Dexamethasone suppression test reversal in rapid transcranial magnetic stimulation-treated depression

Endocrine and immune effects of non-convulsive neurostimulation in depression: A systematic review

BACKGROUND

Non-convulsive neurostimulation is a rapidly-developing alternative to traditional treatment approaches in depression. Modalities such as repetitive Transcranial Magnetic Stimulation (rTMS), transcranial Direct Current Stimulation (tDCS), Vagal Nerve Stimulation (VNS) and Deep Brain Stimulation (DBS) are now recognized as potential treatments. How non-convulsive neurostimulation interventions impact the neurohormonal and neuroimmune changes that accompany depression remains relatively unknown. If this type of intervention can drive endocrine, immune, as well symptom changes in depression, non-convulsive neurostimulation may represent a viable, multi-faceted treatment approach in depression. We were therefore interested to understand the state of the literature in this developing area.

METHODS

A systematic review of all studies that examined the impact of non-convulsive neurostimulation interventions on the hypothalamic-pituitary-adrenal (HPA) axis and immune function in the form of cytokine production in depression.

RESULTS

We identified 15 human studies, 9 that examined rTMS, 2 that examined tDCS, 2 that examined VNS and 2 that examined electroacupuncture. 11 animal studies were also identified, 3 that examined rTMS, 2 that examined DBS and 6 that examined electroacupuncture. All types of non-convulsive neurostimulation were able to revert the increases in cortisol, ACTH and other components of the HPA axis that are seen in depressed patients, as well as to modulate the levels of key cytokines known to be up-regulated in depression, such as IL-1β, IL-6 and TNF-α. Changes in the HPA axis and levels of cytokines in response to non-convulsive neurostimulation often did not correlate with change in depressive symptoms. Most studies were not controlled trials and thus, significant methodologic variability existed. Furthermore, many human studies lacked a sham stimulation comparator arm. We were unable to conduct relevant meta-analyses due to the design heterogeneities, heterogeneity in the reported outcome measures and the limited number of studies retrieved. Animal studies generally supported the findings of those in human, but again, significant variability in methodology and study design were evident.

CONCLUSIONS

Non-convulsive neurostimulation interventions show promise in their ability to alter the endocrine and immune disturbances that accompany depression. Further research, which includes blinded, sham-controlled comparator designs is required.

Neurobiological mechanisms of repetitive transcranial magnetic stimulation of the dorsolateral prefrontal cortex in depression: a systematic review

Depression is one of the most prevalent mental illnesses worldwide and a leading cause of disability, especially in the setting of treatment resistance. In recent years, repetitive transcranial magnetic stimulation (rTMS) has emerged as a promising alternative strategy for treatment-resistant depression and its clinical efficacy has been investigated intensively across the world. However, the underlying neurobiological mechanisms of the antidepressant effect of rTMS are still not fully understood. This review aims to systematically synthesize the literature on the neurobiological mechanisms of treatment response to rTMS in patients with depression. Medline (1996-2014), Embase (1980-2014) and PsycINFO (1806-2014) were searched under set terms. Three authors reviewed each article and came to consensus on the inclusion and exclusion criteria. All eligible studies were reviewed, duplicates were removed, and data were extracted individually. Of 1647 articles identified, 66 studies met both inclusion and exclusion criteria. rTMS affects various biological factors that can be measured by current biological techniques. Although a number of studies have explored the neurobiological mechanisms of rTMS, a large variety of rTMS protocols and parameters limits the ability to synthesize these findings into a coherent understanding. However, a convergence of findings suggest that rTMS exerts its therapeutic effects by altering levels of various neurochemicals, electrophysiology as well as blood flow and activity in the brain in a frequency-dependent manner. More research is needed to delineate the neurobiological mechanisms of the antidepressant effect of rTMS. The incorporation of biological assessments into future rTMS clinical trials will help in this regard.

