Evidence for widespread changes in the structure, composition, and fire regimes of western North American forests.

Implementation of wildfire- and climate-adaptation strategies in seasonally dry forests of western North America is impeded by numerous constraints and uncertainties. After more than a century of resource and land use change, some question the need for proactive management, particularly given novel social, ecological, and climatic conditions. To address this question, we first provide a framework for assessing changes in landscape conditions and fire regimes. Using this framework, we then evaluate evidence of change in contemporary conditions relative to those maintained by active fire regimes, i.e., those uninterrupted by a century or more of human-induced fire exclusion. The cumulative results of more than a century of research document a persistent and substantial fire deficit and widespread alterations to ecological structures and functions. These changes are not necessarily apparent at all spatial scales or in all dimensions of fire regimes and forest and nonforest conditions. Nonetheless, loss of the once abundant influence of low- and moderate-severity fires suggests that even the least fire-prone ecosystems may be affected by alteration of the surrounding landscape and, consequently, ecosystem functions. Vegetation spatial patterns in fire-excluded forested landscapes no longer reflect the heterogeneity maintained by interacting fires of active fire regimes. Live and dead vegetation (surface and canopy fuels) is generally more abundant and continuous than before European colonization. As a result, current conditions are more vulnerable to the direct and indirect effects of seasonal and episodic increases in drought and fire, especially under a rapidly warming climate. Long-term fire exclusion and contemporaneous social-ecological influences continue to extensively modify seasonally dry forested landscapes. Management that realigns or adapts fire-excluded conditions to seasonal and episodic increases in drought and fire can moderate ecosystem transitions as forests and human communities adapt to changing climatic and disturbance regimes. As adaptation strategies are developed, evaluated, and implemented, objective scientific evaluation of ongoing research and monitoring can aid differentiation of warranted and unwarranted uncertainties.

Effect of prescribed fire for tick control in California chaparral.

Prescribed fire was investigated as a method for controlling ixodid and argasid ticks in chaparral habitats in northern California. Two experimental and two adjacent control plots within a wildlife preserve were monitored for 1 yr postburn. Ticks were collected by flagging vegetation, by CO2-baited pitfall trap, and by live-trapping rodents. Twice as many rodents were caught at control sites compared with burn sites and no dusky-footed woodrats, Neotoma fuscipes Baird, were found in the treatment sites postburn. This species is known to be a reservoir of the agents of Lyme disease, Borrelia burgdorferi sensu stricto Johnson, Schmid, Hyde, Steigerwalt & Brenner, and human granulocytic anaplasmosis, Anaplasma phagocytophilum Dumler, Barbet, Bekker, Dasch, Palmer, Ray, Rikihisa, Rurangirwa. Six ixodid tick species were removed from rodents (Ixodes pacificus Cooley & Kohls, Ixodes jellisoni Cooley & Kohls, Ixodes spinipalpis Hadwen & Nuttall, Ixodes woodi Bishopp, Dermacentor occidentalis Marx, and Dermacentor parumapertus Neumann), two of which transmit bacterial zoonotic agents to people in the far-western United States. There was no decrease in number of ticks per animal trapped at either burn site compared with controls; in fact, the mean number of immature I. pacificus per rodent was significantly higher at one burn site than its control site. Soil refugia may protect ticks from fire-induced mortality; the argasid tick Ornithodoros coriaceus Koch, which lives in soil, was unaffected by the prescribed fire as were I. pacificus and D. occidentalis buried in packets 2.5 cm below ground. We conclude that although prescribed fires in chaparral habitats may diminish local rodent abundance, it does not decrease tick loads on rodents. Furthermore, burning chaparral does not result in a decreased abundance of adult ixodid ticks on vegetation and apparently does not affect argasid or ixodid ticks that are sheltered within soil refugia.

Oxytocin as a natural antipsychotic: a study using oxytocin knockout mice.

It has been previously suggested that oxytocin (Oxt) may act as a natural antipsychotic. To test this hypothesis, we investigated whether disruption of the oxytocin gene (Oxt-/-) made mice more susceptible to the psychosis-related effects of amphetamine (Amp), apomorphine (Apo) and phencyclidine (PCP). We examined drug-induced changes in the prepulse inhibition (PPI) of the startle reflex, a measure of sensorimotor gating deficits characteristic of several psychiatric and neurological disorders, including schizophrenia. We found that treatment with Amp, Apo and PCP all had effects on PPI. However, in Oxt-/- mice, but not Oxt+/+ mice, PCP treatment resulted in large PPI deficits. As PCP is a noncompetitive N-methyl-D-aspartic acid receptor antagonist, these findings suggest that the absence of Oxt alters the glutamatergic component of the PPI.

