Parallel processing of short-term memory for sensitization in Aplysia.

How is the short-term memory for a single form of learning distributed among the various elements of a neuronal circuit? To answer this question, we examined the short-term memory for sensitization, using the siphon component of the defensive gill- and siphon-withdrawal reflex. We found that the memory for short-term sensitization is represented by at least four sites of circuit modification, each involving a different type of plasticity. These include (1) presynaptic facilitation of the sensory neuron connections onto both interneurons and motorneurons; (2) presynaptic inhibition at the connections of the L30 inhibitory neurons onto the excitatory interneuron L29; (3) posttetanic potentiation of the excitatory connections made by L29 onto a specific subclass of siphon motorneurons, the LFS cells; and (4) an increase in the tonic firing rate of the LFS siphon motor neurons, resulting in neuromuscular facilitation.

A quantitative analysis of 2-D gels identifies proteins in which labeling is increased following long-term sensitization in Aplysia.

Long-term memory for sensitization of the gill- and siphon-withdrawal reflex in Aplysia, produced by 4 days of training, is associated with increased synaptic efficacy of the connection between the sensory and motor neurons. This training is also accompanied by neuronal growth; there is an increase in the number of synaptic varicosities per sensory neuron and in the number of active zones. Such structural changes may be due to changes in the rates of synthesis of certain proteins.

Long-term heterosynaptic inhibition in Aplysia.

Synaptic transmission between mechanosensory and motor neurons of the gill withdrawal reflex in Aplysia can undergo both short-term and long-term modulation. One form of short-term synaptic depression lasting minutes can be evoked by the peptide Phe-Met-Arg-Phe-amide (FMRFamide), and is mediated by the lipoxygenase pathway of arachidonic acid. We report here using cell culture, that the same monosynaptic sensory-to-motor component of the gill withdrawal reflex can also undergo long-term synaptic depression lasting 24 h after five applications of FMRFamide over a 2-h period.

Long-term facilitation in Aplysia involves increase in transmitter release.

In a variety of vertebrates and invertebrates, long-lasting enhancement of synaptic transmission contributes to the storage of memory lasting one or more days. However, it has not been demonstrated directly whether this increase in synaptic transmission is caused by an enhancement of transmitter release or an increase in the sensitivity of the postsynaptic receptors. These possibilities can be distinguished by a quantal analysis in which the size of the miniature excitatory postsynaptic potential released spontaneously from the presynaptic terminal is used as a reference.

Congenital determinants of violence.

Specialization--the predisposition to violent behavior persisting over an extended period of time--is considered in relation to congenital factors, to determine whether such factors are contributory to this predisposition. Congenital factors include inherited characteristics and perinatal experiences. Evidence for inherited characteristics in criminal behavior is approached through family studies, the study of twins, and adoption studies.

[Sudden hemorrhage into asymptomatic hypophyseal tumors].

In 6 previously asymptomatic patients the hypophysis (adenoma) hemorrhages developed suddenly with prompt severe signs of subarachnoidal hemorrhage or vision loss up to total blindness. Five patients were either operated via transfrontal approach or transnasal stereotaxic cryodestruction of the tumor was performed. One patient died before operation within 24h after admission.

Long-term occupational exposure and the diagnosis of dementia.

Several experiments are reported which concern the possible role of long-term occupational exposure in the etiology of dementia. A case study of a male with memory impairment thought to be due to Alzheimer's disease is reported. Neuropsychological testing revealed impairments in short-term memory, which gradually cleared over months.

Tail shock produces inhibition as well as sensitization of the siphon-withdrawal reflex of Aplysia: possible behavioral role for presynaptic inhibition mediated by the peptide Phe-Met-Arg-Phe-NH2.

Recent studies have shown that, in addition to being modulated by presynaptic facilitation, the sensory neurons of the gill- and siphon-withdrawal reflex of Aplysia are also capable of being modulated by transient presynaptic inhibition produced by the peptide Phe-Met-Arg-Phe-NH2. These two modulatory effects involve different second-messenger systems: the facilitation is mediated through cAMP-dependent protein phosphorylation, and the inhibition is mediated through the lipoxygenase pathway of arachidonic acid. To explore the behavioral function of this inhibition, we have carried out a parametric analysis of the effect of tail shock on the siphon-withdrawal reflex.