Biological markers in noninvasive brain stimulation trials in major depressive disorder: a systematic review

OBJECTIVES

The therapeutic effects of transcranial magnetic stimulation (TMS) and transcranial direct current stimulation in patients with major depression have shown promising results; however, there is a lack of mechanistic studies using biological markers (BMs) as an outcome. Therefore, our aim was to review noninvasive brain stimulation trials in depression using BMs.

METHODS

The following databases were used for our systematic review: MEDLINE, Web of Science, Cochrane, and SCIELO. We examined articles published before November 2012 that used TMS and transcranial direct current stimulation as an intervention for depression and had BM as an outcome measure. The search was limited to human studies written in English.

RESULTS

Of 1234 potential articles, 52 articles were included. Only studies using TMS were found. Biological markers included immune and endocrine serum markers, neuroimaging techniques, and electrophysiological outcomes. In 12 articles (21.4%), end point BM measurements were not significantly associated with clinical outcomes. All studies reached significant results in the main clinical rating scales. Biological marker outcomes were used as predictors of response, to understand mechanisms of TMS, and as a surrogate of safety.

CONCLUSIONS

Functional magnetic resonance imaging, single-photon emission computed tomography, positron emission tomography, magnetic resonance spectroscopy, cortical excitability, and brain-derived neurotrophic factor consistently showed positive results. Brain-derived neurotrophic factor was the best predictor of patients' likeliness to respond. These initial results are promising; however, all studies investigating BMs are small, used heterogeneous samples, and did not take into account confounders such as age, sex, or family history. Based on our findings, we recommend further studies to validate BMs in noninvasive brain stimulation trials in MDD.

Pregnancy and depression: exploring a new potential treatment option

The treatment of major depressive disorder during pregnancy is an important but complex clinical topic. Medications, electroconvulsive therapy, and psychotherapy are all reasonable choices, but each has its limitations. In this article, we propose that a novel device technology known as repetitive transcranial magnetic stimulation should be systematically studied as a potential treatment option for women with major depressive disorder during pregnancy.

The impact of one HF-rTMS session on mood and salivary cortisol in treatment resistant unipolar melancholic depressed patients

BACKGROUND

Recent studies indicate that medication resistant depressed patients can be successfully treated by a series of sessions of High Frequency repetitive Transcranial Magnetic Stimulation (HF-rTMS), delivered on the left dorsolateral prefrontal cortex (DLPFC). However, changes in subjectively experienced mood give only limited insight into the underlying physiological responses. Previous studies in depressed patients, as well as in healthy volunteers, have reported a possible impact of HF-rTMS on the hypothalamic-pituitary-adrenal (HPA) axis.

OBJECTIVE

We wanted to evaluate the emotional and neurobiological impact of one session of HF-rTMS applied on the left DLPFC in a sample of unipolar treatment resistant depressed patients of the melancholic subtype.

METHODS

20 right-handed antidepressant-free depressed patients were studied using a sham-controlled, 'single' blind, crossover design. We examined subjective mood changes with Visual Analogue Scales (VAS). To examine HF-rTMS effects on the HPA-axis, we analyzed salivary cortisol levels. Mood assessment and salivary cortisol levels were assessed before and immediately after stimulation. To detect any delayed effects, all measurements were also re-assessed 30 min post HF-rTMS. The left DLPFC was determined under MRI guidance.

RESULTS

One session of HF-rTMS did not result in any subjectively experienced mood changes. However, salivary cortisol concentrations decreased significantly immediately and 30 min after active HF-rTMS.

CONCLUSIONS

Although one session of HF-rTMS on the left DLPFC did not influence mood subjectively in melancholic unipolar depressed patients, we found support for the hypothesis that a single session has a significant impact on the HPA-axis, as measured by salivary cortisol. Our results may provide more insight into the underlying working mechanisms of HF-rTMS in unipolar melancholic depression, and could add further information about endocrinological functioning in affective disorders.

