Cholecystokinin and cholecystokinin antagonists enhance postsynaptic excitability in the dentate gyrus

Epileptogenesis and chronic seizures in a mouse model of temporal lobe epilepsy are associated with distinct EEG patterns and selective neurochemical alterations in the contralateral hippocampus

Major aspects of temporal lobe epilepsy (TLE) can be reproduced in mice following a unilateral injection of kainic acid into the dorsal hippocampus. This treatment induces a non-convulsive status epilepticus and acute lesion of CA1, CA3c and hilar neurons, followed by a latent phase with ongoing ipsilateral neuronal degeneration. Spontaneous focal seizures mark the onset of the chronic phase. In striking contrast, the ventral hippocampus and the contralateral side remain structurally unaffected and seizure-free. In this study, functional and neurochemical alterations of the contralateral side were studied to find candidate mechanisms underlying the lack of a mirror focus in this model of TLE. A quantitative analysis of simultaneous, bilateral EEG recordings revealed a significant decrease of theta oscillations ipsilaterally during the latent phase and bilaterally during the chronic phase. Furthermore, the synchronization of bilateral activity, which is very high in control, was strongly reduced already during the latent phase and the decrease was independent of recurrent seizures. Immunohistochemical analysis performed in the contralateral hippocampus of kainate-treated mice revealed reduced calbindin-labeling of CA1 pyramidal cells; down-regulation of CCK-8 and up-regulation of NPY-labeling in mossy fibers; and a redistribution of galanin immunoreactivity. These changes collectively might limit neuronal excitability in CA1 and dentate gyrus, as well as glutamate release from mossy fiber terminals. Although these functional and neurochemical alterations might not be causally related, they likely reflect long-ranging network alterations underlying the independent evolution of the two hippocampal formations during the development of an epileptic focus in this model of TLE.

Altered hippocampal expression of neuropeptides in seizure-prone GALR1 knockout mice

PURPOSE

Mice carrying a deletion of the GALR1 galanin receptor have recently showed spontaneous seizure phenotype with 25% penetrance. To better understand the role of neuropeptides, which are known to undergo complex plasticity changes with development of epileptic seizures, we characterized their expression in the hippocampal formation in GALR1- knockout (-KO) mice with or without seizures and in wild-type (WT) mice.

METHODS

Immunohistochemistry and in situ hybridization were used to study expression of galanin, neuropeptide Y (NPY), substance P, enkephalin, dynorphin, and cholecystokinin (CCK).

RESULTS

In GALR1-KO mice that had been displaying seizures, a strong upregulation of galanin immunoreactivity (ir) and messenger RNA (mRNA) was found in the polymorph layer of the dentate gyrus; galanin-ir also appeared in a dense fiber network in the supragranular layer. A strong upregulation of enkephalin was found in the granule cells/mossy fibers, whereas dynorphin mRNA levels were modestly decreased. NPY was strongly expressed in the granule cells/mossy fibers, and an increase of NPY mRNA levels in the polymorph cells was paralleled by an increase of NPY-ir in the molecular layer. An upregulation of substance P-ir was confined to the fibers in the granule and molecular layers, whereas substance P mRNA was increased in the cells of the polymorph layer. Both CCK-ir and mRNA were strongly downregulated in the granule cell/mossy fiber system, but CCK-ir appeared increased in the supragranular and molecular layers. No changes in neuropeptide-ir were found in GALR1-KO mice not displaying seizures.

CONCLUSIONS

Complex changes in neuropeptide expression in some principal hippocampal neurons and interneurons appear as a characteristic feature of the spontaneous-seizure phenotype in GALR1-KO mice. However, to what extent causal relations exist between this "epilepsia peptidergic profile" and development of seizures requires further clarification.

rCBF differences between panic disorder patients and control subjects during anticipatory anxiety and rest

BACKGROUND

Our goal was to identify brain structures involved in anticipatory anxiety in panic disorder (PD) patients compared to control subjects.

METHODS

Seventeen PD patients and 21 healthy control subjects were studied with H(2)(15)O positron emission tomography scan, before and after a pentagastrin challenge.

RESULTS

During anticipatory anxiety we found hypoactivity in the precentral gyrus, the inferior frontal gyrus, the right amygdala, and the anterior insula in PD patients compared to control subjects. Hyperactivity in patients compared to control subjects was observed in the parahippocampal gyrus, the superior temporal lobe, the hypothalamus, the anterior cingulate gyrus, and the midbrain. After the challenge, the patients showed decreases compared to the control subjects in the precentral gyrus, the inferior frontal gyrus, and the anterior insula. Regions of increased activity in the patients compared to the control subjects were the parahippocampal gyrus, the superior temporal lobe, the anterior cingulate gyrus, and the midbrain.

CONCLUSIONS

The pattern of regional cerebral blood flow activations and deactivations we observed both before and after the pentagastrin challenge was the same, although different in intensity. During anticipatory anxiety more voxels were (de)activated than during rest after the challenge.

Cholecystokinin modulation of spontaneous and excitatory amino acid-induced activity in the opossum cerebellum

Cholecystokinin-B (CCK-8) is an octapeptide that was initially described in the gastrointestinal tract. Recent studies have shown that this peptide also has an extensive distribution in the central nervous system, including the cerebellum of the opossum. In addition to the protein, binding sites for CCK-8 also have been described in the granule cell and molecular layer of this species. These anatomical data suggest that CCK-8 has a functional role in cerebellar circuitry. In the present study we have determined the physiological effects of CCK-8 on spontaneous and amino acid-induced activity. The results indicate that this peptide has both excitatory and inhibitory effects on spontaneous activity as well as the excitatory responses elicited by application of the excitatory amino acids aspartate, glutamate and quisqualate. The data suggest that CCK-8 may influence more than one population of cerebellar neurons. The findings support a neuromodulatory role for this peptide in cerebellar circuitry.

Effects of ceruletide and haloperidol on auditory evoked potentials in the cat brain

The influence of cholecystokinin-like peptide, ceruletide, on EEG and auditory evoked potentials (AEPs) was studied in nine cats. The cats were bearing electrodes implanted in the auditory cortex, hippocampus, reticular formation and cerebellum. Reference drugs used were haloperidol and neostigmine. The hippocampus showed the strongest effect of ceruletide, whereas the cerebellum was virtually unresponsive. The amplitude of AEPs was increased by peptide, an effect lasting up to 21 days which, according to amplitude frequency analysis (AFC) was due to an augmented theta response. The latter possibly indicates increased signal transfer to, or through, the brain structure in question, particularly in the hippocampal neurons. The effects of haloperidol and neostigmine did not reflect those of ceruletide and lasted only a few hours.

Pentagastrin induced panic attacks: enhanced sensitivity in panic disorder patients

The effects of pentagastrin, a synthetic analogue of the cholecystokinin tetrapeptide (CCK4), were studied in 15 patients with panic disorder and 15 healthy controls. Three different intravenous dosages of pentagastrin (0.1, 0.3 and 0.6 microgram/kg) and saline were investigated. Subjects were randomly allocated to two of the four treatment groups and tested on two separate occasions, 1 week apart, using an unbalanced double-blind incomplete block design. The mean panic rate with pentagastrin was 55% (12/22) for patients and 5% (1/22) for controls. None of the subjects panicked with saline. The frequency of panic attacks between the three pentagastrin doses in patients was not different. One control subject had a panic-like attack at the highest dose of pentagastrin. These findings concur with previous studies on the panicogenic effect of CCK4 and pentagastrin and suggest a greater sensitivity for CCK receptor agonists in patients suffering from panic disorder than in healthy controls.