Medial septal cholinergic neurons modulate isoflurane anesthesia.

BACKGROUND: Cholinergic drugs are known to modulate the response of general anesthesia. However, the sensitivity of isoflurane or other volatile anesthetics after selective lesion of septal cholinergic neurons that project to the hippocampus is not known. METHODS: Male Long Evans rats had 192 immunoglobulin G-saporin infused into the medial septum (n = 10), in order to selectively lesion cholinergic neurons, whereas control, sham-lesioned rats were infused with saline (n = 12). Two weeks after septal infusion, the hypnotic properties of isoflurane and ketamine were measured using a behavioral endpoint of loss of righting reflex (LORR). Septal lesion was assessed by counting choline acetyltransferase-immunoreactive cells and parvalbumin-immunoreactive cells. RESULTS: Rats with 192 immunoglobulin G-saporin lesion, as compared with control rats with sham lesion, showed a 85% decrease in choline acetyltransferase-immunoreactive, but not parvalbumin-immunoreactive, neurons in the medial septal area. Lesioned as compared with control rats showed increased isoflurane sensitivity, characterized by a leftward shift of the graph plotting cumulative LORR percent with isoflurane dose. However, lesioned and control rats were not different in their LORR sensitivity to ketamine. When administered with 1.375% isoflurane, LORR induction time was shorter, whereas emergence time was longer, in lesioned as compared with control rats. Hippocampal 62-100 Hz gamma power in the electroencephalogram decreased with isoflurane dose, with a decrease that was greater in lesioned (n = 5) than control rats (n = 5). CONCLUSIONS: These findings suggest a role of the septal cholinergic neurons in modulating the sensitivity to isoflurane anesthesia, which affects both induction and emergence. The sensitivity of hippocampal gamma power to isoflurane appears to indicate anesthesia (LORR) sensitivity.

Septohippocampal GABAergic neurons mediate the altered behaviors induced by n-methyl-D-aspartate receptor antagonists.

We hypothesize that selective lesion of the septohippocampal GABAergic neurons suppresses the altered behaviors induced by an N-methyl-D-aspartate (NMDA) receptor antagonist, ketamine or MK-801. In addition, we hypothesize that septohippocampal GABAergic neurons generate an atropine-resistant theta rhythm that coexists with an atropine-sensitive theta rhythm in the hippocampus. Infusion of orexin-saporin (ore-SAP) into the medial septal area decreased parvalbumin-immunoreactive (GABAergic) neurons by ~80%, without significantly affecting choline-acetyltransferase-immunoreactive (cholinergic) neurons. The theta rhythm during walking, or the immobility-associated theta induced by pilocarpine, was not different between ore-SAP and sham-lesion rats. Walking theta was, however, more disrupted by atropine sulfate in ore-SAP than in sham-lesion rats. MK-801 (0.5 mg/kg i.p.) induced hyperlocomotion associated with an increase in frequency, but not power, of the hippocampal theta in both ore-SAP and sham-lesion rats. However, MK-801 induced an increase in 71-100 Hz gamma waves in sham-lesion but not ore-SAP lesion rats. In sham-lesion rats, MK-801 induced an increase in locomotion and an impairment of prepulse inhibition (PPI), and ketamine (3 mg/kg s.c.) induced a loss of gating of hippocampal auditory evoked potentials. MK-801-induced behavioral hyperlocomotion and PPI impairment, and ketamine-induced auditory gating deficit were reduced in ore-SAP rats as compared to sham-lesion rats. During baseline without drugs, locomotion and auditory gating were not different between ore-SAP and sham-lesion rats, and PPI was slightly but significantly increased in ore-SAP as compared with sham lesion rats. It is concluded that septohippocampal GABAergic neurons are important for the expression of hyperactive and psychotic symptoms an enhanced hippocampal gamma activity induced by ketamine and MK-801, and for generating an atropine-resistant theta. Selective suppression of septohippocampal GABAergic activity is suggested to be an effective treatment of some symptoms of schizophrenia.

Vestibular stimulation enhances hippocampal long-term potentiation via activation of cholinergic septohippocampal cells.