In vitro modulation of the glucocorticoid receptor by antidepressants

Clinical studies have demonstrated an impairment of glucocorticoid receptor (GR)-mediated negative feedback on the hypothalamus-pituitary-adrenal (HPA) axis in patients with major depression (GR resistance), and its resolution by antidepressant treatment. Accordingly, reduced GR function has also been demonstrated in vitro, in peripheral tissues of depressed patients, as shown by reduced sensitivity to the effects of glucocorticoids on immune and metabolic functions. We and others have shown that antidepressants in vitro are able to modulate GR mRNA expression, GR protein level and GR function. This paper reviews the in vitro studies that have examined the effect of antidepressants on GR expression, number and function in human and animal cell lines, and the possible molecular mechanisms underlying these effects. Antidepressants are shown to both increase and decrease GR function in vitro, based on different experimental conditions. Specifically, increased GR function is likely to be mediated by an increased intracellular concentration of glucocorticoids, while decreased GR function seems to be the consequence of GR downregulation. We suggest that the study of the effects of antidepressants on glucocorticoid function might help clarify the therapeutic action of these drugs.

Nonpharmacological, somatic treatments of depression: electroconvulsive therapy and novel brain stimulation modalities

Until recently, a review of nonpharmacological, somatic treatments of psychiatric disorders would have included only electroconvulsive therapy (ECT). This situation is now changing very substantially. Although ECT remains the only modality in widespread clinical use, several new techniques are under investigation. Their principal indication in the psychiatric context is the treatment of major depression, but other applications are also being studied. All the novel treatments involve brain stimulation, which is achieved by different technological methods. The treatment closest to the threshold of clinical acceptability is transcranial magnetic stimulation (TMS). Although TMS is safe and relatively easy to administer, its efficacy has still to be definitively established. Other modalities, at various stages of research development, include magnetic seizure therapy (MST), deep brain stimulation (DBS), and vagus nerve stimulation (VNS). We briefly review the development and technical aspects of these treatments, their potential role in the treatment of major depression, adverse effects, and putative mechanism of action. As the only one of these treatment modalities that is in widespread clinical use, more extended consideration is given to ECT Although more than half a century has elapsed since ECT was first introduced, it remains the most effective treatment for major depression, with efficacy in patients refractory to antidepressant drugs and an acceptable safety profile. Although they hold considerable promise, the novel brain stimulation techniques reviewed here will be need to be further developed before they achieve clinical acceptability.

Transcranial magnetic stimulation as a therapeutic tool in psychiatry

Transcranial magnetic stimulation (TMS) is a patient-friendly stimulation technique of the brain with interesting perspectives. In clinical psychiatry, limited data are available on activity in psychosis and anxiety, but much research has been done in depression. Major concerns on published papers are the inconsistency of used parameter settings, the restraint numbers of patients in randomised trials, the lack of real sham controlled studies and the quasi inexistent reproducibility of results. The most stringent meta-analysis of TMS in affective disorders found a modest, statistically significant antidepressant effect after 2 weeks of daily treatment of high frequency repetitive left dorsolateral prefrontal cortex stimulation. Although most results are rather weak and not convincing enough to promote TMS as evidence-based antidepressive therapy, they show a measurable action that should not be ignored. Preclinical and clinical effects were observed analysing heterogeneous data, and results comparing TMS to electroconvulsive therapy (ECT) in affective disorders are encouraging. Efforts should continue with emphasis on increasing homogeneity and reproducibility in data. Further refinement of stimulation parameters should be established, so that new and large double-blind, long-term, sham-controlled trials can bring us to better understanding and standardising TMS procedure, finally leading to definitive conclusions about its efficacy in psychiatry.

Transcranial magnetic stimulation: studying motor neurophysiology of psychiatric disorders

RATIONALE

Transcranial magnetic stimulation (TMS) is a noninvasive tool that directly stimulates cortical neurons by inducing magnetic and secondary electric fields. Traditionally TMS has been used to study the motor neurophysiology of healthy subjects and those with neurological disorders.

