Reduced seizure threshold and altered network oscillatory properties in a mouse model of Rett syndrome.

Rett syndrome (RTT) is a disorder with a pronounced neurological phenotype and is caused mainly by mutations in the X-linked gene MECP2. A common feature of RTT is an abnormal electroencephalography and a propensity for seizures. In the current study we aimed to assess brain network excitability and seizure propensity in a mouse model of RTT. Mice in which Mecp2 expression was silenced (Mecp2(stop/y)) showed a higher seizure score (mean=6 ± 0.8 compared to 4±0.2 in wild-type [WT]) and more rapid seizure onset (median onset=10 min in Mecp2(stop/y) and 32 min in WT) when challenged with the convulsant drug kainic acid (25mg/kg). Hippocampal slices from Mecp2(stop/y) brain displayed no spontaneous field potential activities under control conditions but showed higher power gamma frequency field potential oscillations compared to WT in response to kainic acid (400 nM) in vitro. Brain slices challenged with the GABA(A)-receptor antagonist bicuculline (0.1-10 µM) and the potassium channel blocker 4-aminopyridine (1-50 µM) also revealed differences between genotypes with hippocampal circuits from Mecp2(stop/y) mouse slices showing enhanced epileptiform burst duration and frequency. In contrast to these network level findings, single cell analysis of pyramidal cells by whole-cell patch clamp recording revealed no detectable differences in synaptic or biophysical properties between methyl-CpG-binding protein 2 (MeCP2)-containing and MeCP2-deficient neurons. These data support the proposal that loss of MeCP2 alters network level excitability in the brain to promote epileptogenesis.

Indirect modulation of neuronal excitability and synaptic transmission in the hippocampus by activation of proteinase-activated receptor-2.

BACKGROUND AND PURPOSE: Proteinase-activated receptor-2 (PAR2) is widely expressed in the CNS under normal physiological conditions. However, its potential role in modulating neuronal excitability and synaptic transmission remains to be determined. Here, we have investigated whether PAR2 activation modulates synaptic activity in the hippocampus. EXPERIMENTAL APPROACH: PAR2 activation and its effect on the hippocampus were examined in rat primary cultures and acute slices using whole cell patch clamp and standard extracellular recordings, respectively. KEY RESULTS: PAR2 activation leads to a depolarization of hippocampal neurones and a paradoxical reduction in the occurrence of synaptically driven spontaneous action potentials (APs). PAR2-induced neuronal depolarization was abolished following either the inhibition of astrocytic function or antagonism of ionotropic glutamate receptors whilst the PAR2-induced decrease in AP frequency was also reduced when astrocytic function was inhibited. Furthermore, when examined in acute hippocampal slices, PAR2 activation induced a profound long-term depression of synaptic transmission that was dependent on NMDA receptor activation and was sensitive to disruption of astrocytic function. CONCLUSIONS AND IMPLICATIONS: These novel findings show that PAR2 activation indirectly inhibits hippocampal synaptic activity and indicate that these receptors may play an active role in modulating normal physiological CNS function, in addition to their role in pathophysiological disorders.

Synaptic plasticity deficits in an experimental model of rett syndrome: long-term potentiation saturation and its pharmacological reversal.

Rett syndrome (RTT), a disorder caused almost exclusively by mutations in the X-linked gene, MECP2, has a phenotype thought to be primarily of neurological origin. Disruption of Mecp2 in mice results in a prominent RTT-like phenotype. One of the consequences of MeCP2 absence in the brain is altered functional and structural plasticity. We aimed to characterize synaptic effects related to plasticity in the hippocampus further and establish whether plasticity defects are amenable to pharmacological reversal. Using male mice in which Mecp2 expression was prevented by a stop cassette, we assessed synaptic plasticity in area CA1 at different phenotypic stages, scoring the mice weekly for overt RTT-like signs. Strongly symptomatic Mecp2(stop/y) mice displayed reduced long-term potentiation (LTP, 40.2±1.6% of wild-type), post-tetanic potentiation (PTP, 45±18.8% of wild-type) and paired-pulse facilitation (PPF, 78±0.1% of wild type) (all P<0.05), the impairment increasing with symptom severity score. These plasticity impairments were absent in presymptomatic mice. Repeated high frequency stimulation revealed pronounced LTP saturation in symptomatic Mecp2(stop/y) mice, suggesting an LTP 'ceiling' effect. Bath application of the weak NMDA receptor blocker memantine (1 µM) resulted in partial restoration of a short-term plasticity component. These data support that idea that progressive functional synaptic impairment is a key feature in the RTT brain and demonstrate the potential for the pharmacological restoration of plasticity function.