Cerebral beta-amyloid angiopathy in aged squirrel monkeys.

Cerebral beta-amyloid angiopathy (CAA) is an age-related disorder of the brain vasculature that is involved in up to 20% of non-traumatic cerebral hemorrhage in humans. CAA is a risk factor for cognitive decline, and may exacerbate the dementia of Alzheimer's disease. Progress in discovering the cause and potential therapies for this disorder has been hindered by the paucity of animal models, particularly models of idiopathic CAA. The squirrel monkey (Saimiri spp) develops significant CAA in the natural course of aging. To evaluate the suitability of Saimiri as a model of human CAA, we studied the distribution and composition of Abeta subtypes in CAA and parenchymal (senile plaque) deposits in the brains of aged squirrel monkeys, as well as the relationship between vascular beta-amyloid deposition and comorbid vasculopathies that occur in aged humans. Our findings show that: 1) CAA consists ultrastructurally of classical amyloid fibrils and is the principal type of cerebral beta-amyloidosis in squirrel monkeys; 2) The two primary isoforms of Abeta (Abeta40 and Abeta42) coexist in most microvascular and parenchymal lesions of Saimiri, although Abeta40 tends to predominate in larger arterioles; 3) CAA and parenchymal plaques overlap to a considerable degree in most affected brain areas, and are distributed symmetrically in the two hemispheres; 4) Both CAA and plaques are particularly abundant in rostral regions and comparatively sparse in the occipital lobe; 5) Capillaries are especially vulnerable to CAA in squirrel monkeys; and 6) When CAA is severe, it is associated with a small, but significant, increase in other vasculopathies, including microhemorrhage, fibrinoid extravasation and focal gliosis. These findings, in the context of genetic, vascular and immunologic similarities between squirrel monkeys and humans, support the squirrel monkey as a biologically advantageous model for studying the basic biology of idiopathic, age-related CAA, and for testing emerging therapies for human beta-amyloidoses such as Alzheimer's disease.

Adult-type glycine receptors form clusters on embryonic rat spinal cord neurons developing in vitro.

The time course of development and the cellular and subcellular distributions of adult-type, strychnine-binding glycine receptors (GlyRs) were examined on rat spinal cord neurons in vitro using both the GlyR antagonist strychnine and a specific antibody against the receptor. Spinal cord neurons in vivo had no detectable adult-type GlyRs at embryonic day 14, the age used to establish cell cultures. After being placed in culture, neurons continued for several days to show no expression of adult-type GlyRs. This contrasted with the observation that these neurons began to express receptors for substance P within 24 hr in culture. Beginning after 5-7 d in culture, however, neurons began to express adult-type GlyRs on their surfaces, and the number of such receptors increased abruptly thereafter. Ultimately, about 80% of the neurons in heterogeneous spinal cord cultures came to express adult-type GlyRs, with all of them beginning to express the GlyRs at approximately the same time. The subcellular distribution of adult-type GlyRs on neurons was observed by fluorescence microscopy using both anti-GlyR antibody and a fluorescent derivative of strychnine. On neurons that had been in culture for more than 10 d, GlyRs were localized in focal clusters, or aggregates, that were distributed over both cell bodies and neurites. The apparent location of these clusters on the cell surface was confirmed by the observation that GlyRs could be labeled with the antibody on living neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of substance P receptors on rat motoneurons in vitro.

Experiments were performed to examine the influence of interneuronal interactions on the expression of neurotransmitter receptors by developing mammalian CNS neurons. Receptors for the neuropeptide, substance P (SP), were assayed on embryonic rat motoneurons and other spinal cord neurons developing in vitro by the binding of 125I-SP to live neurons. Scatchard analysis showed the presence of high-affinity binding sites, and binding competition assays using SP, neurokinin A, or neurokinin B indicated that the high-affinity 125I-SP binding sites on these neurons were type NK1 tachykinin receptors, or SP receptors (SPRs). Neurons in the spinal cords of rats at Embryonic Day 14 displayed no SPRs. Cell-surface SPRs were detected on spinal cord neurons within 24 hr after they were placed in culture, however, and the level of 125I-SP binding increased for several days. SPRs were assayed on spinal motoneurons that had been identified by retrograde labeling with a fluorescent tracer, isolated in high purity by fluorescence-activated cell sorting (FACS), and maintained in culture. Motoneurons grown in isolation from other neurons developed SPRs in vitro along the same time course as neurons in heterogeneous spinal cord cultures. These results show that rat spinal motoneurons can express SPRs early in their development, and they suggest that the initial expression of SPRs by developing motoneurons does not require interaction with other neurons.