OBJECTIVE

Given the known motor dysfunctions in many psychiatric disorders supplemental usage of TMS to study the underlying pathophysiology of certain psychiatric disorders and to assess treatment outcomes is underway. Such studies include examination of motor neuronal membrane, corticospinal and intracortical excitability. Our objective is to overview the past findings.

METHODS

We review the past literature that used TMS as an assessment tool in psychiatric disorders such as schizophrenia, mood disorders, Tourette's syndrome, obsessive-compulsive disorder, attention-deficit hyperactivity disorder, and substance abuse.

RESULTS

While the findings are still preliminary due to small sample-size, inconsistent patient population (diagnosis, medication), differences in methodology between research groups, studies restricted to the motor region and possible lack of sensitivity and specificity, the studies are yielding interesting results which could potentially lead to trait- and state-markers of psychiatric disorders.

CONCLUSIONS

Future studies using TMS alone or in combination with other neuroimaging techniques promise to further expand the application of TMS from studies of motor excitability to higher cognitive functions.

Repetitive transcranial magnetic stimulation : does it have potential in the treatment of depression?

Transcranial magnetic stimulation (TMS) has become a major research tool in experimental clinical neurophysiology as a result of its potential to noninvasively and focally stimulate cortical brain regions. Currently, studies are being conducted to investigate whether repetitive TMS (rTMS)-mediated modulation of cortical function may also provide a therapeutic approach in neurological and psychiatric disorders. Preclinical findings have shown that prefrontal rTMS can modulate the function of fronto-limbic circuits, which is reversibly altered in major depression. rTMS has also been found to exert effects on neurotransmitter systems involved in the pathophysiology of major depression (e.g. stimulates subcortical dopamine release and acts on the hypothalamic pituitary adrenal axis, which is dysregulated in depression). To date, numerous open and controlled clinical trials with widely differing stimulation parameters have explored the antidepressant potential of rTMS. Though conducted with small sample sizes, the majority of the controlled trials demonstrated significant antidepressant effects of active rTMS compared with a sham condition. Effect sizes, however, varied from modest to substantial, and the patient selection focused on therapy-resistant cases. Moreover, the average treatment duration was approximately 2 weeks, which is short compared with other antidepressant interventions. Larger multicentre trials, which would be mandatory to demonstrate the antidepressant effectiveness of rTMS, have not been conducted to date.A putative future application of rTMS may be the treatment of patients who did not tolerate or did not respond to antidepressant pharmacotherapy before trying more invasive strategies such as electroconvulsive therapy and vagus nerve stimulation. Theoretically, rTMS may be also applied early in the course of disease in order to speed up and increase the effects of antidepressant pharmacotherapy. However, this application has not been a focus of clinical trials to date. Research efforts should be intensified to further investigate the effectiveness of rTMS as an antidepressant intervention and to test specific applications of the technique in the treatment of depressive episodes.

Duration of transcranial magnetic stimulation effects on the neuroendocrine stress response and coping behavior of adult male rats

BACKGROUND

Transcranial magnetic stimulation (TMS) is a relatively novel, noninvasive method of altering cerebral electrophysiological activity that produces localized and reversible changes in brain tissue. TMS has been shown to have antidepressant properties in both human trials and animal models. Additionally, TMS may alter hypothalamic-pituitary-adrenal (HPA) function resulting in a normalized dexamethasone suppression test in some depressed subjects and an attenuated stress-induced increase in adrenocorticotropic hormone (ACTH) and a possibly lowered basal corticosterone (CORT) concentration in rats. This research was undertaken to investigate the duration of these behavioral and neuroendocrine effects of TMS in rats.