Global changes in the hippocampal proteome following exposure to an enriched environment.

Exposure to an enriched environment promotes neurochemical, structural and neurophysiological changes in the brain and is associated with enhanced synaptic plasticity and improved hippocampal-dependent learning. Using a global proteomics-based approach we have now been able to reveal the altered expression of a diverse range of hippocampal proteins following exposure to an enriched environment. Male Hooded Lister rats (8 weeks) were subjected to a 6-week regimen in which they were housed in either non-enriched (open field) or enriched conditions (toys, wheels etc.). Whole protein extracts from stratum pyramidale and stratum radiatum of area CA1 were then isolated and subjected to differential gel electrophoresis [McNair K, Davies CH, Cobb SR (2006) Plasticity-related regulation of the hippocampal proteome. Eur J Neurosci 23(2):575-580]. Of the 2469 resolvable protein spots detected in this study, 42 spots (1.7% of the detectable proteome) derived from predominantly somatic fractions and 32 proteins spots from dendritic fractions (1.3% of detectable proteome) were significantly altered in abundance following exposure to an enriched environment (somatic: 14 increased/28 decreased abundance, range -1.5 to +1.4-fold change; dendritic: 16 increased, 16 decreased abundance, range -1.6 to +3.0-fold change). Following in-gel tryptic digestion and Maldi-Tof/Q-star mass spectrometry, database searching revealed the identity of 50 protein spots displaying environmental enrichment-related modulation of expression. Identified proteins belonged to a variety of functional classes with gene ontology analysis revealing the majority (>70%) of regulated proteins to be part of the energy metabolism, cytoplasmic organization/biogenesis and signal transduction processes.

Evoked slow muscarinic acetylcholinergic synaptic potentials in rat hippocampal interneurons.

The hippocampus receives an extensive cholinergic input from the medial septal nucleus that ramifies throughout all layers and plays a pivotal modulatory role in cognitive function. Although the pharmacological effects of exogenous application of cholinergic agonists have been extensively studied in hippocampal neurons, much less is known about the effects of synaptically released acetylcholine (ACh). In this respect, most studies have focused on the cholinergic afferent input to pyramidal neurons that produces a characteristically slow depolarizing synaptic response mediated by activation of muscarinic ACh receptors (mAChRs). Here we report that cholinergic afferent stimulation also elicits atropine-sensitive synaptic potentials in hippocampal CA1 interneurons but, in contrast to synaptic responses in pyramidal neurons, these are highly diverse in waveform, although can still be classified into five distinct subtypes. The most common response type (i) 64% of cells) consisted of a slow sustained membrane potential depolarization. The other 36% of responses could be subdivided into responses comprising of (ii) a biphasic membrane potential change in which an initial slow hyperpolarization subsequently transforms into a slow depolarization (20%), (iii) a pure, slow hyperpolarization (13%), and (iv) an oscillatory response persisting for several seconds (2%). Interestingly, there were also interneurons totally insensitive to both synaptic and pharmacological cholinergic challenge. Morphological investigation of recorded cells revealed no obvious correlation between responsiveness to cholinergic afferent stimulation and dendritic and axonal arborization. The current study suggests that synaptic release of ACh results in a complex and differential mAChR-mediated modulation of cellular excitability within the hippocampal interneuron population.

Regulation of epileptiform activity in hippocampus by nicotinic acetylcholine receptor activation.

