Dorsal periaqueductal gray stimulation facilitates anxiety-, but not panic-related, defensive responses in rats tested in the elevated T-maze

The escape response to electrical or chemical stimulation of the dorsal periaqueductal gray matter (DPAG) has been associated with panic attacks. In order to explore the validity of the DPAG stimulation model for the study of panic disorder, we determined if the aversive consequences of the electrical or chemical stimulation of this midbrain area can be detected subsequently in the elevated T-maze. This animal model, derived from the elevated plus-maze, permits the measurement in the same rat of a generalized anxiety- and a panic-related defensive response, i.e., inhibitory avoidance and escape, respectively. Facilitation of inhibitory avoidance, suggesting an anxiogenic effect, was detected in male Wistar rats (200-220 g) tested in the elevated T-maze 30 min after DPAG electrical stimulation (current generated by a sine-wave stimulator, frequency at 60 Hz) or after local microinjection of the GABA A receptor antagonist bicuculline (5 pmol). Previous electrical (5, 15, 30 min, or 24 h before testing) or chemical stimulation of this midbrain area did not affect escape performance in the elevated T-maze or locomotion in an open-field. No change in the two behavioral tasks measured by the elevated T-maze was observed after repetitive (3 trials) electrical stimulation of the DPAG. The results indicate that activation of the DPAG caused a short-lived, but selective, increase in defensive behaviors associated with generalized anxiety.

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 GABA A 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 GABA A receptors. Fear-induced defensive behavior organized by the posterior hypothalamus was more intense than that organized by dorsomedial hypothalamic nuclei. Escape behavior elicited by GABA A 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.

GABA in the central amygdaloid nucleus modulates the electrolyte excretion and hormonal responses to blood volume expansion in rats

We investigated the involvement of GABAergic mechanisms of the central amygdaloid nucleus (CeA) in unanesthetized rats subjected to acute isotonic or hypertonic blood volume expansion (BVE). Male Wistar rats bearing cannulas unilaterally implanted in the CeA were treated with vehicle, muscimol (0.2 nmol/0.2 µL) or bicuculline (1.6 nmol/0.2 µL) in the CeA, followed by isotonic or hypertonic BVE (0.15 or 0.3 M NaCl, 2 mL/100 g body weight over 1 min). The vehicle-treated group showed an increase in sodium excretion, urinary volume, plasma oxytocin (OT), and atrial natriuretic peptide (ANP) levels compared to control rats. Muscimol reduced the effects of BVE on sodium excretion (isotonic: 2.4 ± 0.3 vs vehicle: 4.8 ± 0.2 and hypertonic: 4.0 ± 0.7 vs vehicle: 8.7 ± 0.6 µEq·100 g-1·40 min-1); urinary volume after hypertonic BVE (83.8 ± 10 vs vehicle: 255.6 ± 16.5 µL·100 g-1·40 min-1); plasma OT levels (isotonic: 15.3 ± 0.6 vs vehicle: 19.3 ± 1 and hypertonic: 26.5 ± 2.6 vs vehicle: 48 ± 3 pg/mL), and ANP levels (isotonic: 97 ± 12.8 vs vehicle: 258.3 ± 28.1 and hypertonic: 160 ± 14.6 vs vehicle: 318 ± 16.3 pg/mL). Bicuculline reduced the effects of isotonic or hypertonic BVE on urinary volume and ANP levels compared to vehicle-treated rats. However, bicuculline enhanced the effects of hypertonic BVE on plasma OT levels. These data suggest that CeA GABAergic mechanisms are involved in the control of ANP and OT secretion, as well as in sodium and water excretion in response to isotonic or hypertonic blood volume expansion.

