Karen Gale

Spinal cord contusion in the rat: Behavioral analysis of functional neurologic impairment☆

A graded spinal cord injury in rats was produced by dropping a 10-g weight from 2.5, 5.0, 10,0, or 17.5 cm onto the exposed dura at the T8 vertebral level. Groups of rats (N = 10) for each of these weight drop (WD) levels as well as unoperated and WD controls (0 cm) were subjected to behavioral analysis that included evaluation of simple and complex reflexes as well as spontaneous and evoked motor patterns. On the basis of this analysis, we developed a protocol for evaluating functional deficits that follow spinal cord injury in the rat. The resulting combined behavioral score, a measure of functional deficit, closely correlated with the magnitude of the mechanical injury. The protocol used for neurologic assessment was administered routinely by personnel who were easily and rapidly trained. It should therefore prove useful in detecting the effects of treatment on recovery of function in a rat model of spinal cord injury.

Progression and Generalization of Seizure Discharge: Anatomical and Neurochemical Substrates

Summary: Seizure activity is generated and propagated by specific subcortical circuits. The substantia nigra (SN) and the area tempestas (AT) have been identified as two exemplary substrates for the control of experimental seizures. In animal models, GABAergic transmission has been shown to protect against seizures of different origins and methods of induction. Neuroactive peptides and excitatory amino acids may work with GABA in the SN to control the propagation of a wide variety of seizure types. In contrast, inhibition of AT pons selectively protects against seizures associated with limbic circuits. The AT is also a site from which bilaterally synchronous convulsions can be triggered in response to manipulations of cholinergic, GABAergic, and excitatory amino acid receptors. Definition of other pathways of seizure development and the effects of pharmacologic treatments on discrete brain regions await further research efforts.

Substantia nigra-mediated anticonvulsant actions: Role of nigral output pathways

Bilateral ablation of the superior colliculus in rats abolished the anticonvulsant effect of muscimol, a gamma-aminobutyric acid (GABA) agonist, infused into the substantia nigra. Our data indicate that the ability of intranigral muscimol to protect against maximal electroshock convulsions requires the integrity of the nigrotectal pathway. We present evidence that the nigrotegmental, nigrothalamic, and nigrostriatal projections do not appear to contribute to the nigral-evoked attenuation of electroshock convulsions. Inasmuch as the nigrotectal pathway utilizes the inhibitory neurotransmitter GABA, we hypothesize that the anticonvulsant effect of nigral manipulations in the electroshock test is a result of the disinhibition of neurons in the superior colliculus, the firing of which must therefore be capable of suppressing or disrupting electroshock-induced convulsions.

Dynamic utilization of GABA in substantia nigra: regulation by dopamine and GABA in the striatum, and its clinical and behavioral implications

The neural circuitry of the basal ganglia provides a challenging framework in which to consider the role and regulation of GABA-containing synapses. GABA-containing neurons and terminals are located throughout the various nuclei of the basal ganglia, including caudate and putamen (together referred to as ‘striatum’), globus pallidus, and substantia nigra (SN). In fact, the concentration of GABA in the SN is the highest of all brain areas. In this system we can find an excellent example of a ‘long-distance’ GABAergic neural pathway projecting from the striatum to the SN, as well as a significant population of smaller GABAergic neurons intrinsic to the striatum (interneurons). Moreover, it is likely that the various GABA neurons in the basal ganglia are involved in circuits in which they mutually regulate each other’s activity, as well as the activity of neurons containing other neurotransmitters. At the same time, these GABAergic neurons are subject to the control and influence of several pathways which converge on the striatum; in this context they may serve a significant integrating function.

Lesions of substantia nigra protect against experimentally induced seizures

Bilateral lesions of substantia nigra (SN) were evaluated for anticonvulsant effects in rats. Electrolytic and kainic acid lesions of SN reduced bicuculline-elicited seizure activity; lesions in the ventral midbrain tegmentum adjacent to SN were without an anticonvulsant effect. Lesions of SN also reduced the incidence and duration of tonic hindlimb extension in the maximal electroshock seizure test. Bilateral SN lesions appeared to decrease seizure susceptibility to a given stimulus intensity rather than altering the motor pattern of the seizures. Our results support the view that SN efferents constitute a critical gating mechanism in the propagation of seizure activity.

Regulation of limbic motor seizures by GABA and glutamate transmission in nucleus tractus solitarius.

Summary: Purpose: The nucleus of the solitary tract (NTS) is a primary site at which vagal afferents terminate. Because afferent vagal nerve stimulation has been demonstrated to have anticonvulsant effects, it is likely that changes in synaptic transmission in the NTS can regulate seizure susceptibility. We tested this hypothesis by examining the influence of γ‐amino‐butyric acid (GABA) ergic and glutamatergic transmission in the NTS on seizures evoked by systemic and focal bicuculline and systemic pentylenetetrazol (PTZ) in rats.

