearly established, it encodes multiple, different transcripts, some of which are expressed in the adult brain or in response to neuronal activity. This suggests that the DCLK gene may have additional functions beyond neuronal development. Strikingly, the roles of two DCLK gene products, DCLK-short and CaMK-related peptide (CARP), remain largely elusive. Therefore, we have generated transgenic mice with over-expression of either CARP or a constitutively active form of DCLK-short, called _C-DCLK-short, in the brain. This has opened up the possibility to study the effect of over-expression of these DCLK transcripts in the brain during adulthood. To gain more insight in DCLK gene function in the adult brain we aimed to study and describe the phenotypes of these transgenic mice at different functional levels, such as the genetic, network and behavioural level. Show less
In order to cope with and to predict 24-hour rhythms in the environment, most, if not all, organisms have a circadian timing system. The most important mammalian circadian pacemaker is located in... Show moreIn order to cope with and to predict 24-hour rhythms in the environment, most, if not all, organisms have a circadian timing system. The most important mammalian circadian pacemaker is located in the suprachiasmatic nucleus at the base of the hypothalamus in the brain. Over the years, it has become clear that the circadian system is complex and that additional oscillators exist, both within and outside the central nervous system. The aim of this thesis was to obtain insight in the hierarchical organization of the circadian timing system and to determine whether certain attributes arise at the tissue level. The data reveal that interactions between the SCN and the periphery, as well as interactions between subregions within the SCN, contribute significantly to the functioning of the circadian system. Another important finding is that the multiple components of the circadian system can, under certain circumstances, dissociate. The hierarchical organization of the circadian timing system, the interactions between and within organizational levels, and importantly, the ability of several components to dissociate, may provide the circadian system the required plasticity to adjust to biologically relevant changes in the environment. Show less