Agonistic-like responses from the torus semicircularis dorsalis elicited by GABA A blockade in the weakly electric fish Gymnotus carapo

Findings by our group have shown that the dorsolateral telencephalon of Gymnotus carapo sends efferents to the mesencephalic torus semicircularis dorsalis (TSd) and that presumably this connection is involved in the changes in electric organ discharge (EOD) and in skeletomotor responses observed following microinjections of GABA A antagonist bicuculline into this telencephalic region. Other studies have implicated the TSd or its mammalian homologue, the inferior colliculus, in defensive responses. In the present study, we explore the possible involvement of the TSd and of the GABA-ergic system in the modulation of the electric and skeletomotor displays. For this purpose, different doses of bicuculline (0.98, 0.49, 0.245, and 0.015 mM) and muscimol (15.35 mM) were microinjected (0.1 æL) in the TSd of the awake G. carapo. Microinjection of bicuculline induced dose-dependent interruptions of EOD and increased skeletomotor activity resembling defense displays. The effects of the two highest doses showed maximum values at 5 min (4.3 ± 2.7 and 3.8 ± 2.0 Hz, P < 0.05) and persisted until 10 min (11 ± 5.7 and 8.7 ± 5.2 Hz, P < 0.05). Microinjections of muscimol were ineffective. During the interruptions of EOD, the novelty response (increased frequency in response to sensory novelties) induced by an electric stimulus delivered by a pair of electrodes placed in the water of the experimental cuvette was reduced or abolished. These data suggest that the GABA-ergic mechanisms of the TSd inhibit the neural substrate of the defense reaction at this midbrain level.

Acute phenobarbital administration induces hyperalgesia: pharmacological evidence for the involvement of supraspinal GABA-A receptors

The aim of the present study was to determine if phenobarbital affects the nociception threshold. Systemic (1-20 mg/kg) phenobarbital administration dose dependently induced hyperalgesia in the tail-flick, hot-plate and formalin tests in rats and in the abdominal constriction test in mice. Formalin and abdominal constriction tests were the most sensitive procedures for the detection of hyperalgesia in response to phenobarbital compared with the tail-flick and hot-plate tests. The hyperalgesia induced by systemic phenobarbital was blocked by previous administration of 1 mg/kg ip picrotoxin or either 1-2 mg/kg sc or 10 ng icv bicuculline. Intracerebroventricular phenobarbital administration (5 æg) induced hyperalgesia in the tail-flick test. In contrast, intrathecal phenobarbital administration (5 æg) induced antinociception and blocked systemic-induced hyperalgesia in this test. We suggest that phenobarbital may mediate hyperalgesia through GABA-A receptors at supraspinal levels and antinociception through the same kind of receptors at spinal levels

The primate frontal eye field and the generation of saccadic eye movements: comparison of lesion and acute inactivation/activation studies

The frontal eye field (FEF) of monkeys has been repeatedly implicated in the generation of saccadic eye movements by various experimental approaches. Electrical stimulation of most of the FEF produces saccadic eye movements, many cells have activities related to saccades, and it has anatomical connections with many other oculomotor ares. Surprisingly, complete lesions of the FEF have remarkably little effect on oculomotor behavior. Only when more cognitive aspects are tested is a deficit clearly detected. In contrast, acute inactivation of the FEF on monkeys with the GABA agonist muscimol produced much more severe oculomotor impairment. This difference is probably due to the acute nature of the muscimol effect, which does not allow time for reorganization of the control of eye movements before testing begins. In addition, acute activation of the FEF with the GABA antagonist bicuculline caused the monkey to make irrepressible saccades of the same dimensions as those electrically elicited at the site. These experiments further confirm the strong involvement of the FEF in the control of saccadic eye movements and fixation.