METHODS

In this study, serum ACTH, CORT, testosterone, and luteinizing hormone (LH) concentrations following and immobility parameters during a forced-swim test in adult male rats were evaluated immediately and 1, 3, 5, 7, and 14 days subsequent to a 10-day course of once-daily TMS or sham application.

RESULTS

TMS animals had significantly higher ACTH and CORT concentrations immediately following the 10-day course of TMS compared to sham controls. Higher CORT concentrations (numerically but not statistically) were displayed by TMS-treated animals 1 and 3 days after the 10-day application course, although there were no significant differences between TMS and sham groups for ACTH or CORT levels 1, 3, 5, 7, and 14 days following application of sham or TMS. No significant differences were found between groups for serum testosterone and LH levels at any given collection time point. Immobility time, a measure of coping ability that is predictive of human antidepressant response, was significantly decreased (i.e., time spent actively swimming was significantly increased) immediately after the 10-day course of TMS. Thereafter, a nonsignificant numerical trend at 1 and 3 days after TMS application for immobility times between the TMS and control groups was observed (TMS<control values). No significant differences in immobility between TMS and control animals were found at subsequent time points.

CONCLUSIONS

The present findings suggest that the HPA stress axis is significantly altered immediately following a 10-day course of TMS in that a significant increase in ACTH and CORT levels in TMS-treated animals corresponded to a significant decrease in immobility times in the forced-swim test compared to control values. Finally, based upon the obtained results, the TMS effects in rats appear to be of relatively short duration.

Effects of antidepressant pharmacotherapy after repetitive transcranial magnetic stimulation in major depression: an open follow-up study

An increasing number of clinical studies demonstrates antidepressant effects of repetitive transcranial magnetic stimulation (rTMS). However, limited data are available so far concerning the stability of these effects and the efficacy of subsequent maintenance therapy. Therefore, we examined whether antidepressant pharmacotherapy can stabilize clinical improvement after rTMS monotherapy. Twenty-six drug-free patients suffering from a major depressive episode (DSM-IV criteria) participated in an open rTMS trial over two weeks (10-13 sessions, 10 Hz, left prefrontal stimulation at 100% motor threshold intensity). Subsequently, the patients were followed up during standardized antidepressant pharmacotherapy with mirtazapine for a further 4 weeks. The interval between the last rTMS and the first day of pharmacotherapy varied between one and five days. After two weeks of rTMS monotherapy 39% of the patients responded to rTMS by at least 50% reduction in their Hamilton Rating Scale for Depression (HRSD) scores. Treatment interruption after rTMS resulted in a significant increase in the HRSD score of rTMS responders. The degree of the deterioration was dependent on the length of interval without treatment. However, this deterioration was reverted and the further clinical course stabilized by subsequent mirtazapine treatment. The overall response rate after rTMS and mirtazapine treatment (alone or in combination) was 77%. Our results suggest that (1) antidepressant pharmacotherapy is able to further improve the clinical response to rTMS and (2) that responders to rTMS monotherapy should receive subsequent psychopharmalogical treatment without interruption in order to avoid a deterioration of symptoms.

Left prefrontal transcranial magnetic stimulation (TMS) treatment of depression in bipolar affective disorder: a pilot study of acute safety and efficacy

OBJECTIVES

Repetitive transcranial magnetic stimulation (rTMS) has been shown to improve depressive symptoms. We designed and carried out the following left prefrontal rTMS study to determine the safety, feasibility, and potential efficacy of using TMS to treat the depressive symptoms of bipolar affective disorder (BPAD).

METHODS

We recruited and enrolled 23 depressed BPAD patients (12 BPI depressed state, nine BPII depressed state, two BPI mixed state). Patients were randomly assigned to receive either daily left prefrontal rTMS (5 Hz, 110% motor threshold, 8 sec on, 22 sec off, over 20 min) or placebo each weekday morning for 2 weeks. Motor threshold and subjective rating scales were obtained daily, and blinded Hamilton Rating Scale for Depression (HRSD) and Young Mania Rating Scales (YMRS) were obtained weekly.