Nicotinic acetylcholine receptors (nAChRs) regulate neuronal excitability within the CNS. To assess the possible modulatory influence of nAChRs on epileptiform activity, a range of nAChR ligands were applied during experimentally induced epileptiform activity in rat hippocampal slices. Bath application of the potassium channel blocker 4-aminopyridine (4AP; 10-50 microM) resulted in the development of spontaneous epileptiform bursting activity in area CA3 that consisted of short duration (257+/-15 ms) field events occurring regularly at a frequency of 0.4+/-0.02 Hz. Subsequent co-application of the selective nAChR agonists 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP; 0.3-300 microM), choline (0.01-3mM) and lobeline (3-30 microM) produced sustained and concentration-dependent increases in burst frequency with maximal frequency potentiation of 37+/-5%, 27+/-5% and 24+/-11%, respectively. DMPP (10-30 microM; n=31) also potentiated epileptiform bursting induced by reducing GABA(A) receptor-mediated synaptic transmission using 20 microM bicuculline or enhancing NMDA receptor-mediated excitation by lowering extracellular Mg(2+). Irrespective of the epileptiform model studied all nAChR agonist induced frequency potentiation was reversed upon washout of the agonist or co-application of one of the selective nAChR antagonists dihydro-beta-erythroidine (10-30 microM), mecamylamine (50-200 microM) or alpha-bungarotoxin (100 nM). These results provide compelling evidence that activation of nAChRs exacerbate epileptiform activity in the rat hippocampus.

Activation of Ih is necessary for patterning of mGluR and mAChR induced network activity in the hippocampal CA3 region.

Neuronal networks of the hippocampal CA3 region generate stereotyped patterns of electrical activity in response to activation of metabotropic glutamate receptors (mGluRs) or muscarinic acetylcholine receptors (mAChRs) that consist of intermittent episodes of prolonged oscillatory activity. In light of the slow kinetics of such network responses, we investigated the possible contribution of the hyperpolarisation-activated inward current (I(h)) in the generation and maintenance of hippocampal oscillatory states. Hippocampal 'mini-slice' experiments in which the main subfields of the hippocampus were isolated by transection of the connecting afferents revealed that the CA3 region was the primary generator of both mGluR and mAChR-mediated network responses. Subsequent patch-clamp experiments confirmed the presence of a prominent hyperpolarisation-activated inward current in the principal cells of the CA3 region that was sensitive to caesium chloride and the selective I(h) blocker ZD-7288.Furthermore, in the presence of mAChR or mGluR agonists these cells exhibited a slow membrane potential oscillation that was independent of AMPA receptor-mediated synaptic transmission. Blockade of I(h) suppressed this oscillation as well as mGluR and mAChR-induced theta based intermittent network oscillatory behaviour. These data support the idea that the I(h) pacemaker current is important in the generation of patterned neuronal activities in the hippocampus.

Regulation of muscarinic acetylcholine receptor-mediated synaptic responses by GABA(B) receptors in the rat hippocampus.

1. Both GABA(B) and muscarinic acetylcholine receptors (mAChRs) influence hippocampal-dependent mnemonic processing. Here the possibility of a direct interaction between GABA(B) receptors and mAChR-mediated synaptic responses has been studied using intracellular recording in rat hippocampal slices. 2. The GABA(B) receptor agonist (-)-baclofen (5-10 microM) depressed an atropine-sensitive slow EPSP (EPSP(M)) and occluded the GABA(B)-receptor-mediated IPSP (IPSP(B)) which preceded it. These inhibitory effects were accompanied by postsynaptic hyperpolarization (9 +/- 2 mV) and a reduction in cell input resistance (12 +/- 3 %). 3. The selective GABA(B) receptor antagonist CGP 55845A (1 microM) fully reversed the depressant effects of (-)-baclofen (5-10 microM) such that in the combined presence of (-)-baclofen and CGP 55845A the EPSP(M) was 134 +/- 21 % of control. 4. (-)-Baclofen (5-10 microM) caused a small (28 +/- 11 %) inhibition of carbachol-induced (3.0 microM) postsynaptic depolarizations and increases in input resistance. 5. CGP 55845A (1 microM) alone caused an increase in the amplitude of the EPSP(M) (253 +/- 74 % of control) and blocked the IPSP(B) that preceded it. 6. In contrast, the selective GABA uptake inhibitor NNC 05-0711 (10 microM) increased the amplitude of the IPSP(B) by 141 +/- 38 % and depressed the amplitude of the EPSP(M) by 58 +/- 10 %. This inhibition was abolished by CGP 55845A (1 microM). 7. Taken together these data provide good evidence that synaptically released GABA activates GABA(B) receptors that inhibit mAChR-mediated EPSPs in hippocampal CA1 pyramidal neurones. The mechanism of inhibition may involve both pre- and postsynaptic elements.

