[3] Sher L, Cooper TB, Mann JJ, Oquendo MA. Modified dexa- methasone suppression – corticotropin-releasing hormone stimulation test: a pilot study of young healthy volunteers and implications for alcoholism research in adolescents and young adults. Int J Adolesc Med Health [in press]. [4] Kunzel HE, Binder EB, Nickel T, et al. Pharmacological and nonpharmacological factors influencing hypothalamic- pituitary-adrenocortical axis reactivity in acutely depressed psychiatric in-patients, measured by the Dex-CRH test. Neuropsychopharmacology 2003;28:2169–78. [5] Holsboer F, vonBardeleben U, Wiedemann K, Muller OA, Stalla GK. Serial assessment of corticotropin-releasing hor- mone response after dexamethasone in depression. Impli- cations for pathophysiology of DST nonsuppression. Biol Psychiatry 1987;22:228–34. [6] Holsboer-Trachsler E, Stohler R, Hatzinger M. Repeated administration of the combined dexamethasone–human corticotropin releasing hormone stimulation test during treatment of depression. Psychiatry Res. 1991;38: 163–71. [7] Schule C, Baghai T, Zwanzger P, et al. Attenuation of hypothalamic-pituitary-adrenocortical hyperactivity in depressed patients by mirtazapine. Psychopharmacology (Berl) 2003;166:271–5. [8] Rinne T, de Kloet ER, Wouters L, Goekoop JG, de Rijk RH, van den Brink W. Fluvoxamine reduces responsiveness of HPA axis in adult female BPD patients with a history of sustained childhood abuse. Neuropsychopharmacology 2003;28:126–32. [9] Shimoda K, Yamada N, Ohi K, Tsujimoto T, Takahashi K, Takahashi S. Chronic administration of tricyclic antidepres- sants suppresses hypothalamo-pituitary-adrenocortical activ- ity in male rats. Psychoneuroendocrinology 1988; 13:431–40. Leo Sher Division of Neuroscience, Department of Psychiatry, Columbia University 1051 Riverside Drive, Suite 2917, Box 42, New York, NY 10032, USA Tel.: +1 212 543 6240; fax: +1 212 543 6017. E-mail addresses: LS2003@columbia.edu, drleosher@aol.com. doi:10.1016/j.mehy.2005.12.037 Non-invasive method for selective in vivo destruction of nanomachines by resonant absorption of ultrasound energy In a recent study potential risks associated with application of nanodevices in the human body has been discussed [1]. Another important issue, which should be ad- dressed before the nanomachines are routinely used in humans, is the possibility of their efficient eradication when needed. This is especially impor- tant for self-replicating nanomachines, in order to stop their possible uncontrolled replication. Recently a new method was proposed for the destruction of enveloped viruses possessing highly symmetric structure (e.g. icosahedral symmetry for HIV virus) based on the resonant absorption of sound [2]. Due to existence of high symmetry exists just few isolated resonance frequencies. Essentially the same icosahedral symmetry as HIV virus pos- sesses also buckmisterfullerene molecule, build up from 60 carbon molecules. Without any symme- try vibrational spectra of molecules with 60 atoms consists from 60 · 3À6 = 174 frequencies, but for highly symmetric fullerene molecule are observed just four lines in the infrared spectra [3]. For viruses these resonant frequencies are of the order of gigahertzes [4]. Fortunately essentially the same method of res- onant ultrasound absorption may be used not only for destruction of natural nanostructures like viruses, but also for these unique highly symmetric systems. The resonant frequencies of ultrasound may be calculated by solving sound wave equation, but this is a very complicated task. Fortunately, it is a simple to estimate the order of this quantity, using equation f = c/d, where f is a resonant frequency, c is the velocity of sound, and d is a typical dimension of nanostructure. Using values c = 1000 m/s (ultrasound velocity in tissue or water) and d = 100 nm, we obtain f = 10 GHz. Ultra- sound from the GHz frequency range is almost not absorbed in liquids, as has been shown in the exam- ple of ethanol or trichlorethane, where the sound absorption were studied up to 1 GHz [5]. This principle of resonant absorption may be well illustrated in another more common example which is microwave oven, employing microwave radiation at the resonant frequency of water mol- ecule at 2.45 GHz to heat food containing a rele- vant amount of water. When the food is exposed to microwaves of this frequency, energy is ab- sorbed by the water molecules and released in Correspondence 1249