Role of excitatory amino acid transmission in the genesis of seizures elicited from the deep prepiriform cortex

Previous studies in our laboratory have shown that bilateral motor seizures can be elicited from a discrete site within the deep prepiriform cortex (DPC) after a single, unilateral microinjection of picomole amounts of bicuculline, carbachol or kainic acid. The present work shows that 2-amino-7-phosphonoheptanoic acid (2-APH), a specific antagonist of receptors activated by n-methyl-D-aspartic acid (NMDA), when microinjected into DPC reduces the incidence of clonic seizures elicited by bicuculline, carbachol or kainic acid microinjected into the same site. In addition, NMDA, aspartate and glutamate unilaterally microinjected into DPC produces bilateral motor seizures comparable to those elicited by bicuculline, carbachol or kainic acid. These data suggest that activation of excitatory amino acid receptors is both necessary and sufficient for evoking seizures from DPC.

Intracerebral injection of caspase-3 inhibitor prevents neuronal apoptosis after kainic acid-evoked status epilepticus

In the aftermath of prolonged continuous seizure activity (status epilepticus, SE), neuronal cell death occurs in the brain regions through which the seizure propagates. Recent studies have implicated apoptotic processes in this seizure-related injury. Because activation of caspase-3-like cysteine proteases plays a crucial role in mammalian neuronal apoptosis, we explored the possibility that activation of caspase-3 is involved in the neuronal apoptotic cell death that occurs in rat brain following SE induced by systemic kainic acid. Caspase-3 activity was determined immunocytochemically using CM1 antibodies specific for catalytically active subunit (p17) of the enzyme. We found an induction of caspase-3 activity in rhinal cortex and amygdala at 24 h after SE. To determine whether activation of caspase-3-like proteases is a necessary component of the injury process, we delivered a caspase-3 inhibitor, z-DEVD-fmk, into the lateral ventricle prior to, and following SE. z-DEVD-fmk treatment substantially attenuated apoptotic cell death after SE, both in hippocampus and rhinal cortex, as evaluated by analysis of internucleosomal DNA fragmentation and neuronal nuclear morphology. Our findings implicate caspase-3 cysteine protease in the neurodegenerative response to SE and suggest that this degeneration can be attenuated by inhibition of caspase-3-like enzyme activity.

Anticonvulsant effect of fluoxetine on focally evoked limbic motor seizures in rats

Summary: Fluoxetine was evaluated for anticonvulsant effects in a rat model of focally evoked complex partial seizures (CPS) secondarily generalized. Fluoxetine was administered intraperitoneally (i.p.) 1 h before seizures were induced by focal intracerebral application of the GABAA receptor antagonist, bicuculline methiodide (118 pmol) unilaterally into a discrete epileptogenic site in the deep prepiriform cortex (“area tempestas,” AT) of rats. Significant dose‐dependent protection from clonic motor seizures was obtained after 5‐, 10‐, and 20‐mg/kg doses of fluoxetine, with 50% protection occurring after the 5‐mg/kg dose. Suppression of electrographic seizure activity was concomitant with suppression of motor seizures. These observations support and extend previous findings of other investigators who showed that fluoxetine exerts anticonvulsant actions against maximal electroshock (MES) convulsions and audiogenic convulsions in genetically seizure‐prone rodents.

Basic fibroblast growth factor mRNA increases in specific brain regions following convulsive seizures

Basic fibroblast growth factor (bFGF) is a trophic factor synthesized in the central nervous system (CNS), where it is believed to play a role in neuronal maintenance and repair. Little is known about the regulation of this growth factor in the CNS. To determine whether the expression of the bFGF gene in the brain of adult animals changes in response to alterations of neuronal activity, we examined bFGF mRNA levels in several brain regions of rats experiencing focally-evoked convulsive seizures. Seizures were induced by microinjecting bicuculline unilaterally into an epileptogenic site within the deep prepiriform cortex, area tempestas (AT). By 5 h after initiation of brief limbic motor seizures from AT, there was a four fold increase in the levels of bFGF mRNA in the entorhinal cortex, hippocampus and olfactory bulb, but not in the caudate-putamen. The maximal expression of bFGF mRNA was reached by 10 h after seizure onset. In the same animals, the mRNA encoding nerve growth factor (NGF) was increased in entorhinal cortex and hippocampus, but not in the olfactory bulb. Our results demonstrate that neuronal activity can influence bFGF expression in an anatomically selective fashion and that acute changes in bFGF can occur in the uninjured mature brain. The increase in bFGF expression in response to excessive activation of specific neuronal circuitry may represent an adaptive response to protect against potential injury in those circuits.