RESULTS

Stimulation was well tolerated with no significant adverse events and with no induction of mania. We failed to find a statistically significant difference between the two groups in the number of antidepressant responders (>50% decline in HRSD or HRSD <10 - 4 active and 4 sham) or the mean HRSD change from baseline over the 2 weeks (t = -0.22, p = 0.83). Active rTMS, compared with sham rTMS, produced a trend but not statistically significant greater improvement in daily subjective mood ratings post-treatment (t = 1.58, p = 0.13). The motor threshold did not significantly change after 2 weeks of active treatment (t = 1.11, p = 0.28).

CONCLUSIONS

Daily left prefrontal rTMS appears safe in depressed BPAD subjects, and the risk of inducing mania in BPAD subjects on medications is small. We failed to find statistically significant TMS clinical antidepressant effects greater than sham. Further studies are needed to fully investigate the potential role, if any, of TMS in BPAD depression.

Applications of TMS to therapy in psychiatry

Transcranial magnetic stimulation (TMS) has been applied to a growing number of psychiatric disorders as a noninvasive probe to study the underlying neurobiologic processes involved in psychiatric disorders and as a putative treatment. Transcranial magnetic stimulation is unparalleled in its ability to test the hypotheses generated by functional neuroimaging studies by modulating activity in selected neural circuits. As a focal intervention that may in some cases exert lasting effects, TMS offers the hope of targeting and ameliorating the circuitry underlying psychiatric disorders. The ultimate success of such an approach depends on our knowledge of the neural circuitry underlying these disorders, of how TMS exerts its effects, and of how to control the application of TMS to exert the desired effects. Although most clinical trials have focused on the treatment of major depression, increasing attention has been paid to schizophrenia and anxiety disorders. Many of these trials have supported a significant effect of TMS, but in some studies the effect is small and short lived. Current challenges in the field include determining how to enhance the efficacy of TMS in these disorders and how to identify patients for whom TMS may be efficacious.

Transcranial magnetic stimulation (TMS) effects on testosterone, prolactin, and corticosterone in adult male rats

BACKGROUND

Transcranial magnetic stimulation is a relatively new technique for inducing small, localized, and reversible changes in living brain tissue. Although transcranial magnetic stimulation generally results in no immediate changes in plasma corticosterone, prolactin, and testosterone, it normalizes the dexamethasone suppression test in some depressed subjects and has been shown to attenuate stress-induced increases in adrenocorticotropic hormone in rats.

METHODS

In this study, serum corticosterone and testosterone concentrations were assayed in male rats immediately and 3, 6, 9, 12, 24, and 48 hours following a single transcranial magnetic stimulation or sham application. Serum prolactin concentrations were determined immediately and 2 hours following a one-time application of either transcranial magnetic stimulation or sham.

RESULTS

Transcranial magnetic stimulation animals displayed significantly lower corticosterone concentrations at 6 and 24 hours following a single application compared with sham-control values. Transcranial magnetic stimulation also resulted in lower corticosterone concentrations numerically but not statistically in transcranial magnetic stimulation animals immediately after application (p =.089). No significant differences were found between groups for serum prolactin or testosterone levels at any given collection time point.

CONCLUSIONS

These findings 1) suggest that transcranial magnetic stimulation alters the hypothalamic-pituitary-adrenal stress axis and 2) provide time-course data for the implications of the hormonal mechanism that may be involved in the actions of transcranial magnetic stimulation.

Transcranial magnetic stimulation for treating depression

BACKGROUND

Transcranial magnetic stimulation can either excite or inhibit cortical areas of the brain, depending on whether the speed of the repetitive stimulation is applied at high or low frequencies. It has been used for physiological studies and it has also been proposed as a treatment for depression.

OBJECTIVES

To assess the clinical efficacy and safety of transcranial magnetic stimulation for treating depression.

