Nesse estudo investigamos os efeitos da hipóxia tecidual aguda (HA) sobre as propriedades eletrofisiológicas intrínsecas dos neurônios pré-simpáticos bulboespinhais da área rostro-ventrolateral do bulbo (RVLM) de ratos jovens adultos submetidos previamente à hipóxia crônica intermitente (HCI) e os seus respectivos controle. Para marcarmos os neurônios pré-simpáticos bulboespinhais da RVLM, ratos Wistar jovens (P19-P21) anestesiados com ketamina e xilazina, receberam microinjeções bilaterais de rodamina, um traçador fluorescente retrógrado, na coluna intermediolateral da medula espinhal (T3-T6) e 2 dias após a recuperação da cirurgia, os animais foram submetidos ao protocolo de HCI, enquanto que ratos controle foram mantidos em condições de normóxia, durante 10 dias. No décimo primeiro dia, os ratos foram novamente anestesiados para a remoção do cérebro e as fatias do tronco cerebral contendo neurônios pré-simpáticos com marcação positivas foram registrados. Utilizamos a técnica de whole cell patch-clamp para estudo das propriedades eletrofisiológicas desses neurônios. As propriedades eletrofisiológicas intrínsecas foram analisadas antes e após a HA, a qual foi produzida pela perfusão das fatias do tronco cerebral com uma solução hipóxica (95% N2 + 5% CO2) durante 2 minutos na presença de bloqueadores sinápticos excitatórios e inibitórios. Todos os neurônios pré-simpáticos apresentaram característica intrínseca de autodespolarização e a frequência de disparos basal de potenciais de ação (PAs) desses neurônios de ratos do grupo controle e HCI foram similares [Controle= 5,03 ± 0,4 Hz (n=39) vs HCI= 6,31 ± 0,7 Hz (n=31); p > 0,05]. No grupo controle, a HA não alterou a frequência média de disparos de PAs (BS = 5,03 ± 0,4 Hz vs HA = 5,24 ± 0,3 Hz (n=39); p > 0,05], porém revelou diferentes perfis de disparo de PAs após 2 min de exposição à HA: i) 11 neurônios com aumento na frequência de disparos (BS = 5,1 ± 0,7 Hz vs HA = 7 ± 0,7 Hz; p < 0,05]; ii) 21 neurônios sem alteração na frequência de disparos (BS = 4,8 ± 0,5 Hz vs HA = 5,36 ± 0,6 Hz; p > 0,05] e iii) 7 neurônios com diminuição na frequência de disparos (BS = 7,3 ± 1,1 Hz vs HA = 3,6 ± 0,7 Hz; p < 0,05). No grupo HCI, a HA produziu aumento na frequência média de disparos (BS= 6,31 ± 0,7 Hz vs HA= 7,25 ± 0,8 Hz; n=31 - p < 0,05) e na análise do perfil de disparo de PAs, a HA revelou 2 subpopulações: i) 9 neurônios com aumento na frequência de disparos (BS = 4,7 ± 0,8 Hz vs HA = 8,2 ± 1,4 Hz; p < 0,05) e ii) 22 neurônios sem alteração na frequência de disparos (BS = 7,0 ± 1,0 Hz vs HA = 6,8 ± 1,0 Hz; p > 0,05). Esse estudo nos permitiu revelar diferentes subpopulações de neurônios pré-simpáticos que responderam de forma distintas à HA. Os resultados também sugerem que a HCI teria um efeito pré- condicionante na excitabilidade intrínseca dos neurônios pré-simpáticos em resposta à HA / In this study we evaluated the effects of acute hypoxia (AH) on the intrinsic electrophysiological properties of presympathetic neurons from rostro ventrolateral medulla (RVLM) of juvenile rats exposed to chronic intermittent hypoxia (CIH) or normoxic condition (control group). To label the RVLM bulbospinal presympathetic neurons, young Wistar rats (P 19 - 21) anesthetized with ketamine and xylazine, received bilateral microinjections of a fluorescent retrograde tracer (rhodamine retrobeads) were performed into the intermediolateral column of spinal cord (T3-T6) and two days after recovery of the surgery, the animals were submitted to CIH or normoxic protocol, during 10 days. On the 11th day, under anesthesia, brainstem slices were obtained and only the labeled RVLM presympathetic neurons were recorded, using whole-cell patch-clamp approach to study the electrophysiological properties of these neurons. The intrinsic electrophysiological properties were analyzed before and after AH, which was produced by slice perfusion with hypoxic solution (95% N2 and 5% CO2) during 2 min in the presence of excitatory and inhibitory synaptic antagonists. All recorded RVLM presympathetic neurons presented intrinsic pacemaker activity and the baseline firing frequency of these neurons from control and CIH group were similar [Control= 5,03 ± 0,4 Hz (n=39) vs HCI= 6,31 ± 0,7 Hz (n=31); p > 0,05]. In the control group, AH do not change the firing rate (BS = 5,03 ± 0,4 Hz vs HA = 5,24 ± 0,3 Hz (n=39); p > 0,05), but revealed different pattern of firing frequency after 2 min of AH: i) 11 neurons increased the firing frequency (BS = 4,9 ± 0,9 Hz vs HA = 6,9 ± 1,0 Hz; p < 0,05) ; ii) 21 neurons do not change the firing frequency (BS = 4,8 ± 0,5 Hz vs HA = 5,36 ± 0,6 Hz; p > 0,05) and iii) 7 neurons decreased the firing frequency (BS = 7,3 ± 1,1 Hz vs HA = 3,6 ± 0,7 Hz; p < 0,05). In the CIH group, the AH increased the firing rate comparing with basal condition (SB= 6,31 ± 0,7 Hz vs AH= 7,25 ± 0,8 Hz; n=31 - p < 0,05) and analyzing the pattern of action potential, AH revealed 2 subpopulations in this group: i) 9 neurons increased the firing frequency (SB = 4,7 ± 0,8 Hz vs AH = 8,2 ± 1,4 Hz; p < 0,05) and ii) 22 neurons do not change the firing frequency (SB = 7,0 ± 1,0 Hz vs AH = 6,8 ± 1,0 Hz; p > 0,05).. The data shows that AH revealed different subpopulations of presympathetic neurons and suggest that CIH plays a preconditioning in the intrinsic excitability of presympathetic neurons in response to acute hypoxia

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Nesse estudo investigamos os efeitos da hipóxia tecidual aguda (HA) sobre as propriedades eletrofisiológicas intrínsecas dos neurônios pré-simpáticos bulboespinhais da área rostro-ventrolateral do bulbo (RVLM) de ratos jovens adultos submetidos previamente à hipóxia crônica intermitente (HCI) e os seus respectivos controle. Para marcarmos os neurônios pré-simpáticos bulboespinhais da RVLM, ratos Wistar jovens (P19-P21) anestesiados com ketamina e xilazina, receberam microinjeções bilaterais de rodamina, um traçador fluorescente retrógrado, na coluna intermediolateral da medula espinhal (T3-T6) e 2 dias após a recuperação da cirurgia, os animais foram submetidos ao protocolo de HCI, enquanto que ratos controle foram mantidos em condições de normóxia, durante 10 dias. No décimo primeiro dia, os ratos foram novamente anestesiados para a remoção do cérebro e as fatias do tronco cerebral contendo neurônios pré-simpáticos com marcação positivas foram registrados. Utilizamos a técnica de whole cell patch-clamp para estudo das propriedades eletrofisiológicas desses neurônios. As propriedades eletrofisiológicas intrínsecas foram analisadas antes e após a HA, a qual foi produzida pela perfusão das fatias do tronco cerebral com uma solução hipóxica (95% N2 + 5% CO2) durante 2 minutos na presença de bloqueadores sinápticos excitatórios e inibitórios. Todos os neurônios pré-simpáticos apresentaram característica intrínseca de autodespolarização e a frequência de disparos basal de potenciais de ação (PAs) desses neurônios de ratos do grupo controle e HCI foram similares [Controle= 5,03 ± 0,4 Hz (n=39) vs HCI= 6,31 ± 0,7 Hz (n=31); p > 0,05]. No grupo controle, a HA não alterou a frequência média de disparos de PAs (BS = 5,03 ± 0,4 Hz vs HA = 5,24 ± 0,3 Hz (n=39); p > 0,05], porém revelou diferentes perfis de disparo de PAs após 2 min de exposição à HA: i) 11 neurônios com aumento na frequência de disparos (BS = 5,1 ± 0,7 Hz vs HA = 7 ± 0,7 Hz; p < 0,05]; ii) 21 neurônios sem alteração na frequência de disparos (BS = 4,8 ± 0,5 Hz vs HA = 5,36 ± 0,6 Hz; p > 0,05] e iii) 7 neurônios com diminuição na frequência de disparos (BS = 7,3 ± 1,1 Hz vs HA = 3,6 ± 0,7 Hz; p < 0,05). No grupo HCI, a HA produziu aumento na frequência média de disparos (BS= 6,31 ± 0,7 Hz vs HA= 7,25 ± 0,8 Hz; n=31 - p < 0,05) e na análise do perfil de disparo de PAs, a HA revelou 2 subpopulações: i) 9 neurônios com aumento na frequência de disparos (BS = 4,7 ± 0,8 Hz vs HA = 8,2 ± 1,4 Hz; p < 0,05) e ii) 22 neurônios sem alteração na frequência de disparos (BS = 7,0 ± 1,0 Hz vs HA = 6,8 ± 1,0 Hz; p > 0,05). Esse estudo nos permitiu revelar diferentes subpopulações de neurônios pré-simpáticos que responderam de forma distintas à HA. Os resultados também sugerem que a HCI teria um efeito pré- condicionante na excitabilidade intrínseca dos neurônios pré-simpáticos em resposta à HA / In this study we evaluated the effects of acute hypoxia (AH) on the intrinsic electrophysiological properties of presympathetic neurons from rostro ventrolateral medulla (RVLM) of juvenile rats exposed to chronic intermittent hypoxia (CIH) or normoxic condition (control group). To label the RVLM bulbospinal presympathetic neurons, young Wistar rats (P 19 - 21) anesthetized with ketamine and xylazine, received bilateral microinjections of a fluorescent retrograde tracer (rhodamine retrobeads) were performed into the intermediolateral column of spinal cord (T3-T6) and two days after recovery of the surgery, the animals were submitted to CIH or normoxic protocol, during 10 days. On the 11th day, under anesthesia, brainstem slices were obtained and only the labeled RVLM presympathetic neurons were recorded, using whole-cell patch-clamp approach to study the electrophysiological properties of these neurons. The intrinsic electrophysiological properties were