Coincident activation of mGluRs and mAChRs imposes theta frequency patterning on synchronised network activity in the hippocampal CA3 region.

Activation of metabotropic glutamate receptors (mGluRs) with the broad spectrum mGluR agonist 1S,3R ACPD (10-50 microM) induced spontaneous field potentials at low frequencies ('burst-mode' activity; <1 Hz) in the CA3 region of rat hippocampal slices. At higher concentrations (100-400 microM) ACPD switched this form of activity to a second, more complex pattern of activity in which intermittent episodes of theta frequency oscillations predominated ('theta-mode' activity; 4-14 Hz). Both patterns of activity were evoked by selective activation of group I mGluRs and, in particular, could be induced by activation of mGluR5 alone using the subtype selective agonist CHPG (0.5-5 mM). In contrast, activation of group II mGluRs (DCG IV; 100 microM) produced only burst-mode behaviour whilst activation of group III mGluRs (L-AP4; 100 microM) did not result in synchronised network activity. Concurrent extra- and intracellular recordings demonstrated that this mGluR-induced theta-mode activity represented the synchronous firing of CA3 pyramidal cells and that it shared a similar temporal signature to that generated by activation of muscarinic acetylcholine receptors (mAChRs). Furthermore, application of mGluR and mAChR agonists at concentrations sufficient to produce only burst-mode activity when applied individually, produced theta-mode activity when co-applied. These data suggest that the level of activation of different mGluRs and mAChRs crucially determine the pattern of rhythmical network activity generated in the hippocampal CA3 network. These results also indicate that individual receptor subtypes (i.e. mGluR5) can initiate patterns of coherent network activity but that interactions between the cholinergic and glutamatergic transmitter systems may also be important factors in governing the temporal patterning of hippocampal network activity.

Regulation of depolarizing GABA(A) receptor-mediated synaptic potentials by synaptic activation of GABA(B) autoreceptors in the rat hippocampus.

The role of GABA(B) autoreceptors in the regulation of GABA(A) and GABA(B) receptor-mediated inhibitory post-synaptic potentials (IPSPs) during repetitive synaptic activation has been established. In the present study the role of these receptors in the regulation of depolarising GABA(A) receptor-mediated synaptic potentials (DPSP(A)s) in the CA1 region of the hippocampus is documented. Following blockade of AMPA and NMDA receptor-mediated synaptic excitation, DPSP(A)s could be evoked by a single stimulus. The size of this response was enhanced by increasing the stimulus number (1-10 shocks) or stimulus frequency (10-100 Hz). Conversely, the amplitude of the DPSP(A) was dramatically reduced by a priming pulse (single shock) or priming burst (four shocks) delivered 200 ms beforehand. This activity-dependent depression was eliminated by the GABA(B) receptor antagonist CGP 35348 (1 mM). As such, GABA(B) autoreceptor-mediated regulation of DPSP(A)s prevented a pronounced, potentially epileptogenic, DPSP(A) from occurring during theta burst stimulation. Thus, during repetitive stimulation, activation of GABA(B) autoreceptors not only enables a transient reduction in GABA(A) receptor-mediated synaptic inhibition sufficient to enable NMDA receptor-dependent synaptic plasticity [Davies, C.H., Collingridge, G.L., 1996. J. Physiol. 496.2, 451-470] but also prevents the development of a potentially pathogenic depolarising GABA-mediated synaptic potential.

Activation of nicotinic acetylcholine receptors patterns network activity in the rodent hippocampus.