SEARCH STRATEGY

An electronic search was performed including the Cochrane Collaboration Depression, Neurosis and Anxiety Review Group trials register (last searched June, 2001), the Cochrane Controlled Trials Register (Issue 2, 2001), MEDLINE (1966-2001), EMBASE (1974-2001), PsycLIT (1980-2001), and bibliographies from reviewed articles. Unpublished data and grey literature were searched through personal communications with researchers.

SELECTION CRITERIA

Randomised controlled trials assessing the therapeutic efficacy and safety of transcranial magnetic stimulation for depression.

DATA COLLECTION AND ANALYSIS

All reviewers independently extracted the information and verified it by cross-checking. Disagreements were resolved through discussion. Continuous data: When similar studies were grouped, the overall standardised mean difference was calculated under a fixed effect model weighted by the inverse variance method with 95% confidence intervals. (In the presence of statistical heterogeneity, a random effects model was to be used.)

MAIN RESULTS

Sixteen trials were included in the review and fourteen contained data in a suitable form for quantitative analysis. Most comparisons did not show differences between rTMS and other interventions. No difference was seen between rTMS and sham TMS using the Beck Depression Inventory or the Hamilton Depression Rating Scale, except for one time period (after two weeks of treatment) for left dorsolateral prefrontal cortex and high frequency; and also for right dorsolateral prefrontal cortex and low frequency, both in favour of rTMS and both using the Hamilton scale. Comparison of rTMS (left dorsolateral prefrontal cortex and high frequency) with electroconvulsive therapy showed no difference except for psychotic patients after two weeks treatment, using the Hamilton scale, which indicated that electroconvulsive therapy was more effective than rTMS.

REVIEWER'S CONCLUSIONS

The information in this review suggests that there is no strong evidence for benefit from using transcranial magnetic stimulation to treat depression, although the small sample sizes do not exclude the possibility of benefit.

Transcranial magnetic stimulation applications and potential use in chronic pain: studies in waiting

Transcranial magnetic stimulation (TMS) is a new technology which uses electromagnetic principles to produce small electrical currents in the cortex. Evidence indicates that TMS can produce plastic changes in the CNS which are observable at both the cellular and physiological levels. It is proposed that studies are justified to determine whether TMS can provide short-term or long-term relief in chronic pain.

A formicine in New Jersey cretaceous amber (Hymenoptera: formicidae) and early evolution of the ants

A worker ant preserved with microscopic detail has been discovered in Turonian-aged New Jersey amber [ca. 92 mega-annum (Ma)]. The apex of the gaster has an acidopore and, thus, allows definitive assignment of the fossil to the large extant subfamily Formicinae, members of which use a defensive spray of formic acid. This specimen is the only Cretaceous record of the subfamily, and only two other fossil ants are known from the Cretaceous that unequivocally belong to an extant subfamily (Brownimecia and Canapone of the Ponerinae, in New Jersey and Canadian amber, respectively). In lieu of a cladogram of formicine genera, generalized morphology of this fossil suggests a basal position in the subfamily. Formicinae and Ponerinae in the mid Cretaceous indicate divergence of basal lineages of ants near the Albian (ca. 105-110 Ma) when they presumably diverged from the Sphecomyrminae. Sphecomyrmines are the plesiomorphic sister group to all other ants, or they are a paraphyletic stem group ancestral to all other ants-they apparently became extinct in the Late Cretaceous. Ant abundance in major deposits of Cretaceous and Tertiary insects indicates that they did not become common and presumably dominant in terrestrial ecosystems until the Eocene (ca. 45 Ma). It is at this time that modern genera that form very large colonies (at least 10,000 individuals) first appear. During the Cretaceous, eusocial termites, bees, and vespid wasps also first appear-they show a similar pattern of diversification and proliferation in the Tertiary. The Cretaceous ants have further implications for interpreting distributions of modern ants.