Juliana Almeida da Silva

Panic-like defensive behavior but not fear-induced antinociception is differently organized by dorsomedial and posterior hypothalamic nuclei of Rattus norvegicus (Rodentia, Muridae)

The hypothalamus is a forebrain structure critically involved in the organization of defensive responses to aversive stimuli. Gamma-aminobutyric acid (GABA)ergic dysfunction in dorsomedial and posterior hypothalamic nuclei is implicated in the origin of panic-like defensive behavior, as well as in pain modulation. The present study was conducted to test the difference between these two hypothalamic nuclei regarding defensive and antinociceptive mechanisms. Thus, the GABAA antagonist bicuculline (40 ng/0.2 µL) or saline (0.9% NaCl) was microinjected into the dorsomedial or posterior hypothalamus in independent groups. Innate fear-induced responses characterized by defensive attention, defensive immobility and elaborate escape behavior were evoked by hypothalamic blockade of GABAA receptors. Fear-induced defensive behavior organized by the posterior hypothalamus was more intense than that organized by dorsomedial hypothalamic nuclei. Escape behavior elicited by GABAA receptor blockade in both the dorsomedial and posterior hypothalamus was followed by an increase in nociceptive threshold. Interestingly, there was no difference in the intensity or in the duration of fear-induced antinociception shown by each hypothalamic division presently investigated. The present study showed that GABAergic dysfunction in nuclei of both the dorsomedial and posterior hypothalamus elicit panic attack-like defensive responses followed by fear-induced antinociception, although the innate fear-induced behavior originates differently in the posterior hypothalamus in comparison to the activity of medial hypothalamic subdivisions.

Cellular prion protein regulates the motor behaviour performance and anxiety-induced responses in genetically modified mice.

The cellular prion protein (PrP(C)) is a sialoglycoprotein involved in neuroplasticity processes and synaptic transmission. This study investigated behavioural responses (balance in the rota-rod test at 24 rpm, motility in the open-field test, anxiety in the elevated plus-maze test) in Zurich developed wild-type adult mice (WT, controls of normal PrP(C) expression), in knockout (KO) mice (Prnp(0/0), with no PrP(C) expression), and in PrP(C) overexpressing Tg-20 mice. After 8 min in the rota-rod test, Tg-20 animals presented significantly fewer falls (1.08+/-1.56 falls) than both WT (7.27+/-4.36) and KO (7.6+/-6.15) mice (p<0.01). In the open field test, Tg-20 animals showed significantly increased motility [rearing=23.4+/-7.85, crossing=97.30+/-32.11) when compared with KO mice (rearing=5.45+/-3.69 and crossing=59.73+/-15.43) or WT mice (rearing=6.5+/-20.23 and crossing=45.18+/-20.33) (p<0.01). In the elevated plus-maze test, Tg-20 mice showed less anxiety (head projections=7.3+/-1.62) when compared with WT animals (3.38+/-0.67) (p<0.05). Moreover, KO mice spent more time in the centre of the plus maze (37.80+/-5.57 s) than did WT mice (22.57+/-3.82) (p<0.05). PrP(C) overexpressing mice evoked increased motility, less anxiety, and increased equilibrium when compared with WT control animals in the behavioural protocols used. KO animals also tended to evoke fewer anxiety-related responses in the elevated plus-maze test. These findings indicate that the levels of PrP(C) in adult life are associated with possible changes in motility, anxiety, and equilibrium.

5-Hydroxytryptamine(1A) receptors in the dorsomedial hypothalamus connected to dorsal raphe nucleus inputs modulate defensive behaviours and mediate innate fear-induced antinociception

The dorsal raphe nucleus (DRN) is an important brainstem source of 5-hydroxytryptamine (5-HT), and 5-HT plays a key role in the regulation of panic attacks. The aim of the present study was to determine whether 5-HT1A receptor-containing neurons in the medial hypothalamus (MH) receive neural projections from DRN and to then determine the role of this neural substrate in defensive responses. The neurotracer biotinylated dextran amine (BDA) was iontophoretically microinjected into the DRN, and immunohistochemical approaches were then used to identify 5HT1A receptor-labelled neurons in the MH. Moreover, the effects of pre-treatment of the dorsomedial hypothalamus (DMH) with 8-OH-DPAT and WAY-100635, a 5-HT1A receptor agonist and antagonist, respectively, followed by local microinjections of bicuculline, a GABAA receptor antagonist, were investigated. We found that there are many projections from the DRN to the perifornical lateral hypothalamus (PeFLH) but also to DMH and ventromedial (VMH) nuclei, reaching 5HT1A receptor-labelled perikarya. DMH GABAA receptor blockade elicited defensive responses that were followed by antinociception. DMH treatment with 8-OH-DPAT decreased escape responses, which strongly suggests that the 5-HT1A receptor modulates the defensive responses. However, DMH treatment with WAY-100635 failed to alter bicuculline-induced defensive responses, suggesting that 5-HT exerts a phasic influence on 5-HT1A DMH neurons. The activation of the inhibitory 5-HT1A receptor had no effect on antinociception. However, blockade of the 5-HT1A receptor decreased fear-induced antinociception. The present data suggest that the ascending pathways from the DRN to the DMH modulate panic-like defensive behaviours and mediate antinociceptive phenomenon by recruiting 5-HT1A receptor in the MH.

