Dominick P. Purpura

Spread of transcallosally evoked responses in immature association cortex.

Abstract Stimulation of the anterior middle suprasylvian gyrus (AMSG) in kittens (newborn to 6 weeks of age) elicits maximal transcallosally evoked responses (TCR) from homotopic sites in contralateral AMSG and smaller responses at variable distances from the site of homotopic registration. Distant (nonhomotopic) TCRs survive incisions of cortex around the site of stimulation which preserve callosal projections but interrupt lateral connections of the site of stimulation with other regions of AMSG. Nonhomotopic responses may be differentially enhanced or suppressed by changes in stimulus parameters or when conditioned by direct cortical responses. These observations indicate that nonhomotopic TCRs are generated by spread of synaptic activity linearly along the AMSG from homotopic projection sites. In kittens less than 3 weeks old spread of TCRs along the AMSG occurs with greater facility when stimulation is applied to contralateral rostral portions of AMSG than when caudal regions are stimulated. Thus in very young kittens activity generated by TCRs spreads preferentially in a rostral-to-caudal direction. This situation is reversed in kittens older than 3–4 weeks. This reversal of the polarity of preferred spread of TCRs occurs in the late postanatal period and constitutes a maturational event that may be related to the functional development of interhemispheric transactions in association cortex.

Development of Synaptic Substrates for Drug Actions in Immature Brain

Studies of the effects of drugs and hormones on the immature brain must of necessity proceed from an understanding of the nature of the neural and synaptic substrate that constitutes the primary target of action of the pharmacological agent under investigation. Unfortunately this has rarely been possible for the obvious reason that there is a paucity of data available on the organization and properties of different subsystems during the development of the central nervous system in different species. Development implies change, and this cardinal feature of maturation introduces variables in the assessment of drug action in immature animals which may be major determinants of overt effects. An instructive example of the manner in which the developmental processes may influence drug actions is illustrated in Fig. 1 which summarizes data obtained over a decade ago in studies of the effects of topically applied aliphatic ω-amino acids on the immature brain (Purpura, 1961a). In these studies local responses elicited by cortical surface stimulation were utilized to determine the responsiveness of axodendritic synaptic pathways (Purpura, 1961b) to e-amino caproic acid, a six-carbon aliphatic ω-amino acid which in adult animals produces rapid potentiation of superficial negative responses and subsequent convulsant activity (Purpura et al., 1959).

Studies on the Piriform Lobe.

Stimulation of basal telencephalic structures has been shown to produce a wide variety of autonomic and somatomotor responses, as well as more complex behavioral activities in animals and man. In these studies particular attention has been focused on the amygdaloid complex which has been shown to be a major component in the operation of rhinencephalic and limbic-midbrain systems. Despite the large volume of neurophysiological and behavior data on the functional organization of the amygdaloid complex, little has been known concerning the anatomic relations of different nuclear groups in the complex and other cortical and subcortical structures. This monograph represents the most detailed analysis of this problem currently available. The author not only demonstrates his mastery of the Golgi method as applied to the study of the intrinsic organization of piriform lobe structures, but also reveals his skillful use of the Nauta-Gygax techniques in combination with the Golgi studies. The result

The Rhinencephalon and Related Structures. vol 3. Progress in Brain Research.

Although numerous attempts have been made in recent years to define the functional and anatomical organization of the rhinencephalon, relatively few of these attempts have met with any measure of success. The major reason for this, as noted by the conference chairman of this symposium (Brodal), is the lack of definition of the term rhinencephalon. And if the participants at this conference held in Kield, in 1962, failed to come to some agreement on the meaning of this term, at least their efforts have yielded a collection of essays which should contribute to the final resolution of this important problem. A total of fourteen reports are contained in this symposium volume of which three are concerned with the relationship of electrophysiological and behavioral findings with anatomical features of different components of the rhinencephalon. The remainder are primarily anatomical and consider subjects ranging from studies of the gross morphology of the