Vestibular stimulation induced acetylcholine release in the hippocampus, and acetylcholine is known to facilitate long-term potentiation (LTP) in the hippocampus. Thus, we hypothesize that vestibular stimulation enhances LTP in CA1 in freely behaving rats, and this enhancement depends on the activation of septohippocampal cholinergic neurons. Field excitatory postsynaptic potentials were recorded in CA1 area of behaving rats following stimulation of the basal dendritic afferents. LTP was induced by a single stimulation train (100 pulses at 200 Hz) during passive whole-body rotation or during awake-immobility. LTP induced during rotation was significantly larger than that induced during immobility. Pretreatment with cholinergic antagonist atropine sulfate (50mg/kg i.p.) abolished the facilitation of LTP during rotation as compared to immobility. Selective lesion of cholinergic cells in the medial septum (MS) with 192 IgG-saporin (0.49 µg in 1.4 µl) also abolished the difference in LTP induced during rotation and immobility, which was found in sham-lesion rats. 192 IgG-saporin lesioned rats, as compared to sham-lesion rats, revealed a depletion of MS cells immunopositive to choline acetyltransferase and paling of acetylcholinesterase staining in the hippocampus, without significant change in the number of parvalbumin-immunopositive cells. We conclude that enhancement of LTP during vestibular stimulation is mediated by the activation of cholinergic septohippocampal cells. This is the first direct evidence that vestibular stimulation facilitates hippocampal synaptic plasticity via a cholinergic input.

Activation of immobility-related hippocampal theta by cholinergic septohippocampal neurons during vestibular stimulation.

The vestibular system has been suggested to participate in spatial navigation, a function ascribed to the hippocampus. Vestibular stimulation during spatial navigation activates a hippocampal theta rhythm (4-10 Hz), which may enhance spatial processing and motor response. We hypothesize that a cholinergic, atropine-sensitive theta is generated during passive whole-body rotation in freely behaving rats. Hippocampal EEGs were recorded by implanted electrodes in CA1 while rats were rotated on a vertical axis, for a minute or longer, at different angular velocities. Rotation induced a continuous hippocampal theta rhythm while the rat was immobile, in both light and dark conditions. Theta peak frequency showed a significant increase during high (50-70 rpm) as compared with a lower (20-49 rpm) rotational velocity. Rotation-induced theta was abolished by muscarinic receptor antagonist atropine sulfate (50 mg/kg i.p.) but not by atropine methyl nitrate (50 mg/kg i.p.), which did not pass the blood-brain barrier. Theta was attenuated in rats in which cholinergic neurons in the medial septum (MS) were lesioned with 192 IgG-saporin (0.14 µg in 0.4 µl), as confirmed by depletion of MS cells immunoreactive to choline acetyltransferase and an absence of acetylcholinesterase staining in the hippocampus. Bilateral lesion of the vestibular receptors by sodium arsanilate (30 mg in 0.1 ml, intratympanically) also attenuated the rotation-induced theta rhythm. In intact rats, field excitatory postsynaptic potentials (fEPSPs) in CA1 evoked by commissural stimulation were smaller during walking or rotation as compared with during immobility. Modulation of fEPSP was absent following atropine sulfate in intact rats and in 192 IgG-saporin lesion rats. In summary, this is the first report of a continuous atropine-sensitive hippocampal theta in the rat induced by vestibular stimulation during rotation, and accompanied by cholinergic modulation of hippocampal synaptic transmission. Vestibular-activated septohippocampal cholinergic activity could be an important component in sensorimotor processing and spatial memory.

Ketamine-induced deficit of auditory gating in the hippocampus of rats is alleviated by medial septal inactivation and antipsychotic drugs.