analyzed before and after AH, which was produced by slice perfusion with hypoxic solution (95% N2 and 5% CO2) during 2 min in the presence of excitatory and inhibitory synaptic antagonists. All recorded RVLM presympathetic neurons presented intrinsic pacemaker activity and the baseline firing frequency of these neurons from control and CIH group were similar [Control= 5,03 ± 0,4 Hz (n=39) vs HCI= 6,31 ± 0,7 Hz (n=31); p > 0,05]. In the control group, AH do not change the firing rate (BS = 5,03 ± 0,4 Hz vs HA = 5,24 ± 0,3 Hz (n=39); p > 0,05), but revealed different pattern of firing frequency after 2 min of AH: i) 11 neurons increased the firing frequency (BS = 4,9 ± 0,9 Hz vs HA = 6,9 ± 1,0 Hz; p < 0,05) ; ii) 21 neurons do not change the firing frequency (BS = 4,8 ± 0,5 Hz vs HA = 5,36 ± 0,6 Hz; p > 0,05) and iii) 7 neurons decreased the firing frequency (BS = 7,3 ± 1,1 Hz vs HA = 3,6 ± 0,7 Hz; p < 0,05). In the CIH group, the AH increased the firing rate comparing with basal condition (SB= 6,31 ± 0,7 Hz vs AH= 7,25 ± 0,8 Hz; n=31 - p < 0,05) and analyzing the pattern of action potential, AH revealed 2 subpopulations in this group: i) 9 neurons increased the firing frequency (SB = 4,7 ± 0,8 Hz vs AH = 8,2 ± 1,4 Hz; p < 0,05) and ii) 22 neurons do not change the firing frequency (SB = 7,0 ± 1,0 Hz vs AH = 6,8 ± 1,0 Hz; p > 0,05).. The data shows that AH revealed different subpopulations of presympathetic neurons and suggest that CIH plays a preconditioning in the intrinsic excitability of presympathetic neurons in response to acute hypoxia

Post-traumatic stress disorder (PTSD) is a psychiatric condition caused by exposure to a traumatic event. Veterans are at especially high risk of PTSD. In Canada, in a survey conducted in 2016, 16% of Regular Force Veterans released during 1998-2015 reported having PTSD, which is at least two times higher than the estimated prevalence rate in the general population. Individuals with PTSD experience a range of debilitating symptoms, such as the intrusion of unwanted and distressing memories, persistent flashbacks, hypervigilance and nightmares. The neuropathophysiological mechanisms underlying symptoms of PTSD are not well understood, which remains a significant barrier to developing effective treatments. Hallmark PTSD symptoms such as hyperarousal and sleep disturbances may be related to dysregulation of noradrenaline (NA), a neurotransmitter produced in the locus coeruleus (LC) known to modulate cognition, arousal and sleep. This thesis examines the possible associations between dysregulation in rapid-eye-movement (REM) sleep and dysfunction in NA-containing neurons in the LC among veterans with PTSD. Twenty-two operationally deployed veterans with a history of PTSD were recruited through the Royal Ottawa Mental Health Centre in Ontario, Canada. A novel, non-invasive neuroimaging method, neuromelanin-sensitive magnetic resonance imaging (NM-MRI), was used to detect a by-product of NA called neuromelanin (NM) in the LC of each participant. Then a contrast-to-noise ratio (CNR) was calculated to obtain a marker of the NA function. The LC was segmented into three subdivisions to assess whether the association between NM and REM sleep may differ across regions of the LC. As hypothesized, we observed different associations between NM and REM sleep across regions of the LC. After controlling for antidepressant usage, there was (i) a moderate, negative, significant correlation between the percentage of REM sleep and rostral LCCNR, r(19) = -.476, p = .029, (ii) a weak positive non-significant correlation between the percentage of REM sleep and caudal LCCNR, r(19) = .33, p = .145, and (iii) no significant correlation between REM sleep percentage and LCCNR in the middle LC, r(19) = -.04, p = .876. This thesis is the first study to show that NM and REM sleep may be related in veterans with PTSD and that this relationship may vary across subdivisions of the LC. These results improve understanding of REM sleep among individuals with PTSD. The results may stimulate the investigation of novel pharmacotherapy focused on sleep disturbances in PTSD, the development of personalized treatments for PTSD, and the search for clinical biomarkers of PTSD based on brain function. The current study also made methodological contributions that may be applicable beyond the research on PTSD to the field of REM sleep and the NA system. Specifically, the current study showed the suitability of the NM-MRI method for examining the connections between NM and REM sleep, and it showed that segmenting the LC can lead to a more nuanced understanding of its role in the human body.