Magnetic Resonance Diffusion W Imaging in Cerebral Fat Embolism

The use of diffusion weighted imaging with apparent diffusion coefficient mapping in the diagnosis of cerebral fat embolism is shown here to demonstrate infarcts secondary to fat emboli more intensely than T2 weighted sequences 24 hours after the onset of symptoms. Embolic foci are hypointense on apparent diffusion coefficient mapping consistent with cytotoxic edema associated with cell death and restricted water diffusion. This technique increases the sensitivity for detecting cerebral fat embolism and offers a potentially important tool in its diagnosis.

Odor-induced fast waves in the dentate gyrus depend on a pathway through posterior cerebral cortex: effects of limbic lesions and trimethyltin

Previous research has shown that the odor of a variety of organic solvents and of components of the anal scent gland excretions of various predators will elicit a burst of fast waves of about 20 Hz in the olfactory bulb, pyriform cortex, and dentate gyrus of the rat. The present experiments show that large lesions of the caudal cerebral cortex, involving particularly the entorhinal and subicular cortices and the angular bundle, abolish the olfactory fast wave response of the dentate gyrus, but not the similar response of the olfactory bulb. In confirmation of previous work, such a lesion also abolishes an average evoked response elicited in the dentate gyrus by electrical stimulation of the olfactory bulb. Systemic treatment with the neurotoxin trimethyltin abolished the olfactory fast wave response in the olfactory bulb and both the olfactory fast wave and the olfactory evoked potential in the dentate gyrus. Large lesions of the amygdala or the septal nuclei did not eliminate either the dentate olfactory evoked potential or the odor-induced dentate fast wave response. However, the septal lesion reduced the amplitude of both spontaneous and odor-induced dentate fast wave activity. It is suggested that olfactory stimuli elicit 20 Hz dentate fast waves via a pathway from the olfactory bulb through the entorhinal cortex and, further, that cholinergic interneurons in the dentate gyrus may be essential to the dentate fast wave response.

Sexually dimorphic aspects of spontaneous activity in meadow voles (Microtus pennsylvanicus): effects of exposure to fox odor

In this study, a multivariate analysis of the locomotor activity of adult, breeding male and female meadow voles (Microtus pennsylvanicus) was conducted. Overall, male voles made more movements and spent more time in the center of the activity chambers than did female voles. The authors further investigated the effects of brief exposure (3 min) to predator (red fox [Vulpes vulpes]) odor and various control odors (butyric acid, extract of orange) on subsequent activity. Control odors had no effects. Immediately following exposure to the fox odor, male voles exhibited significantly lower levels of activity and decreased center time. No significant changes in any activity variable were observed in the female voles following exposure to fox odor. This study provides evidence for sex differences in both basal activity levels of meadow voles and activity following exposure to a predator odor.

Sexually dimorphic aspects of spontaneous activity in meadow voles (Microtus pennsylvanicus): effects of exposure to fox odor

In this study, a multivariate analysis of the locomotor activity of adult, breeding male and female meadow voles (Microtus pennsylvanicus) was conducted. Overall, male voles made more movements and spent more time in the center of the activity chambers than did female voles. The authors further investigated the effects of brief exposure (3 min) to predator (red fox [Vulpes vulpes]) odor and various control odors (butyric acid, extract of orange) on subsequent activity. Control odors had no effects. Immediately following exposure to the fox odor, male voles exhibited significantly lower levels of activity and decreased center time. No significant changes in any activity variable were observed in the female voles following exposure to fox odor. This study provides evidence for sex differences in both basal activity levels of meadow voles and activity following exposure to a predator odor.

Effect of colchicine-induced cell loss in the dentate gyrus and Ammon's horn on the olfactory control of feeding in rats

Normal rats offered a choice between scented and unscented food pellets: (a) avoid food scented with toluene (an aromatic organic solvent) or 2-propylthietane (a component of the anal scent gland secretions of weasels); (b) prefer food scented with cadaverine (a diamine component of the odor of rotting flesh); but (c) neither prefer nor avoid food scented with butyric acid (a component of the odor of rancid butter) or caproic acid (a component of the odor of goats). Lesions of the dentate gyrus and CA1 (induced by local injections of colchicine) and/or the neocortex overlying the hippocampus produce a complex pattern of changes in these normal olfactory reactions, but do not affect the normal reaction to food flavored with sucrose or quinine. Cell loss in the hippocampal formation results in an abnormal aversion to butyric acid, in particular, but neocortical damage also alters the behavioral reaction to scented food. The results are consistent with the view that the hippocampal formation and the neocortex play differing roles in the olfactory control of behavior.