Dissociation between the panicolytic effect of cannabidiol microinjected into the substantia nigra, pars reticulata, and fear-induced antinociception elicited by bicuculline administration in deep layers of the superior colliculus: The role of CB1-cannabinoid receptor in the ventral mesencephalon

Many studies suggest that the substantia nigra, pars reticulata (SNpr), a tegmental mesencephalic structure rich in γ-aminobutyric acid (GABA)- and cannabinoid receptor-containing neurons, is involved in the complex control of defensive responses through the neostriatum-nigral disinhibitory and nigro-tectal inhibitory GABAergic pathways during imminently dangerous situations. The aim of the present work was to investigate the role played by CB1-cannabinoid receptor of GABAergic pathways terminal boutons in the SNpr or of SNpr-endocannabinoid receptor-containing interneurons on the effect of intra-nigral microinjections of cannabidiol in the activity of nigro-tectal inhibitory pathways. GABAA receptor blockade in the deep layers of the superior colliculus (dlSC) elicited vigorous defensive behaviour. This explosive escape behaviour was followed by significant antinociception. Cannabidiol microinjection into the SNpr had a clear anti-aversive effect, decreasing the duration of defensive alertness, the frequency and duration of defensive immobility, and the frequency and duration of explosive escape behaviour, expressed by running and jumps, elicited by transitory GABAergic dysfunction in dlSC. However, the innate fear induced-antinociception was not significantly changed. The blockade of CB1 endocannabinoid receptor in the SNpr decreased the anti-aversive effect of canabidiol based on the frequency and duration of defensive immobility, the frequency of escape expressed by running, and both the frequency and duration of escape expressed by jumps. These findings suggest a CB1 mediated endocannabinoid signalling in cannabidiol modulation of panic-like defensive behaviour, but not of innate fear-induced antinociception evoked by GABAA receptor blockade with bicuculline microinjection into the superior colliculus, with a putative activity in nigro-collicular GABAergic pathways.

Panicolytic-like effects caused by substantia nigra pars reticulata pretreatment with low doses of endomorphin-1 and high doses of CTOP or the NOP receptors antagonist JTC-801 in male Rattus norvegicus

RationaleGamma-aminobutyric acid (GABA)ergic neurons of the substantia nigra pars reticulata (SNpr) are connected to the deep layers of the superior colliculus (dlSC). The dlSC, in turn, connect with the SNpr through opioid projections. Nociceptin/orphanin FQ peptide (N/OFQ) is a natural ligand of a Gi protein-coupled nociceptin receptor (ORL1; NOP) that is also found in the SNpr. Our hypothesis is that tectonigral opioid pathways and intranigral orphanin-mediated mechanisms modulate GABAergic nigrotectal connections.ObjectivesTherefore, the aim of this work was to study the role of opioid and NOP receptors in the SNpr during the modulation of defence reactions organised by the dlSC.MethodsThe SNpr was pretreated with either opioid or NOP receptor agonists and antagonists, followed by dlSC treatment with bicuculline.ResultsBlockade of GABAA receptors in the dlSC elicited fear-related defensive behaviour. Pretreatment of the SNpr with naloxone benzoylhydrazone (NalBzoH), a μ-, δ-, and κ1-opioid receptor antagonist as well as a NOP receptor antagonist, decreased the aversive effect of bicuculline treatment on the dlSC. Either μ-opioid receptor activation or blockade by SNpr microinjection of endomorphin-1 (EM-1) and CTOP promoted pro-aversive and anti-aversive actions, respectively, that modulated the defensive responses elicited by bicuculline injection into the dlSC. Pretreatment of the SNpr with the selective NOP receptor antagonist JTC801 decreased the aversive effect of bicuculline, and microinjections of the selective NOP receptor agonist NNC 63-0532 promoted the opposite effect.ConclusionsThese results demonstrate that opioid pathways and orphanin-mediated mechanisms have a critical role in modulating the activity of nigrotectal GABAergic pathways during the organisation of defensive behaviours.

Blockade of synaptic activity in the neostriatum and activation of striatal efferent pathways produce opposite effects on panic attack-like defensive behaviours evoked by GABAergic disinhibition in the deep layers of the superior colliculus

The dorsal periaqueductal grey matter (dPAG) and the deep layers of the superior colliculus (dlSC) have been implicated in the organisation of innate fear-related defensive behaviours. Furthermore, GABAergic neurons from the substantia nigra pars reticulata (SNpr) connected to the dlSC and dPAG receive convergent disinhibitory inputs from the caudate-putamen (CPu), comprising the neostriatum, and modulate defence responses elicited by midbrain tectum stimulation. The purpose of this work was to study the effect of either excitatory cortico-neostriatal input blockade or neostriato-nigral GABAergic disinhibitory output activation on the responsivity of GABAergic nigro-collicular tonic inhibitory pathways during the elicitation of panic attack-like defensive responses produced by bicuculline administration into the dlSC. Thus, we investigated the effects of microinjection of either the synaptic activity blocker cobalt chloride (CoCl2) or the NMDA receptor agonist N-methyl-D-aspartic acid in the CPu on the elaboration of the defensive behaviour elicited by the selective blockade of GABAA receptors in the dlSC. Our findings showed that pretreatment of the neostriatum with CoCl2 caused clear anxiolytic and panicolytic-like effects, reducing the incidence and duration of alertness and diminishing defensive immobility and explosive escape responses. On the other hand, pretreatment of the neostriatum with NMDA (40 nmol) caused a pro-aversive effect, enhancing running and jumping responses elicited by GABAergic disinhibition in the dlSC. We conclude from the data that the neostriato-nigral disinhibitory and nigro-collicular inhibitory GABAergic pathways modulate innate fear and panic attack-like responses organised by dlSC neurons.