RATIONALE: Gating of sensory responses is impaired in schizophrenic patients and animal models of schizophrenia. Ketamine, an N-methyl-D-aspartate receptor antagonist, is known to induce schizophrenic-like symptoms including sensory gating deficits in humans. OBJECTIVE: This study aims to investigate the mechanisms underlying ketamine's effect on gating of auditory evoked potentials in the hippocampus of freely moving rats. METHODS: Gating was measured by the ratio of the test-click response (T) to the conditioning-click response (C), or T/C, with T and C measured as peak amplitudes. RESULTS: Ketamine (1, 3, or 6 mg/kg s.c.) injection dose-dependently increased T/C ratio as compared to saline injection (s.c.). T/C ratio was 0.48 +/- 0.05 after saline injection and 0.73 +/- 0.17 after ketamine (3 mg/kg s.c.) injection. The increase in T/C ratio after ketamine was blocked by prior inactivation of the medial septum with GABA(A) receptor agonist muscimol or by systemic administration of antipsychotic drugs, including chlorpromazine (5 mg/kg i.p.), haloperidol (1 mg/kg i.p.), or clozapine (7.5 mg/kg i.p.). Infusion of muscimol into the medial septum or injection of an antipsychotic drug alone did not affect the T/C ratio. However, rats with selective lesion of the septohippocampal cholinergic neurons by 192 IgG-saporin showed a significantly higher T/C ratio (0.86 +/- 0.10) than sham lesion rats (0.26 +/- 0.07), and ketamine did not further increase T/C ratio in rats with septohippocampal cholinergic neuron lesion. CONCLUSIONS: Ketamine's disruption of hippocampal auditory gating was normalized by inactivation of the medial septum; in addition, septal cholinergic neurons participate in normal auditory gating.

Hippocampal theta state in relation to formalin nociception.

In the present study using extracellular electrophysiological recording techniques, we explored the temporal characteristics of hippocampal theta activation in relation to formalin nociception. Results indicate that, compared to hind paw injection of saline, formalin injection in behaving rat evoked biphasic increase in duration of dorsal CA1 theta. Such an increase broadly paralleled animal biphasic behavioral activation, especially lick and moment-to-moment agitated behaviors. Correspondingly, theta-modulated cell firing was observed following formalin injection in anesthetized rat. The formalin-induced theta activation in behaving rat was most marked during peak of theta activation in the 2nd theta state (11-40 min post-injection) comprising 73% of the time in the 5 min block. An increase in theta peak frequency was also observed with respect to pre-injection control. However, the peak of theta in the 2nd theta state mostly preceded the peak of lick and flinch of the affected paw. In the 41-60 min, following formalin injection while the animals displayed robust nociceptive flinching and lifting, the theta activity approached control levels. Furthermore, the theta peak frequency at peak of theta was higher than the corresponding values of sustained theta observed in correlation with the nociceptive behaviors; in contrast, high frequency theta rhythm was observed during formalin-induced other moment-to-moment agitated behaviors. These findings favor the notion that in the formalin model the theta state of the hippocampus reflects a neural drive that is dissociated from the duration of nociceptive experience and is not selective to the typical nociceptive indices of lick, flinch, and lift of the injured paw.

Differential expression of metallothionein 1 and 2 isoforms in breast cancer lines with different invasive potential: identification of a novel nonsilent metallothionein-1H mutant variant.

Metallothionein (MT), a low-molecular weight protein with pleiotropic functions, is believed to play an important role in tumorigenesis. The aim of this study was to compare the expression of functional MT-1 and MT-2 mRNA isoforms in five breast cancer cell lines ranging from noninvasive MCF7 breast cancer cells to highly aggressive MDA-MB-231 breast cancer cells together with breast myoepithelial cells in vitro by conventional semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative real-time RT-PCR. The MT-2A isoform was observed to be differentially upregulated in the invasive phenotype. The MT-1E isoform was found to be present in estrogen receptor-negative breast cancer cell lines (MDA-MB-231 and Hs578T) but not detectable in the estrogen receptor-positive cell lines (T47D, MCF7, and ZR75-1 cells). Only the myoepithelial cells exhibited the presence of the MT-1G transcript. Direct sequencing of the RT-PCR products revealed the occurrence of a variant MT-1H isoform with changes in amino acid residues in the protein sequence and notable differences in the predicted secondary protein structure. The observations in this study are relevant to the development of novel approaches to metastatic breast cancer disease, and may herald the search for novel MT mutants and the elucidation of their biological roles.