1. Intracellular and extracellular recordings from area CA3 of rat and mouse hippocampal slices revealed two distinct modes of synchronous network activity in response to continuous application of muscarinic acetylcholine receptor (mAChR) agonists. At low concentrations (e.g. 0.1-1 microM oxotremorine-M), 'burst-mode' activity comprised regular individual AMPA receptor-mediated depolarizing events, each generating several action potentials. At higher concentrations (5-50 microM), 'theta-mode' prevailed in which ordered clusters of depolarizing theta-frequency oscillations occurred. 2. Whilst theta-mode activity was abolished by the mAChR antagonist atropine (5 microM), the nicotinic acetylcholine receptor (nAChR) antagonists tubocurarine (100 microM), mecamylamine (100-500 microM) and dihydro-beta-erythroidine (250 microM) converted this mode of activity to burst-mode. 3. Likewise, disruption of synaptically available ACh using inhibitors of choline uptake (hemicholinium-3; 20-50 microM) or vesicular ACh transport (vesamicol; 50 microM) converted theta-mode into burst-mode activity. 4. Hippocampal slices prepared 2-3 weeks after transection of the primary cholinergic efferent pathway from the medial septum exhibited reduced vesicular ACh transporter immunoreactivity but still supported nAChR-dependent theta-mode activity suggesting that ACh released from this pathway was not critical for the activation of these receptors. 5. In summary, ACh-mediated activation of nAChRs tailors the pattern of network activity into theta-frequency depolarizing episodes as opposed to synchronized individual events at much lower frequencies.

Synaptic effects of identified interneurons innervating both interneurons and pyramidal cells in the rat hippocampus.

GABAergic interneurons sculpt the activity of principal cells and are themselves governed by GABAergic inputs. To determine directly some of the sources and mechanisms of this GABAergic innervation, we have used dual intracellular recordings with biocytin-filled microelectrodes and investigated synaptic interactions between pairs of interneurons in area CA1 of the adult rat hippocampus. Of four synaptically-coupled interneuron-to-interneuron cell pairs, three presynaptic cells were identified as basket cells, preferentially innervating somata and proximal dendrites of pyramidal cells, but one differing from the other two in the laminar distribution of its dendritic and axonal fields. The fourth presynaptic interneuron was located at the border between strata lacunosum moleculare and radiatum, with axon ramifying within stratum radiatum. Action potentials evoked in all four presynaptic interneurons were found to elicit fast hyperpolarizing inhibitory postsynaptic potentials (mean amplitude 0.35 +/- 0.10 mV at a membrane potential of -59 +/- 2.8 mV) in other simultaneously recorded interneurons (n=4). In addition, three of the presynaptic interneurons were also shown to produce similar postsynaptic responses in subsequently recorded pyramidal cells (n=4). Electron microscopic evaluation revealed one of the presynaptic basket cells to form 12 synaptic junctions with the perisomatic domain (seven somatic synapses and five synapses onto proximal dendritic shafts) of the postsynaptic interneuron in addition to innervating the same compartments of randomly-selected local pyramidal cells (50% somatic and 50% proximal dendritic synapses, n=12). In addition, light microscopic analysis also indicated autaptic self-innervation in basket (12 of 12) and bistratified cells (six of six). Electron microscopic investigation of one basket cell confirmed six autaptic junctions made by five of its boutons. Together, these data demonstrate that several distinct types of interneuron have divergent output to both principal cells and local interneurons of the same (basket cells) or different type. The fast synaptic effects, probably mediated by GABA in both postsynaptic interneurons and principal cells are similar. These additional sources of GABA identified here in the input to GABAergic cells could contribute to the differential temporal patterning of distinct GABAergic synaptic networks.

Synchronization of neuronal activity in hippocampus by individual GABAergic interneurons.

SYNCHRONIZATION of neuronal activity is fundamental in the operation of cortical networks. With respect to an ongoing synchronized oscillation, the precise timing of action potentials is an attractive candidate mechanism for information coding. Networks of inhibitory interneurons have been proposed to have a role in entraining cortical, synchronized 40-Hz activity. Here we demonstrate that individual GABAergic interneurons can effectively phase spontaneous firing and subthreshold oscillations in hippocampal pyramidal cells at 0 frequencies (4-7 Hz). The efficiency of this entrainment is due to interaction of GABAA-receptor-mediated hyperpolarizing synaptic events with intrinsic oscillatory mechanisms tuned to this frequency range in pyramidal cells. Moreover, this GABAergic mechanism is sufficient to synchronize the firing of pyramidal cells. Thus, owing to the divergence of each GABAergic interneuron, more than a thousand pyramidal cells may share a common temporal reference established by an individual interneuron.