Mecanismos de acción de la DL-4-hidroxi, 4-etil, 4-fenil butiramida (HEPP) sobre la actividad epileptiforme en el hipocampo / Mechanisms of action of DL-4-hydroxy, 4-ethyl, 4-phenyl butyramide (HEPB) on the epileptiform activity in the hippocampus

El objetivo del presente estudio fue el de explorar los mecanismos de acción del anticonvulsionante DL-4-hidroxy, 4-etil, 4-fenil butiramida (HEPB). En laminillas del hipocampo del cobayo se indujo actividad epileptiforme mediante la perfusión (15 min) de una concentración de 10mM de bicoculina en solución de Krebs conteniendo alto potasio (8mM). El registro extracelular de las descargas epileptiformes se llevó a cabo usando un electrómetro AC, y mediante electrodos de vidrio (NaCI 2 M, 5-10 M) colocados en el estrato piramidal de la región CA. A partir de los registros digitalizados, y mediante programas de computadora, se analizaron los efectos de HEPB (10-100mM, en solución de Krebs normal, por 6 min) sobre la frecuencia, índice de contorno, y amplitud de la poshiperpolarización de la descarga epileptiforme, cuya magnitud fue dependiente de la concentración. Dichos efectos se correlacionaron con un incremento en la amplitud de la poshiperpolarización de la descarga epileptiforme, sin cambio en el número o amplitud de las espigas por descarga. Estos resultados sugieren que HEPB podría ejercer una acción anticonvulsionante mediante el control de la frecuencia de la descarga epileptiforme a través de un incremento en la poshiper-polarización

Atividade epileptiforme interictal espontânea e ictal induzida no cérebro isolado in vitro da tartaruga / Spontaneous interictal and induced ictal epileptiform activity in the in vitro isolated turtle brain

Um dos principais objetivos da pesquisa experimental em epilepsia é o estudo dos mecanismos envolvidos nas descargas epilépticas ictais e interictais. A maioria dos estudos in vitro utilizam fatias de cérebro ("brain slices"), mas a atividade epileptiforme registrada geralmente é breve e mais se assemelha a atividade interictal. Velluti e colaboradores (1991) desenvolveram um modelo experimental in vitro que permite o registro prolongado dos potenciais extracelulares (EEG) e da atividade intracelular (MP). O objetivo do presente trabalho foi o de propor um modelo in vitro para estudo da atividade epileptiforme interictal e ictal. Os experimentos foram realizados utilizando espécimes juvenis da tartaruga de água doce Chrysemys dorbigni. O hemisfério cerebral isolado e aberto através de uma secçäo rostro-caudal na superfície lateral do encéfalo foi transferido para uma câmara de registro perfundidas com soluçäo de Ringer (1-1.5 ml/min), à temperatura ambiente (20-22-C). O córtex medial foi exposto para o posicionamento dos eletrodos de estimulaçäo de níquel-cromo e micropipetas de vidro para o registro do EEG e MP. Foram obtidos 43 registros estáveis da atividade de campo e intracelular. A adiçäo subsequente de bicuculina, antagonista do GABA, aumentou a freqüência de descarga em salva e induziu atividade epileptiforme ictal. As características celulares de epileptogênese (descargas em salva e desinibiçäo) foram identificadas neste modelo

Bases celulares da epilepsia / Cellulary bases of epilepsy

O conhecimento dos mecanismos básicos das epilepsias provém, geralmente, dos estudos em modelos animais. Há necessidade de entendimento da relaçäo entre esses modelos e a situaçäo clínica real. Com o objetivo de estudar as bases celulares da epilepsia Velluti e colaboradores (1991) (50) desenvolveram um modelo experimental para o estudo da epilepsia utilizando o hemisfério cerebral isolado in vitro da tartaruga, Chrysemys d'orbigny. Este modelo permite registros estáveis e prolongados da atividade de campo (EEG) e intracelular (MP) e sua correlaçäo. Descrevemos a atividade epileptiforme espontânea de tipo intercrítico ou induzida intercrítica e crítica no córtex medial in vitro. As características celulares da epileptogênese tais como as descargas em salva, a desinibiçäo e a excitaçäo recorrente foram identificadas nestes estudos. Realizamos uma breve revisäo dos mecanismos básicos que constituem o substrato celular da epilepsia a partir da sua identificaçäo nos registros intra e extracelulares que obtivemos durante as descargas interictais e ictais. Concluimos que cada modelo experimental de epilepsia apresenta suas particularidades e compreensäo dos mecanismos subjacentes nesta entidade requer conhecimento do comportamento neuronal