Biochemical correlates of short-term sensitization in Aplysia: temporal analysis of adenylate cyclase stimulation in a perfused-membrane preparation.

During short-term sensitization, a simple form of nonassociative learning in Aplysia, the presentation of a single brief noxious stimulus results in enhancement of the defensive withdrawal reflex lasting minutes to tens of minutes. This behavioral plasticity involves presynaptic facilitation of synaptic transmission from the mechanosensory neurons that mediate the reflex to their central target cells. This facilitation is due to cAMP-dependent protein phosphorylation.

[Destruction of the entry zone of the posterior roots as a method of treating chronic pain in traumatic damage to the brachial plexus].

To relieve a severe pain syndrome caused by trauma of the brachial plexus, the authors performed operation for destruction in places of traumatic avulsion of the posterior roots from the spinal cord in the projection of the posterior lateral sulcus ("destruction of the entry zone of the posterior roots"). Those roots whose representation corresponded to the spread of the pain syndrome were torn away as a rule. In cases of its wider spread along the dermatomes destruction was combined with residue-tomy of the preserved neighboring roots located above and below the avulsion.

Selective elimination of mRNAs in vivo: complementary oligodeoxynucleotides promote RNA degradation by an RNase H-like activity.

Oligodeoxynucleotides lead to translation arrest of complementary mRNAs in the wheat germ translation system by a degradation of the mRNA. In an attempt to develop an effective reverse genetic approach in vivo, we demonstrate that injection of short (15- to 30-nucleotide) oligonucleotides into Xenopus oocytes leads to complete degradation of both injected and endogenous mRNAs by means of an RNase H-like activity.

Lipoxygenase metabolites of arachidonic acid as second messengers for presynaptic inhibition of Aplysia sensory cells.

Biochemical and biophysical studies on Aplysia sensory neurons indicate that inhibitory responses to the molluscan peptide FMRFamide are mediated by lipoxygenase metabolites of arachidonic acid. These compounds are a new class of second messengers in neurons.

Serotonin produces long-term changes in the excitability of Aplysia sensory neurons in culture that depend on new protein synthesis.

When isolated and grown in cell culture, the sensory and motor neurons of the gill withdrawal reflex of Aplysia readily form synaptic connections. Repeated exposures to 5-HT cause facilitation of the synaptic connections between co-cultured sensory and motor neurons lasting at least 24 hr. As a first step toward understanding the locus and the mechanisms underlying this long-term synaptic facilitation, we have examined the membrane excitability of the isolated presynaptic sensory neurons grown alone in dissociated cell culture.

Stereotactic clipping of arteriovenous malformations of the brain.

The authors have developed a new technique for the stereotactic clipping of the feeding vessels of deep-seated arteriovenous malformations (AVM), for use when direct attack may be very dangerous or impossible. A special clipping device and the technique for its application are described. The instrument is introduced through a burr hole using the stereotactic apparatus designed by the authors.

[Stereotaxic removal of intracranial hematomas].

The high lethality and frequent postoperative complications in surgical treatment of intracerebral hemorrhages stimulate the search for new methods of their management. The introduction of computer tomography into clinical practice provided the grounds for elaborating a stereotaxic method for sparing removal of intracerebral hematomas. Experience in the clinical use of the method (54 operations on 51 patients) allows its results to be considered encouraging.

[Combined surgical treatment of associated lesions of the major arteries of the head].

Concurrent affection of the main arteries of the head is the cause of vascular cerebral insufficiency in more than half of the patients, which makes necessary combined operations on the extra- and intracranial arteries. The sequence of the operations is determined by the degree of the threat of occlusion of the stenosed artery or by the side on which the cerebrovascular insufficiency is manifested. Information on the regional cerebral blood flow and the results of ultrasonic dopplerography and computed tomography are additional criteria for determining the sequence and the terms of the operations.