Properties of unitary IPSPs evoked by anatomically identified basket cells in the rat hippocampus.

Hippocampal pyramidal cells receive GABA-mediated synaptic input from several distinct interneurons. In order to define the effect of perisomatic synapses, intracellular recordings were made with biocytin-containing microelectrodes from synaptically connected inhibitory and pyramidal cell pairs in subfields CA1 and CA3 of the rat hippocampus. Subsequent physiological analysis were restricted to the category of cells, here referred to as basket cells (n = 14), which had an efferent synaptic target profile (n = 282 synaptic contacts) of predominantly somatic (48.2%) and proximal dendritic synapses (45.0%). Electron microscopic analysis revealed that in two instances identified postsynaptic pyramidal cells received a total of 10 and 12 labelled basket cell synapses respectively. At an average membrane potential of -57.8 +/- 4.6 mV, unitary inhibitory postsynaptic potentials (IPSPs; n = 24) had a mean amplitude of 450 +/- 238 microV, a 10-90% rise time of 4.6 +/- 3.2 ms and, measured at half-amplitude, a mean duration of 31.6 +/- 18.2 ms. In most instances (n = 19) the IPSP decay could be fitted with a single exponential with a mean time constant of 32.4 +/- 18.0 ms. Unitary basket cell-evoked IPSPs (n = 5) was extrapolated to be at -74.9 +/- 6.0 mV. Averages of unitary IPSPs had a mean calculated conductance of 0.95 +/- 0.29 nS, ranging from 0.52 to 1.16 nS. Unitary basket cell IPSPs (n = 3) increased in amplitude by 26.6 +/- 19.9% following bath application of the GABAB receptor antagonist CGP 55845A [correction of CGP 35845A] (1-4 microM), whereas subsequent addition of the GABAA receptor antagonist bicuculline (10-13 microM) reduced the IPSP amplitude to 13.5 +/- 3.1% of the control response. Rapid presynaptic trains of basket cell action potentials resulted in the summation of up to four postsynaptic responses (n = 5). However, any increase in the rate of tonic firing (2- to 10-fold) led to a > 50% reduction of the postsynaptic response amplitude. At depolarized membrane potentials, averaged IPSPs could be followed by a distinct depolarizing overshoot or postinhibitory facilitation (n = 4). At firing threshold, pyramidal cells fired postinhibitory rebound-like action potentials, the latter in close temporal overlap with the depolarizing overshoot. In conclusion, hippocampal basket cells have been identified as one source of fast, GABAA receptor-evoked perisomatic inhibition. Unitary events are mediated by multiple synaptic release sites, thus providing an effective mechanism to avoid total transmission failures.

On a possible explanation as to why most people have small refractive errors.

The case is made that there must be a feedback mechanism operating during the development of the human eye which means that over a population most people have relatively small refractive errors. The possible feedback mechanisms are examined and the conclusion is drawn that chromatic aberration of the human eye may produce visual cues which could be utilized in such a feedback system.

Hearing loss and temporal bone structure in achondroplasia.

Characteristic temporal bone changes have recently been defined by high resolution CT in nine patients with achondroplasia (Cobb et al., Am J Neuroradiol 9:1195, 1988). These included narrowing of the skull base and "towering" petrous ridges resulting in abnormal orientation of the inner and middle ear structures. In order to determine whether these morphologic changes are the cause of the hearing deficit in achondroplasia, audiometric studies and ENT evaluation were performed in eight of the nine patients. All had a history of frequent otitis media and four had experienced tympanic membrane tube insertion. Three patients had significant sensorineural hearing loss, two had conductive hearing loss and one patient had combined hearing loss. None of the temporal bone morphologic changes were found to be correlated with the degree of either sensorineural or conductive hearing loss. Fusion of the ossicular chain was not present in any of our cases. Appropriate treatment of frequent acute otitis media and early awareness of middle ear effusions and conductive hearing loss in children with achondroplasia may be of great importance in preventing permanent hearing loss.

CT of the temporal bone in achondroplasia.