The neurotoxins colchicine and kainic acid block odor-induced fast waves and olfactory-evoked potentials in the dentate gyrus of the behaving rat

It has previously been shown that the hilus of the dentate gyrus responds to odors (e.g. toluene) with a burst of fast waves and to electrical stimulation of the olfactory bulb with an evoked potential consisting of an early component immediately after the stimulus artifact, a second component with a 16-18-ms latency and additional late components. Spectral analysis revealed that odor-induced fast-wave bursts in the olfactory bulb and dentate gyrus both had a peak frequency of 15-20 Hz and were highly coherent. Unilateral intrahippocampal injections of colchicine or kainic acid were used in an attempt to destroy granule and pyramidal cells, respectively, while saline was injected on the opposite side as a control. Recordings from chronically implanted electrodes in the olfactory bulb and dentate gyrus demonstrated that saline had no effect while either neurotoxin abolished the odor-induced fast waves. In addition, the late 16-18-ms component of the dentate-evoked potentials after single-pulse stimulation of the olfactory bulb was abolished by either kainic acid or colchicine; the early dentate response, probably a volume-conducted olfactory response, was not abolished. Histological analysis indicated that kainic acid produced widespread non-specific damage in the hippocampal formation. Kainic acid-treated tissue exhibits a thinning of granule cell and molecular layers of the dentate gyrus as well as cell loss in CA3 and part of CA1.

Scopolamine blocks olfaction-induced fast waves but not olfactory evoked potentials in the dentate gyrus

The presentation of some odorous materials such as xylene or toluene under the snout of rats has been shown to elicit 15-30 Hz fast-wave bursts in both the olfactory bulb and dentate gyrus. Electrical stimulation of the olfactory bulb elicits an evoked potential (latency of first peak is 16-18 ms) in the dentate gyrus. The present study demonstrates that scopolamine or atropine blocks toluene-induced fast-wave bursts in the dentate region and to a lesser degree in the olfactory bulb while leaving dentate gyrus electrically evoked potentials intact. Further, rhythmical burst stimulation of the olfactory bulb at fast-wave frequencies will elicit fast-wave-like oscillations in the dentate gyrus. These fast-wave-like events, unlike evoked potentials to single-pulse stimulation, are abolished after muscarinic receptor antagonism with atropine. Mechanisms at the olfactory bulb and dentate gyrus that produce fast oscillations may involve muscarinic cholinergic synapses while the simple transmission of single, non-oscillatory olfactory signals to the dentate gyrus does not.

Components of weasel and fox odors elicit fast wave bursts in the dentate gyrus of rats

Previous work has shown that olfactory stimulation with toluene, xylene and other organic solvents elicits a burst of 15-30 Hz fast waves in the dentate gyrus of male rats. Other odorous substances including food, rat vaginal secretions and rat excrement were much less effective. In the present study we confirm that water, ammonia, rat food, rat cage litter and the presence of a conspecific did not reliably elicit dentate fast wave responses but that toluene and methyl methacrylate were very effective. We further show that both 2-propylthietane, which is a component of weasel gland secretions, and trimethyl thiazoline, an ingredient of fox droppings, elicited dentate fast waves as effectively as toluene and methyl methacrylate and that putrescine, cadaverine, butyric acid, caproic acid and indole were ineffective by comparison. Similarly, orally administered solutions of acetic acid, quinine, sodium chloride and sucrose were ineffective. These findings raise the possibility that the dentate fast waves elicited in the rat may be part of a cerebral response to the odor of a potential predator, such as the weasel or fox.

Dentate gyrus and olfactory bulb responses to olfactory and noxious stimulation in urethane anaesthetized rats

Recent research has shown that olfactory stimuli such as toluene vapor, but not visual, auditory, tactile or gustatory stimuli, elicit a burst of fast waves (15-30 Hz) in the hilus of the dentate gyrus in waking rats. In urethane-anaesthetized rats, toluene odors elicit similar fast waves. The present study shows that noxious stimulation (tail clamp) produces a blockade of spontaneous slow waves (1-12 Hz) in the hilus of the dentate gyrus but does not increase fast wave activity in urethane-anaesthetized rats. This slow wave blockade, which resembles neocortical activation, is independent of olfaction since it is not affected by tracheotomy. In contrast, tracheotomy abolishes the fast wave response to toluene presentation to the snout unless the toluene vapor is drawn into the nasal passages by suction at the rostral end of the severed trachea. Both the toluene odor-induced fast wave and the tail clamp-induced activation responses are abolished by scopolamine hydrobromide (5.0 mg/kg, i.p.) but not by scopolamine methyl bromide (5.0 mg/kg, i.p.) which does not cross the blood-brain barrier. However, evoked potentials elicited in the dentate hilus by single pulse stimulation of the olfactory bulb are not blocked by scopolamine in urethane-anaesthetized rats. The results suggest that several different types of electrical activity in the hippocampal formation are mediated by cholinergic inputs and that the dentate gyrus plays a role in olfaction.