Abba J. Kastin

Neuropeptide Influences on the Central Nervous System: A Psychobiological Perspective

The pituitary gland is a small organ (weighing about 60 mg in a human adult male and slightly more in an adult female) which is located at the base of the brain immediately below the hypothalamus. It is divided into three basic regions: the anterior lobe, the intermediate lobe and the posterior lobe. Each region secretes a different group of polypeptide hormones, which has specific physiological significance for the biological integrity of essential organismic functions. Many of the effects occur at a distance from the pituitary and appear to energize other organs of the endocrine system, hence the name tropic hormones. This regulatory capacity of the pituitary hormones led early investigators to refer to the pituitary as the master gland (Lewin, 1972).

Inverse relationship between onset and duration of EEG effects of six peripherally administered peptides

Electrical activity in the rat brain after the peripheral injection of equimolar (0.1 mM) doses of Metenkephalin, Leu-enkephalin, beta-endorphin, gamma-endorphin, DSIP, and alpha-MSH was assessed by power spectral analysis. The mean onset of EEG activity for each peptide varied between 13.7 and 20.7 minutes and lasted between 27.8 and 40.8 minutes. The significant (p less than 0.001) interaction between duration and latency revealed that the longer the latency, the shorter the duration. Similar findings were observed after injection of the same peptides at a fixed dose of 80 microgram/kg body weight. Thus, the results demonstrate that peripherally injected peptides can exert EEG effects that last longer the sooner they start.

Behavioural Modulation by Systemic Administration of Enkephalins and Endorphins

After the discovery of opiate receptors in the brain by Goldstein et al. (1971), Pert and Snyder (1973), Simon et al. (1973) and Terenius (1973), and the subsequent identification of endogenous opiates by Hughes et al. (1975) and Terenius and Wahlstrom (1975a, b), several groups began to examine the role of these peptides in modulating behaviour. Initially, Jacquet and Marks (1976) and Bloom et al. (1976) noticed that the central administration of brain opiates resulted in profound analgesic and muscular effects. However, subsequent attempts to replicate these findings with systemic injections (Kosterlitz and Hughes, 1977) were not successful, thus restricting interest to effects of centrally administered opiates and their analogs.