In an attempt to better define the changes affecting the temporal bone that might predispose achondroplastic dwarfs to otitis media, nine achondroplastic subjects who were evaluated for hearing loss underwent high-resolution CT scanning of the temporal bone. Comparisons were made with 10 nonachondroplastic subjects. A number of morphologic changes were seen, including (1) poor development of mastoid air cells, (2) foreshortening of the carotid canals, (3) narrowing of the skull base, (4) "towering" petrous ridges, and (5) relative "rotation" of the cochlea and other temporal bone structures. The most significant change was the rotational effect, which was more pronounced medially, resulting in an abnormal orientation of inner ear structures relative to middle ear structures and of middle ear structures relative to the external auditory canal. There was a notable lack of evidence for otitis media or its sequelae in any of the achondroplastic subjects. Audiograms were obtained in six of the nine achondroplastic subjects (two adults and four children). There was evidence of mixed hearing loss in the four children, but only of sensorineural hearing loss in the adults. We believe that the persistent hearing loss in achondroplasia is not due to sequelae of otitis media as some authors have suggested. Intrinsic vestibulocochlear changes below the limits of resolution of high-resolution CT scanning may be responsible.

Preoperative splenic artery occlusion as an adjunct for high risk splenectomy.

High risk splenectomy is often encountered in cases of hypersplenism with massive splenomegaly (10 times usual weight of 150-200 g) resulting from myelophthisic processes. Intra-operative ligation of the splenic artery through the lesser sac is a technically useful method of gaining vascular control prior to mobilizing the challenging spleen. However, a massive or inaccessible spleen imposes mechanical limitations during surgery and may be complicated by torrential intra-operative hemorrhage in the setting of severe thrombocytopenia refractile to platelet transfusions. The authors describe pre-operative intravascular proximal splenic artery control in four adult patients (3 men, 1 woman) with extreme splenomegaly (2,250-10,000 g). The massive splenomegaly in this group resulted from chronic myelogenous leukemia (n = 2), isolated splenic lymphoma (n = 1), and agnogenic myeloid metaplasia (n = 1). Chief symptom manifestations included left upper quadrant abdominal pain, early satiety, post-prandial emesis, dyspnea, petechiae, and associated easy bruising. Prior to surgery, all the patients were taken to the radiology suite where either detachable silastic balloons or stainless steel coils were placed selectively into the splenic artery under fluoroscopic guidance requiring approximately 35 minutes. Splenic artery occlusion aided normalization of thrombocytopenia (average increases 19,000/microliter to 215,000/microliter) with prolongation in survival of platelets. Successful splenectomy was subsequently performed with no additional transfusion requirements and was made technically easier by reducing splenic bulk. There were no adverse consequences of intravascular occlusion and no peri-operative morbidity or mortality. Preoperative intravascular selective splenic artery occlusion, used as an important potential adjunct to anticipated high risk splenectomy, is recommended.(ABSTRACT TRUNCATED AT 250 WORDS)

CT of subinsular infarction and ischemia.

A number of CT head scans, covering a 2-year period and showing a variety of distinct curvilinear subinsular lucent lesions, were collected and reviewed. Variations in extent of involvement, tendency toward bilateral symmetry, and clinical background allowed the lesions to be grouped into four general patterns, most of which, to our knowledge, have not been specifically described in the radiologic literature. This project was undertaken first to bring to the attention of those involved in interpretation of cranial CT images several patterns of injury they may not heretofore have been aware of and second to attempt to derive a specific etiology for each of the patterns described. Pattern 1, which appears as a distinct curvilinear lesion (sometimes cystic) apparently limited to the lateral aspect of the putamen, is thought to represent the residua of previous lateral striatal hemorrhage. Pattern 2, occurring in a markedly younger age group appears as relatively symmetrical bilateral subinsular lucencies, which in one case completely resolved. A specific etiology for this pattern remains uncertain. Acute demyelination, either secondary to a variant of anoxic leukoencephalopathy or to a limited form of diffuse encephalomyelitis, is postulated. A third pattern, which extends from generalized deep frontal white-matter lucency across the anterior limb of the internal capsule and tapering posteriorly in the subinsular area is thought to be on the basis of chronic ischemia similar to subcortical arteriosclerotic encephalopathy. The fourth pattern, occurring as a broad band of lucency extending from the frontal horn of the lateral ventricle and also tapering posteriorly is due to relatively proximal occlusion of the lateral lenticulostriate arteries.