Behavioral effects of neurotensin applied to periventricular structures of rats

Neurotensin (NT), n active neuropeptide, and bicuculline, a GABA-A receptor antagonist, were microinjected into the rat hypothalaamus (MH) or the dorsal periaqueductal gray matter (DPAG). Bicuculline (80 pmol) produced behavioral activation which included jumping and NT (1-20 nmol) caused a dose-dependent behavioral activation accompanied by catalepsy rather than jumping. These results suggest that the behavioral activation produced by NT may be due to an interaction of the neuropeptide with specific receptors while its cataleptic effect may be attributed to the blockade of dopamine receptors

Increased susceptibility of detelencephalated rats to audiogenic seizures induced by microinjection of bicuculline into the inferior colliculus

The participation of telencephalic forebrain structures in the induction of audiogenic seizure (AGS) susceptibility and in the behavioral expression of AGS was investigated in rats. Rats that were initially susceptible (N = 12) or non-susceptible (N = 28) to audiogenic seizure were surgically detelencephalated. A unilateral microinjection of a low dose (30 pmol) of the GABA antagonist bicuculline methiodide (BM) was applied to the inferior colliculus (IC) before the animals were exposed to a 120-dB acoustic stimulus. All susceptible rats still exhibited all components of audiogenic seizure after removal of the telencephalon. After BM microinjection, a higher incidence (66% vs 41%) and shorter latencies (6-20 s vs 9-55) s) of occurrence of tonic seizures were observed in the detelencephalated non-susceptible rats when compared to non-operated non-susceptible rats(N = 12). These results suggest that the induction of the behavioral expression of audiogenic seizures issubserved by brain stem neuronal networks but does not require the telencephalon and that telencephalic structures may exert control over audiogenic seizures by inhibiting IC cells through GABAergic neurons

Gabaergic fibers from substantia nigra para reticulata modulate escape bahavior induced by midbrain central gray stimulation

Eletrical stimulation or microinjection of GABA antagonists into the dorsal periaqueductal gray (DPAG) produces escape behavior. In order to determine whether the nigrocollicular gabaergic fibers exert some control over this behavior, rats bearing kainic acid lesion of the substantia nigra pars reticulata were submitted to microinjections of bicuculline or electrical stimulation of the DPAG at the escape threshold. Rats thus treated exhibited a significant decrease in the escape threshold while bicuculline increased the expression of flight behavior. These results suggest an inhibitory control of gabaergic fibers from the substantia nigra pars reticulata on aversive behavior induced by DPAG stimulation

Citrate Synthase ande lactate dehydrogenase activities in rat cerebral cortex following the administration of the convulsants bicuculline and 3-mercaptopropionic acid

La administración intraperitoneal de bicuculina (Bic) y ácido 3-mercaptopropiónico (MP) produce convulsiones generalizadas en animales de laboratorio. En este trabajo se estudió el efecto de estos convulsivantes sobre la actividad de la lactato deshidrogenasa y de citrato sintasa de corteza cerebral de rata. La Bic se administró en dosis de1.0 mg/Kg (subconvulsiva) y 7.5 mg/Kg (convulsiva) y el MP en dosis de 150 mg/Kg (convulsiva). La actividad de lactato deshidrogenasa en fracciones solubre y particulada de corteza cerebral no se modificó por la administración de Bic o MP. La actividad de citrato sintasa en homogeneizados de corteza cerebral aumentó alrededor del 40% por la administración de Bic en dosis subconvulsiva y convulsiva; un aumento semejante se encontró por la administración de MP. No se encontró modificación en la actividad de la enzima hepática, sugiriendo especificidad de tejido. La mayor actividad de citrato sintasa en homogeneizados de corteza cerebral encontrada luego de la administración de los convulsivantes se correlaciona con el aumento en los niveles de citrato cerebral descriptos en estados convulsivos